The study of intermolecular interactions at interfaces is essential for a number of applications, in addition
to the understanding of mechanisms involved in sensing and biosensing with liquid samples. There are,
however, only a few methods to probe such interfacial phenomena, one of which is the atomic force
spectroscopy (AFS) where the force between an atomic force microscope tip and the sample surface is
measured. In this study, we used AFS to estimate adhesion forces for a nanostructured film of poly(oethoxyaniline)
(POEA) doped with various acids, in measurements performed in air. The adhesion force
was lower for POEA doped with inorganic acids, such as HCl and H2SO4, than with organic acids, because
the counterions were screened by the ethoxy groups. Significantly, the morphology of POEA both in the
film and in solution depends on the doping acid. Using small-angle X-ray scattering (SAXS) we observed
that POEA dissolved in amixture of dimethyl acetamide exhibits a more extended coil-like conformation,
with smaller radius of gyration, than for POEA in water, as in the latter POEA solubility is lower. In AFS
measurements in a liquid cell, the force curves for a POEA layer displayed an attractive region for pH 5
due to van der Waals interactions, with no contribution from a double-layer since POEA was dedoped. In
contrast, for pH 3, POEA was doped and the repulsive double-layer force dominated. With AFS one is
therefore able to correlate molecular-level interactions with doping and morphology of semiconducting
polymers.
The present paper describes the influence of the chemical structure of two aminoalkoxysilanes: 3-
aminopropyltriethoxysilane (APTS) and N-(3-(trimethoxysilyl)-propyl)-ethylenediamine (TSPEN) on the
morphology of thin layer hybrid films with phosphotungstic acid (HPW), a Keggin heteropolyanion. X-ray
photoelectron spectroscopy analyses indicated that both silane films showed protonated amine species interacting
with the heteropolyanion by electrostatic forces as well as the presence of secondary carbamate anions.
The hybrid films have different surface morphology according to atomic force microscopy analyses.
The hybrid film with TSPEN forms flatter surfaces than the hybrid film with APTS. This effect is ascribed to
higher flexibility and chelating ability of the TSPEN on adsorbed molecules. Ultrasonication effect on surface
morphology of the hybrid film with APTS plays a fundamental role on surface roughness delivering enough
energy to promote surface diffusion of the HPW heteropolyanions. This diffusion results in agglomerate formation,
which corroborates with the assumption of electrostatic bonding between the HPW heteropolyanions
and the protonated amine surface. These hybrid films could be used for electrochemical sensor
design or to build photochromic and electrochromic multilayers.
Adsorption characteristics of a cationic porphyrin on nanoclay at various pHZachary Rice
- The document analyzes the adsorption behavior of a cationic porphyrin molecule (TMAP) onto montmorillonite clay at various pH levels using buffers.
- Spectroscopic analysis showed TMAP adsorbed to the clay in a monolayer at low and high pH, while slightly acidic/neutral pH caused it to possibly rearrange or form aggregates on the surface.
- Absorption spectra of TMAP on clay exhibited red shifts compared to free TMAP in solution, indicating flattening and electron delocalization of the porphyrin rings when adsorbed.
This document summarizes research on the synthesis, characterization, and application of mesoporous niobium and tantalum oxides in heterogeneous catalysis. Mesoporous transition metal oxides were synthesized using a ligand-assisted templating approach with surfactants. Characterization techniques including powder XRD, nitrogen adsorption, SEM, TEM, FT-IR and NMR confirmed the mesoporous structure. The materials were tested in benzylation, alkylation and isomerization reactions and showed high activity and selectivity due to their high surface area and acidity. Pore size effects on catalytic performance were also investigated.
Kinetics of Substituted Bis- and Mono-azo Dyes as Corrosion Inhibitors for Al...Al Baha University
This investigation is designed to apply an advanced kinetic^thermodynamic model on the data obtained from acidic and alkaline corrosion of aluminium using bis- and mono-azo dyes as corrosion inhibitors.
Sensing of volatile organic compounds by MOFsMohammadRad12
1. The document discusses a presentation about sensing volatile organic compounds (VOCs) using metal organic frameworks (MOFs).
2. MOFs are porous materials composed of metal ions or clusters linked by organic ligands to form one, two, or three-dimensional structures. They have potential applications for gas storage, separation, catalysis and sensing.
3. The presentation describes several MOFs that exhibit color changes or fluorescence changes when exposed to different VOCs, allowing them to function as sensors for VOCs.
The document discusses testing the reactivity between various Good's buffers and vernadite (δ-Mn(IV)O2). X-ray diffraction analysis found structural modifications to vernadite when reacted with EPPS, MOPSO, HEPES, and MOPS buffers, indicating partial reduction of Mn(IV) to Mn(III). The inertness of BES may be due to its molecular geometry lacking nitrogen-containing rings found in the other buffers. Diffraction patterns of vernadite reacted with varying concentrations of MOPS and EPPS showed stacking order was not directly proportional to buffer concentration.
Metal organic Frameworks for sensor applicationABHISHEK KATOCH
This document summarizes a student's research project on synthesizing and characterizing transition metal-based metal-organic frameworks for sensor applications. The student synthesized MOF-5 and nickel-doped MOF-5 at various concentrations using a solvothermal method. Characterization using XRD, FTIR, UV-Vis, and photoluminescence showed the materials maintained their crystalline structure and porous nature after doping. Testing showed the materials were responsive to NO2 gas, indicating potential for sensor applications. Future work could aim to improve sensitivity, selectivity, and response time for detecting harmful gases.
The interaction between poly(o-ethoxyaniline) (POEA) adsorbed onto solid substrates and humic substances
(HS) and Cu2+ ions has been investigated using UV–vis spectroscopy and atomic force microscopy
(AFM). Both HS and Cu2+ are able to dope POEA and change film morphology. This interaction was
exploited in a sensor array made with nanostructured films of POEA, sulfonated lignin and HS, which
could detect small concentrations of HS and Cu2+ in water.
The present paper describes the influence of the chemical structure of two aminoalkoxysilanes: 3-
aminopropyltriethoxysilane (APTS) and N-(3-(trimethoxysilyl)-propyl)-ethylenediamine (TSPEN) on the
morphology of thin layer hybrid films with phosphotungstic acid (HPW), a Keggin heteropolyanion. X-ray
photoelectron spectroscopy analyses indicated that both silane films showed protonated amine species interacting
with the heteropolyanion by electrostatic forces as well as the presence of secondary carbamate anions.
The hybrid films have different surface morphology according to atomic force microscopy analyses.
The hybrid film with TSPEN forms flatter surfaces than the hybrid film with APTS. This effect is ascribed to
higher flexibility and chelating ability of the TSPEN on adsorbed molecules. Ultrasonication effect on surface
morphology of the hybrid film with APTS plays a fundamental role on surface roughness delivering enough
energy to promote surface diffusion of the HPW heteropolyanions. This diffusion results in agglomerate formation,
which corroborates with the assumption of electrostatic bonding between the HPW heteropolyanions
and the protonated amine surface. These hybrid films could be used for electrochemical sensor
design or to build photochromic and electrochromic multilayers.
Adsorption characteristics of a cationic porphyrin on nanoclay at various pHZachary Rice
- The document analyzes the adsorption behavior of a cationic porphyrin molecule (TMAP) onto montmorillonite clay at various pH levels using buffers.
- Spectroscopic analysis showed TMAP adsorbed to the clay in a monolayer at low and high pH, while slightly acidic/neutral pH caused it to possibly rearrange or form aggregates on the surface.
- Absorption spectra of TMAP on clay exhibited red shifts compared to free TMAP in solution, indicating flattening and electron delocalization of the porphyrin rings when adsorbed.
This document summarizes research on the synthesis, characterization, and application of mesoporous niobium and tantalum oxides in heterogeneous catalysis. Mesoporous transition metal oxides were synthesized using a ligand-assisted templating approach with surfactants. Characterization techniques including powder XRD, nitrogen adsorption, SEM, TEM, FT-IR and NMR confirmed the mesoporous structure. The materials were tested in benzylation, alkylation and isomerization reactions and showed high activity and selectivity due to their high surface area and acidity. Pore size effects on catalytic performance were also investigated.
Kinetics of Substituted Bis- and Mono-azo Dyes as Corrosion Inhibitors for Al...Al Baha University
This investigation is designed to apply an advanced kinetic^thermodynamic model on the data obtained from acidic and alkaline corrosion of aluminium using bis- and mono-azo dyes as corrosion inhibitors.
Sensing of volatile organic compounds by MOFsMohammadRad12
1. The document discusses a presentation about sensing volatile organic compounds (VOCs) using metal organic frameworks (MOFs).
2. MOFs are porous materials composed of metal ions or clusters linked by organic ligands to form one, two, or three-dimensional structures. They have potential applications for gas storage, separation, catalysis and sensing.
3. The presentation describes several MOFs that exhibit color changes or fluorescence changes when exposed to different VOCs, allowing them to function as sensors for VOCs.
The document discusses testing the reactivity between various Good's buffers and vernadite (δ-Mn(IV)O2). X-ray diffraction analysis found structural modifications to vernadite when reacted with EPPS, MOPSO, HEPES, and MOPS buffers, indicating partial reduction of Mn(IV) to Mn(III). The inertness of BES may be due to its molecular geometry lacking nitrogen-containing rings found in the other buffers. Diffraction patterns of vernadite reacted with varying concentrations of MOPS and EPPS showed stacking order was not directly proportional to buffer concentration.
Metal organic Frameworks for sensor applicationABHISHEK KATOCH
This document summarizes a student's research project on synthesizing and characterizing transition metal-based metal-organic frameworks for sensor applications. The student synthesized MOF-5 and nickel-doped MOF-5 at various concentrations using a solvothermal method. Characterization using XRD, FTIR, UV-Vis, and photoluminescence showed the materials maintained their crystalline structure and porous nature after doping. Testing showed the materials were responsive to NO2 gas, indicating potential for sensor applications. Future work could aim to improve sensitivity, selectivity, and response time for detecting harmful gases.
The interaction between poly(o-ethoxyaniline) (POEA) adsorbed onto solid substrates and humic substances
(HS) and Cu2+ ions has been investigated using UV–vis spectroscopy and atomic force microscopy
(AFM). Both HS and Cu2+ are able to dope POEA and change film morphology. This interaction was
exploited in a sensor array made with nanostructured films of POEA, sulfonated lignin and HS, which
could detect small concentrations of HS and Cu2+ in water.
This document describes a new fluorescent sensor called DDS (dibenzimidazolo diimine sensor) that was designed and synthesized to selectively detect acetate ions. DDS exhibits a remarkable near-infrared emission through an excited state intramolecular proton transfer process. Upon addition of acetate ions, DDS solution changes color visibly from light yellow to pink under normal light. It also shows a large fluorescence enhancement in the near-infrared region, indicating selective detection of acetate ions over other competing anions. Density functional theory calculations help explain the selective binding and sensing mechanism of DDS for acetate ions.
SAMMS is an award-winning technology that can be tailored for applications in remediation, water treatment, catalysis, sensors and controlled release. SAMMS materials are created by attaching self-assembled monolayers to mesoporous ceramic supports, producing a material with fast kinetics, high loading capacity and selectivity. SAMMS has been developed specifically for removing mercury and other heavy metals from liquid media, demonstrating high adsorption, fast sorption kinetics and the ability to bind various forms of mercury and selectively remove other metals while not binding alkali and alkaline earth metals. The technology is being developed by Pacific Northwest National Laboratory and Steward Environmental Solutions.
This document summarizes three methods for preparing hollow metal-organic frameworks (MOFs): 1) the exterior-template method where templates are coated with MOF shells and then removed, 2) the self-template method where intermediate products or reactants act as sacrificial templates, and 3) the two-phase interface method using gas-liquid, liquid-liquid, or solid-liquid interfaces. It also discusses using hollow MOFs for drug delivery by loading drugs through immersion or one-pot synthesis and zinc-based MOFs for delivering 5-fluorouracil.
MOFs are ideal candidates as gas-sensing materials and have been widely used to detect oxygen, water vapor, toxic and hazardous gases, special air pollutants, and VOCs.
ACETYLATION OF BENZYLIC ALCOHOLS OVER BiFeO3 (BFO), Bi0.86Sm0.07Eu0.07FeO3 (B...EDITOR IJCRCPS
BiFeO3 (BFO), Bi0.86Sm0.07Eu0.07FeO3 (BSEFO), and Bi0.86Sm0.07Cd0.07FeO3 (BSCFO) nanopowders were prepared by the sol-gel
combustion method and the catalytic performances were evaluated in acetylation reaction of benzyl alcohol. The physical chemical
properties of catalysts were characterized by using XRD, FT-IR, scanning electron microscope (SEM), EDX and BET surface.
Efficient acetylation of benzyl alcohol was carried out over all the nano powders using acetyl chloride/ acetonitrile at room
temperature. Among the nanopowders, BSCFO showed the highest catalytic performance and the yield of benzyl acetate was 89,
45, and 69 percent over BSCFO, BFO, and BSEFO, respectively. Partial substitution of Sm-Eu and Sm-Cd in bismuth ferrite
improved the catalytic performance and increased the specific surface area of the catalysts. A direct relationship was resulted
between catalytic performance and surface of catalysts, where BSCFO with the highest surface area (111m2/g) exhibited the
superior catalytic performance. The quantitative yield for acetate product was also resulted for acetylation of p-methyl benzyl
alcohol, p-nitro benzyl alcohol and p-chloro benzyl alcohol on BSCFO. The catalysts showed good reusability in the process. The
study confirmed the catalysts could be promising catalyst for acetylation of alcohols.
Keywords: Europium, Samarium, Bismuth ferrites, nano perovskite, doping, Acetylation, benzylic alcohols.
Computationally Driven Characterization of Magnetism, Adsorption, and Reactiv...Joshua Borycz
Metal organic frameworks (MOFs) are a class of nanoporous materials that are com- posed of metal-containing nodes connected by organic linkers. The study of MOFs has grown in importance due to the wide range of possible node and linker combinations, which allow tailoring towards specific applications. This work demonstrates that the- ory can complement experiment in a way that advances the chemical understanding of MOFs. This thesis contains the results of several investigations on three different areas of MOF research: 1) magnetism, 2) CO2 adsorption, and 3) catalysis.
Graphene oxide is synthesized by treating graphite with strong oxidizing agents like potassium chlorate, potassium permanganate, and acids. It has a layered structure with oxygen-containing functional groups such as hydroxyl and epoxy groups bonded to the basal graphene planes. These functional groups make graphene oxide hydrophilic and soluble in water. Graphene oxide can be chemically reduced by removing oxygen groups or chemically functionalized by reacting functional groups on the basal planes with other molecules through covalent bonding.
This document discusses using ion mobility mass spectrometry to quantify linear impurities in cyclic polylactide samples. It finds that the method was unable to accurately determine low levels of linear contamination, as cyclic ions at lower polymerization degrees were less likely to adopt the triply charged state analyzed. This led to an overestimation of linear content. Considering additional charge states or shifting ion conformations may help address this issue in future work. The document introduces the topic, experimental methods, data analysis, results showing inconsistent quantification at different polymerization degrees, and conclusions about limitations and potential improvements.
Swift and efficient_sono-hydrolysis_of_nKarlitox Saoj
This document discusses the hydrolysis of nitriles to carboxylic acids under basic conditions using ultrasound activation. Key findings include:
- Ultrasound significantly increases the rate of nitrile hydrolysis to carboxylic acids under basic conditions compared to thermal activation alone.
- The positive effect of ultrasound is attributed to more than just mechanical effects and likely involves a radical mechanism with the oxide anion radical (OÅÀ).
- Model reactions converting benzonitrile and adiponitrile to benzoic acid and adipic acid, respectively, demonstrate this sono-hydrolysis method under basic conditions.
This document summarizes metal-organic frameworks (MOFs), including their properties and applications. MOFs are highly porous materials formed by combining metal ions or metal clusters with organic ligands. They have extremely large surface areas, often exceeding 7,000 m2/g. Due to their tunable porous structures, MOFs show promise for applications such as gas storage, carbon capture, catalysis, and luminescence. While MOF research has advanced significantly in recent decades, further developing their potential applications and improving stability remains an active area of research.
Methylene Blue (MB) is thiazine dyes that widely use to color product in many industry such as textile, printing, leather, cosmetic and paper. Xanthogenated-Modified Chitosan Microbeads (XMCM) is use to observe the new alternative adsorbent in removing MB from water body through adsorption process. The interactions between MB and functional group in XMCM were confirmed by Fourier Transform Infrared (FT-IR). Several parameters that influence adsorption ability such as the effect of adsorbent dosage of XMCM and the effect of initial pH of MB aqueous solution were studied. This study were done at optimum condition which is at pH 4 of initial pH of MB solution, 0.01 g of initial XMCM dosage, 6 hours stirring time and temperature of (30 ± 2 ). The adsorption data fit well Langmuir model more than Freundlich model. Based on Langmuir model, the maximum monolayer adsorption capacity of MB was 21.62 mg g-1 which indicated that XMCM can be a new alternative adsorbent for removing MB.
Global Journal of Environmental Science and Management (GJESM)
Application of amorphous zirconium (hydr)oxide/MgFe layered double hydroxides composite in fixed-bed column for phosphate removal from water.
Si-Imidazole-HSO4 Functionalized Magnetic Fe3O4 Nanoparticles as an Efficient...Iranian Chemical Society
An efficient and simple method for the preparation of Si-Imidazole-HSO4 functionalized magnetic Fe3O4 nanoparticles (Si-Im-HSO4 MNPs) and used as an efficient and reusable magnetic catalysts for the regioselective ring opening of epoxides under green conditions in water. This catalyst was used for the ring opening of epoxide corresponding to the thiocyanohydrins and azidohydrines. Compared to the classical ring opening of epoxides, this new method consistently has the advantage of excellent yields, short reaction times, and methodological simplicity.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
This document discusses the use of a large-pore metal-organic framework (MOF) called MJ3' for sensing and discriminating explosives at variable concentrations. MJ3' showed good sensitivity and quenching of its fluorescence for a range of explosives like tetryl, TNT, RDX, PETN, and 2,4-DNT in solution. In particular, its large pore size allowed for interactions with PETN, one of the more difficult explosives to detect. Testing revealed concentration limits of detection in the ppm range, suggesting potential applications in homeland security and environmental monitoring. The document concludes that carefully designed MOFs with ultrahigh porosity and stability can enable interior functionalization for applications like
This document summarizes research on synthesizing a transition metal-based Metal-Organic Framework (MOF) for sensor applications. Key points:
- A zinc-based MOF was synthesized using terephthalic acid as the organic linker through a solvothermal method.
- Characterization with XRD, FTIR, UV-VIS and photoluminescence showed the MOF had a crystalline structure with pores and displayed dynamic luminescent properties essential for chemical sensing.
- The MOF exhibited red-shifted fluorescence compared to the free linker molecule, indicating coordination interaction between the zinc and linker affected its luminescence.
Final Photocatalysis Lab Report (1) (1)Henry Hsieh
The document summarizes an experiment analyzing the effect of hydrogen peroxide concentration on the methylene blue degradation kinetic constant. When 5mL and 10mL of hydrogen peroxide were added, kinetic constants of 0.07 min-1 and 0.12 min-1 were obtained, respectively, indicating faster degradation with more hydrogen peroxide. However, decreasing kinetics from excess hydrogen peroxide was not observed due to the limited concentration range studied. Absorbance measurements and kinetic plots were used to determine the degradation constants.
Gas storage in metal organic frameworks(MOFs)Nitish Kumar
Gas storage in metal organic frameworks.
1. Metal organic frameworks has surface area more than 40 tennis courts per gram. So, it has high adsorption capacity.
2. Gas storage in a cylinder filled with MOFs can store much more gas than empty cylinder.
3. Apart from storage ,MOFs can also be used for Gas Separation.
This document discusses a study on mixed-linker zeolitic imidazolate frameworks (ZIFs) containing two types of imidazole linkers. The researchers show that these mixed-linker ZIFs have tunable properties including pore size, hydrophilicity, and organophilicity. They synthesized a series of ZIF-8x-90100-x materials with different ratios of two linkers, resulting in a wide range of crystal sizes from 338 nm to 120 μm. Using various characterization and measurement techniques, they demonstrate that properties like hydrocarbon and alcohol diffusion can be continuously tuned over 2-3 orders of magnitude by varying the mixed-linker composition. This tunability allows mixed-linker ZIFs to
Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for their use in technological applications, since film properties vary considerably with the experimental conditions utilized for film fabrication. In this paper, we employ small-angle X-ray
scattering (SAXS) to investigate solutions of polyanilines and correlate the chain conformations with morphological features of the nanostructured films obtained with atomic force microscopy (AFM). It is shown that aggregates formed already in solution affect the film morphology; in
particular, at early stages of adsorption film morphology appears entirely governed by the chain conformation in solution and adsorption of aggregates. We also use SAXS data for modeling poly(o-ethoxyaniline) (POEA) particle shape through an ab initio procedure based on simulated
annealing using the dummy atom model (DAM), which is then compared to the morphological features of POEA films fabricated with distinct pHs and doping acids. Interestingly, when the derivative POEA is doped with p-toluene sulfonic acid (TSA), the resulting films exhibit a fibrillar morphology—seen with atomic force microscopy and transmission electron microscopy—that is consistent with the cylindrical shape inferred from the SAXS data. This is in contrast with the globular morphology observed for POEA films doped with other acids.
Foram investigadas as interações entre os pesticidas atrazina, imazaquin, metribuzin e paraquat com o polímero condutor poli-(o-etoxianilina)-POEA, utilizando-se as técnicas de microscopia de força atômica (AFM), espectrofotometria de ultravioleta visível (UV-Vis) e
espectroscopia de impedância eletroquímica. Os estudos de microscopia de força atômica em filmes automontados mostraram um aumento na rugosidade do filme polimérico, quando exposto aos pesticidas atrazina, imazaquin e metribuzin e uma diminuição na rugosidade do filme
polimérico exposto ao pesticida paraquat. Isso evidencia a existência de interação química, provavelmente, ligação iônica entre o nitrogênio presente na POEA e os grupos presentes nos pesticidas estudados. Os estudos de ultravioleta visível mostraram uma maior interação entre a
POEA e o pesticida imazaquin. Por meio de medidas elétricas realizadas (espectroscopia de impedância eletroquímica) com um sensor formado por filme de POEA, foi possível distinguir e determinar o limite de detecção dos pesticidas em solução aquosa, o que corrobora com os estudos por AFM e UV-Vis.
This document describes a new fluorescent sensor called DDS (dibenzimidazolo diimine sensor) that was designed and synthesized to selectively detect acetate ions. DDS exhibits a remarkable near-infrared emission through an excited state intramolecular proton transfer process. Upon addition of acetate ions, DDS solution changes color visibly from light yellow to pink under normal light. It also shows a large fluorescence enhancement in the near-infrared region, indicating selective detection of acetate ions over other competing anions. Density functional theory calculations help explain the selective binding and sensing mechanism of DDS for acetate ions.
SAMMS is an award-winning technology that can be tailored for applications in remediation, water treatment, catalysis, sensors and controlled release. SAMMS materials are created by attaching self-assembled monolayers to mesoporous ceramic supports, producing a material with fast kinetics, high loading capacity and selectivity. SAMMS has been developed specifically for removing mercury and other heavy metals from liquid media, demonstrating high adsorption, fast sorption kinetics and the ability to bind various forms of mercury and selectively remove other metals while not binding alkali and alkaline earth metals. The technology is being developed by Pacific Northwest National Laboratory and Steward Environmental Solutions.
This document summarizes three methods for preparing hollow metal-organic frameworks (MOFs): 1) the exterior-template method where templates are coated with MOF shells and then removed, 2) the self-template method where intermediate products or reactants act as sacrificial templates, and 3) the two-phase interface method using gas-liquid, liquid-liquid, or solid-liquid interfaces. It also discusses using hollow MOFs for drug delivery by loading drugs through immersion or one-pot synthesis and zinc-based MOFs for delivering 5-fluorouracil.
MOFs are ideal candidates as gas-sensing materials and have been widely used to detect oxygen, water vapor, toxic and hazardous gases, special air pollutants, and VOCs.
ACETYLATION OF BENZYLIC ALCOHOLS OVER BiFeO3 (BFO), Bi0.86Sm0.07Eu0.07FeO3 (B...EDITOR IJCRCPS
BiFeO3 (BFO), Bi0.86Sm0.07Eu0.07FeO3 (BSEFO), and Bi0.86Sm0.07Cd0.07FeO3 (BSCFO) nanopowders were prepared by the sol-gel
combustion method and the catalytic performances were evaluated in acetylation reaction of benzyl alcohol. The physical chemical
properties of catalysts were characterized by using XRD, FT-IR, scanning electron microscope (SEM), EDX and BET surface.
Efficient acetylation of benzyl alcohol was carried out over all the nano powders using acetyl chloride/ acetonitrile at room
temperature. Among the nanopowders, BSCFO showed the highest catalytic performance and the yield of benzyl acetate was 89,
45, and 69 percent over BSCFO, BFO, and BSEFO, respectively. Partial substitution of Sm-Eu and Sm-Cd in bismuth ferrite
improved the catalytic performance and increased the specific surface area of the catalysts. A direct relationship was resulted
between catalytic performance and surface of catalysts, where BSCFO with the highest surface area (111m2/g) exhibited the
superior catalytic performance. The quantitative yield for acetate product was also resulted for acetylation of p-methyl benzyl
alcohol, p-nitro benzyl alcohol and p-chloro benzyl alcohol on BSCFO. The catalysts showed good reusability in the process. The
study confirmed the catalysts could be promising catalyst for acetylation of alcohols.
Keywords: Europium, Samarium, Bismuth ferrites, nano perovskite, doping, Acetylation, benzylic alcohols.
Computationally Driven Characterization of Magnetism, Adsorption, and Reactiv...Joshua Borycz
Metal organic frameworks (MOFs) are a class of nanoporous materials that are com- posed of metal-containing nodes connected by organic linkers. The study of MOFs has grown in importance due to the wide range of possible node and linker combinations, which allow tailoring towards specific applications. This work demonstrates that the- ory can complement experiment in a way that advances the chemical understanding of MOFs. This thesis contains the results of several investigations on three different areas of MOF research: 1) magnetism, 2) CO2 adsorption, and 3) catalysis.
Graphene oxide is synthesized by treating graphite with strong oxidizing agents like potassium chlorate, potassium permanganate, and acids. It has a layered structure with oxygen-containing functional groups such as hydroxyl and epoxy groups bonded to the basal graphene planes. These functional groups make graphene oxide hydrophilic and soluble in water. Graphene oxide can be chemically reduced by removing oxygen groups or chemically functionalized by reacting functional groups on the basal planes with other molecules through covalent bonding.
This document discusses using ion mobility mass spectrometry to quantify linear impurities in cyclic polylactide samples. It finds that the method was unable to accurately determine low levels of linear contamination, as cyclic ions at lower polymerization degrees were less likely to adopt the triply charged state analyzed. This led to an overestimation of linear content. Considering additional charge states or shifting ion conformations may help address this issue in future work. The document introduces the topic, experimental methods, data analysis, results showing inconsistent quantification at different polymerization degrees, and conclusions about limitations and potential improvements.
Swift and efficient_sono-hydrolysis_of_nKarlitox Saoj
This document discusses the hydrolysis of nitriles to carboxylic acids under basic conditions using ultrasound activation. Key findings include:
- Ultrasound significantly increases the rate of nitrile hydrolysis to carboxylic acids under basic conditions compared to thermal activation alone.
- The positive effect of ultrasound is attributed to more than just mechanical effects and likely involves a radical mechanism with the oxide anion radical (OÅÀ).
- Model reactions converting benzonitrile and adiponitrile to benzoic acid and adipic acid, respectively, demonstrate this sono-hydrolysis method under basic conditions.
This document summarizes metal-organic frameworks (MOFs), including their properties and applications. MOFs are highly porous materials formed by combining metal ions or metal clusters with organic ligands. They have extremely large surface areas, often exceeding 7,000 m2/g. Due to their tunable porous structures, MOFs show promise for applications such as gas storage, carbon capture, catalysis, and luminescence. While MOF research has advanced significantly in recent decades, further developing their potential applications and improving stability remains an active area of research.
Methylene Blue (MB) is thiazine dyes that widely use to color product in many industry such as textile, printing, leather, cosmetic and paper. Xanthogenated-Modified Chitosan Microbeads (XMCM) is use to observe the new alternative adsorbent in removing MB from water body through adsorption process. The interactions between MB and functional group in XMCM were confirmed by Fourier Transform Infrared (FT-IR). Several parameters that influence adsorption ability such as the effect of adsorbent dosage of XMCM and the effect of initial pH of MB aqueous solution were studied. This study were done at optimum condition which is at pH 4 of initial pH of MB solution, 0.01 g of initial XMCM dosage, 6 hours stirring time and temperature of (30 ± 2 ). The adsorption data fit well Langmuir model more than Freundlich model. Based on Langmuir model, the maximum monolayer adsorption capacity of MB was 21.62 mg g-1 which indicated that XMCM can be a new alternative adsorbent for removing MB.
Global Journal of Environmental Science and Management (GJESM)
Application of amorphous zirconium (hydr)oxide/MgFe layered double hydroxides composite in fixed-bed column for phosphate removal from water.
Si-Imidazole-HSO4 Functionalized Magnetic Fe3O4 Nanoparticles as an Efficient...Iranian Chemical Society
An efficient and simple method for the preparation of Si-Imidazole-HSO4 functionalized magnetic Fe3O4 nanoparticles (Si-Im-HSO4 MNPs) and used as an efficient and reusable magnetic catalysts for the regioselective ring opening of epoxides under green conditions in water. This catalyst was used for the ring opening of epoxide corresponding to the thiocyanohydrins and azidohydrines. Compared to the classical ring opening of epoxides, this new method consistently has the advantage of excellent yields, short reaction times, and methodological simplicity.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
This document discusses the use of a large-pore metal-organic framework (MOF) called MJ3' for sensing and discriminating explosives at variable concentrations. MJ3' showed good sensitivity and quenching of its fluorescence for a range of explosives like tetryl, TNT, RDX, PETN, and 2,4-DNT in solution. In particular, its large pore size allowed for interactions with PETN, one of the more difficult explosives to detect. Testing revealed concentration limits of detection in the ppm range, suggesting potential applications in homeland security and environmental monitoring. The document concludes that carefully designed MOFs with ultrahigh porosity and stability can enable interior functionalization for applications like
This document summarizes research on synthesizing a transition metal-based Metal-Organic Framework (MOF) for sensor applications. Key points:
- A zinc-based MOF was synthesized using terephthalic acid as the organic linker through a solvothermal method.
- Characterization with XRD, FTIR, UV-VIS and photoluminescence showed the MOF had a crystalline structure with pores and displayed dynamic luminescent properties essential for chemical sensing.
- The MOF exhibited red-shifted fluorescence compared to the free linker molecule, indicating coordination interaction between the zinc and linker affected its luminescence.
Final Photocatalysis Lab Report (1) (1)Henry Hsieh
The document summarizes an experiment analyzing the effect of hydrogen peroxide concentration on the methylene blue degradation kinetic constant. When 5mL and 10mL of hydrogen peroxide were added, kinetic constants of 0.07 min-1 and 0.12 min-1 were obtained, respectively, indicating faster degradation with more hydrogen peroxide. However, decreasing kinetics from excess hydrogen peroxide was not observed due to the limited concentration range studied. Absorbance measurements and kinetic plots were used to determine the degradation constants.
Gas storage in metal organic frameworks(MOFs)Nitish Kumar
Gas storage in metal organic frameworks.
1. Metal organic frameworks has surface area more than 40 tennis courts per gram. So, it has high adsorption capacity.
2. Gas storage in a cylinder filled with MOFs can store much more gas than empty cylinder.
3. Apart from storage ,MOFs can also be used for Gas Separation.
This document discusses a study on mixed-linker zeolitic imidazolate frameworks (ZIFs) containing two types of imidazole linkers. The researchers show that these mixed-linker ZIFs have tunable properties including pore size, hydrophilicity, and organophilicity. They synthesized a series of ZIF-8x-90100-x materials with different ratios of two linkers, resulting in a wide range of crystal sizes from 338 nm to 120 μm. Using various characterization and measurement techniques, they demonstrate that properties like hydrocarbon and alcohol diffusion can be continuously tuned over 2-3 orders of magnitude by varying the mixed-linker composition. This tunability allows mixed-linker ZIFs to
Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for their use in technological applications, since film properties vary considerably with the experimental conditions utilized for film fabrication. In this paper, we employ small-angle X-ray
scattering (SAXS) to investigate solutions of polyanilines and correlate the chain conformations with morphological features of the nanostructured films obtained with atomic force microscopy (AFM). It is shown that aggregates formed already in solution affect the film morphology; in
particular, at early stages of adsorption film morphology appears entirely governed by the chain conformation in solution and adsorption of aggregates. We also use SAXS data for modeling poly(o-ethoxyaniline) (POEA) particle shape through an ab initio procedure based on simulated
annealing using the dummy atom model (DAM), which is then compared to the morphological features of POEA films fabricated with distinct pHs and doping acids. Interestingly, when the derivative POEA is doped with p-toluene sulfonic acid (TSA), the resulting films exhibit a fibrillar morphology—seen with atomic force microscopy and transmission electron microscopy—that is consistent with the cylindrical shape inferred from the SAXS data. This is in contrast with the globular morphology observed for POEA films doped with other acids.
Foram investigadas as interações entre os pesticidas atrazina, imazaquin, metribuzin e paraquat com o polímero condutor poli-(o-etoxianilina)-POEA, utilizando-se as técnicas de microscopia de força atômica (AFM), espectrofotometria de ultravioleta visível (UV-Vis) e
espectroscopia de impedância eletroquímica. Os estudos de microscopia de força atômica em filmes automontados mostraram um aumento na rugosidade do filme polimérico, quando exposto aos pesticidas atrazina, imazaquin e metribuzin e uma diminuição na rugosidade do filme
polimérico exposto ao pesticida paraquat. Isso evidencia a existência de interação química, provavelmente, ligação iônica entre o nitrogênio presente na POEA e os grupos presentes nos pesticidas estudados. Os estudos de ultravioleta visível mostraram uma maior interação entre a
POEA e o pesticida imazaquin. Por meio de medidas elétricas realizadas (espectroscopia de impedância eletroquímica) com um sensor formado por filme de POEA, foi possível distinguir e determinar o limite de detecção dos pesticidas em solução aquosa, o que corrobora com os estudos por AFM e UV-Vis.
This document summarizes an article that appeared in a journal published by Elsevier. The attached copy is for the author's internal non-commercial use, including instruction and sharing with colleagues. Other uses like reproduction, distribution, selling or posting to websites are prohibited without permission. Authors are allowed to post their version of the article to their personal or institutional websites or repositories, with some restrictions on commercial use. The document provides a link to Elsevier's full copyright and archiving policies.
Nanostructured films of poly(o-ethoxyaniline) (POEA) were studied by atomic force microscopy (AFM), which indicated a globular morphology for films containing one or more layers of POEA. Consistent with the nucleation and growth model for the adsorption process, the mean roughness and fractal dimension were found to increase with the time of adsorption and with the number of POEA layers in the initial stages of adsorption, reached maximum values and then decreased after 10 min of adsorption or after deposition of five POEA layers. Such behavior has
been explained in terms of the decrease in the film irregularities, with voids being filled with polymeric material leading to smoother surfaces.
This document summarizes a study on the effect of different solvent systems on poly(lactic acid) (PLA) nanofibres produced through electrospinning. PLA solutions were prepared using various single solvents and mixed solvent systems. Of the single solvents tested, only acetone produced continuous nanofibres, while the others resulted in beads. The addition of acetone to other solvents in a 50/50 mixture improved fibre production. Solutions of acetone/dimethylformamide and acetone/dimethylacetamide produced smooth, bead-free nanofibres with the narrowest diameter distribution. The mixed solvent systems had lower viscosity and surface tension but higher conductivity than single solvents, enabling better fibre formation
This study synthesized pH- and temperature-responsive magnetic nanoparticles (MNPs) by grafting a block copolymer of poly(itaconic acid) and poly(N-isopropylacrylamide) (PIA-b-PNIPAM) onto iron oxide nanoparticles via atom transfer radical polymerization. Characterization using techniques such as transmission electron microscopy, dynamic light scattering, and Fourier transform infrared spectroscopy demonstrated the successful synthesis and responsiveness of the Fe3O4@PIA-b-PNIPAM nanocomposites to changes in pH and temperature. The nanoparticles have potential applications for stimuli-responsive drug delivery and
Question 1 - 4 marks (750 words)Conceptual frameworks have ident.docxmakdul
Question 1 - 4 marks (750 words)
Conceptual frameworks have identified a number of qualitative criteria that financial information should possess if it is to be useful to decision making. The AASB framework Chapter 3 QC12-16 for example makes reference to ‘faithful representation’, with neutrality being one of the key components of ‘faithful representation’. Critically evaluate whether it is possible for financial information to ever be neutral and/or representationally faithful. In your discussion you should consider why standard setters might want to make reference to representational faithfulness within conceptual frameworks.
Question 3 - 4 marks (750 words)
The Conceptual Framework Chapter 1 OB2 states that "the objective of general purpose financial reporting is to provide financial information about the reporting entity that is useful to existing and potential investors, lenders and other creditors in making decisions about providing resources to the entity" Does the identification of these particular users have implications for the measurement basis chosen by the IASB? In your response you will need to consider whether fair values or historical costs will be more relevant to the users identified within the conceptual framework.
text book - Deegan, C. (2014). Financial accounting theory (4th ed.). McGraw-Hill: Sydney.
w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 1 1 5 0 – 1 1 5 8
A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w a t r e s
Sorption of perfluorooctane sulfonate and perfluorooctanoate
on activated carbons and resin: Kinetic and isotherm study
Qiang Yua,b,c, Ruiqi Zhanga, Shubo Denga,b,c,*, Jun Huanga,b,c, Gang Yua,b,c
aDepartment of Environmental Science and Engineering, Tsinghua University, Beijing 100084, PR China
bPOPs Research Center, Tsinghua University, Beijing 100084, PR China
cState Key Joint Laboratory of Environment Simulation and Pollution Control, Tsinghua University, Beijing 100084, PR China
a r t i c l e i n f o
Article history:
Received 5 August 2008
Received in revised form
30 November 2008
Accepted 1 December 2008
Published online 13 December 2008
Keywords:
PFOS
PFOA
Activated carbon
Anion-exchange resin
Sorption kinetics
Sorption isotherm
* Corresponding author. Department of En
Tel.: þ86 10 6279 2165; fax: þ86 10 6279 4006
E-mail address: [email protected]
0043-1354/$ – see front matter ª 2008 Elsevi
doi:10.1016/j.watres.2008.12.001
a b s t r a c t
Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) have increasingly attrac-
ted global concerns in recent years due to their global distribution, persistence, strong
bioaccumulation and potential toxicity. The feasibility of using powder activated carbon
(PAC), granular activated carbon (GAC) and anion-exchange resin (AI400) to remove PFOS
and PFOA from water was investigated with regard to their sorption kinetics and
isotherms ...
Layer-by-layer (LbL) films have been produced with poly(o-ethoxyaniline) (POEA), chitosan and chitosan-poly(methacrylic acid) (CS-PMAA) nanoparticles. Because the adsorption of LbL films depends on ionic interactions and H-bonding, optimized conditions had to be established for the growth of multilayer films. Unusually thick
films were obtained for POEA and CS-PMAA, thus demonstrating the importance of using chitosan in the form of nanoparticles. These nanostructured films were deposited on chromium electrodes to form a sensor array (electronic tongue) based on impedance spectroscopy. This system was used to detect copper ions in aqueous solutions.
This document presents the results of a neutron reflectometry study investigating the hydration of ultrathin antifouling organosilane adlayers on oxidized silicon wafers. The study finds that for a monoethylene glycol silane adlayer, there exists a relatively thick, continuous transition zone of water stemming from within the adlayer. In contrast, for a less effective adlayer lacking internal ether oxygen atoms, this physically distinct interfacial water phase is much thinner and confined to the adlayer-bulk water interface. These results provide further insight into the link between surface hydration and antifouling properties of organosilane adlayers.
The document summarizes research investigating the interface phenomena of poly(o-ethoxyaniline) (POEA) films using atomic force spectroscopy. The study found that POEA films consist of conducting islands surrounded by a less conductive matrix. The conducting islands were characterized by the presence of double-layer forces and visualized using transmission electron microscopy. The conducting islands were only 15 nm in diameter and could only be identified using adhesion mapping, not contact mode atomic force microscopy which showed larger aggregates. The degree of doping and pH affected the morphology and interactions observed, with fully dedoped POEA at pH 5 and partially conducting polyaniline.
This article discusses electroluminescence of MEH-PPV and poly(styrene-co-acrylic acid-co-1-pyrenylmethyl methacrylate) (SAA) blends. The SAA copolymer contains 3 mol% acrylic acid units and a small amount of pyrenyl groups. Blend films with various MEH-PPV/SAA ratios were prepared and their morphology was studied using microscopy. Devices using MEH-PPV alone had a turn-on voltage of 3.5 V and luminance of 500 cd/m2 at 5 V, while a 50/50 blend showed a turn-on of 2.5 V and luminance of 2300 cd
A model HA-type polymer of para-benzoquinone synthetic humic acid (SHA) and its complexes with copper, iron and manganese metal ions were studied using atomic force microscopy (AFM). Natural humic acids (HA) and synthetic humic acids (SHA) were examined by fluorescence spectroscopy, which indicated similarity of SHA and HA spectra. The AFM images of SHA and its complexes revealed variable morphologies, such as small spheres, aggregates and a sponge-like structure. The SHA complexes displayed morphologies similar to those of natural HA. The presence of copper, iron and manganese ions led to the formation of aggregate-type structures in an apparent arrangement of smaller SHA particles.
This document describes the development of a quantitative structure-activity relationship (QSAR) model to estimate the ecotoxicity of ionic liquids expressed as EC50 values for the bioluminescent bacteria Vibrio fischeri. The QSAR was developed using a training set of 96 data points for ionic liquids containing 9 different cations and 17 different anions. A multiple linear regression analysis was performed to correlate molecular descriptor values with experimental and literature EC50 values. The resulting QSAR model can estimate ecotoxicity values for new ionic liquids in the range of log EC50 from -0.23 to 5.00 based on their molecular structure.
This document summarizes a new technique called "jet blowing" that can produce polytetrafluoroethylene (PTFE) and polycaprolactone (PCL) microfibers and nanofibers. PTFE is difficult to process due to its extremely high melt viscosity and insolubility. Jet blowing involves forcing a mixture of heated polymer and gas through a nozzle, where high pressure and extensional stretching facilitate fiber formation inside the nozzle. For PTFE, fibers up to 4 mm long were produced below its melting point. Characterization showed the PTFE fibers were highly crystalline and chemically similar to the starting material. Jet blowing was also used to produce PCL fibers and could potentially process other polymers.
Chemical sensors made from nanostructured films of poly(o-ethoxyaniline) POEA and poly(sodium 4-styrene sulfonate) PSS are produced and
used to detect and distinguish 4 chemicals in solution at 20 mM, including sucrose, NaCl, HCl, and caffeine. These substances are used in order to
mimic the 4 basic tastes recognized by humans, namely sweet, salty, sour, and bitter, respectively. The sensors are produced by the deposition of
POEA/PSS films at the top of interdigitated microelectrodes via the layer-by-layer technique, using POEA solutions containing different dopant
acids. Besides the different characteristics of the POEA/PSS films investigated by UV–Vis and Raman spectroscopies, and by atomic force
microscopy, it is observed that their electrical response to the different chemicals in liquid media is very fast, in the order of seconds, systematical,
reproducible, and extremely dependent on the type of acid used for film fabrication. The responses of the as-prepared sensors are reproducible and
repetitive after many cycles of operation. Furthermore, the use of an “electronic tongue” composed by an array of these sensors and principal component analysis as pattern recognition tool allows one to reasonably distinguish test solutions according to their chemical composition.
- The document describes using multistage reactive transmission mode desorption electrospray ionization mass spectrometry (rTM-DESI MS) to study the oxidation of various substrates like rhodamine B, rhodamine 6G, fluorescein, and lauric acid catalyzed by iron porphyrins.
- The workflow involves detecting the substrate without oxidant or catalyst, then adding oxidant to check for oxidation, and finally adding the catalyst to observe the oxidized substrate.
- The results show that alkyl chain oxidation was observed more frequently than aromatic hydroxylation for the substrates. Multistage rTM-DESI provides a simple method to study catalyst reactivity towards multiple substrates in solution
This document investigates three pyrazolo-pyrimidine derivatives (APP, HPP, MPP) as corrosion inhibitors for copper in sulfuric acid solution. Electrochemical measurements, surface analysis techniques, and theoretical calculations were used. The results show that the inhibitors were effective at inhibiting copper corrosion, with inhibition efficiency increasing with concentration. XPS and molecular dynamics simulations helped explain the adsorption and inhibition mechanisms. HPP and MPP were found to be more effective inhibitors than APP.
Experimental and theoretical investigations of some pyrazolo-pyrimidine deriv...Al Baha University
The anticorrosion performance of three pyrazolo-pyrimidine derivatives, namely, 4-amino pyrazolo-pyrimidine
(APP), 4-hydroxy pyrazolo-pyrimidine (HPP), and 4-mercapto pyrazolo-pyrimidine (MPP) on copper in 0.5M
H2SO4 solution have been investigated using electrochemical, surface analysis, as well as theoretical techniques.
The results indicate that these inhibitors have largely inhibited the corrosion of copper and the inhibition efficiency
increased with increasing concentration. Moreover, the inhibitors adsorb on copper surface following
Langmuir adsorption isotherm. XPS analysis were performed for describing the bonding characteristics between
inhibitors and copper substrate. Furthermore, DFT and molecular dynamics simulation calculations were applied
to further explain the anti-corrosion mechanism.
1) The document examines the role of various catalysts (HCl, H2SO4, CH3COOH, HF, NH4OH) in the fabrication of silica films using a sol-gel process.
2) It was found that different catalysts can have dramatic effects on the porosity, optical quality, shrinkage, thickness, structural evolution during thermal treatment, and stress of the films. For example, using H2SO4 instead of HCl as the catalyst increased the porosity of thermally treated films from 2.8% to 31%.
3) Experiments were conducted to study the effects of various catalysts on silica films fabricated via spin coating of precursor solutions and subsequent thermal
The document summarizes the evolution of the thin film rotating disk electrode (TF-RDE) technique for characterizing oxygen reduction reaction (ORR) activity of platinum electrocatalysts. Early work developed ink formulations containing platinum catalysts and Nafion ionomer to create relatively thick catalyst layers. Subsequent studies examined how thin Nafion films or "caps" affected oxygen diffusion measurements. More recent improvements involved optimizing ink dispersion and fabrication methods to produce more uniform, thinner catalyst layers. However, the document notes that reported ORR activities still vary significantly depending on experimental conditions. Specifically, the presence of Nafion ionomer creates a complex interface that can affect measured kinetics in poorly defined ways.
Similar to Doping in poea nanostructured films studied with atomic force spectroscopy (afs) (20)
The accurate knowledge of the size distribution of
the soil clay particles (φ ≤ 2 μm) can improve the
understanding of the soil surface chemical processes,
which, in their turn, occur mainly in this smallest
sized fraction. However, there are few available
techniques for particle size evaluation at the
nanoscale.
In this work, the synthetic Hydroxyapatite (HAP)
was studied using different preparation routes to
decrease the crystal size and was studied the
temperature effect on the nano-sized hydroxyapatite
crystallization. X-ray diffraction (XRD) analysis
indicated the all samples were composed by a
crystalline HAP phase and another amorphous part.
A low-cost sensor array system for banana ripeness monitoring is presented. The sensors are constructed by employing a graphite line-patterning technique (LPT) to print interdigitated graphite electrodes on tracing paper and then coating the printed area with a thin film of polyaniline (PANI) by in-situ polymerization as the gas-sensitive layer. The PANI layers were used for the detection of volatile organic compounds (VOCs), including ethylene, emitted during ripening. The influence of the various acid dopants, hydrochloric acid (HCl), methanesulfonic acid (MSA), p-toluenesulfonic acid (TSA) and camphorsulfonic acid (CSA), on the electrical properties of the thin film of PANI adsorbed on the electrodes was also studied. The extent of doping of the films was investigated by UV-Vis absorption spectroscopy and tests showed that the type of dopant plays an important role in the performance of these low-cost sensors. The array of three sensors, without the PANI-HCl sensor, was able to produce a distinct pattern of signals, taken as a signature (fingerprint) that can be used to characterize bananas ripeness.
Nanobiosensors can be built via functionalization of atomic force microscopy (AFM) tips with
biomolecules capable of interacting with the analyte on a substrate, and the detection being
performed by measuring the force between the immobilized biomolecule and the analyte.
The optimization of such sensors may require multiple experiments to determine suitable
experimental conditions for the immobilization and detection. In this study we employ molecular
modeling techniques to assist in the design of nanobiosensors to detect herbicides. As a proof
of principle, the properties of acetyl co-enzyme A carboxylase (ACC) were obtained with
molecular dynamics simulations, from which the dimeric form in an aqueous solution was
found to be more suitable for immobilization owing to a smaller structural fluctuation than
the monomeric form. Upon solving the nonlinear Poisson–Boltzmann equation using a
finite-difference procedure, we found that the active sites of ACC exhibited a positive surface
potential while the remainder of the ACC surface was negatively charged. Therefore, optimized
biosensors should be prepared with electrostatic adsorption of ACC onto an AFM tip
functionalized with positively charged groups, leaving the active sites exposed to the analyte.
The preferential orientation for the herbicides diclofop and atrazine with the ACC active site
was determined by molecular docking calculations which displayed an inhibition coefficient
of 0.168 mM for diclofop, and 44.11 mM for atrazine. This binding selectivity for the herbicide
family of diclofop was confirmed by semiempirical PM6 quantum chemical calculations which
revealed that ACC interacts more strongly with the herbicide diclofop than with atrazine,
showing binding energies of 119.04 and +8.40 kcal mol1, respectively.
Atomic force spectroscopy, a technique derived from Atomic Force Microscopy (AFM), allowed us to distinguish nonspecific and specific interactions between the acetolactate synthase enzyme (ALS) and anti-atrazine antibody biomolecules and the herbicides imazaquin, metsulfuron-methyl and atrazine. The presence of specific interactions increased the adhesion force (Fadh) between the AFM tip and the herbicides, which made the modified tip a powerful biosensor. Increases of approximately 132% and 145% in the Fadh values were observed when a tip functionalized with ALS was used to detect imazaquin and metsulfuron-methyl, respectively. The presence of specific interactions between the atrazine and the anti-atrazine antibody also caused an increase in the Fadh values (approximately 175%) compared to those observed when using an unfunctionalized tip. The molecular modeling results obtained with the ALS enzyme suggest that the orientation of the biomolecule on the tip surface could be suitable for allowing interaction with the herbicides imazaquin and metsulfuron-methyl
Emeraldine-salt polyaniline form (ES-PANI) was chemically synthesized using hydrochloric acid at time
synthesis ranging from 0.5 to 48 h and characterized by X-ray diffraction (XRD), LeBail fit, Small-angle
X-ray diffraction (SAXD), Small-angle X-ray Scattering (SAXS) and Scanning Electron Microscopy
(SEM). Crystallinity and crystal data (a = 5.7122, b = 17.8393, c = 22.8027, a = 83.1575, b = 84.6971 and
c = 88.4419) were obtained by XRD and showed that the crystallinity did not vary with the time
synthesis. LeBail fit revealed that the crystallites were very small lamellae with global average size
around 39 Å. By SAXS it was obtained the particle Radius of Giration (Rg) of 320 Å. The maximum particle
size (Dmax) of 650 Å was obtained from the pair-distance distribution function (p(r)). SEM images showed
a fiber morphology formed by interconnected non homogeneous nanospheres. Electrical conductivity of
the samples was in 1.84 104 S/cm.
The use of agrochemicals has increased considerably in recent years, and consequently, there has been increased exposure of ecosystems and human populations to these highly toxic compounds. The study and development of methodologies to detect these substances with greater sensitivity has become extremely relevant. This article describes, for the first time, the use of atomic force spectroscopy (AFS) in the detection of enzyme-inhibiting herbicides. A nanobiosensor based on an atomic force microscopy (AFM) tip functionalised with the acetolactate synthase (ALS) enzyme was developed and characterised. The herbicide metsulfuron-methyl, an ALS inhibitor, was successfully detected through the acquisition of force curves using this biosensor. The adhesion force values were considerably higher when the biosensor was used. An increase of ~250% was achieved relative to the adhesion force using an unfunctionalised AFM tip. This considerable increase was the result of a specific interaction between the enzyme and the herbicide, which was primarily responsible for the efficiency of the nanobiosensor. These results indicate that this methodology is promising for the detection of herbicides, pesticides, and other environmental contaminants.
The immobilization of enzymes on atomic force microscope tip (AFM tip) surface is a crucial step in thedevelopment of nanobiosensors to be used in detection process. In this work, an atomistic modeling ofthe attachment of the acetyl coenzyme A carboxylase (ACC enzyme) on a functionalized AFM tip surface isproposed. Using electrostatic considerations, suitable enzyme–surface orientations with the active sitesof the ACC enzyme available for interactions with bulk molecules were found. A 50 ns molecular dynamicstrajectory in aqueous solution was obtained and surface contact area, hydrogen bonding and proteinstability were analyzed. The enzyme–surface model proposed here with minor adjustment can be appliedto study antigen–antibody interactions as well as enzyme immobilization on silica for chromatographyapplications.
In this work, the synthetic hydroxyapatite (HAP) was studied using different preparation routes to decrease the crystal size and to study the temperature effect on the HAP nano-sized hydroxyapatite crystallization. X-ray diffraction (XRD) analysis indicated that all samples were composed by crystalline and amorphous phases . The sample with greater quantity of amorphous phase (40% of total mass) was studied. The nano-sized hydroxyapatite powder was heated and studied at 300, 500, 700, 900 and 1150 °C. All samples were characterized by XRD and their XRD patterns refined using the Rietveld method. The crystallites presented an anisotropic form, being larger in the [001] direction. It was observed that the crystallite size increased continuously with the heating temperature and the eccentricity of the ellipsoidal shape changed from 2.75 at 300 °C to 1.94, 1.43, 1.04 and 1.00 respectively at 500, 700, 900 and 1150 °C. In order to better characterize the morphology of the HAP the samples were also examined using atomic force microscopy (AFM), infrared spectrometry (IR) and thermogravimetric analysis (TGA).
The increasing importance of studies on soft matter and their impact on new
technologies, including those associated with nanotechnology, has brought intermolecular
and surface forces to the forefront of physics and materials science, for these are the
prevailing forces in micro and nanosystems. With experimental methods such as the atomic
force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition
to providing information on local material properties such as elasticity, hardness and
adhesion. This review provides the theoretical and experimental background of AFS,
adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution
In this work, is presented the thermal behavior of polyaniline (PANI) and its derivatives poly(oethoxyaniline)
(POEA) and poly(o-methoxyaniline) (POMA), which were studied by using differential
scanning calorimetry (DSC), modulated DSC (TMDSC), respectively, and thermal gravimetric analysis
(TGA). The results from diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and thermal
analysis showed the formation of crosslinking isomerization reaction during the heating process. The
results showed that the maximum weight loss and the crystallinity degree depend on the type of the
aromatic ring substituent group, i.e. hydrogen, ethoxy or methoxy.
Suspensions of white and colored nanofibers
were obtained by the acid hydrolysis of white
and naturally colored cotton fibers. Possible differences
among them in morphology and other characteristics
were investigated. The original fibers were
subjected to chemical analysis (cellulose, lignin and
hemicellulose content), X-ray diffraction (XRD)
analysis, and scanning electron microscopy (SEM).
The nanofibers were analyzed with respect to yield,
elemental composition (to assess the presence of
sulfur), zeta potential, morphology (by scanning
transmission electron microscopy (STEM)) and
atomic force microscopy (AFM), crystallinity
(XRD) and thermal stability by thermogravimetric
analysis in air under dynamic and isothermal temperature
conditions. Morphological study of several
cotton nanofibers showed a length of 85–225 nm and
diameter of 6–18 nm. The micrographs also indicated
that there were no significant morphological differences
among the nanostructures from different cotton
fibers. The main differences found were the slightly
higher yield, sulfonation effectiveness and thermal
stability under dynamic temperature conditions of the
white nanofiber. On the other hand, in isothermal
conditions at 180 C, the colored nanofibers showed
a better thermal stability than the white.
This document describes research on the electrochemical synthesis of polyaniline nanoparticles and nanofibers. The researchers used potentiodynamic electrochemical polymerization to control the synthesis. They found that varying the monomer concentration and scan rate resulted in different nanostructure morphologies. Higher aniline concentration (0.5 M) produced nanofibers with a mean diameter of 48 nm, while lower concentration (0.02 M) yielded nanoparticles with a mean diameter of 88 nm. The type and size of nanostructures formed depended on the nucleation and growth processes during polymerization, which could be influenced by the experimental conditions.
This document summarizes research on fabricating and characterizing nanostructured films containing both conducting poly(o-ethoxyaniline) (POEA) and magnetic maghemite nanoparticles. The layer-by-layer technique was used to deposit films by alternately dipping substrates in POEA and sulfonated polystyrene (PSS) solutions, with some POEA solutions additionally containing maghemite nanoparticles. Characterization found the POEA remained doped in the films and a similar conductivity was observed even when maghemite nanoparticles were incorporated. Magnetic measurements also indicated the maghemite nanoparticles were incorporated in the film. The research demonstrates the feasibility of obtaining nanocomposite films exhibiting both conducting and magnetic properties using the layer
The existence of conducting islands in polyaniline
films has long been proposed in the literature, which
would be consistent with conducting mechanisms based on
hopping. Obtaining direct evidence of conducting islands,
however, is not straightforward. In this paper, conducting
islands were visualized in poly(o-ethoxyaniline) (POEA)
films prepared at low pH, using Transmission Electron Microscopy
(TEM) and atomic force spectroscopy (AFS). The
size of the islands varied between 67 and 470 Å for a
pH = 3.0, with a larger average being obtained with AFS,
probably due to the finite size effect of the atomic force microscopy
tip. In AFS, the conducting islands were denoted
by regions with repulsive forces due to the double-layer
forces. On the basis of X-ray diffraction (XRD) patterns for
POEA in the powder form, we infer that the conducting islands
are crystalline, and therefore a POEA film is believed
to consist of conducting islands dispersed in an insulating,
amorphous matrix. From conductivity measurements we inferred the charge transport to be governed by a typical quasione dimensional variable range hopping (VRH) mechanism.
The document studies the interactions between the conductive polymer poly(o-ethoxyaniline) (POEA) and four herbicides (atrazine, imazaquin, metribuzin, paraquat) using atomic force microscopy (AFM), UV-visible spectrophotometry, and electrochemical impedance spectroscopy. AFM showed the polymer surface became rougher when exposed to atrazine, imazaquin, and metribuzin, but smoother with paraquat, indicating chemical interactions between nitrogen in the polymer and groups in the herbicides. UV-Vis showed a stronger interaction between POEA and imazaquin. Electrochemical impedance spectroscopy using a POEA-
Nanometric TiO2 powders were obtained from low tem-perature calcination of a TiO2 resin prepared using the Pechini’s method. Firing the TiO2 resin at 500 oC/2h a powder with anatase phase was obtained, otherwise firing the TiO2 resin at 700 oC/2h a powder with rutile phase was achieved as measured by X-ray diffraction (XRD). The anatase powder presented average particle size of 60 nm observed by Scanning Electronic Microscopy (SEM-FEG) micrographs and average crystallite size of 13 nm calcu-lated from the XRD, while the rutile powder presented av-erage crystallite size of 34 nm. Nanocrystalline TiO2 films with good homogeneity and optical quality were obtained with 80 nm and 320 nm in thickness by Electron Beam Physical Vapour Deposition (EB-PVD) in vacuum on amorphous quartz substrates submitted at 350oC during the evaporation. The 80 nm-thick film presented average particle size of 140 nm and roughness (Ra) of 1.08 nm and the 320 nm-thick film showed average particle size of 350 nm and roughness (Ra) of 2.14 nm measured by Atomic Force Microscopy (AFM). In these conditions of deposi-tion the films presented only anatase phase observed by XRD and MicroRaman spectroscopy.
The fabrication of nanostructured layer-by-layer (LbL) films strives for molecular control of the film properties directly connected with modifications in the film architecture. In the present report, the photoinduced birefringence and formation of the surface-relief gratings in LbL films obtained with an azopolymer (PS119) are shown to be strongly affected by the generation of the dendrimer employed in the alternating layers. Stronger adsorption of PS119 occurred when polypropylenimine tetrahexacontaamine dendrimer (DAB) of higher generations is used, due to a larger number of sites available to interact with azochromophores in PS119. In contrast, the photoinduced birefringence for LbL films
made with the generation 1 dendrimer (DABG1) was higher, which can be explained by weaker interactions between
adjacent layers. Strong interactions in LbL films consisting of PS119 and generation 3 or 5 dendrimers restrict the
chromophore mobility, leading to a smaller birefringence. The interpretation is supported by the fact that surface-relief gratings with larger amplitudes were obtained for 35-bilayer films of DABG1/PS119 (31 nm) in comparison with films from DABG5/PS119 (5 nm). These gratings were formed with mass transport arising from a light-driven mechanism, as photoinscription was successful only with p-polarized light and not with s-polarized light.
Atomic force microscopy (AFM) was used to study the nanoscale surface chemistry and morphological
changes caused by chemical treatment of sisal fibers. Scanning Electron Microscopy (SEM)
micrographs indicated that sisal. The adhesion
force (pull-off force) between the AFM tip and the fibers surface increased after benzylation,
pointing to a decrease in the polar groups on the sisal fiber.
This document describes research on developing inexpensive taste sensors using bare metal electrodes. Key points:
- Chrome-deposited electrodes were able to detect small amounts (M) of substances representing basic tastes (salt, sour, sweet) and copper ions, with high sensitivity attributed to interface effects between the metal and liquid.
- Surprisingly, no nanostructured films were needed on the electrodes, further reducing costs.
- The array of nominally identical electrodes showed cross-sensitivity, distinguishing tastes and complex liquids like wines.
- Control experiments confirmed detection of deliberately introduced substances like copper, distinguishing them from manipulated water samples.
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Doping in poea nanostructured films studied with atomic force spectroscopy (afs)
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2. Author's personal copy
Doping in poly(o-ethoxyaniline) nanostructured films studied with
atomic force spectroscopy (AFS)
F.L. Leite a,b,
*, W.F. Alves a
, M. Oliveira Neto b
, I. Polikarpov b
, P.S.P. Herrmann a
,
L.H.C. Mattoso a
, O.N. Oliveira Jr b
a
Alan G. MacDiarmid Institute for Innovation and Business and National Nanotechnology Laboratory for Agribuseness (LNNA), Embrapa Agricultural Instrumentation,
Rua XV de Novembro 1452, P.O. Box 741, CEP 13560-970 Sa˜o Carlos, SP, Brazil
b
Institute of Physics of Sa˜o Carlos, University of Sa˜o Paulo (USP), P.O. Box 369, CEP 13560-970 Sa˜o Carlos, SP, Brazil
1. Introduction
In recent years, molecular assemblies in the nanometer scale
have been achieved mostly with the Langmuir–Blodgett (LB) (Gaffo
et al., 2007; de Souza et al., 2007) and self-assembly or layer-by-
layer (LbL) methods (Lvov et al., 1997; Xing et al., 2007). The LbL
method, in particular, is experimentally very simple and versatile,
which has made it possible to employ nanostructured films in
sensors (Kim et al., 2008), biosensors (Liang et al., 2008), and in
chemically modified surfaces (Yu et al., 2007). Though the method
was originally conceived for polyelectrolytes, now a variety of
materials are used, including semiconducting polymers such as
polyanilines (Kilmartin et al., 2008; Liu et al., 2008). These
polymers exhibit significant overlap of delocalized p-electrons
along the polymer chain, and may have electrical and optical
properties varying considerably by doping (Suarez and Compton,
1999). The polymer may be reversibly switched from the
insulating into the conducting states, a process accompanied by
insertion or removal of dopant ions (Barisci et al., 2000).
In addition to the doping level and other features of the
semiconducting polymer chains, the final film properties depend
strongly on film morphology, especially in nanostructured films.
Here, processibility of the polymers is essential, which has
prompted many researchers to seek ways to improve solubility
of polyanilines (Wei et al., 1990). Indeed, substituted polyanilines,
such as poly(o-toluidine) (POT), poly(o-methoxyaniline) (POMA)
and poly(o-ethoxyaniline) (POEA) (Kim et al., 2001; Horvat-
Radosevic et al., 2006), normally maintain the electrical and
optical properties of the parent polyaniline, with the added
solubility in some organic solvents and even in aqueous media in
special cases. Therefore, attempts to understand the mechanisms
Micron 39 (2008) 1119–1125
A R T I C L E I N F O
Article history:
Received 15 April 2008
Received in revised form 29 June 2008
Accepted 5 July 2008
Keywords:
Force spectroscopy
Atomic force microscopy
Conducting polymers
Poly(o-ethoxyaniline)
Adhesion forces
SAXS
Force curve
Doping
Self-assembly
Layer-by-layer
A B S T R A C T
The study of intermolecular interactions at interfaces is essential for a number of applications, in addition
to the understanding of mechanisms involved in sensing and biosensing with liquid samples. There are,
however, only a few methods to probe such interfacial phenomena, one of which is the atomic force
spectroscopy (AFS) where the force between an atomic force microscope tip and the sample surface is
measured. In this study, we used AFS to estimate adhesion forces for a nanostructured film of poly(o-
ethoxyaniline) (POEA) doped with various acids, in measurements performed in air. The adhesion force
was lower for POEA doped with inorganic acids, such as HCl and H2SO4, than with organic acids, because
the counterions were screened by the ethoxy groups. Significantly, the morphology of POEA both in the
film and in solution depends on the doping acid. Using small-angle X-ray scattering (SAXS) we observed
that POEA dissolved in a mixture of dimethyl acetamide exhibits a more extended coil-like conformation,
with smaller radius of gyration, than for POEA in water, as in the latter POEA solubility is lower. In AFS
measurements in a liquid cell, the force curves for a POEA layer displayed an attractive region for pH ! 5
due to van der Waals interactions, with no contribution from a double-layer since POEA was dedoped. In
contrast, for pH 3, POEA was doped and the repulsive double-layer force dominated. With AFS one is
therefore able to correlate molecular-level interactions with doping and morphology of semiconducting
polymers.
ß 2008 Elsevier Ltd. All rights reserved.
* Corresponding author at: Institute of Physics of Sa˜o Carlos, University of Sa˜o
Paulo (USP), P.O. Box 369, CEP 13560-970 Sa˜o Carlos, SP, Brazil.
Tel.: +5516 3373 9333; fax: +5516 3371 5365.
E-mail addresses: leite@cnpdia.embrapa.br, fabiolimaleite@gmail.com
(F.L. Leite).
Contents lists available at ScienceDirect
Micron
journal homepage: www.elsevier.com/locate/micron
0968-4328/$ – see front matter ß 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.micron.2008.07.003
3. Author's personal copy
behind the usefulness of semiconducting polymers for the various
applications must involve studies of intermolecular interactions
(Guimard et al., 2007; Rahman et al., 2008). For the sensing ability
in liquids, for instance, one has to investigate how minute changes
in the liquid affect the film properties.
One method suitable for probing interactions at the molecular
level is the atomic force spectroscopy (AFS) (Drelich and Mittal,
2005; Leite and Herrmann, 2005; Leite et al., 2005, 2008), in which
an atomic force microscope is used to measure the force – for
varying distances – between a tip and the sample surface. AFS was
used for studying the doping degree, morphology and non-specific
interactions of POEA (Leite et al., 2007a). Here we employ AFS to
study properties of POEA in the form of a one-layer, nanostructured
film, adsorbed using the concepts of the LbL method. Emphasis is
placed on the dependence with the doping acid used to process
POEA in the film fabrication procedure. Unique to this system, as we
shall show, is the ability to control the degree of attractive and
repulsive interactions through the selective doping or dedoping of
the POEA film.
2. Materials and methods
POEA was chemically synthesized according to the method
described by Mattoso et al. (1995). Polymeric solutions were
prepared by dissolving 0.005 g of POEA dedoped (emeraldine base)
in 10 mL of N,N-dimethylacetamide (DMAc), and then adding one
of the following acids: p-toluenesulfonic (p-TSA), camphorsulfonic
acid (CSA), sulfanilic acid (SAA), H2SO4, HNO3 and HCl. After
ensuring that there were no precipitates, 40 mL of ultrapure water
were added and the pH adjusted to the desired value with the acid,
thus completing a final volume of 50 mL. Then, the final polymer
concentration was 0.5 Â 10À3
mol LÀ1
in a 1:4 (v/v) mixture of
DMAc and ultrapure water. Using this solution one-layer LbL films
were produced by immersion of the substrate into a POEA solution
for several adsorption times, viz. 10, 30, 60 and 180 s for each layer.
AFM images were obtained with a Topometrix TMX 2010
Discoverer, operating in the contact mode, being analyzed using
WSxM (Nanotec Electronica S.L.) (Horcas et al., 2007). The
cantilevers had a spring constant, k = 0.08 Æ 0.02 N mÀ1
, and tip
curvature radius R = 38 Æ 3 nm. The tip and cantilever were made of
silicon nitride (Si3N4). The low contact force was chosen to reduce
deformation or indentation of the POEA surfaces. Before acquiring the
images, the piezoscanner of the AFM system was calibrated, since its
behavior may depart from linearity between the force and displace-
ment. In order to check the accuracy of the measurements, subsidiary
experiments were performed with a Topometrix standard grade
silicon (Si) coated with quartz (average height: 24.0 mm and
pitch: 15.0 mm). The errors in length measurements were lower
than those expected for the standard grade (AFM Standard-B, P/N
10-10299, Topometrix. maximum deviation: average height = 8%
and pitch = 2.5%), being 2.5% and 0.1% for average height and pitch,
respectively. The scanner used in the experiments has maximum
scan ranges of 70 mm in both x and y axes. Force curves were
measured in solution with a cell developed by Topometrix
consisting of a glass support with two orifices for the inlet and
outlet of liquids and an O-ring for sealing it. The curves were also
acquired in ambient conditions, at several points over the sample
scanned area. The theoretical background and possible applications
of AFS are given in the reviews (Cappella and Dietler, 1999; Leite
and Herrmann, 2005).
Fig. 1. Average dummy atom model (DAM) for POEA in (a) water and (b) DMAc/water (1:4, v/v).
Fig. 2. AFM image of a POEA film doped with HCl (pH 3) for different immersion times on mica. (a) 10; (b) 60 and (c) 180 s.
F.L. Leite et al. / Micron 39 (2008) 1119–11251120
4. Author's personal copy
The small angle X-ray scattering (SAXS) experiments were
conducted at the National Synchrotron Light Laboratory (LNLS),
Campinas, Brazil, using a monochromatic X-ray beam
(l = 1.488 A˚ ). To perform the SAXS measurement, the aqueous
solution was placed in a flat cell and sealed. The SAXS curves were
normalized with respect to (i) the decreasing intensity of the
coming synchrotron beam and (ii) the sample absorption. The
SAXS intensity produced by the solvent (water and DMAc) was
measured and subtracted from the total scattering intensity before
the analysis. Since solutions containing particles of different sizes
(polydisperse) show several linear regions in the Guinier plot, in
order to generate low resolution models we considered only the
SAXS curve from the last linear region (Leite et al., 2007b). This was
performed as an attempt to include the information due to the
smallest particles in solution as if the system were monodisperse
(three-dimensional models).
3. Results and discussion
The properties of polymer films produced with the layer-by-
layer (LbL) technique depend on a number of experimental
parameters, including the solvent for preparing the solutions and
the time of adsorption of each layer. Fig. 1 shows the low-
resolution particle shape for POEA molecules in solution,
determined from the SAXS data using the ab initio procedure
(Semenyuk and Svergun, 1991). A less-packed, coiled structure is
observed for POEA dissolved in DMAc/water (Fig. 1b), while for
POEA dissolved in water blobs are formed (Fig. 1a). The values of
radii of gyration, Rg, for POEA dissolved in water and water/DMAc
are 64 and 32 A˚ , respectively. The larger radius for POEA in water
may be caused by larger aggregates arising from the rod-like
Fig. 3. Typical force curve obtained in air for a POEA film adsorbed on mica. This
force curve was taken with a frequency of jump of 104
mm/s. If the force curve were
obtained with a frequency of jump 1 mm/s, an attraction peak would appear due
to stretching of POEA chains (adapted from Leite et al., 2007a).
Fig. 4. (a) Cantilever deflection (representing adhesion force) for POEA films doped with various acids (pH 3) and non-doped POEA-EB. In all cases, the films were adsorbed on
mica with 3 min of immersion. Also shown are the structural formulas of the organic acids (b); AFM images for (c) POEA doped with HCl and (d) POEA doped with TSA.
Measurements performed in air.
F.L. Leite et al. / Micron 39 (2008) 1119–1125 1121
5. Author's personal copy
conformation of the polymer chains. For POEA in water/DMAc, the
chains assume a more extended coil-like conformation due to the
higher solubility. It is known that aggregates formed already in
solution affect film morphology (Leite et al., 2005); in particular at
early stages of adsorption film morphology appears entirely
governed by the chain conformation in solution and adsorption of
aggregates (Leite et al., 2007b). A careful investigation of the
Guinier plots revealed a larger size of chain aggregates for POEA
dissolved in water; the size of the aggregates decreased with
increasing amount of DMAc in the solution. In fact, the best
tradeoff between solubility and aggregation is attained in a 1:4 (v/
v) mixture of DMAc and water.
The influence from the time of adsorption on the film properties
was investigated by adsorbing POEA molecules on mica within
short time periods. If full coverage of the substrate by a POEA layer
is desired, one has to use adsorption times above 180 s. In AFM
experiments, we observed that non-covered areas were apparent
when shorter adsorption times were employed, as depicted in the
images of Fig. 2. For 10 s of immersion time, for instance, most of
the substrate area appears to be uncoated. For 60 s, granular
structures characteristic of POEA films become apparent, which
only occupy the whole area for the 3rd image obtained with 180 s
of adsorption (Fig. 2c).
Fig. 3 shows typical force curves for POEA in air, in which the
adhesion force was 30 Æ 5 nN, whereas the van der Waals was
1.3 Æ 0.6 nN, for measurements performed in five distinct regions.
The total downward force in air comprises several contributions,
including the van der Waals and bridge forces, with the adhesion
force between the tip and the sample surface being the sum of them
all. On the other hand, when force curve measurements are
performed in solution, electrostatic and hydration forces may appear
between the tip and sample. The interaction forces most relevant to
the present work are contact, van der Waals, capillary and
electrostatic forces. van der Waals forces are significant for smooth
contacts and in solution but are expected to be small compared to
other forces involving relatively rough surfaces in air. Liquid bridges
provide the dominant adhesion forces only above $40% of relative
humidity (Xu et al., 1998). It should be mentioned that for a POEA
film, the force curves obtained in air may vary depending on the spot
chosen for the measurement due to the intrinsic film roughness.
Furthermore, the force may depend on how many times that spot has
been used in previous measurements as the area of contact varies
with consecutive measurements because polymer chains may be
adsorbed (desorbed) onto the tip. Generally, the adhesion force is
lower in the first 3 measurements, especially in a liquid cell. This
occurs because the tip is at least partially covered with the polymer
after a series of measurements, giving rise to the so-called bridge
forces between tip and sample (Leite et al., 2007a). The bridge forces
depend on the frequency in the tapping mode, because at high
frequencies the relaxation time of the polymer may be exceeded
(Biggs and Proud, 1997).
The type of acid used to dope POEA affects the interaction with
the AFM tip, most probably due to the different chemical nature of
the dopant counterion and also because of distinct ‘chain
conformations’ on the substrate. Fig. 4a shows the cantilever
deflection due to the adhesion force between the AFM tip and POEA
Fig. 5. (a) Force curves (pull-on forces) for a POEA film deposited on mica in solutions of various pH values (HCl); (b) AFM image of POEA (pH 3) and (c) AFM image of POEA (pH
9). The curves have been shifted vertically to facilitate visualization. Only the approach curves were included.
F.L. Leite et al. / Micron 39 (2008) 1119–11251122
6. Author's personal copy
films doped with various acids, with the measurements performed
in air. The pull-off force measured is higher for POEA films doped
with organic acids, such as p-toluenesulfonic (p-TSA), camphor-
sulfonic (CSA) and sulfanilic (SAA) acids, whose structures are
shown in Fig. 4b. The smaller adhesion for inorganic acids may be
due to the polymer steric protection, i.e. the counterions (SO4
2À
and ClÀ
) are screened by ethoxy groups of POEA, being less
attracted by the AFM tip. This is why the forces for POEA doped
with HCl and H2SO4 are close to that measured with dedoped POEA
(emeraldine base (EB)), as shown in Fig. 4a.
For the comparison of adhesion forces in POEA doped with
organic acids, one notes that the sample doped with SAA has more
polar groups on the surface due to the presence of amine groups
(NH2-polar). Therefore, interaction with the tip may occur via H-
bonding between the oxygen from the oxidized silicon nitride tip
and the hydrogen from the amines, in addition to van der Waals
forces. This additional interaction increases adhesion. The POEA
film doped with CSA has methyl groups (CH3-apolar) and oxygen
atoms bonded to sulfur and carbon, which imparts polarity to the
polymer chains. From AFM images it was possible to infer that the
film doped with TSA has hydrophobic groups on the surface,
leading to a distinct chain conformation on the surface, i.e. fibrillar
morphology (Fig. 4d), while the film doped with HCl has globular
morphology (Fig. 4c). These conformations are affected by the
doping degree and acid used. A more extended structure is
obtained by increasing the doping level. Indeed, POEA molecules in
solution have a less-packed coiled structure for pH 3.0 while at pH
10.0 blobs are formed. POEA solutions doped with TSA at pH 3.0
showed a cylindrical-like conformation (Leite et al., 2007a,b),
which gives origin to the fibrilles observed in AFM images of
Fig. 4d. These distinct conformations may lead to different pull-off
forces, since the contact area between the AFM tip and the sample
varies.
In force curves obtained in a liquid cell, the interaction
between two surfaces depends on several factors, including
surface charge density and conformation of the polymer chains at
the interface. Also important is the possible aggregation of
particles. We investigated first bare substrates and adsorbed
POEA in contact with pure water. For a mica substrate immersed in
water, there is no interaction down to a separation of 6.7 Æ 0.7 nm
between the tip and the mica surface. Some dispersion is observed
when measurements are carried out in different regions of a sample
(Leite et al., 2003). The force at all regions is attractive, approxi-
mately 0.7 nN. For POEA adsorbed onto the mica, an attractive force
of 3.2 nN appears for the tip-surface distance of 12.0 Æ 0.8 nm. In
both cases, bare mica and POEA film, the forces occur for almost
neutral or hydrophobic surfaces, since the attractive van der Waals
forces will operate at distances smaller than 5 nm. The long-range
interactions responsible for the force measured are hydrophobic,
which arise from repulsion of water. This induces hydrophobic
particles to aggregate.
The force curves in solution are also affected by the level of
POEA doping, which may be studied by measuring forces with
POEA in liquid cells at different pHs. Fig. 5a shows force curves for
POEA adsorbed onto mica in contact with aqueous solutions of
various pHs. For pH ! 5.0, the attractive force ranged from 0.6 to
1 nN. POEA is expected to be non-protonated, and therefore there
is no double-layer, the attractive force being entirely due to van der
Waals forces. For pHs between 4 and 5 POEA becomes doped and
the repulsive force from the double-layer counterbalances the van
der Waals forces. For pH 3, where POEA is almost completely
charged, the double-layer contribution dominates and leads to a
repulsive force, which is even more evident for the curve at pH 1. It
is recalled that the tip becomes charged because in aqueous
solutions the surface of silicon tips comprises amphoteric silanol
and basic silylamine (secondary (silazane, –Si2NH2) and possibly
primary (silylamine, –SiNH3) amines though the latter are rapidly
hydrolyzed) surface groups (Drummond and Senden, 1994). The
commercial silicon nitride tip surface has been found to be almost
electrically neutral over a wide pH range, from at least pH 6–8.5,
thus indicating equal densities of silanol and sylamine surface
groups (Borato et al., 2006). For Si3N4 tip on mica, the total tip-
sample force changes from attractive for pH 6 to repulsive at
pH $ 8, because mica is negatively charged at any pH value, while
the isoelectric point for Si3N4 tip is ca. pH 6.3 (de Souza et al., 2001).
The morphology for POEA is globular, with the size of the
globules increasing with pH. At pH 3, the interactions between
doped chains and with the surface are less significant, favoring a
less condensed packing of polymer chains (Fig. 5b). These results
are consistent with the literature (Leite et al., 2007b), according to
which charged polyelectrolytes form thin films as the charged
molecules adsorbed create a potential barrier that prevents more
molecules from adsorbing. For undoped POEA, the repulsive forces
are minimized, leading to denser packing of molecules in solution
or at the surface (Fig. 5c). Indeed, the potential barrier does not
exist for undoped POEA, which can adsorb via hydrogen bonds. The
measurements performed in pH 1 showed a larger double-layer
force than for pH 3. However, in pH 1 the interaction map is more
inhomogeneous, with several repulsive regions seen in Fig. 6.
A further possible control of film properties may be imparted if
surfactant acids are used. This is the case of dodecylbenzene
sulfonic acid (DBSA), which may help form the so-called hairy rod
polymers, which are rigid polymers with a dense set of flexible side
Fig. 6. Interaction maps (20 mm  20 mm) for (a) POEA-ES (pH % 3.0) and (b) POEA-
ES (pH % 1.0).
F.L. Leite et al. / Micron 39 (2008) 1119–1125 1123
7. Author's personal copy
chains (such as alkyl tails) covalently bonded to the backbone
(Ballauff, 1989). The repulsion between alkyl tails and the rigid
backbone controls self-organized structures. In conjugated poly-
mers, lamellar self-organization in polypyrrole-alkyl, sulfates
(Wernet et al., 1984) and polyaniline-dodecylbenzenesulfonates
(Zheng et al., 1995) has been observed. Fig. 7a shows the
morphology of POEA doped with dodecylbenzene sulfonic acid
(POEA-DBSA), whose structure differs from those of POEA films
doped with the acids mentioned above with regard to the size of
the globules and roughness. The excess DBSA forms micellar
structures that also act as a surfactant, as depicted in Fig. 7b. The
hydrophobic tails of free and bonded DBSA molecules are so
arranged as to turn to the aqueous phase, since the molecular
conformation of POEA-DBSA chains is affected both by inter-
molecular interactions and interactions with the aqueous medium
(Levon et al., 1995).
4. Conclusions
The AFS technique was used to study physicochemical proper-
ties of nanostructured films of the semiconducting poly(o-
ethoxyaniline) (POEA) and interactions between the film and an
AFM tip. Various effects could be identified since the polymer used,
POEA, has a variable degree of doping, which depends on the acid
used to process the polymer and on the pH. The structure and size
of the acid counterions are important for the interaction forces
because of steric effects. Force curves were obtained for POEA films
displaying attractive regions due to van der Waals interactions and
repulsive interactions owing to double-layer contributions. When
a liquid cell was used, the AFS measurements served to investigate
specific interactions and the doping degree of POEA, which can be
useful in the study of electronic properties of thin films. Also
investigated was the influence of the solvent for the formation of
aggregates, from which we concluded that the best tradeoff
between solubility and aggregation is attained in a 1:4 (v/v)
mixture of DMAc and water.
The interaction forces measured with AFS, especially in liquid
cells, may help understand the mechanisms behind the high
sensitivity of taste sensors, which has been attributed to interfacial
phenomena between the liquid under analysis and the film-
forming molecules of the sensing unit (Borato et al., 2006).
Acknowledgments
The authors are grateful to Embrapa for the facilities provided
and to FAPESP, CNPq, Nanobiotec and CT-Hidro (Brazil) for the
financial support.
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