Doldet Tantraviwat

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.

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.