The Effect Of Cocatalysts’ Composition On Photocatalytic Performance Of Semiconductor Photocatalysts For Hydrogen Evolution

Photocatalytic water splitting into hydrogen has been considered as a promising strategy to solve the global energy crisis and environmental issues.The absorption of light,charge separation and surface reaction are important in the photocatalytic water splitting reaction that affect the photocatalytic performance of photocatalysts.The loading of proper cocatalysts on the surface of photocatalysts could provide the reaction sites and facilitate oxidation or reduction reactions,promote the charge separation while suppressing the charge recombination and reverse reactions.Therefore,cocatalysts play a significant role in improving the activity of semiconductor photocatalysts.This paper focuses on the effects of the composition and loading amounts of cocatalysts on the photocatalytic activity of g-C₃N₄ and TiO₂.g-C₃N₄ nanosheets were synthesised by a quick thermal treatment method with large amounts of defects.Pt,Pd and PtPd alloy were loaded on g-C₃N₄ nanosheets as reduction co-catalysts by the in-situ reduction of ascorbic acid.The photocatalytic hydrogen evolution performance of 4 wt%PtPd/g-C₃N₄ can be enhanced by 55%in comparison with 4 wt%Pt/g-C₃N₄.Due to the insufficient control of Pt/Pd loading amounts and degree of reduction via this method,the PtPd/g-C₃N₄ photocatalysts were prepared by electrostatic adsorption method.The periodic structure of g-C₃N₄ was seriously broken during the reduction by hydrogen to produce Pd and Pt.The visible light absorption was enhanced due to the increased defects in graphitic carbon nitride.The as prepared PtPd/g-C₃N₄ exhibits the highest activity with hydrogen generation rate of 172.9μmol·h^-1,much higher than that of Pt/g-C₃N₄ and Pd/g-C₃N₄.CuO and Co₃O₄ nanoparticles about 2-5 nm were successfully decorated on TiO₂surface as reduction and oxidation cocatalyst with an easy milling process,in which P25,Copper nanoparticles and Co（NO₃）₂ were used as the precursors.The effects of dual cocatalysts on photocatalytic hydrogen production rates in both methanol-water and pure water were investigated.By the comparison of photocatalytic activity for H₂ evolution in water and methanol system,the synergetic effects of CuO and Co₃O₄ on photocatalytic H₂evolution were investigated whether there is sacrificial reagent or not.The photocatalytic H₂ production activity in water can be increased by approximately 4.5 times than 1 wt%CuO/TiO₂ after co-loading trace Co₃O₄ on CuO/TiO₂ photocatalysts.However,the loading of Co₃O₄ contributes little to the improvement of H₂ evolution rate in methanol.The oxidation cocatalysts are necessary to inhibit electron-hole recombination and balance the reduction and oxidation reaction rates in photocatalytic reactions in pure water.