Natda Wetchakun

BiVO4/CeO2 nanocomposites with high visible-light-induced photocatalytic activity

Preparation of bismuth vanadate and cerium dioxide (BiVO4/CeO2) nanocomposites as visible-light photocatalysts was successfully obtained by coupling a homogeneous precipitation method with hydrothermal techniques. The BiVO4/CeO2 nanocomposites with different mole ratios were synthesized and characterized by X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). Absorption range and band gap energy, which are responsible for the observed photocatalyst behavior, were investigated by UV-vis diffuse reflectance (UV-vis DR) spectroscopy. Photocatalytic activities of the prepared samples were examined by studying the degradation of model dyes Methylene Blue, Methyl Orange, and a mixture of Methylene Blue and Methyl Orange solutions under visible-light irradiation (>400 nm). Results clearly show that the BiVO4/CeO2 nanocomposite in a 0.6:0.4 mol ratio exhibited the highest photocatalytic activity in dye wastewater treatment.

Enhanced visible-light photocatalytic activity of g-C3N4/TiO2 films.

Enhanced photocatalytic degradation of methylene blue (MB) using graphitic carbon nitride/titanium dioxide (g-C3N4/TiO2) catalyst films has been demonstrated in this present work. The g-C3N4/TiO2 composites were prepared by directly heating the mixture of melamine and pre-synthesized TiO2 nanoparticles in Ar gas flow. The g-C3N4 contents in the g-C3N4/TiO2 composites were varied as 0, 20, 50 and 70 wt%. It was found that the visible-light-induced photocatalytic degradation of MB was remarkably increased upon coupling TiO2 with g-C3N4 and the best degradation performance of ~70% was obtained from 50 wt% g-C3N4 loading content. Results from UV-vis absorption study, Electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy suggest that the improved photoactivity is due to a decrease in band gap energy, an increased light absorption in visible light region and possibly an enhanced electron-hole separation efficiency as a result of effective interfacial electron transfer between TiO2 and g-C3N4 of the g-C3N4/TiO2 composite film. Based on the obtained results, the possible MB degradation mechanism is ascribed mainly to the generation of active species induced by the photogenerated electrons.

Photocatalytic Degradation of Methyl Orange by CeO2 and Fe–doped CeO2 Films under Visible Light Irradiation

Undoped CeO2 and 0.50–5.00 mol% Fe-doped CeO2 nanoparticles were prepared by a homogeneous precipitation combined with homogeneous/impreganation method, and applied as photocatalyst films prepared by a doctor blade technique. The superior photocatalytic performances of the Fe-doped CeO2 films, compared with undoped CeO2 films, was ascribed mainly to a decrease in band gap energy and an increase in specific surface area of the material. The presence of Fe3+ as found from XPS analysis, may act as electron acceptor and/or hole donor, facilitating longer lived charge carrier separation in Fe-doped CeO2 films as confirmed by photoluminescence spectroscopy. The 1.50 mol% Fe-doped CeO2 film was found to be the optimal iron doping concentration for MO degradation in this study.

Photocatalytic Mineralization of Organic Acids over Visible-Light-Driven Au/BiVO4 Photocatalyst

Au/BiVO4 visible-light-driven photocatalysts were synthesized by coprecipitation method in the presence of sodium dodecyl benzene sulfonate (SDBS) as a dispersant. Physical characterization of the obtained materials was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), UV-Vis diffuse reflectance spectroscopy (DRS) and Brunauer, and Emmett and Teller (BET) specific surface area measurement. Photocatalytic performances of the as-prepared Au/BiVO4 have also been evaluated via mineralizations of oxalic acid and malonic acid under visible light irradiation. XRD and SEM results indicated that Au/BiVO4 photocatalysts were of almost spherical particles with scheelite-monoclinic phase. Photocatalytic results showed that all Au/BiVO4 samples exhibited higher oxalic acid mineralization rate than that of pure BiVO4, probably due to a decrease of BiVO4 band gap energy and the presence of surface plasmon absorption upon loading BiVO4 with Au as evidenced from UV-Vis DRS results. The nominal Au loading amount of 0.25 mol% provided the highest pseudo-first-order rate constant of 0.0487 min−1 and 0.0082 min−1 for degradations of oxalic acid (C2) and malonic acid (C3), respectively. By considering structures of the two acids, lower pseudo-first-order rate constantly obtained in the case of malonic acid degradation was likely due to an increased complexity of the degradation mechanism of the longer chain acid.

Enhancement of the Photocatalytic Performance of Ru-Doped TiO2 Nanoparticles

Pure TiO2 nanoparticles were synthesized by the modified sol-gel method using titanium tetraisopropoxide (TTIP) precursor dissolved in absolute ethanol. A pouch type cellophane membrane was employed as barrier between the precursor solution and the mixture of absolute ethanol (1:1 v/v) and distilled water with 0.5-1.0 % concentrated of ammonia in order to fix the reaction activity inside the pouch and control diffusion rate of hydrolysis and condensation reaction. The doping of TiO2 nanoparticles with 0.1, 0.2, 0.5, 1.0 and 2.0 at.% Ru was performed by the impregnation method using ruthenium acetyl acetonate in toluene as dopant. The properties of the all samples were characterized by X-ray diffraction (XRD), Brunauer, Emmett and Teller (BET)-specific surface area, Scanning electron microscopy-Energy dispersive spectroscopy (SEM-EDS) and transmission electron microscopy (TEM). The crystalline size of pure TiO2 and Ru-doped TiO2 nanopaticles were found to be in the range of 10-20 nm. The photocatalytic mineralization of formic acid, oxalic acid, sucrose and glucose was investigated using Degussa P25, pure TiO2 and Ru-doped TiO2 nanoparticles as photocatalysts in aqueous solutions under UVA irradiation. The rate of 50% mineralization of formic acid by 0.1 at.% Ru-doped TiO2 was 1.53 times and 1.34 times higher than that of pure TiO2 and Degussa P25, respectively showing the enhancement of the photocatalytic performance of TiO2 by doping with an optimum amount of ruthenium.

Effect of Palladium on Photocatalytic Activity of SnO2 Nanoparticles

SnO2 nanoparticles were successfully synthesized with either the presence (PS) or absence (NPS) of the Broussonetia papyrifera (L.) Vent Pulp as the dispersant by the precipitation coupling with the thermal decomposition methods using tin tetrachloride pentahydrate (Sn4Cl.5H2O) and ammonium hydroxide (NH4OH) as the starting material and precipitant respectively. The pulp was soaked in SnCl4 solution and NH4OH was slowly added dropwise. The white gelable precipitate of Sn(OH)4 was obtained. Afterward, the white precipitate was filtered and washed until it was free from chloride. The white precipitate was then dried at 80°C for 24h and calcined for 1h at 600°C, 650°C, and 700°C respectively. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and Brunauer-Emmett-Teller (BET) measurement of specific surface area. The crystallite sizes of SnO2 nanoparticles with the presence and absence of the pulp were found to be ranging from 5-15 nm and 5-30 nm respectively. The specific surface areas (SSABET) were 62.53 m2/g and 26.60 m2/g for PS and NPS samples respectively. SnO2 nanoparticles were doped with palladium in the range from 0.25-1.00 mol% by the impregnation method. The photocatalytic activity of SnO2 and Pd-doped SnO2 nanoparticles were investigated for the degradation of sucrose and glucose under UVA-light irradiation. The results showed that the photocatalytic activity of Pd-doped SnO2 was higher than pure SnO2 and the best photocatalytic activity for the degradation of sucrose and glucose were obtained in the case of Pd-doped SnO2 nanoparticles with 0.5 mol % and 1.0 mol % Pd loading respectively.

Influence of Cu doping on the visible-light-induced photocatalytic activity of InVO4

The photocatalytic degradation of methylene blue (MB) in the presence of pure InVO4 or a 0.5–5.0 mol% Cu-doped InVO4 composite under visible light irradiation (λ ≥ 400 nm) was studied in this research. The structural and photophysical properties of the as-prepared samples in the photocatalytic degradation process were investigated. The doping of InVO4 with a Cu photocatalyst results in wide absorption in the visible-light region and superior visible-light-driven photocatalytic activities in the degradation of MB. The results indicate that the InVO4 sample doped with 1.0 mol% of Cu shows the highest photocatalytic activity. The enhanced photocatalytic activity was attributed to the copper ions acting as trapping sites, facilitating the separation of charge carriers. The main active species for the degradation of MB were investigated to explain the enhancement of the photocatalytic performance of Cu-doped InVO4. A possible photocatalytic degradation pathway for aqueous MB dye and a charge transfer mechanism for Cu-doped InVO4 were proposed.

The effect of iron doping on the photocatalytic activity of a Bi2WO6–BiVO4 composite

Visible-light-driven Fe-doped Bi2WO6–BiVO4 composites have been synthesized via a hydrothermal method with varying nominal iron contents in the range of 0.5–5.0 mol%. The physicochemical properties of the obtained materials were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET)-specific surface area, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and photoluminescence (PL) techniques. Methylene blue (MB) as probe pollutant was adopted to investigate the photocatalytic activity of all samples under visible light irradiation. The Fe-doped Bi2WO6–BiVO4 composites showed an enhanced photocatalytic activity for the degradation of MB under visible light, which was attributed to the iron ions acting as good electron and hole traps for facilitating the separation of charge carriers. Simultaneously, the high stability of the sample was also investigated by five successive photodegradation tests of MB under visible light. The relationship between the photocatalytic activities and the structures of Fe-doped Bi2WO6–BiVO4 composites was discussed. The possible photocatalytic mechanism of the composites was proposed to guide the further improvement of their photocatalytic performance.

Kinetics study of photocatalytic activity of flame-made unloaded and Fe-loaded CeO2 nanoparticles

Unloaded CeO2 and nominal 0.50, 1.00, 1.50, 2.00, 5.00, and 10.00 mol% Fe-loaded CeO2 nanoparticles were synthesized by flame spray pyrolysis (FSP). The samples were characterized to obtain structure-activity relation by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Brunauer, Emmett, and Teller (BET) nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), and UV-visible diffuse reflectance spectrophotometry (UV-vis DRS). XRD results indicated that phase structures of Fe-loaded CeO2 nanoparticles were the mixture of CeO2 and Fe2O3 phases at high iron loading concentrations. HRTEM images showed the significant change in morphology from cubic to almost-spherical shape observed at high iron loading concentration. Increased specific surface area with increasing iron content was also observed. The results from UV-visible reflectance spectra clearly showed the shift of absorption edge towards longer visible region upon loading CeO2 with iron. Photocatalytic studies showed that Fe-loaded CeO2 sample exhibited higher activity than unloaded CeO2, with optimal 2.00 mol% of iron loading concentration being the most active catalyst. Results from XPS analysis suggested that iron in the Fe3

Synthesis and Characterization of a Magnetically Separable CoFe2O4/TiO2 Nanocomposite for the Photomineralization of Formic Acid

A CoFe2O4/TiO2 nanocomposite was successfully synthesized by coupling the modified sol-gel with hydrothermal techniques. The obtained CoFe2O4/TiO2 nanocomposite was characterized by X-ray diffraction for phase composition and crystallinity. TEM images revealed that the shape of the as prepared samples was almost spherical and the average particle sizes were found to be in the range of 5–35 nm. The saturation magnetization (Ms) of CoFe2O4/TiO2 nanocomposite was determined to be 29.64 emu g-1. Photocatalytic activity and cycle stability were studied by the photomineralization of formic acid under solar light irradiation.