This document describes research on using magnetic chitosan nanoparticles for removing Cr(VI) from aqueous solutions. The researchers introduced a simple method to prepare magnetic chitosan nanoparticles via co-precipitation and epichlorohydrin cross-linking. Characterization showed the nanoparticles were spherical and around 30 nm in size. Adsorption experiments found Cr(VI) removal was highly dependent on pH, with maximum adsorption of 55.80 mg/g occurring at pH 3. Kinetic data fit a pseudo-second order model and isotherm data fit the Langmuir model well. The magnetic chitosan nanoparticles showed potential for use in wastewater treatment applications to remove Cr(VI).
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.
Influence of reaction medium on morphology and crystallite size of zinc oxidejournal ijrtem
ABSTRACT : Zinc oxide nanoparticles were prepared by reacting zinc chloride and sodium hydroxide in different mediums such as chitosan, poly vinyl alcohol, ethanol and starch. The materials were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) studies, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Elemental analysis was done by energy dispersive X-ray Analysis (EDAX).
KEY WORDS : Nano zinc oxide, morphology, crystallite size
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.
Influence of reaction medium on morphology and crystallite size of zinc oxidejournal ijrtem
ABSTRACT : Zinc oxide nanoparticles were prepared by reacting zinc chloride and sodium hydroxide in different mediums such as chitosan, poly vinyl alcohol, ethanol and starch. The materials were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) studies, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Elemental analysis was done by energy dispersive X-ray Analysis (EDAX).
KEY WORDS : Nano zinc oxide, morphology, crystallite size
Synthesis and charecterization studies of nano ti o2 prepared via sol gel methodeSAT Publishing House
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
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.
Visible Light Assisted Degradation of Eosin Yellow using Heteroatom Functiona...IJERA Editor
10 ppm EY dye were successfully photodegraded using visible light active 0.75wt% Ba & 0.25wt% Zr codoped
TiO2 nanomaterial that were synthesized by Sol-gel method as nanomaterials under irradiation for 20
minutes and characterized by various advanced instrumental techniques. The X-ray Diffraction Spectroscopic
showed that the prepared nanomaterial were in the anatase phase with 2θ at 25.3º. UV-visible Diffuse
Reflectance Spectra analysis explained that the dopants found in the TiO2, imparts a significance absorption
shift towards visible region and their exisistance were confirmed by X-ray Photoelectron Spectral data.
Quantitatively the formation of hydroxyl radical by the nanomaterial in aqueous solution under visible
light irradiation was investigated by the photoluminiscent technique. Finally the effects of different parameters
in the photocatalytic degradation of EY were established in aqueous solution
Synthesis and Application of C-Phenylcalix[4]resorcinarene in Adsorption of C...Jacsonline.Org
Synthesis and Application of C-Phenylcalix[4]resorcinarene in Adsorption of Cr(III) and Pb(II), for more information visit our website http://jacsonline.org/
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.
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.
Synthesis and charecterization studies of nano ti o2 prepared via sol gel methodeSAT Publishing House
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
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.
Visible Light Assisted Degradation of Eosin Yellow using Heteroatom Functiona...IJERA Editor
10 ppm EY dye were successfully photodegraded using visible light active 0.75wt% Ba & 0.25wt% Zr codoped
TiO2 nanomaterial that were synthesized by Sol-gel method as nanomaterials under irradiation for 20
minutes and characterized by various advanced instrumental techniques. The X-ray Diffraction Spectroscopic
showed that the prepared nanomaterial were in the anatase phase with 2θ at 25.3º. UV-visible Diffuse
Reflectance Spectra analysis explained that the dopants found in the TiO2, imparts a significance absorption
shift towards visible region and their exisistance were confirmed by X-ray Photoelectron Spectral data.
Quantitatively the formation of hydroxyl radical by the nanomaterial in aqueous solution under visible
light irradiation was investigated by the photoluminiscent technique. Finally the effects of different parameters
in the photocatalytic degradation of EY were established in aqueous solution
Synthesis and Application of C-Phenylcalix[4]resorcinarene in Adsorption of C...Jacsonline.Org
Synthesis and Application of C-Phenylcalix[4]resorcinarene in Adsorption of Cr(III) and Pb(II), for more information visit our website http://jacsonline.org/
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.
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.
In this work, we synthesized and characterized mesoporous thin fims
of SiO 2 and NiTiO3 structured by a surfactant called Brij58. These fims
were fabricated by the method of dip coating and the best conditions for
well-structured thin fims were investigated as a function of surfactant
concentration and diffrent types of substrates. These fims have been
characterized by X-ray reflctivity which was calculated using the matrix
formalism. We demonstrated that the silicon substrate had a great effct
on the structure and porosity of the fabricated fims for both SiO2 and
NiTiO3. Furthermore, we found that mesoporosity has been increased
as a function of the surfactant concentration in the solution. This experimental procedure allows also to produce NiTiO3 powders which have
been characterized by X-ray diffaction. The XRD coupled to the crystallographic software “Maud”shows that the samples are constituted by 98,
2% NiTiO 3 powders.
SYNTHESIS AND CHARACTERIZATION OF KAOLINITE COATED WITH CU-OXIDE AND ITS EFFE...Premier Publishers
In this paper, a novel copper oxide coated kaolinite was prepared as an adsorbent of Hg(II) ions from aqueous media. The materials used for this study were synthesized, characterised and the product tested for mercury ion removal using standard laboratory procedures. Reactivity and removal kinetic models derived from Freundlich isotherm were used to investigate contact time and pH effects on the coefficient of protonation and rate of mass transfer of Hg(II) ions to the reactive sites, Proton coefficient of 0.89 indicated a decrease in proton consumption function when compared with uncoated kaolinite. At the 12th h reaction time, a maximum adsorption capacity of 85% was achieved. Mass transfer rates of 0.9359h-1 and 0.0748h-1 for the first and second reaction phases indicated a reduction when compared with uncoated kaolinite. These changes may be ascribed to masking of reaction sites and exposed surface area of the Cu-Oxide coated kaolinite.
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Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
2. out in inert gas (N2). Fe3O4 nanoparticles were synthesized by
co-precipitation of ferric and ferrous salts. The amount 6.4795 g of
FeCl3·6H2O and 3.3339 g of FeSO4·7H2O were dissolved into 150 mL
of deoxygenated distilled water. After stirring for 30 min, chemical pre-
cipitation was achieved at 30 °C under vigorous stirring by adding
20 mL of NH3·H2O solution (28%, v/v). During the reaction process, pH
was maintained at about 10. The reaction system was kept at 70 °C for
1 h. 1 g chitosan flake was dissolved in a 150 mL CH3COOH solution
2% (w/v). The chitosan solution was then dropped into the obtained
magnetic fluid in the flask through a dropper. Afterwards, 2 mL of
pure epichlorohydrin was added into reaction flask and stirred at
85 °C for 3 h, before the flask was cooled down to room temperature.
The precipitate was washed with distilled water to remove all existing
in the effluents. Silver nitrate (AgNO3) was used to detect residue of
Cl−
. The precipitate was then washed with ethanol and dried at 50 °C,
in the vacuum oven.
2.3. Adsorption experiments
The sorption experiments were performed by batch method. Sam-
ples of 0.1 g of magnetic chitosan nanoparticles were equilibrated with
50 mL of solution containing various amount of Cr(VI). The pH value
of solutions was adjusted by using diluted solution of NaOH and HCl.
The temperature of the solutions (25 °C, 35 °C, 45 °C) was controlled
with the thermostatic bath. The adsorbed amount of Cr(VI) per unit
weight of magnetic chitosan nanoparticles, qt (mg·g−1
), was calculated
from the mass balance equation as:
qt ¼
C0−Ctð Þ⋅V
m
ð1Þ
where C0 and Ct (mg/L) are the initial Cr(VI) concentration and the Cr(VI)
concentrations at any time t, respectively; V (L) is the volume of the
Cr(VI) solution; and m (g) is the mass of the magnetic chitosan
nanoparticles. Samples of the Cr(VI) solution were collected at pre-
determined time intervals and analyzed using a UV–Vis Spectrophotom-
eter (model UV-PC1600, Shimadzu), at λmax=540 nm, according to the
1,5-diphenyl-carbazide method [21]. All measurements were conducted
triplicate.
2.4. Characterization methods
X-ray diffraction (XRD) patterns were obtained at room tempera-
ture by D8 Advance, Bruker ASX, using CuKα radiation (λ=1.5406 Å)
Fig. 1. Camera pictures (a, b); FE-SEM images (c, d) and TEM images (e, f) of magnetic chitosan nanoparticles.
1215N.N. Thinh et al. / Materials Science and Engineering C 33 (2013) 1214–1218
3. in the range of 2θ=10°–60°, and a scanning rate of 0.02°·s−1
. Mor-
phology of magnetic chitosan nanoparticles was analyzed by Field
Emission Hitachi S-4500 Scanning Electron Microscope (FE-SEM) and
Transmission Electron Microscope (TEM, JEOL, Voltage: 80 kV). Absor-
bance measurements were carried out using Shimadzu UV-PC1600
spectrophotometer in the range of 400–800 nm.
The magnetic properties were measured with home-made vibrat-
ing sample magnetometer (VSM) and evaluated in terms of satura-
tion magnetization and coercivity. Chemical composition of samples
was determined by JEOL Scanning Electron Microscope and Energy
Dispersive Spectroscopy (SEM/EDS) JSM-5410 Spectrometer.
3. Results and discussion
3.1. Characterization of magnetic chitosan nanoparticles
TEM and SEM micrograph of magnetic chitosan particles provides in-
formation on their size and morphology. It can be observed from Fig. 1
that the magnetic particles have a spherical shape with a diameter of
about 30 nm.
XRD pattern of magnetic chitosan nanoparticles shows six charac-
teristic peaks for Fe3O4 corresponding to (220), (311), (400), (422),
(511) and (440) (JCPDS file, PDF No. 65-3107) (Fig. 2). Quite weak dif-
fraction lines of composite indicated that Fe3O4 particles have been coat-
ed by amorphous chitosan, which did not affect the phase and structure
of Fe3O4. Particle size of magnetic chitosan nanoparticles can be estimat-
ed approximately as 30 nm, via line broadening in the pattern, using
Debye–Scherrer equation (d=kλ/βcos θ).
Typical magnetization loops were recorded by VSM and shown on
Fig. S1 (supporting information). From the plot of magnetization vs.
magnetic field and its enlargement near the origin, the saturation
magnetization, remanence magnetization, coercivity and squareness
could be calculated. Because of no remanence and coercivity, it can be
suggested that the beads are superparamagnetic. It can also be observed
from this figure that magnetization moment of Fe3O4 nanoparticles
decreases very little after chitosan surface coating, meaning that chito-
san does not affect magnetic properties of these magnetic chitosan
nanoparticles. Therefore, maintaining such a high saturation magnetiza-
tion value (Ms) after coating these nanoparticles is advantageous and
susceptible to the external magnetic field for magnetic separation.
3.2. Effect of initial pH on the adsorption process
It is well known that some metals are preferentially adsorbed in acid-
ic media while chitosan can dissolve under this acidic condition. In this
regard, the chemical modification of chitosan by using crosslinking reac-
tion offers an important pathway for producing chemically more stable
chitosan derivatives, extending the potential applications of this bio-
polymer. In our study, the crosslinking approach with epichlorohydrin
to block/crosslink via hydroxyl (OH) group is expected to improve
chemical stability, mechanical resistance and adsorption/desorption
properties, compared to that with glutaraldehyde (to block amino
(NH2) group respectively), when keeping reactive amino groups intact
for complexing reaction with heavy metal ions [14,16,19].
Next, selecting an optimum pH is very important for the adsorp-
tion process, since pH affects not only the surface charge of adsorbent,
but also the degree of ionization and the speciation of the adsorbate
during the reaction. The effect of pH on the adsorption process was
investigated over the range from 2 to 6. As indicated in Fig. 3, the
maximum capacity of Cr(VI) absorption occurred at pH of 3. The ex-
planation would be addressed as the pH of the aqueous solution af-
fects to stability of chromium speciation and the surface charge of
the adsorbent. At pH 1, the chromium ions exists in the form of
H2CrO4, while in the pH range of 1–6, different forms of chromium
such as Cr2O7
2−
, HCrO4
−
, and Cr3O10
2−
coexist while HCrO4
−
predominates.
As the pH increases, those form shifts to Cr2O4
2−
and Cr2O7
2−
[11]. Cr(VI)
exists predominantly as HCrO4
−
in aqueous solution below pH 4 and the
amino groups (–NH2) of magnetic chitosan nanoparticles would be in
protonated cationic form (–NH3
+
) to a higher extent in acidic solution.
This results in the stronger attraction for negatively charged ions.
Electrostatic interaction between the sorbent and HCrO4
−
ions also con-
tributes to the high chromium removal. However, at the pH lower than
3, decrease in uptake capacity is observed as the predomination of
H2CrO4 and the strong competition for adsorption sites between
H2CrO4 and protons. The decreasing of the adsorption capacity at higher
pH values may be explained by the dual competition of CrO4
2−
and OH−
for adsorption [11]. Thus, pH 3 was selected as the optimum pH value for
the following adsorption experiment.
3.3. Adsorption isotherms
Equilibrium experimental data were successfully fitted to the
Langmuir isotherm whose equation can be expressed as
q ¼
qm⋅KL⋅Ce
1 þ KL⋅Ce
ð2Þ
where qm (mg·g−1
) is the maximum sorption capacity (corresponding
to complete monolayer coverage), Ce is the equilibrium concentration
in the solution (mg/L), qe is the equilibrium Cr(VI) concentration in
20 30 40 50 60 70
(440)
(511)
(422)
(400)
(311)
(220)
Intensity
2θ
Fig. 2. XRD pattern of magnetic chitosan nanoparticles.
2 3 4 5 6
50
55
60
65
70
75
80
85
R(%)
pH
Fig. 3. The influence of initial pH value on the adsorption of the Cr(VI) on magnetic
chitosan nanoparticles.
1216 N.N. Thinh et al. / Materials Science and Engineering C 33 (2013) 1214–1218
4. the sorbent (mg·g−1
), and KL is the sorption affinity constant related to
the binding energy of sorption (L·mg−1
). The experimental data
(Table 1) fitted well with Langmuir model (R2
>0.99), confirming that
the adsorption process is monolayer adsorption. The results of adsorp-
tion studies by Langmuir model, indicating improved Cr(VI) uptake
properties of magnetic chitosan nanoparticles (55.80 mg·g−1
, pH 3,
room temperature, compared to the other adsorbents (Table 2)), proba-
bly relates to the smaller loss of amine groups of chitosan, involved in
the cross-linking reaction when using epichlorohydrin as a cross-linker.
Cr(VI) removal by adsorbent as a function of contact time with
different initial concentrations (40, 80 and 180 mg·L−1
) of Cr(VI) is
shown in Fig. 4, where the adsorption rate of metal uptake was
quite slow and the maximum uptake was observed within 100 min.
3.4. Thermodynamic and kinetic studies
In this section, thermodynamic and kinetic aspects of the adsorp-
tion process will be considered. The experimental data obtained at
different temperatures were used in calculating the thermodynamic
parameters such as Gibbs free energy (ΔG), enthalpy (ΔH) and entro-
py (ΔS) according to the following equations:
ΔG ¼ ΔH−T Â ΔS ð3Þ
lnK ¼ ln qe=Ceð Þ ¼ −ΔH=RT þ ΔS=R: ð4Þ
Where K is the equilibrium constant, obtained from Langmuir iso-
therms at different temperature and R is the universal gas constant.
ΔH and ΔS were obtained from the slope and intercept of the plot
log (qe/Ce) vs. 1/T (Fig. 5), namely:
ΔH ¼ −0:6853 kJ⋅mol
−1
and ΔS ¼ −115:7366 J⋅mol
−1
⋅K
−1
:
Table 1
Adsorption equilibrium constants obtained from Langmuir isotherm in the adsorption
of Cr(VI) onto magnetic chitosan nanoparticles (volume: 50 mL; absorbent dose: 0.1 g;
initial concentrations: 60, 80 and 180 mg·L−1
; pH value: 3.0; temperature: 298,308,
318 K).
Temperature (K) qmax (mg·g−1
) KL R2
298 55.80 0.366 0.993
308 46.71 0.119 0.997
318 43.29 0.138 0.994
Table 2
Comparison of adsorption capacities of Cr(VI) with other adsorbents.
Adsorbents Adsorption capacity
(mg·g−1
)
pH Ref.
Tires activated carbon 58.50 2.0 [23]
Rubberwood activated carbon 44.05 2.0 [3]
Coconut shell activated carbon 20.00 2.0 [24]
Hazelnut shell activated carbon 17.70 2.0 [25]
Beech sawdust 16.10 1.0 [26]
Sugarcane bagasse 13.40 2.0 [27]
Coconut shell charcoal 10.88 4.0 [28]
Coconut tree sawdust 3.60 3.0 [29]
Chitosan 22.09 3.0 [30]
Non-cross linked chitosan 78.00 5 [31]
Cross linked chitosan 50.00 5 [31]
Magnetic chitosan nanoparticles (this
study)
55.80 3
0 50 100 150 200 250 300 350 400
10
15
20
25
30
35
40
45
50
55
60
65
70
q(mg/g)
t(min)
40mg/L
80mg/L
180mg/L
Fig. 4. Effect of contact time on Cr(VI) adsorption (volume: 50 mL; absorbent dose: 0.1 g;
initial concentrations: 40, 80 and 180 mg·L−1
; pH value: 3.0; temperature: 298 K).
3.20 3.22 3.24 3.26 3.28 3.30 3.32 3.34 3.36
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
y=-13.92069+4.38115x,R=0.99017
Ln(qe/Ce)
1/T*10-3
(1/K)
C=80 mg/L
Fig. 5. Thermodynamic plot of ln (qe/Ce) vs. 1/T.
Table 3
Thermodynamic data of Cr(VI) adsorption process.
T (K) ΔG (kJ·mol−1
) ΔH (kJ·mol−1
) ΔS (J·mol−1
·K−1
)
298 −35.164 −0.6853 −115.7366
303 −35.742
307 −36.205
312 −36.784
-50 0 50 100 150 200 250 300 350
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
t(min)
40mg/L
80mg/L
180mg/L
ln(qe-qt)
Fig. 6. Kinetic pseudo-first order sorption kinetics of Cr(VI) (volume: 50 mL; absorbent dose:
0.1 g; initial concentrations: 40, 80 and 180 mg·L−1
; pH value: 3.0; temperature: 298 K).
1217N.N. Thinh et al. / Materials Science and Engineering C 33 (2013) 1214–1218
5. The negative value of ΔG obtained from Eq. (3) reflects a spontane-
ous (favorable) adsorption process of Cr(VI) (Table 3), while the nega-
tive value of ΔH indicates that the adsorption reaction is exothermic
and the adsorption of Cr(VI) is more effective at lower temperatures.
Kinetically, in order to understand the behavior of the adsorbent and
to examine the controlling mechanism of the adsorption process, the
pseudo-first-order and the pseudo-second-order were applied to the ex-
perimental data (Figs. 6 and 7). The pseudo-first-order rate expression of
Lagergren is given as: ln(qe−qt)=ln(qe)−k1⋅t where qe and qt are the
amounts of Cr(VI) (mg·g−1
) adsorbed on the adsorbent at equilibrium
and at time t, respectively and k1 is the rate constant of first-order adsorp-
tion (min−1
). The slopes and intercepts of plots of ln(qe−qt) vs. t were
used to determine the first-order rate constant k1. The pseudo-
second-order kinetic model is expressed as: t
qt
¼ 1
k2⋅qe
2 þ 1
qe
 t where k2
(g·mg−1
·min−1
) is the rate constant of second order adsorption. The
slopes and intercepts of plots of t/qt vs. t were used to calculate the
second-order rate constant k2 and qe [22]. Adsorption rate constants
were summarized in Table 4. The values of regression coefficient for
pseudo-second-order model were close to 1 for all initial Cr(VI) concen-
trations. The calculated values qe,cal were very close to obtained qe,exp
values. Hence, the adsorption of Cr(VI) onto magnetic chitosan nano-
particles could obey the pseudo-second-order kinetic model.
4. Conclusion
In this work, cross-linked with epichlorohydrin magnetic chitosan
nanoparticles were prepared and characterized. The Cr(VI) adsorption
behavior on the prepared magnetic chitosan nanoparticles has been
studied under various conditions of different solution pH values and ad-
sorption contact times. Optimal adsorption conditions of Cr(VI) were
found at pH 3, and contact time of 100 min, with maximum adsorption
capacity of 55.80 mg·g−1
. The Langmuir model was found to fit
well with the experimental data (correlation coefficient R2
0.99),
indicating the occurrence of monolayer adsorption process. Ther-
modynamically, the adsorption of Cr(VI) is spontaneous (in term
of ΔG) and exothermic (in term of ΔH) process. Kinetically, the
adsorption of Cr(VI) onto magnetic chitosan nanoparticles obeyed
the pseudo-second-order model. Compared to the other adsor-
bents, magnetic chitosan nanoparticles shows greatly improved
uptake properties of Cr(VI), probably due to high concentration of
remaining active sites on the surface of magnetic chitosan nano-
particles. The improved magnetic and adsorption uptake properties
are two main features of the synthesized nanoparticles that can be
advantageously used in water treatment.
Acknowledgments
Funding of this work was provided by Vietnam Ministry of Science
and Technology (grant 08/2011/HÐ-NÐT).
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.msec.2012.12.013.
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0 50 100 150 200 250 300 350
0
2
4
6
8
10
12
14
16
18
40mg/L
80mg/L
180mg/L
t/qt(min.g/mg)
t(min)
Fig. 7. Kinetic pseudo-second order sorption kinetics of Cr(VI) (volume: 50 mL; absor-
bent dose: 0.1 g; initial concentrations: 40, 80 and 180 mg·L−1
; pH value: 3.0;
temperature: 298 K).
Table 4
Comparison of the first-order and second-order adsorption rate constants, calculated qe,cal and experimental qe,exp values for different initial Cr(VI) concentrations.
C0 (mg·L−1
) qe,exp (mg/g) First-order kinetic model Second-order kinetic model
k1 (min−1
) qe,cal (mg·g−1
) R2
k2(g·mg−1
·min−1
) qe,cal (mg·g−1
) R2
40 19.42 0.029 5.59 0.946 8.38×10−3
19.94 0.994
80 37.05 0.030 25.43 0.876 2.08×10−3
38.46 0.992
180 53.8 0.025 22.04 0.956 2.16×10−3
55.55 0.996
1218 N.N. Thinh et al. / Materials Science and Engineering C 33 (2013) 1214–1218