Engineering Oxidation States of a Platinum Cocatalyst over Chemically Oxidized Graphitic Carbon Nitride Photocatalysts for Photocatalytic Hydrogen Evolution
Duc Quang Dao, Thi Kim Anh Nguyen, Sung Gu Kang, Eun Woo Shin
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/g-C3N4.