Influence of Pt Oxidation State on the Activity and Selectivity of g-C3N4-Based Photocatalysts in H2 Evolution Reaction

Abstract

Graphitic carbon nitride g-C3N4 has been modified using platinum and platinum oxide (0.5–5 wt.%) and studied in photocatalytic H2 evolution reactions with ethanol aqueous solution under visible light irradiation (λ = 409 nm). An analysis of the by-products of the reaction (CO2, CH4, C2H6 etc.) was also carried out. The morphology, particle size distribution, and optical properties of the photocatalysts, and the chemical states of platinum cations were examined using various methods. The photocatalysts were investigated using a wide range of methods to clarify the morphology, particle size distribution, optical properties, and the chemical states of platinum cations. Factors affecting not only the activity, but also the selectivity of the photocatalyst in the target process of hydrogen production, have been established. The highest rate of H2 evolution achieved over 0.5 wt.% Pt/g-C3N4 photocatalyst is 0.6 mmol h−1 g−1 (selectivity 98.9%), which exceeds the activity of pristine g-C3N4 by 250 times. Increasing the Pt or PtO content up to 5 wt.% leads to an increase in the rate of formation of by-products (CH4, C2H6, and CO2) and a decrease in the selectivity of H2 evolution. The study also delves into the role of platinum and the mechanism of charge transfer in PtO/g-C3N4 and Pt/g-C3N4 photocatalysts due to light irradiation.