Burapat Inceesungvorn

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.

CoTiO3/Ag3VO4 composite: A study on the role of CoTiO3 and the active species in the photocatalytic degradation of methylene blue

The role of CoTiO3 and the possible active species in the methylene blue (MB) degradation over the visible-light-driven CoTiO3/Ag3VO4 catalyst have firstly been investigated in this work. CoTiO3 is found to play important roles in enhancing the visible light-harvesting ability of the composite and increasing electron-hole separation efficiency due to the hybrid effect between Ag3VO4 and CoTiO3. The indirect probe experiments reveal that CoTiO3/Ag3VO4 heterostructure provides large amount of active species, therefore a high photocatalytic activity could be obtained. The results clearly suggest that the photocatalytic MB degradation over this hybrid catalyst is mainly governed by direct hole oxidation.

Visible light photocatalytic performance and mechanism of highly efficient SnS/BiOI heterojunction

Novel SnS/BiOI heterostructures with excellent photocatalytic degradation of methyl orange were successfully prepared by a facile hydrothermal-coprecipitation method. The maximum methyl orange degradation activity under visible light irradiation (λ>400nm) was found for 10wt% SnS/BiOI. The composite also showed better stability and good recyclability compared to BiOI. The energy band diagram and band offsets from X-ray photoelectron spectroscopy investigation indicated that the novel composite was a type-II heterojunction where the photogenerated electron-hole can be efficiently separated and transferred. Results from UV-vis DRS, PL-TA and photocurrent response measurement suggested that the improved photodegradation efficiency of the SnS/BiOI heterojunction was mainly attributed to enhanced light absorption capability, strong ability to generate and transfer photoexcited charge carriers and high active species formation. Additionally, radical scavenging experiments demonstrated that holes and superoxide radicals are dominant active species, whereas hydroxyl radicals are of secondary importance in this system. A plausible photocatalytic mechanism of the SnS/BiOI composite was also discussed.

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.

Low temperature preparation of oxygen-deficient tin dioxide nanocrystals and a role of oxygen vacancy in photocatalytic activity improvement

The introduction of oxygen vacancies (Vos) into tin dioxide crystal structure has been found as an effective method to improve its photocatalytic performance. Herein, oxygen-deficient tin dioxide (SnO2-x) nanocrystals were successfully prepared via a facile, one-step hydrothermal method at the temperature lower than those reported previously. The effect of hydrothermal temperature on phase composition and Vos content was also firstly investigated. Due to its high oxygen vacancy concentration, the SnO2-x prepared at 80 °C provides the best photocatalytic degradation of methyl orange under UV-visible light. Scavenger trapping and nitroblue tetrazolium experiments also show that the Vos act as electron trapped sites and molecular oxygen adsorption sites, therefore increasing the production of active O2- radical which is the main species governing the photocatalytic activity of SnO2-x nanocrystals. Raman spectroscopy, X-ray photoelectron spectroscopy, photoluminescence measurement and electron spin resonance investigation clearly indicate that increasing the hydrothermal temperature results in the coexistence of SnO2-x and Sn3O4 phases and the reduction of Vos concentration which are detrimental to the photocatalytic performance. Density functional theory calculations also reveal that the presence of Vos is responsible for the upshift of valence band maximum and an extended conduction band minimum, hence a valence band width broadening and band gap narrowing which consequently enhance the photocatalytic performance of the oxygen-deficient SnO2-x.

Controlled synthesis of barium chromate multi-layered microdiscs and their photocatalytic activity

BaCrO4 microdiscs composed of multi-layered microplates were successfully synthesized by a facile oxalate-assisted precipitation method for the first time. Herein, the oxalate ion helps slow down the nucleation rate of BaCrO4 crystals by complexing with the barium ion and offers control over the crystal growth and self-assembly processes via selective adsorptions probably on the facets containing elevated barium ions of the growing BaCrO4 crystals. Based on the time-dependent experiments, the dissolution–recrystallization–self-assembly process has been proposed for a possible formation mechanism of the multi-layered microdiscs. A preliminary photocatalytic study suggests that the multilayered microdiscs preferentially degrade methyl orange over methylene blue and phenol due to their positive surface charge. Further investigation on the MO degradation performance under UV and visible irradiations clearly shows that the three-dimensional hierarchical structure provides better photocatalytic activity than its low-dimensional counterpart, potentially due to its higher optical absorption ability originating from the unique morphology. The synthetic method developed in this work not only provides a one-step, facile and effective control over the morphology of BaCrO4, but also offers an alternative approach toward the design of efficient photocatalytic materials.