- The document summarizes a seminar presentation on carbon quantum dots (CDs), which are nanoscale carbon materials less than 10 nm in size that exhibit fluorescence.
- CDs can be synthesized through top-down methods that break down bulk carbon sources or bottom-up methods that build CDs from small precursor molecules. Their properties can be tuned through surface functionalization and doping.
- CDs have potential applications in chemical sensing, bioimaging, optoelectronics and more due to their tunable fluorescence, biocompatibility and photostability. Their synthesis, properties, characterization and applications were discussed in detail in the presentation.
This includes what is Quantum Dots and their properties ,types of synthesis methods of nano materials such as top down, bottom up etc.It includes few things about Carbon Quantum Dots.
This includes what is Quantum Dots and their properties ,types of synthesis methods of nano materials such as top down, bottom up etc.It includes few things about Carbon Quantum Dots.
Carbon containing Nanomaterials: Fullerenes & Carbon nanotubesMayur D. Chauhan
The following presentation is only for quick reference. I would advise you to read the theoretical aspects of the respective topic and then use this presentation for your last minute revision. I hope it helps you..!!
Mayur D. Chauhan
This topic includes a brief description of CDs, synthesis methods, factors influencing their properties, characterization tools, and recently used applications.
Nitrogen-Enriched Carbon Nanobubbles and Nanospheres for Applications in Ener...Devika Laishram
Multifunctional carbon nanomaterials have attracted remarkable consideration for use in various energy
conversion and storage devices because of their ultrahigh specific
surface area, unique morphology, and excellent electrochemical
properties. Herein, we report the synthesis of highly uniform and
ordered nitrogen-enriched carbon nanospheres (CS) and nanobubbles (CNB) by a modified Stöber reaction using resorcinol and
formaldehyde in the presence of ethylenediamine as a nitrogen
source. A comparative study of the prepared CS and CNB
nanomaterials is presented here with potential use in a wide variety
of applications involving large surface area and electrical
conductivity. As counter electrode materials in solar cells, CNB and CS showed enhanced photoelectrochemical activity for
catalytically reducing I3
− to I− and improved capacitive behavior with a low charge transfer resistance and remarkable power
conversion efficiency (PCE) of 10.40% with improved Jsc (20.20 mA/cm2
) and Voc (0.73 V). The enhanced performance of the
fabricated photoelectrochemical cell is due to the excellent point contact and good conductivity that offered better charge
transportation of electrons with minimum recombination. The enhanced adsorption upon increasing the pressure without an
apparent saturation level signified the large CO2 adsorption with 2 mmol/g for the CS. Additionally, the rectangular-shaped CV
curve indicated the double-layer capacitive behavior, good electrochemical reversibility, and high-power characteristics, prerequisites
for supercapacitor application. This study probes the practical possibility of nitrogen-enriched carbon nanostructures as a
multifunctional material for prospective applications.
Carbon-cuprous oxide composite nanoparticles
were chemically deposited on surface of thin glass tubes of spent
energy saving lamps for solar heat collection. Carbon was
obtained from fly ash of heavy oil incomplete combustion in
electric power stations. Impurities in the carbon were removed by
leaching with mineral acids. The mineral free-carbon was then
wet ground to have a submicron size. After filtration, it was
reacted with concentrated sulfuric/fuming nitric acid mixture on
cold for 3-4 days. Potassium chlorate was then added drop wise on
hot conditions to a carbon slurry followed by filtration.
Nanocarbon sample was mixed with 5% by weight PVA to help
adhesion to the glass surface. Carbon so deposited was doped with
copper nitrate solution. After dryness, the carbon/copper nitrate
film was dipped in hydrazine hydrate to form cuprous oxide -
carbon composite, It was then roasted at 380-400 °C A heat
collector testing assembly was constructed of 5 glass coils
connected in series with a total surface area of 1250 cm2
. Heat
collection was estimated by water flowing in the glass coils that
are coated with the carbon/copper film,. Parameters affecting the
solar collection efficiency such as time of exposure and mass flow
rate of the water were studied. Results revealed that the prepared
glass coil has proven successful energy collector for solar heat.
Carbon containing Nanomaterials: Fullerenes & Carbon nanotubesMayur D. Chauhan
The following presentation is only for quick reference. I would advise you to read the theoretical aspects of the respective topic and then use this presentation for your last minute revision. I hope it helps you..!!
Mayur D. Chauhan
This topic includes a brief description of CDs, synthesis methods, factors influencing their properties, characterization tools, and recently used applications.
Nitrogen-Enriched Carbon Nanobubbles and Nanospheres for Applications in Ener...Devika Laishram
Multifunctional carbon nanomaterials have attracted remarkable consideration for use in various energy
conversion and storage devices because of their ultrahigh specific
surface area, unique morphology, and excellent electrochemical
properties. Herein, we report the synthesis of highly uniform and
ordered nitrogen-enriched carbon nanospheres (CS) and nanobubbles (CNB) by a modified Stöber reaction using resorcinol and
formaldehyde in the presence of ethylenediamine as a nitrogen
source. A comparative study of the prepared CS and CNB
nanomaterials is presented here with potential use in a wide variety
of applications involving large surface area and electrical
conductivity. As counter electrode materials in solar cells, CNB and CS showed enhanced photoelectrochemical activity for
catalytically reducing I3
− to I− and improved capacitive behavior with a low charge transfer resistance and remarkable power
conversion efficiency (PCE) of 10.40% with improved Jsc (20.20 mA/cm2
) and Voc (0.73 V). The enhanced performance of the
fabricated photoelectrochemical cell is due to the excellent point contact and good conductivity that offered better charge
transportation of electrons with minimum recombination. The enhanced adsorption upon increasing the pressure without an
apparent saturation level signified the large CO2 adsorption with 2 mmol/g for the CS. Additionally, the rectangular-shaped CV
curve indicated the double-layer capacitive behavior, good electrochemical reversibility, and high-power characteristics, prerequisites
for supercapacitor application. This study probes the practical possibility of nitrogen-enriched carbon nanostructures as a
multifunctional material for prospective applications.
Carbon-cuprous oxide composite nanoparticles
were chemically deposited on surface of thin glass tubes of spent
energy saving lamps for solar heat collection. Carbon was
obtained from fly ash of heavy oil incomplete combustion in
electric power stations. Impurities in the carbon were removed by
leaching with mineral acids. The mineral free-carbon was then
wet ground to have a submicron size. After filtration, it was
reacted with concentrated sulfuric/fuming nitric acid mixture on
cold for 3-4 days. Potassium chlorate was then added drop wise on
hot conditions to a carbon slurry followed by filtration.
Nanocarbon sample was mixed with 5% by weight PVA to help
adhesion to the glass surface. Carbon so deposited was doped with
copper nitrate solution. After dryness, the carbon/copper nitrate
film was dipped in hydrazine hydrate to form cuprous oxide -
carbon composite, It was then roasted at 380-400 °C A heat
collector testing assembly was constructed of 5 glass coils
connected in series with a total surface area of 1250 cm2
. Heat
collection was estimated by water flowing in the glass coils that
are coated with the carbon/copper film,. Parameters affecting the
solar collection efficiency such as time of exposure and mass flow
rate of the water were studied. Results revealed that the prepared
glass coil has proven successful energy collector for solar heat.
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
Reduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
tReduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
A facile method to prepare CdO-Mn3O4 nanocompositeIOSR Journals
CdO-Mn3O4 nanocomposite has been prepared by a simple solvothermal method using a domestic microwave oven. Cadmium acetate, manganese acetate and urea were used as the precursors and ethylene glycol as the solvent. The as-prepared sample was annealed for 1 hour in each case at different temperatures, viz. 100, 200 and 300°C. The as-prepared and annealed samples were characterized by X-ray diffraction and scanning electron microscopic analyses. Results indicate that annealing at 300°C is required to get the sample with high phase purity and homogeneity. The present study indicates that the method adopted can be considered as an economical and scalable one to prepare the proposed nanocomposite with reduced size, phase purity and homogeneity.
Optical Control of Selectivity of High Rate CO2 Photoreduction Via Interband-...Pawan Kumar
Photonic crystals consisting of TiO2 nanotube arrays (PMTiNTs) with periodically modulated diameters were fabricated using a precise charge-controlled pulsed anodization technique. The PMTiNTs were decorated with gold nanoparticles (Au NPs) to form plasmonic photonic crystal photocatalysts (Au-PMTiNTs). A systematic study of CO2 photoreduction performance on as-prepared samples was conducted using different wavelengths and illumination sequences. A remarkable selectivity of the mechanism of CO2 photoreduction could be engineered by merely varying the spectral composition of the illumination sequence. Under AM1.5 G simulated sunlight (pathway#1), the Au-PMTiNTs produced methane (302 µmol h-1) from CO2 with high selectivity (89.3%). When also illuminated by a UV-poor white lamp (pathway#2), the Au-PMTiNTs produced formaldehyde (420 µmol h-1) and carbon monoxide (323 µmol h-1) with almost no methane evolved. We confirmed the photoreduction results by 13C isotope labeling experiments using GC-MS. These results point to optical control of the selectivity of high-rate CO2 photoreduction through selection of one of two different mechanistic pathways. Pathway#1 implicates electron-hole pairs generated through interband transitions in TiO2 and Au as the primary active species responsible for reducing CO2 to methane. Pathway#2 involves excitation of both TiO2 and surface plasmons in Au. Hot electrons produced by plasmon damping and photogenerated holes in TiO2 proceed to reduce CO2 to HCHO and CO through a plasmonic Z-scheme.
Synthesis and structural characterization of cd s nanocrystals added with pb2+eSAT Journals
Abstract
For the past few years, the prepration and characterization of nanocrystals of materials have become an interesting area in the
research activity. CdS (Cadmium Sulphide) is a well known semi conducting material which finds applications in optical devices.
In the present study, we have made an attempt to investigate the effect of Pb2+ as impurity on the properties of CdS nanocrystals.
The samples were prepared by using simple domestic microwave assisted solvothermal method with ethylene glycol as solvant.
The samples prepared were annealed to have good ordering. X-ray diffraction measurements were carried out for all the smples.
The grain size, lattice parameter and yield were determined. The colour before and after annealing was noted. EDX and SEM
analyses were also done. The prepared samples were electrically characterized by making dielectric measurements on the
prepared pellets. The present study indicates that the polarization mechanism in the nano crystals considered is mainly
contributed by the space charge polarization.
Keywords: Semiconducting II –IV materieals, Cadmium sulphide, XRD patterns, solvothermal method, electrical
measurements
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after 24 h irradiation was 9934 μmol g−1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride 145 μmol g−1cat under identical conditions. The presence of triethylamine was found to be vital for the higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for subsequent six runs without significant loss in photo activity.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used
for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after
24 h irradiation was 9934 mmol g1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a
sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride
145 mmol g1cat under identical conditions. The presence of triethylamine was found to be vital for the
higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for
subsequent six runs without significant loss in photo activity.
Metal-organic hybrid: Photoreduction of CO2 using graphitic carbon nitride su...Pawan Kumar
A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used
for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after
24 h irradiation was 9934 mmol g1cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a
sacrificial donor, which was significantly higher as compared to the semiconductor carbon nitride
145 mmol g1cat under identical conditions. The presence of triethylamine was found to be vital for the
higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for
subsequent six runs without significant loss in photo activity.
Carbon Nitride Grafted Cobalt Complex (Co@npg-C3N4) for Visible LightAssiste...Pawan Kumar
Azide containing bipyridine complex of cobalt was grafted to
the propargylated nanoporous graphitic carbon nitride (npg-C3
N4) via click reaction to obtain heterogenized photocatalyst
which could efficiently provide direct esterification of aldehydes
under visible light irradiation at room temperature. The use of
click reaction as grafting strategy provided covalent attachment
of the cobalt complex to support which not only provided
higher loading but also precluded the leaching. Furthermore,
the presence of carbon nitride support exhibited synergistic
effect to enhance the reaction rate. In addition, the milder basic
nature of nitrogen containing graphitic support provided
efficient ester synthesis without the need for an external base.
The synthesized photocatalyst was found to be quite robust
which could easily be recovered and reused several times
without significantly losing activity.
Analysis Of Carbon Nanotubes And Quantum Dots In A Photovoltaic Device Slide ...M. Faisal Halim
Francis' presentation to Louis Stokes Association for Minority Participation. Since I co-authored this work I think I have the right to a copy. I was the graduate student Francis was working with.
International Journal of Research in Engineering and Science is an open access peer-reviewed international forum for scientists involved in research to publish quality and refereed papers. Papers reporting original research or experimentally proved review work are welcome. Papers for publication are selected through peer review to ensure originality, relevance, and readability.
An Update on Gas CCS Project: Effective Adsorbents for Establishing Solids Looping as a Next Generation NG PCC Technology - presentation by Colin Snape in the Natural Gas CCS session at the UKCCSRC Cardiff Biannual Meeting, 10-11 September 2014
— CdTe quantum dots (QDs)/Poly (diallyldimethylammonium chloride) (PDDA) multilayer films (QDMF) have been self-assembled by layer-by-layer (LBL) technique. CdTe quantum dots (QDs) were synthesized by using Te, NaBH 4 , and CdCl 2 as precursors and mercaptopropionic acid (MPA) as stabilizer. The as-prepared composites were characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV-vis adsorption spectrum(UV-vis), and Fluorescence spectrum(FS), respectively. It was shown that the self-assembled QDMF in this study could be used as gaseous sensors for detecting organic gases, such as ammonia, acetone, methanol and formaldehyde. The quenching mechanism of CdTe QDs multilayer films by formaldehyde was studied in detail and The detection limit was 10-236ppm.
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.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Richard's entangled aventures in wonderlandRichard 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.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
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.
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.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
1. ADAMA SCIENCE AND TECHNOLOGY UNIVERSITY
DEPARTMENT OF APPLIED CHEMISTRY
MATERIALS CHEMISTRY PhD PROGRAM
SEMINAR – I PRESENTATION ON
CARBON QUANTUM DOTS
SYNTHESIS, PROPERTIES AND APPLICATION
ENDALE KEBEDE FEYIE
MONDAY JULY 1, 2019
2. 2
Fig. One-pot synthesis and purification route for CDs with distinct fluorescence characteristics. (B) Eight CD
samples under 365 nm UV light. (C) Corresponding PL emission spectra of the eight samples, with maxima
at 440, 458, 517, 553, 566, 580, 594, and 625 nm.
4. 1. INTRODUCTION
What are carbon quantum dots?
Novel class of carbon nanomaterials with prominent fluorescence and are composed
of discrete, quasi-spherical carbogenic material with sizes less than 10 nm. (H. Yu et al.
2016)
Are known as carbon dots(CDs), carbon nanodots(CNDs), carbon quantum dots
(CQDs).
Discovery
• Xu et al., 2004; synthesis of SWCNTs from graphite
Composition and structure
• Their core is mostly carbon
• Contain 5-50 wt.% oxygen and other elements (H, N, S, P, …)
• Their morphology is mostly quasi-spherical, and the structure can be graphitic or
amorphous (K. Hola et al. 2014, L. Bao et al. 2011) 4
5. WHAT IS UNIQUE ABOUT CARBON QUANTUM
DOTS?
• exhibit some distinctive properties due to occurrence of
the quantum confinement and edge effect.
• tunable and stable photoluminescence (PL)
• Upconverted photoluminescence (UPCL)
• Biocompatible, inert, non toxic
• Tunable surface functionalization
• high resistance to photobleaching, photoblinking
• marked electron donating and accepting capabilities
• Excellent water solubility
• low cost and ease of synthesis
Can replace semiconductor quantum dots and dyes in
different areas of applications ranging from sensing to
optoelectronics. (X. Wang et al. 2009, W. Kwon et al. 2014)
5
6. WHY CARBON QUANTUM
DOTS?
• As a group of newly emerging fluorescent nanomaterials, CQDs have shown
tremendous potential as versatile nanomaterials for a wide range of applications,
including (R. Q. Ye et al. 2013)
• chemical sensing, biosensing,
• bioimaging,
• drug delivery,
• photodynamic therapy, photothermal therapy
• Photocatalysis, electrocatalysis
• Optoelectronics
• Solar cells
• Light emitting devices
• Capacitors, …. 6
7. 2. STRUCTURE
• CQDs are commonly described in terms of a carbogenic
core with surface shell. (X. Li et al. 2015)
• Core structure: Mostly carbon
• Could be amorphous or crystalline/sp2 or sp3 carbon
• Graphitic, graphene like, amorphous
• surface shell
• envelops the core
• Results from surface functionalization and passivation
• hosts a variety of functional groups
• Hydroxyl, Carboxyl, Carboxylate, Amine, and Amide
• complex molecules: polyethylene glycol (PEG), or
polyethyleneimine
7
8. STRUCTURE:
DEFECTS
• Core and surface structures of CDs are quite
synthesis-dependent
• Defects are created during synthesis through
surface functionalization and doping
• Density of defects is related to synthesis method
and precursors used
• may serve as capture centres for excitons, thus
giving rise to surface-state-related PL
• Can be revealed by characterization techniques
such as:
• X- ray diffraction (XRD)
• Raman spectroscopy
• X-ray photo electron spectroscopy (XPS)
• Fourier transform infrared spectroscopy ((FTIR)
• TEM/HRTEM
8
9. DEFECTS IN CQDs
• XRD: peak at 26 corresponding to the (002)
planes of graphite, two new peaks emerged at
22.59 (labelled *) and 18.20, which refer to the
amorphous carbon and (103) planes (belonging
to hexagonal carbon) in the XRD pattern
• Raman spectra: The intensity ratio of the D and
G band (ID/IG) is a measurement of the disorder
extent, as well as the ratio of sp3/sp2 carbons.
• XPS: the XPS spectra of C1s, from which we can
see that from graphite to C-dots, the peak
intensity (located at about 288 eV) has a
noticeable increase, indicating more oxidation
groups (C–O, C=O) appeared in C-dots, which is
consistent with the Raman results.
Figure (A) XRD patterns, (B) Raman spectra λex =
633 nm), (C) C1s XPS spectra and (D) FTIR spectra of
graphite and CQDs produced electrochemically from
graphite. (H. Ming et al. 2012)
9
11. 3.1. TOP-DOWN
METHODS
• Involve the disruption of bulk carbon
precursors or nanomaterials such as:
• graphite (bulk),
• carbon nanotubes,
• activated carbon.
• The methods include:
• arc-discharge,
• laser ablation,
• electrochemical oxidation,
• chemical oxidation
• Require additional passivating and
functionalizing their surface with various
polar/apolar moieties.
(A. Sciortino et al. 1018)
11
Advantages
• abundant raw materials
• produce oxygen containing functional
groups at the edge,
• facilitating their solubility and
functionalization.
Limitation
• low yield,
• large density of defects,
• Little fluorescent or have low
fluorescence quantum yield
• control of size and shape
12. 3.1.1. LASER ABLATION
Involves ablating a piece of bulk carbon material using a laser beam
Only after an acidic treatment of the surface and the following
surface passivation by organic molecules, these carbon nanoparticles
become bright luminescent
Sun et al.: graphite target in a flow of argon gas carrying water
vapor at 900 °C and 75 kPa.
Gonçalves et al.: carbon targets immersed in deionized water
Hu et al.: graphite flakes dispersed in PEG solution
Reyes et al. graphite target in acetone
Size of CQDs can be controlled by:
Wave length of the laser
Laser pulse with (pulse duration)
12
Y.-P. Sun et al., 2006
S.-L. Hu et al. 2009
D. Reyes et al. 2016
13. 3.1.2. ELECTROCHEMICAL OXIDATION
the most common method to synthesize CQDs with
the advantages of high purity, low cost, high yield,
easy manipulation of size and good reproducibility
Carried out in an electrochemical cell using the
precursors graphite/carbon nano tubes as electrodes
Size control can be achieved by manipulating applied
potential, current density, nature of electrolyte/pH,
temperature
J. G. Zhou et al.: MWCNTs used as electrode
H. Li et al.: graphite electrode with NaOH/ethanol as
the electrolyte
Shinde et al.: MWCNTs as electrode and propylene
carbonate/LiClO4 electrolyte
13
Fig. The schematic diagram of
electrochemical fabrication of C-dots.
14. 3.1.3. CHEMICAL OXIDATION
• an effective and convenient approach for large scale production and requires no complicated devices.
• provides a simple approach to synthesize CQDs using cheap, abundant precursors: carbon fibre, coal,
carbon soot
• The precursor heated in the mixture of strong acids (sulfuric acid and nitric acid) and requires
additional passivation step
• The oxygen-containing groups such as C=O, C–O, O–H are introduced to the surface of CQDs during
the oxidation.
• The strength/concentration of the acid and duration of treatment determines size, PL quantum yield
14
Qiao et al. 2010
S. Hu et al. 2013
15. 3.2. BOTTOM-UP APPROACHES
• fabricate CQDs from molecular precursors such as citric acid,
sucrose and glucose through
• microwave synthesis,
• thermal decomposition,
• Hydrothermal/solvothermal treatment,
• template-based routes.
• Involves carbonization of the molecular precursors carried out
at relatively low temperatures.
• Besides “pure” carbon-core CQDs, mixing the carbon sources
with other molecular precursors, as urea and thiourea can be
used as a method to dope the structure of CQDs with nitrogen,
sulphur, or other heteroatoms.
• They are particularly simple and surface passivation can be
usually achieved in “one pot” without the need of post-synthesis
chemical processing. 15
Advantages
• fewer defects
• controllable size and
morphology;
Disadvantage
• poor solubility,
• small dot size
• aggregation issue
16. 3.2.1. HYDROTHERMAL/SOLVOTHERMAL SYNTHESIS
• are economical, eco-friendly, easy to handle, and route to synthesize
CDs from diverse carbon-based precursors.
• In a typical procedure,
• the precursors are dissolved in a suitable solvent and heated to high
temperature (100−200 °C) in the absence of air in a Teflon-lined
autoclave.
• The small organic moieties join together to form carbogenic cores
and then grow into CDs ranging from 2 to 10 nm in size.
• The PL can be modulated by varying the experimental conditions, i.e.,
varying the molar mass of precursors, the nature of the solvent, heating
time, and temperature.
• Zboril et al. prepared CDs from citric acid and urea in N,N-
dimethylformamide
• Mehta et al. prepared CQDs from sugar cane juice in ethanol
• Bourlinos et al. synthesized CQDs from ammonium citrate in water
• Although not the very latest and has been used in practice for many
years, it is still a very efficient, facile, versatile, and cost-effective
approach for the synthesis of CDs.
16
Fig a) Preparation of MCBF-CQDs from blue to
red by solvothermal treatment of CA and DAN. b)
Photographs of MCBF-CQDs under daylight(left)
and fluorescence images (right) under UV light
(excited at 365 nm) . Yuan F. et al.
17. 3.2.2. MICROWAVE-ASSISTED HEATING METHOD
• is an augmentation to the solvothermal/ hydrothermal technique where microwave is utilize
instead of heat.
• can effectively shorten the reaction time and provide simultaneous, homogeneous heating,
which leads to uniform size distribution of quantum dots
• is facile, less energy/time consuming, and easily scalable for the preparation of highly
fluorescent CQDs
• Zhu et al.: sugar and polyethylene glycol (PEG) in distilled water
• Tang et al.: glucose + water
17
18. 3.2.3. THERMAL DECOMPOSITION (PYROLYSIS)
• involves heating of the precursor organic molecules at high temperature for a predefined
time followed by dissolution in water and separation
• offers advantages of easy operation, solvent-free approach, wide precursor tolerance, short
reaction time, low cost and scalable production
• Ma et al. synthesized N-doped GQDs with graphene-like structures by the direct carbonization of
ethylene diamine tetra acetic acid (EDTA) heated in a sand bath at 260–280 ℃
• Martindale et al. prepared CQDs with a high quantum yield of 45% by the straightforward
pyrolysis of citric acid at 180 ℃ for 40 h .
18
19. 3.2.4. TEMPLATE BASED METHOD – CONFINED PYROLYSIS
• Discrete CQDs with tunable and uniform sizes can be prepared via
confined pyrolysis of an organic precursor in nanoreactors. The
synthesis involved three steps:
• absorbing the organic precursor into porous nanoreactors via
capillary force,
• pyrolysis of the organic precursor confined in the nanoreactors into
carbonaceous matter,
• release of the as-synthesized CQDs by removing the nanoreactors.
• J. Zong et al. synthesized hydrophilic CQDs with mesoporous
silica nanospheres as nanoreactors by impregnation of a citric
acid precursor
• Polymeric core–shell nanoparticles are also effective nanoreactors with
thermally cross-linkable core and thermally removable shell
• pyrolysis of PAN@PMMA core–shell nanoparticles
Schematic illustration of the
preparation of CQDs via confined
pyrolysis of an organic precursor in
nanoreactors.
19
Y. Wang et al. 2013
X. Guo et al. 2012
20. 3.3. TAILORING THE PROPERTIES OF CQDs
• CQDs prepared by most of the methods are generally not fluorescent or
fluorescence quantum yields are low, limiting their application.
• surfaces of CQDs is sensitive to contaminants in their environment,
• In order to alleviate these problems, surface passivation, functionalization
and doping of CQDs is performed to stabilize fluorescence and improve
the fluorescence quantum yields.
• Surface passivation is usually attained by the formation of a thin
insulating layer, usually by the attachment of polymeric materials, such as
oligomeric PEG
• Functionalization of CQDs
• oxidative treatment using strong acids
• Attaching various organic molecules
• doping with heteroatoms, nitrogen in particular, has shown great
potential to significantly enhance the quantum yield of CQDs
• Doping is carried out during synthesis by using appropriate precursors 20
H. P. Liu et al. 2007
Y. Q. Dong et al 2010
X. Zhai et al. 2012
S. Zhu et al. 2013
21. 4. PHOTOPHYSICAL
PROPERTIES
4.1. LIGHT ABSORPTION
• typically show optical absorption in the UV region with a tail extending to the visible
range
• Most of the C-dots, have an absorption band around 260–320 nm.
• The peaks are usually imputed to π-π* transitions of conjugated C=C system and n-
π* transitions of C=O, C-N, or C−S groups.
• The absorption band could be modulated via various surface
passivation/functionalization techniques
• absorbance of C-dots was found to increase to longer wavelength after surface
passivation with 4,7,10-trioxa-1,13-tridecanediamine (TTDDA) or organosilane (350–
550 nm; 340–410 nm, 360 nm center, respectively).
(Y.-P. Sun et al. 2006; S.-L. Hu et al. 2009) 21
22. 4.2. PHOTOLUMINESCENCE (PL)
• Origin of PL: not clearly known
• bandgap transitions corresponding to conjugated π-domains - quantum size effect
• Surface states - defects in the graphene structures
• Most CDs exhibit excitation-dependent photoluminescence, with strong emission in the blue-
wavelength region that decays rapidly in the red-wavelength region
• For CDs with well-defined crystalline cores, photoluminescence often depends strongly on the size
• The intensity and wavelength of PL depends on various factors:
• Synthesis methods, synthesis parameters, nature of precursors
• CD surface: degree of oxidation, functional group, doping
• CD core crystallinity/amorphous nature
Quantum yield:
• CDs possessed rather low QYs
• QY depends on the synthesis route and the surface chemistry
22
24. 4.3. UP-CONVERTED PHOTOLUMINESCENCE (UCPL)
• For UCPL emission the emission wavelength is shorter than the excitation wavelength
• the mechanism of this unique character is not fully understood
• multi-photon excitation mechanism (Cao et al.)
• relaxation of electrons from 𝜋∗
to 𝜎 (Shen et al. )
A) UCPL spectra of the CQDs dispersed
in water at excitation wavelengths
progressively increasing from 700
nm.
B) B) UCPL properties of CQDs
dispersed in water at excitation
wavelengths from 805 nm to 1035
nm
(M. Li et al. 2012; Q. Feng et al. 2013)
24
25. 5. CHARACTERIZATION
• Varied analytical methods are routinely
applied to characterize CQDs and their
physical properties:
• shape and size
• crystalline organization of the carbon
atoms,
• type and abundance of functional units
displayed upon the CQDs’ surface.
• optical properties (light absorption and
luminescence)
25
The commonly used characterization methods
include:
• Fourier transform infrared spectroscopy
(FTIR),
• Nuclear magnetic resonance (NMR),
• Transmission electron microscope
(TEM)/high resolution TEM(HRTEM)
• X-ray photoelectron spectroscopy (XPS),
• Raman spectroscopy,
• X-ray diffraction (XRD)
• Uv –Vis absorption spectroscopy
• Fluorimetry
26. TRANSMISSION ELECTRON MICROSCOPE (TEM)/HRTEM
• A primary technique for visualization of Carbon-Dots, providing important information
upon particle morphology, size distribution, and crystalline organization.
• High-resolution TEM (HRTEM) experiments have been applied to confirm the periodicity of
the graphitic core, reflecting its crystalline nature.
X-ray diffraction (XRD)
• evaluation of the crystalline nature of Carbon-Dots.
• information upon the unit cell dimensions and crystal spacing within the crystalline
carbon cores.
Raman spectroscopy
• Disorder in the structure/degree of defect
13C – NMR
• type of carbon (sp2/sp3)
26
27. X-RAY PHOTOELECTRON SPECTROSCOPY (XPS)
• provides information upon specific atomic units present upon CQDs’ surface.
27
• An example of an XPS analysis of a carbon dot sample surface containing C=C, C-OH, C-N, C=N and
C=O groups is provided in Figure.
• The spectral analysis reveals the distinct nitrogen-, oxygen-, and carbon-bonded units displayed upon
the CQDs’ surface.
Fig XPS spectra of a CQD
28. FOURIER TRANSFORM INFRARED (FTIR)
• FTIR usually complements XPS, illuminating distinct
functional units through recording of typical vibration
bands
• FTIR can be used to characterize the modified CQDs
in order to determine whether they were effectively
passivated.
Fig FTIR spectra contrast of Carbon Fiber and CQD
prepared by chemical oxidation of the CF
• Characteristic absorption peaks at 3307 cm-1
and 1724 cm-1 suggested the presence of
carboxyl groups on their surface;
• absorption peak at 1579 cm-1 demonstrated the
existence of a double bond;
• absorption peak at 1097 cm-1 implied the
existence of ether linkage.
28
29. 6. APPLICATIONS
• Because of their unique blend of properties, CQDs
are very promising for many applications
• Their bright emission, combined with the marked
electron-donor capability can be exploited in
optoelectronic devices.
• The sensitivity of the PL emission to ions and
other molecules in solution can be exploited to
create nanosensors
• Their non-toxicity and biocompatibility is a key
advantage to perform in vivo and in vitro
bioimaging experiments and drug delivery
• Their light absorption properties have been
exploited as means to enhance photocatalysis
29
30. 6.1. SENSING
• could serve as sensors for a broad range of analytes, such as
ions, small molecules, macromolecules, cells and bacteria.
• Based on change in intensity, wavelength, anisotropy, or lifetime
of fluorescence
• Nanosensors based on CQDs were developed by two different
strategies:
• the nanosensors simply consisted of “pure” CDs, as-synthesized or
passivated through specific target groups;
• the functional sensing material was a nano-composite fabricating by
coupling CQDs with other nano- or micro-materials
• Applicable in sensing of:
• Ions
• Small molecules
• Macromolecules
• Cells, bacteria and viruses 30
Fig. Schematic illustration of the
heavy metal ions detection
mechanism via CQD fluorescence
quenching in
a) absence and
b) b) presence of Hg2+ ions.
31. 6.2. BIOIMAGING
• CQDs possess great potential for fluorescent bioimaging due to their superior fluorescent properties,
possibility of multimodal bioimaging of cells and tissues, biocompatibility and low toxicity
• Sun et al. used PEGylated CQDs for in vivo optical imaging of different organs including bladder, kidney
and liver of a mice
31
32. 6.3. NANOMEDICINE
Photodynamic Therapy
• Photodynamic therapy is a clinical treatment mainly
for superficial tumours.
• It involves the localisation and accumulation of
CQDs in the tumour tissue, following which they are
irradiated with a specific wavelength, triggering the
formation of singlet oxygen species that result in cell
death.
Drug and Gene delivery
• CQDs could function as nano-carriers for tracking
and delivery of drugs or genes
• Besides serving as drug carriers and fluorescent
tracers, CQDs were found to be able to control drug
release.
Figure. A schematic illustration for the gene delivery
and real-time monitoring of cellular trafficking
utilizing CD-PEI/Au-PEI/pDNA assembled
nanohybrids
32
33. 6.4. PHOTOCATALYSIS/ELECTROCATALYSIS
• A photocatalyst is a substance which, upon photo-excitation,
becomes capable of speeding up a chemical process.
• Their light absorption and electron transfer properties, and the
ease of coupling to other materials such as TiO2 , Fe2O3 , ZnO
are particularly beneficial for these applications
• In general, CDs are employed in two different ways
• as a photo-sensitizers: improves light harvesting capability of
semiconductors
• as acceptor of charge carriers from the photoexcited semiconductor
Examples:
• Green synthesis of organic compounds:
• oxidation of organic cpds with H2O2 in visible light
• Degradation of dyes using TiO2
• Splitting of water using light and TiO2 as a catalyst
• Reduction of oxygen in fuel cells
33
Fig. photocatalytic mechanism for the
CQDs/TiO2 nanotube composite under
visible light irradiation
Fig Oxidation process of benzyl alcohol to
benzaldehyde in the presence of CQDs
under NIR light irradiation
34. 34
Fig. Mechanisms of photocatalysis enhanced by carbon-dots coupled to a semiconductor
material.
a. Carbon-Dots (small green spheres) act as light absorbers, transferring the photoexcited electrons to
the semiconductor;
b. Carbon-Dots serve as “electron sinks” thereby extending the lifetimes of the electron-hole pairs.
Xie et al.
35. 6.6. OPTOELECTRONICS
Solar cells
• sensitizers in dye-sensitized solar cells or organic solar
cells to improve the photoelectric conversion efficiency
Light-emitting devices (LED)
• CDs are used in the construction of light emitting diodes
(LED), CDs can be used in two different ways:
• as fluorescent downconverters – phosphor applications
• as the active layer in an electroluminescent device
• Advanced Information Encryption
• electric double-layer capacitors (EDLCs)
• photodetectors
35
Illustrative
diagrams and
results on the
application of
CQDs in
LEDs.
Diagrams
on the
different
structures
of solar
cells based
on CQDs.
36. 7. CONCLUSION AND OUTLOOK
In this article,
• recent developments in the field of CQDs, concentrating on their synthetic approaches, surface
modification methods, various optical properties and their applications in bioimaging, photocatalysis,
sensing and medicine and optoelectronics have been discussed.
• The synthesis of CQDs is usually quite easy and only requires cheap and abundant materials. Furthermore,
simple chemical experiments are needed for surface modification of CQDs that could be performed in a
standard elementary level chemistry laboratory.
• Compared to QDs, due to nontoxic behaviour of CQDs, they stand to have an enormous influence on
environmental and biotechnological applications.
• Furthermore, because of excellent light absorbing ability of CQDs as well as their unique photo-induced
electron transfer capability, they are considered as an excellent candidate for photocatalytic applications.
• High QY, high photo and chemical-stability, beside non-blinking behaviour of CQDs encourage researchers
to develop highly sensitive biosensors in different environments.
• It seems clear that the future of CQDs remains promising.
36
37. CHALLENGES
• Although there are many important advantages and potential applications of CQDs,
further research to enhance the properties of the material is required in order to meet
the application requirements.
• Therefore, the studies of CQDs should continue to address issues such as
• Low product yield
• Low quantum yield
• Control of size and shape
• Mechanism of photoluminescence
• Narrow spectral coverage
37