Decrease In Size Of Nanoparticles Research Articles

Study the effect of dip in reaction temperature on thermal and electrical properties of ZnO nanoparticles

The present study reports thermal and electrical properties of Zinc oxide (ZnO) nanoparticles prepared using co-precipitation route. Sudden dip in reaction temperature observed during the synthesis process created defects in the crystal lattice of ZnO which leads to reduction in crystallite size from 33 nm to 28 nm with increase in reaction temperature. This is confirmed by the X-ray diffraction studies. Thermal analysis of the samples shows better thermal stability for smaller nanoparticles. Temperature-dependent current-voltage characteristics of the ZnO samples show reduction in the conductivity and increase in dielectric constant with respect to rise in reaction temperature. Increase in dielectric constant with decrease in size of nanoparticles may be useful in the field of nanoelectronics like memory-storage devices, etc.

Chemical synthesis of L1 Fe-Pt-Ni alloy nanoparticles

This work focuses on the study of the magnetic and structural properties of chemically synthesized FePt1-xNix nanoparticles, with Ni content x in the range 0.2-0.4. We report the effect of Ni substitution on the L10 structure, on both the as-synthesized and annealed nanoparticles. A decrease in nanoparticle size as well as in chemical order is observed with an increase in Ni content, for both the as-made and annealed nanoparticles. The results also show that the post annealing procedure at 700oC significantly enhanced the L10 ordering of the nanoparticles. Substitution of nickel leads to a decrease in coercivity from 14.9 kOe in FePt to 0.8 kOe for FePt0.6Ni0.4 alloy, while the magnetization at 3 T is increased from 48 emu/g to 88 emu/g.

Facile preparation of Pt/CdS photocatalyst by a modified photoreduction method with efficient hydrogen production

A series of 0.75 wt% Pt/CdS photocatalysts were successfully synthesized via a modified photoreduction process, with the assistance of a protective agent (polyvinylpyrrolidone, PVP) and/or structural inducer (NaI, NaBr, and NaCl). The physicochemical properties of the obtained 0.75 wt% Pt/CdS photocatalysts were characterized in more detailed. Their photocatalytic efficiencies were evaluated by visible-light photocatalytic hydrogen production. The results show that the photocatalytic activities of 0.75 wt% Pt/CdS photocatalysts for H2 production mainly depend on the type of structural inducer. Furthermore, a suitable ratio of PVP/NaI is necessary to optimize the photocatalytic performance of Pt/CdS composites. Notably, 0.75 wt% Pt/CdS (PVP/NaI = 4:1) gains the highest hydrogen production activity with a rate of 1155.8 μmol h−1, which is 1.8 times higher than that of 0.75 wt% Pt/CdS obtained from the traditional photoreduction method (640.9 μmol h−1) and 17.3 times higher than that of the bare CdS sample (66.9 μmol h−1). The as-prepared 0.75 wt% Pt/CdS photocatalyst (PVP/NaI = 4:1) also exhibits a good stability. An optimum ratio of PVP/NaI not only causes a decrease in particle size of Pt nanoparticles but also leads to an increase in BET specific surface area of Pt/CdS and an enhanced electron transfer capability of Pt nanoparticles, which should be responsible for the enhanced photocatalytic performance.

Titanium butoxide molar ratio effect in the TiO2 nanoparticles size and methylene blue degradation

This work focuses on the studies of titanium butoxide (Ti(OBu)4) molar ratio effect in the TiO2 nanoparticles size via solvothermal method for methylene blue degradation. The materials used for the synthesis were: Ti(OBu)4 as titanium source, anhydrous ethanol (EtOH) as solvent, and nitric acid (HNO3) as catalyst. The TiO2 nanoparticles demonstrate growth in a pure anatase phase tetragonal crystalline structure, where other phases or amorphous material is not present. The TiO2 nanoparticles reveal a rounded shaped and when the amount of titanium precursor increases, the nanoparticle size decreases. The photocatalytic degradation of methylene blue is influenced by the nanoparticle size where the material with a 2:30:2 molar ratio, Ti(OBu)4:EtOH:HNO3, presents the minor nanoparticle size and a degradation similar to results obtained by commercial TiO2 (P25) at a time of 90 min.

EDTA-functionalized Fe3O4 nanoparticles

This study analyzes the synthesis and characterization of functionalized Fe3O4 nanoparticles by ethylenediaminetetraacetic acid (EDTA). The syntheses were performed using the co-precipitation method under different experimental conditions: nitrogen atmosphere versus ambient atmospheric conditions, and temperatures of 25 °C versus 90 °C. X-ray diffraction techniques, Fourier transform infrared (FTIR) spectroscopy, zeta potential, and transmission electron microscopy (TEM) were used to characterize these nanoparticles. The co-precipitation method produced high homogeneity in nanostructure shape and size. The functionalization of the magnetite surface was confirmed by the FTIR analyses and the development of new bands associated with EDTA as well as by zeta potential change. The addition of EDTA was also found to change the mechanism of nucleation and nanostructure growth; EDTA was found to favor nucleation, thus decreasing nanoparticle size.

Influence of zinc doping on the photocatalytic activity of nanocrystalline SnO2 particles synthesized by the polyol method for enhanced degradation of organic dyes

Undoped and Zn-doped SnO2 nanocrystals were prepared using a straightforward polyol method and the influence of the doping on the structural, textural, and optical properties was carefully studied. X-ray diffraction (XRD) patterns revealed after annealing the formation of cassiterite, i.e. rutile-like, tetragonal SnO2 crystallites and the absence of any crystalline zinc phase whatever the doping concentration. However, the average crystallite size decreased from 9 to 6.5 nm when the doping concentration increased from 0 to 10 at%, respectively. Furthermore, Transmission Electron Microscopy (TEM) and N2 sorption porosimetry showed that all samples prepared were made of an aggregated network of almost spherical nanoparticles, the size of which decreased when increasing the doping concentration up to 10 at%. The presence of SnO2 and zinc oxide species was assessed by EDX (Energy Dispersive X-ray spectroscopy) analysis. According to UV–visible absorption measurements, this decrease in nanoparticle size was accompanied by a decrease in the band gap value from 3.50 eV for undoped SnO2 to 3.17 eV for 10 at% Zn-doped SnO2. The photocatalytic properties of undoped and Zn-doped SnO2 nanoparticles were evaluated by studying the photodecomposition of methylene blue (MB) and methyl orange (MO) as organic pollutant models. The 10 at% Zn-doped SnO2 nanoparticles showed the highest photocatalytic activity for both MB and MO decomposition and led to an almost complete discoloration of MB solutions, i.e. 98%, after irradiation of 120 min and to an apparent MB degradation constant rate reaching 0.058 min−1.

An Experimental and First Principles Study of the Energetics of Lithium Insertion into Fe3O4 and γ-Fe2O3

Inverse spinel magnetite, Fe3O4, has been studied as an electrode material for lithium-ion batteries due to its low cost, high abundance, and low environmental impact.1 Experimental discharge profiles of Fe3O4 initially show a concentration dependent voltage profile. The lithium concentration range of that profile varies as a function of nanoparticle size, with smaller particles exhibiting a larger intercalation regime.2,3 Thackeray et al. proposed initial lithium intercalation into magnetite on 16c sites, where the lattice accommodates a critical concentration of lithium without significant structural rearrangements. Above a critical concentration of lithium, Thackeray et al. proposed that with further discharge, lithium insertion to 16c sites leads to Fe8a displacement to vacant 16c sites in the material.4 It is also known that magnetite is iron deficient, Fe3-δO4 in the bulk and in the nanoparticulate forms with vacancies on the octahedral 16d sites.5–7 The most drastic manifestation of this oxidation process is maghemite, with δ=1/3, the topotactic oxidative product written as (Fe1 3+)8a[Fe1.66 3+♦0.33]16dO4 with ♦ as a 16d iron defect, or γ-Fe2O3. Menard et al. showed that the defects in nanoparticulate magnetite increase with decreasing nanoparticle size, but a thorough investigation of how defects affect the electrochemistry is yet to be presented.2 Using DFT+U calculations, we have investigated lithium intercalation in Fe3O4 magnetite. Our results show that stoichiometric Fe3O4 is not an intercalation material, with no stable phases for the LixFe3O4 0<x<1 convex hull. Resultantly, a voltage plateau at approximately 2.0 V is predicted, corresponding to a continuous phase transformation from inverse spinel Fe3O4 to rock-salt LiFe3O4with Li and Fe occupying 16c sites. This rules out the original hypothesis for a critical concentration of lithium hosted on the 16c sites resulting in a concentration dependent voltage at low concentrations of lithium in magnetite. We have performed DFT+U calculations on lithiated Fe3-δO4 with δ=0,1/8, and 1/3 to understand how 16d iron defects affect the open circuit potential of magnetite and therefore the discharge behaviour. In the presence of 16d iron defects, we have found that even at low concentrations of lithium, insertion on vacant 16c sites causes significant Fe8a rearrangements. When lithium is inserted on 16c positions, its proximity to Fe8a induces Coulombic repulsion between the Li16c and the Fe8a, and the resultant material is thermodynamically unstable against phase segregation. On the other hand, when lithium is inserted on vacant 16d sites available in the δ=1/8 and 1/3 cases, a structurally stable intercalated material results and DFT+U predicted voltages align with experimental observation. We further hypothesize that the concentration of defects is a function of nanoparticle size. Then we are able to explain the experimentally observed size-dependent open circuit potential and the variation of discharge capacity with particle size in a natural way. Finally, with DFT+U calculations we are able to provide a mechanism for intercalation and phase-segregation that is consistent with the nanoparticle size dependence observed in the electrochemical experiments. This work was supported as part of the Center for Mesoscale Transport Properties, an Energy Frontier Research Center supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, under award #DE-SC0012673. This research used resources of the Center for Functional Nanomaterials, a U.S. DOE Office of Science User Facility, at Brookhaven National Laboratory, Contract No. DE-SC0012704. The Extreme Science and Engineering Discovery Environment (XSEDE) was used, supported by National Science Foundation grant number ACI-1548562. The Yeti Shared HPC Cluster at Columbia University was used, which includes support from Empire State Development's Division of Science, Technology, and Innovation, contract number C090171. C. N. L. acknowledges the support of the National Science Foundation Graduate Research Fellowship under Grant No. DGE-11-44155. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. (1) Ito, S.; Nakaoka, K.; Kawamura, M.; Ui, K.; Fujimoto, K.; Koura, N. J. Power Sources 2005, 146, 319–322. (2) Menard, M. C.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Electrochim. Acta 2013, 94, 320–326. (3) Menard, M. C.; Takeuchi, K. J.; Marschilok, C.; Takeuchi, E. S. 2013, 15, 18539–18548. (4) Thackeray, M. M.; David, W. I. F.; Goodenough, J. B. Mater. Res. Bull. 1982, 17, 785–793. (5) Daniels, J. M.; Rosencwaig, a. J. Phys. Chem. Solids 1969, 30, 1561–1571. (6) Dieckmann, R. Berichte der Bunsen-Gesellschaft fur Phys. Chemie 1982, 86, 112–118. (7) Johnson, C. E.; Johnson, J. A.; Hah, H. Y.; Cole, M.; Gray, S.; Kolesnichenko, V.; Kucheryavy, P.; Goloverda, G. Hyperfine Interact. 2016, 237, 1–10.

Natural convection from a pair of differentially-heated horizontal cylinders aligned side by side in a nanofluid-filled square enclosure

A two-phase model based on the double-diffusive approach is used to perform a numerical study on natural convection from a pair of differentially-heated horizontal cylinders set side by side in a nanofluid-filled adiabatic square enclosure. The study is conducted under the assumption that Brownian diffusion and thermophoresis are the only slip mechanisms by which the solid phase can develop a significant relative velocity with respect to the liquid phase. The system of the governing equations of continuity, momentum and energy for the nanofluid, and continuity for the nanoparticles, is solved by the way of a computational code which incorporates three empirical correlations for the evaluation of the effective thermal conductivity, the effective dynamic viscosity, and the thermophoretic diffusion coefficient, all based on a wide number of literature experimental data. The pressure-velocity coupling is handled through the SIMPLE-C algorithm. Simulations are executed for three different nanofluids, using the diameter and the average volume fraction of the suspended nanoparticles, as well as the cavity width, the inter-cylinder spacing, the average temperature of the nanofluid, and the temperature difference imposed between the cylinders, as controlling parameters, whose effects are thoroughly analyzed and discussed. It is found that the impact of the nanoparticle dispersion into the base liquid increases remarkably with increasing the average temperature, whereas it increases just moderately as the nanoparticle size decreases, as well as the imposed temperature difference and the cavity width increase. Conversely, the distance between the cylinders seems to have marginal effects. Moreover, an optimal particle loading for maximum heat transfer is detected for most configurations investigated.

Amphiphilic nanoparticles suppress droplet break-up in a concentrated emulsion flowing through a narrow constriction.

This paper describes the break-up behavior of a concentrated emulsion comprising drops stabilized by amphiphilic silica nanoparticles flowing in a tapered microchannel. Such geometry is often used in serial droplet interrogation and sorting processes in droplet microfluidics applications. When exposed to high viscous stresses, drops can undergo break-up and compromise their physical integrity. As these drops are used as micro-reactors, such compromise leads to a loss in the accuracy of droplet-based assays. Here, we show droplet break-up is suppressed by replacing the fluoro-surfactant similar to the one commonly used in current droplet microfluidics applications with amphiphilic nanoparticles as droplet stabilizer. We identify parameters that influence the break-up of these drops and demonstrate that break-up probability increases with increasing capillary number and confinement, decreasing nanoparticle size, and is insensitive to viscosity ratio within the range tested. Practically, our results reveal two key advantages of nanoparticles with direct applications to droplet microfluidics. First, replacing surfactants with nanoparticles suppresses break-up and increases the throughput of the serial interrogation process to 3 times higher than that in surfactant system under similar flow conditions. Second, the insensitivity of break-up to droplet viscosity makes it possible to process samples having different composition and viscosities without having to change the channel and droplet geometry in order to maintain the same degree of break-up and corresponding assay accuracy.

Surface Decomposition of Dimethyl Methylphosphonate on SnO2 Nanoparticles: Role of Nanoparticle Size

We report the effect of SnO2 particle size on the adsorption behaviour of dimethyl methylphosphonate (DMMP). SnO2 nanoparticles with different particle sizes have been successfully synthesised by the reverse microemulsion method. Transmission electron microscopy and X-ray diffraction results were used to evaluate size distribution, shape and structure of the prepared SnO2 nanoparticles. The infrared spectra of adsorbed DMMP on SnO2 show that the adsorption is dissociative. In addition, it is shown that the size of SnO2 nanoparticles does not affect the reaction mechanism. Adsorption isotherms of DMMP show that by decreasing the size of SnO2 nanoparticles, the amount of DMMP adsorbed is increased. In addition, the calculated heats of adsorption of DMMP are increased as the SnO2 nanoparticle size decreases.

CO Chemisorption on Ultrathin MgO-Supported Palladium Nanoparticles

The adsorption of CO on Pd nanoparticles (NP) supported on MgO ultrathin films is studied by sum frequency generation (SFG) vibrational spectroscopy at room temperature as a function of CO coverage for NP lateral sizes ranging from 3 to 6 nm. While the spectroscopic signature of CO on (100) top facets dominates the spectra, other new bands are attributed to (111) facets, edges, and defects. CO remains strongly bonded for all sizes, but spectroscopic and kinetic parameters evolve as NP size decreases. It is only for the smallest NPs ∼3 nm in diameter that the deviation from Pd(100) single crystal is important. Modeling of adsorption kinetics, dipolar coupling and DFT calculations allow rationalizing the observations: the size dependent Pd–Pd bond extension by the substrate is the main parameter that controls CO frequency in the low coverage limit. SFG sensitivity is found to increase up to 10–4 ML as NP size decreases. This makes SFG particularly well suited to probe molecular adsorption in the submonolaye...

Exploration of the Effect of Chitosan and Crosslinking Agent Concentration on the Properties of Dual Responsive Chitosan-g-Poly (N-Isopropylacrylamide) Co-polymeric Particles

The objective of the present study was to synthesize and evaluate the effect of change in concentration of chitosan (CS) and N,N-methylenebisacrylamide (MBA)- a cross linking agent, on various properties such as lower critical solution temperature (LCST), zeta potential, particle size and poly dispersity index (PDI) of the synthesized co-polymer. Nine different formulations of chitosan-g-poly (N-isopropylacrylamide) (CS-g-PNIPAAm) co-polymer with varying CS and MBA concentrations were synthesized by a surfactant free dispersion copolymerization method. The synthesized co-polymer was further characterized and confirmed for its structure, morphology, particle size, zeta-potential, thermo and pH responsive properties, in-vitro cyto-compatability and stability studies using various analytical tools. The data confirms the successful synthesis of co-polymer. The increase in the concentrations of CS and MBA during the polymerization of co-polymer, resulted in proportional increase of LCST and zeta potential with decrease in particle size of co-polymeric nanoparticles. pH responsive studies showed that as the pH of the medium increases particle size and zeta potential decreases with increase in LCST of co-polymeric nanoparticles. From the results, it can be inferred that the synthesized co-polymeric nanoparticles exerted thermo and pH responsive properties with biocompatibility. By varying the CS and MBA concentrations in the co-polymer, desired LCST, particle size and zeta potential for co-polymeric nanoparticles can be obtained and thus the synthesized co-polymer may have great potential to be used as a drug carrier (nanoform) with both thermo and pH responsiveness.

Preparation and characterization of Ba0.2Sr0.2La0.6MnO3 nanoparticles and investigation of size & shape effect on microwave absorption

In this paper, the design and characterization of a radar absorbing material (RAM) was investigated at microwave frequency. Ba0.2Sr0.2La0.6MnO3 magnetic nanoparticles was synthesized thru a facile hydrothermal method in the presence of polymethyl methacrylate (PMMA) and the possibility of shape and size-controlled synthesis of nanoparticles (NPs) over the range 15–50Nm was also explored. Afterward, the effect of shape and size of the synthesized Ba0.2Sr0.2La0.6MnO3 NPs on microwave absorption properties was investigated in KU-band. The crystal structures and morphology of as-synthesized nanoparticles were characterized and confirmed by FESEM, XRD, VSM, FTIR analysis. The RAM samples were prepared by dispersion of magnetic NPs in silicone rubber in an ultrasonic bath. The maximum reflection loss (RL) values NPs were 12.04dB at 14.82GHz and a broad absorption band (over 1.22GHz) with RL values <−10dB are obtained and the maximum reflection loss (RL) values of decrease and shaped NPs were 22.36dB at 14.78GHz and a broad absorption band (over 2.67GHz) with RL values <−10dB are obtained. The results indicated that the particle size and shape play a major role on the absorption properties of the composites in the 12.4–18GHz frequency range. It is observed that microwave absorption properties increased with the decrease in average particle size of NPs.

Low temperature-high selectivity carbon monoxide methanation over yttria-stabilized zirconia-supported Pt nanoparticles

The high purity hydrogen, free from any traces of carbon monoxide is crucial for the efficient operation of hydrogen proton exchange membrane fuel cells (PEMFCs). In this study we report the low temperature (25–120 °C) carbon monoxide methanation in hydrogen-rich streams over 1 wt. % Pt nanoparticles supported on yttria-stabilized zirconia (YSZ) support. Pt nanoparticles with four average particle sizes 1.9, 3.0, 4.4 and 6.7 nm are investigated. The turnover frequency at 30 °C of CO methanation reaction rate doubles with decreasing Pt mean particle size from 6.7 to 1.9 nm. The high activity of Pt/YSZ catalyst is due to the backspillover of ionic species Oδ− from YSZ support to Pt active sites. Under the reaction conditions, Oδ− forms an “effective” double layer at the catalyst surface that weakens CO (electron acceptor) adsorption and strengthens H2 (electron donor) adsorption bonds and this effect becomes more pronounced as nanoparticle size decreases.

Influence of nanosizing on hydrogen electrosorption properties of rhodium based nanoparticles/carbon composites

Composites made of ultra-small Rh hydride nanoparticles (NP) with controlled average sizes of 1.3, 1.9 and 2.3nm dispersed in high surface area graphite powders were synthesized. The hydrogen electrosorption properties of the Rh nanohydride that is stable under ambient conditions were characterized by cyclic voltammetry under various scan rates in the hydrogen potential domain with the help of a cavity microelectrode. During the first cycles, an evolution of the voltammograms, characterized by an isopotential point, is observed that corresponds to a surface conversion of RhHx into Rh, the core of the NP remaining in the hydride phase. After stabilization, the voltammograms exhibit the classical hydrogen electrosoprtion peaks of Rh, but a shift to positive potentials indicates that H is more weakly bounded to the surface as the NP size decreases. The onset of the HER follows the same trend. Interestingly, it is observed that the quantity of electrosorbed hydrogen strongly increases when downsizing the NPs, with the H/Rh ratio reaching 0.47±0.11 for NPs with an average size of 1.3nm. This enhancement cannot be explained just by the increase in surface area by NP downsizing. It may arise from the creation of new multi-fold adsorption surface and sub-surface sites due to the presence of many corner and edge atoms in ultra-small NPs with strong surface curvature.

Preparation of tunable-sized iron nanoparticles based on magnetic manipulation in inert gas condensation (IGC)

Iron nanoparticles (NPs) prepared by inert gas condensation were studied using high resolution transmission electron microscopy and Wulff construction shape analysis. The NP size and shape show strong dependence on the magnetic field above the target surface. The effect of the magnetic field could be tuned by adjusting the thickness of the protective backing plate positioned in-between the target and the magnetron head. With increasing backing plate thickness, the particle size decreases and the NP morphologies evolve from faceted to close-to-spherical polyhedral shapes. Moreover, with changes in size and shape, the particle structure also varies so that the NPs exhibit: (i) a core-shell structure for the faceted NPs with size ∼15–24 nm; (ii) a core-shell structure for the close-to-spherical NPs with size ∼8–15 nm; and (iii) a fully oxidized uniform structure for NPs with sizes less than ∼8 nm having a void in the center due to the Kirkendall effect. The decrease of NP size with the increasing backing plate thickness can be attributed to a reduced magnetic field strength above the iron target surface combined with a reduced magnetic field confinement. These results pave the way to drastically control the NP size and shape in a simple manner without any other adjustment of the aggregation volume within the deposition system.

Growth and optical properties of nanostructured ZnS:Mn films

Nanostructured ZnS:Mn films have been grown and their structure, optical properties, and photoluminescence have been studied. The nanostructured ZnS:Mn films have been grown on silicon and glass substrates via hydrochemical deposition from solution. The crystal structure and microstructure of the films have been studied by X-ray diffraction and atomic force microscopy. The band gap of the nanostructured ZnS:Mn films has been determined. The intensity of their photoluminescence bands has been shown to increase with decreasing nanoparticle size.

Characterization and Electrochemical Properties of Nanostructured Zr-Doped Anatase TiO2 Tubes Synthesized by Sol–Gel Template Route

A series of nanostructured Zr-doped anatase TiO2 tubes with the Zr/Ti molar ratio of 0.01, 0.02, 0.03, and 0.09 were prepared by a sol–gel technology on a carbon fiber template. The electrochemical performance of Zr-doped anatase TiO2 as anodes for rechargeable lithium batteries was investigated and compared with undoped titania. Tests represented that after 35-fold charge/discharge cycling at C/10 the reversible capacity of Zr-doped titania (Zr/Ti = 0.03) reaches 135 mA h g−1, while the capacity of undoped titania (Zr/Ti = 0) yielded only 50 mA h g−1. Based on the results of the physicochemical investigation, three reasons of improving electrochemical performance of Zr-doped titania were suggested. According to the scanning electron microscopy and transmission electron microscopy, Zr4+ doping induces a decrease in nanoparticle size, which facilitates the Li+ diffusion. The Raman investigations show the more open structure of Zr-doped TiO2 as compared to undoped titania due to changing of the unit cell parameters, that significantly affects on the reversibility of the insertion/extraction process. The electrochemical impedance spectroscopy results indicate that substitution of Zr4+ for Ti4+ into anatase TiO2 has favorable effects on the conductivity.

Effect of solvent on crystallographic, morphological and optical properties of SnO2 nanoparticles

SnO2 nanoparticles were synthesized by co-precipitation method using different solvent media (Methanol:Water: 100:0; 80:20; 60:40; and 0:100). X-ray diffraction (XRD) patterns showed highly crystalline single phase tetragonal structure, with predominant (110) plane in all samples. High resolution transmission electron microscopy (HR-TEM) images indicated the decrease in the particle size of nanoparticles with an increase in methanol to water ratio. The Raman shifts revealed that with increase in the water content as solvent, the intensity of A1g and B2g Raman modes decreases, indicating the distortion in crystal structure, which is in agreement with HR-TEM results. Fourier transform infrared (FTIR) spectroscopy spectra confirmed SnO stretching mode and also complemented Raman spectroscopy results. The optical band gap of SnO2 decreased from 3.66eV to 3.54eV with a decrease in methanol to water solvent ratio, thereby implying that the optical properties of these materials are affected by the synthesis medium, used during synthesis.

Effects of TiO2 nanoparticle Size on Solar-to-Hydrogen Efficiency in Photoelectrochemical Cells

The photocatalytic splitting of water into oxygen and hydrogen using solar light is a promising clean and renewable source for hydrogen fuel1. Metal-oxides are one type of material that researchers are studying to overcome this scientific challenge. TiO2 is one of the most studied and promising photocatalysts. This is due to TiO2 having a band gap with edge positions that makes it capable of splitting water. However, due to its large band gap (3.0-3.3eV) hindering its ability to utilize portions of the solar spectrum, TiO2 has a low solar-to-hydrogen efficiency2. Therefore, steps have been made to improve this material. Going to nanoscale has shown to have potential, but research comparing different sized nanoparticles hasn’t been as prevalent as other methods, such as doping. Having smaller particle size, particularly in the lower nanometer range, can give materials unique properties that could increase photoactivity3. Some properties, such as quantum confinement, aren’t as beneficial for large band gap materials like TiO2. When a material reaches a small enough size, quantum confinement effects take over, changing the electrochemical properties. One of these properties is the band gap energy, which increases as particle size decreases4. Therefore, it is imperative to find a particle size that gives a material the most optimal balance of these effects, leading to a material with the highest water splitting efficiency. The purpose of this study was to test the differences in efficiencies, such as solar-to-hydrogen efficiency (STH), of TiO2 for decreasing nanoparticle size. Nanoparticle sizes ranging from 100 nm down to 5 nm were tested using photoelectrochemical(PEC) measurements. It was our prediction that smaller particle size will result in an overall increase in photoactivity, as per other literature3, and therefore a higher solar-to-hydrogen efficiency (STH). The process of putting together the working electrode, as well as procedure and results of experiments, will be discussed.