Unprecedented high photocatalytic activity of nanocrystalline (original) (raw)
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Novel Synthesis of Cobalt Nickel Tungstate Nanopowders and its Photocatalytic Application
Journal of Cluster Science, 2014
Nanocrystalline cobalt nickel tungstate powders (CO 1-X Ni X WO 4 where X = 0, 0.5 and 1) have been synthesized by a microemulsion method. The results indicate that pure monoclinic wolframite tungstate structure was obtained from the precipitated precursors at pH 10 calcined at a temperature 600°C for 6 and 10 h. Meanwhile, the average particle sizes of the formed tungstate powders were about 12-35 nm. The specific surface areas of the produced materials were about 33.8-42.8 cm 3 /g and the average pore diameters were 4.5-6.3 nm. The NiWO 4 material indicated band gap energy E g value of 3.2 eV whereas that of CoW-O 4 revealed a value of 2.7 eV. TEM images investigated that the formed particles were nearly nanoclusters. Furthermore, HRTEM results revealed that NiWO 4 powders have (0 1 0) and (1 0 0) planes which led to the highest photocatalytic activity. Photocatalytic decomposition of methylene blue (MB) as a model pollutant was used to evaluate the photocatalytic activity of CO 1-X Ni X WO 4 catalysts under UV irradiations. The MB degradation rate with the irradiation time using NiWO 4 , CoWO 4 and Co 0.5 Ni 0.5 WO 4 catalysts was estimated apparent first kinetic rate constants of 0.013, 0.012 and 0.010 min-1 , respectively.
Materials, 2016
A traditional semiconductor (WO 3) was synthesized from different precursors via hydrothermal crystallization targeting the achievement of three different crystal shapes (nanoplates, nanorods and nanostars). The obtained WO 3 microcrystals were analyzed by the means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectroscopy (DRS). These methods contributed to the detailed analysis of the crystal morphology and structural features. The synthesized bare WO 3 photocatalysts were totally inactive, while the P25/WO 3 composites were efficient under UV light radiation. Furthermore, the maximum achieved activity was even higher than the bare P25's photocatalytic performance. A correlation was established between the shape of the WO 3 crystallites and the observed photocatalytic activity registered during the degradation of different substrates by using P25/WO 3 composites.
Photocatalytic and antimicrobial activity of NiWO4 nanoparticles stabilized by the plant extract
Materials Science in Semiconductor Processing, 2015
In recent years, biosynthesis of nanoparticles using plant extract has attracted great attention owing to its cost effective, non-toxic, eco-friendly and as an alternative approach to physical and chemical methods. Nickel tungstate (NiWO 4) nanoparticles were synthesised via the aqueous leaf extract of Azadirachta indica plant. The prepared nanoparticles were characterized using UV-visible diffuse reflectance spectroscopy (UV-vis-DRS), fourier transform infra-red spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) techniques. SEM results showed that plant extract modified NiWO 4 (PNT) was composed of tiny sphere in shape. XRD results revealed that the average crystallite size of PNT was smaller (12.12 nm) when compared to the bare NiWO 4 (NT) prepared using precipitation method (31.11 nm). The photocatalytic activity of NiWO 4 nanoparticles were investigated using methylene blue (MB) as a model organic pollutant under visible light irradiation. PNT showed high efficiency for the degradation of MB compared to NT. The effect of operation parameters such as initial dye concentration, pH and catalyst concentration has been investigated in detail. PNT was subjected to antimicrobial studies and significant results were obtained.
Superior photoelectrochemical activity of self-assembled NiWO4–WO3 heteroepitaxy
Nano Energy, 2016
Self-assembled nanocomposites with a high interface-to-volume ratio offer tremendous opportunities of tailoring functionalities by a proper combination of components. In this study, we report the first fabrication of self-assembled NiWO 4-WO 3 heteroepitaxy and its excellent performance on photoelectrochemical water splitting. The heteroepitaxy is evidenced by a combination of x-ray diffraction and transmission electron microscopy. The energy band diagram of NiWO 4-WO 3 heterostructure probed by x-ray photoelectron spectroscopy suggests an efficient charge separation at their interface by injecting photo-generated electrons from NiWO 4 to WO 3 and holes from WO 3 to NiWO 4. Therefore, a great improvement in the photoelectrochemical activity of self-assembled NiWO 4-WO 3 heteroepitaxy was achieved (1400 mA cm À 2 at 0.7 V vs. Ag/AgCl). This work delivers a new category of composite materials for promising photoelectrode in photoelectrochemical cells. & 2016 Elsevier Ltd. All rights reserved. been realized, such as the bilayer films of α-Fe 2 O 3-TiO 2 [14] and BiVO 4-WO 3 [15,16], the quasi-core-shell nanorod arrays of WO 3-TiO 2 and TiO 2-WO 3 [17], and the nanoparticle composites of α-Fe 2 O 3-WO 3 [18,19] and α-Fe 2 O 3-CoAl 2 O 4 [20]. Therefore, owing to the advantages over conventional nanostructures (high interface-to-volume ratio and perfectly ordered crystal orientation), self-assembled heteroepitaxial nanocomposites are strongly expected to have potential applications as photoactive components Contents lists available at ScienceDirect
2018
In this work, WO 3 nanostructures have been synthesized through simple chemical co-precipitation method under optimized synthesis conditions. The prepared sample was characterized through XRD, Raman, FTIR, SEM, EDS, XPS, and DRS for structural, vibrational, Raman, morphological, elemental, compositional, and optical properties respectively. The detailed structural investigation has revealed the highly crystalline, single phase monoclinic structure of WO 3 as demonstrated by XRD, FTIR and Raman spectroscopy results. The morphological analysis have clearly depicted nanostructures like morphology of prepared WO 3 sample with average size of 10 nm. EDS and XPS results indicated the high elemental and chemical compositional purity of the synthesized nanostructures. DRS results have shown that the optical band gap energy of WO 3 nanostructures lies in the visible region. The WO 3 nanostructures have shown significantly high photocatalytic activity and completely degraded Methylene Blue (MB) dye in short time of 40 min under sunlight illumination.
Research on Chemical Intermediates
An original, facile way based on a non-aqueous sol-gel solvothermal process has been developed to synthesize 2D tungsten trioxide (WO3) nanoplatelets in one pot. The reaction between Tungstic acid (H2WO4) and 1-hexanol was a simple process, which resulted in the formation of highly crystalline metal oxide based on WO3 with an average size ranging between 30 and 50 nm, and with a correspondingly high surface area. The structural, morphological, functional group, optical qualities of the materials and the properties of the adsorption surfaces were all examined , and the degree of surface hydroxyls (-OH groups) has been examined. The products of the reaction were characterized by X-ray Powder Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, Nitrogen adsorption ,and pore-size distribution Brunauer-Emmett-Teller, Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance Spectroscopy techniques. which indicated the formation of di-hexyl ether as a result of the solvothermal reaction. The optical absorption, measured using UV-Vis Diffuse Reflectance Spectroscopy, revealed a narrow bandgap (Eg = 2.18 and 2.48 eV for WO3-24 and WO3-48, respectively) compared to that of for bulk WO3 (2.7 eV), attributable to oxygen vacancies. Upon increasing dwell time from 24 to 48 h, a blue-shift was observed, highlighting a quantum size effect. The as-prepared WO3 nanoplatelets displayed excellent photocatalytic performance for degrading Rhodamine B under visible light-emitting diode light with up 99 % degradation rate was achieved in 120 min. Thus, the enhanced Rhodamine B photodegradation in the presence WO3-24 along with H2O2 was assigned to the reactive oxygen species (ROS) such as • OH and RhB *+ , involving in the strong synergistic effect between WO3 and H2O2, effectively separating of photocarriers and, as a consequence, boosting the photocatalytic efficiency.
Journal of Nanomaterials, 2016
Series of WO3/TiO2nanocomposites were obtained by hydrothermal method followed by calcination in the temperature range from 400°C to 900°C. The characteristics of photocatalysts by X-ray diffractometry (XRD), scanning electron microscope (SEM), and diffuse reflectance spectroscopy (DRS) showed that increasing the calcination temperature from 400 to 900°C resulted in change of photocatalytic activity under UV-Vis light. Moreover, the amount of WO3crystalline phase and amorphous phase in WO3/TiO2aggregates, as revealed by XRD analysis, was dependent on the calcination temperature. The WO3/TiO2samples with 8 mol% load of WO3in respect to TiO2calcinated at 500 and 800°C possess the highest photocatalytic activity in reaction of phenol degradation, which is about 1.2 and 1.5 times that with calcination at 400°C. The increase in calcination temperature above 400°C resulted in increase of WO3crystallinity and reduction of the amount of amorphous phase in the nanocomposite structure. Moreov...
Electrospun tungsten oxide/nickel tungstate (WO 3 /NiWO 4 ) composite nanofibers were tested for photoelectrochemical (PEC) performance under visible light irradiation under three voltages, 1.6, 1.8 and 2.0 V with reference to Ag/ AgCl electrode in 0.5 M H 2 SO 4 . It was found that the photocurrent density of this novel nanostructure fiber is about 70% higher than the pristine electrospun WO 3 fibers under similar conditions. WO 3 /NiWO 4 heterojunction was identified within the fiber through high-resolution transmission electron microscopy imaging. The fibrous form is expected to provide greater exposure to the WO 3 /NiWO 4 heterojunctions for the photocatalytic reaction. This heterojunction within the fibrous form is expected to provide a higher photoanode performance due to a lower charge-transfer resistance than the pristine WO 3 fibers as also confirmed through the electrochemical impedance spectra. Interestingly, calcination of these composite fibers at 800°C instead at 550°C increased the percentage of NiWO 4 phase, yet with a contemporaneous increase in larger crystallites of metal tungstate. The latter was responsible for giving lower photocurrents which helped in understanding the PEC performance with respect to material structure for the composite fiber under the current study.
Synthesis, Surface Acidity and Photocatalytic Activity of WO3/TiO2 Nanocomposites – An Overview
Titania has been studied to be one of the best photocatalysts for the decomposition of many organic pollutants present in aqueous medium. Because of the wide band gap energy of TiO 2 (3.2 eV) it can be activated only under UV light region which is present 4 % in the solar light spectrum. The photocatalytic activity of TiO 2 was enhanced by means of several methods. TiO 2 coupled with other semiconductor has gained additional importance, owing to improving the efficient charge separation by trapping the photogenerated electrons. WO 3 is a better semiconductor having relatively lower band gap energy (2.8 eV) and absorb broad solar light spectrum. The formation of WO x monolayer on TiO 2 notably increases the surface acidity of TiO 2 . This increasing the surface acidity of WO 3 /TiO 2 photocatalyst facilitates the adsorption of the more hydroxyl group in addition to more organic reactants on its surface which obviously facilitate the enhancement of photocatalytic activity. In this review, the synthesis methods and photocatalytic activity of some selected and unique results related to WO 3 /TiO 2 photocatalyst were discussed. The efficient charge separation, increased absorption of the reactants by increasing the surface acidity and high aspect ratio structures of WO 3 /TiO 2 are also reviewed.
Electrochimica Acta, 2018
A novel hetero-junction anode composed of NiWO 4 /WO 3 , formed at various metal molar ratios (Ni/W) and fabricated hydrothermally via simple salt solution addition method using polyethylene glycol, was characterized using XRD, TEM-SAED, N 2 sorptiometry, UV-Vis diffuse reflectance and FTIR spectrometry. Increasing NiO especially at the Ni/W ratio of 4 stimulates the develop of a tailored morphology (nanoplates/nanowires with crystallites size of 11 nm) with entailed mesoporous surface texturing values (S BET = 100.7 m 2 /g and V p = 0.186 cm 3 /g) exceeding those exhibited at Ni/W ratio of 1 and 2 and rather shows a monomodal type of pores at 3.5 nm. The electrocatalytic performances of all nanocomposites toward methanol oxidation (0.6 M) were examined in comparison with pristine NiO and WO 3 samples by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) measurements. Strikingly, the NiWO 4 /WO 3 electrode; synthesized at Ni/W ratio of 4, shows higher current density exceeding those of NiW(1:1) and NiW(2 :1) by 3.4 and 2.6 fold, respectively. This pronounced electrocatalytic activity is mostly attributed to increasing the electrochemically active surface area of the former (16.9 cm 2) and superior mesoporous nanostructures, which facilitate not only the diffusional electrochemical kinetics but also the long term cycle durability towards the CO poisoning species. This encountered stability was also due to the strong interaction between Ni and W to form small NiWO 4 crystals of higher carrier density; as evaluated from the resistivity measurement, and to the hybridization with WO 3 moieties of high electron transport properties, as confirmed by the EIS results.