Engineering Oxidation States of a Platinum Cocatalyst over Chemically Oxidized Graphitic Carbon Nitride Photocatalysts for Photocatalytic Hydrogen Evolution

Abstract

In this study, we prepared platinum (Pt)-containing graphitic carbon nitride (g-C3N4) catalysts using Pt photodeposition onto g-C3N4 modified by chemical oxidation, and the chemically oxidized Pt/g-C3N4 catalysts were applied to photocatalytic hydrogen evolution tests. The hydrogen production rates of the chemically oxidized Pt/g-C3N4 photocatalysts (2471.7 and 3640.8 μmol g?1 h?1) were found to be at least 5 times higher than those of bulk Pt/g-C3N4 (429.3 and 728.8 μmol g?1 h?1). Compared with bulk g-C3N4, the chemically oxidized g-C3N4 was composed of more positively charged locales induced nearby the oxygen-containing edges, which was proven by DFT calculations. As a result, the chemically oxidized Pt/g-C3N4 catalysts maintained the high ratio of Pt2+/Pt0 among the Pt nanoparticles during the Pt photodeposition. The higher proportion of Pt2+ sites on the chemically oxidized g-C3N4 enhanced the hydrogen evolution rate by their favorable water adsorption and hydrogen intermediates (Hads) desorption, thus suppressing the reversible reaction route of H2 to 2H+. Additionally, the chemically oxidized g-C3N4 with oxygen-containing functional groups improved the separation efficiency of photoexcited charges over Pt/gC3N4.