Preparation of Pt-loaded WO3 with different types of morphology and photocatalytic degradation of methylene blue

Four types of shape and crystal structure-controlled WO3 (normal: N-WO3, disk: D-WO3, cuboid: C-WO3, hexagonal plate: H-WO3) were synthesized from starting reagent of (NH4)10W12O41·5H2O by pyrolysis (N-WO3), precipitation (D-WO3) and hydrothermal (C-WO3 and H-WO3) methods. N-WO3 and D-WO3 have monoclinic and triclinic mixed phases each. C-WO3 has monoclinic phase, and H-WO3 has hexagonal phase mixed with monoclinic phase. Pt particles-loaded WO3 (Pt/WO3) was prepared to improve photocatalytic activity. Among four types of Pt/WO3, Pt/C-WO3 shows the highest photocatalytic activity for the degradation of methylene blue (MB) under visible-light irradiation, and photocatalytic activity decreases in the order Pt/C-WO3 ≈ Pt/H-WO3 > Pt/D-WO3 ≫ Pt/N-WO3. The MB degradation ability per unit specific surface area after visible-light irradiation for 6 h decreases in the order Pt/H-WO3 ≫ Pt/C-WO3 > Pt/D-WO3 > Pt/N-WO3, suggesting that with similar specific surface area of WO3, the hexagonal phase is more favorable for MB degradation than the monoclinic phase. This is believed to be due to the high MB adsorption ability of the hexagonal phase. Scavengers for OH radicals, holes and excited electrons were added to MB aqueous solution to investigate the degradation mechanism of MB on each Pt/WO3. In the case of Pt/C-WO3 and Pt/H-WO3, OH radicals and holes were the main oxidants in the degradation process of MB, where OH radical (OH) generation could be attributed to oxidation of H2O by holes.