Glycerol photoreforming for photocatalytic hydrogen production on binary and ternary Pt-g-C3N4-TiO2 systems: a comparative study

Abstract

Photocatalytic hydrogen production using two sacrificial agents (triethanolamine and glycerol) was conducted on several binary (Pt/TiO2 and Pt/g-C3N4) and ternary systems (Pt on a heterojunction between TiO2 and g-C3N4 (Pt/(g-C3N4-TiO2) and on a physical mixture of semiconductors (Pt/(TiO2 +g-C3N4)). Reactions were carried out under visible light (450 nm) and UV (365 nm) radiation, from 10% (v/v) and 0.5% (v/v) sacrificial agent aqueous solutions, hydrogen production values being ca- 2–3 times greater in the former case. For visible light, the heterojunction was the most active system using triethanolamine whereas Pt/TiO2 system and glycerol was the best option under UV radiation. All in all, the highest hydrogen production value from a 10% (v/v) glycerol in water solution was on Pt/TiO2 (named Ptuv/Ti), under UV light, yielding around 165 mmol H2·gcat−1·after 6 h (that is, ca. 27.5 mmol·gcat−1·h−1). Hydrogen photoproduction studies from glyceraldehyde, dihydroxyacetone, and glycerol either alone or in binary mixtures (i.e., competitive reactions) cast further light on the glycerol reaction mechanism. Results evidenced that the adsorption strength on the catalysts follows the sequence glyceraldehyde > dihydroxyacetone > glycerol, adsorption of the former being particularly high on the heterojunction. Reactions were ca. twice as fast on Pt/TiO2 as on the Pt/(g-C3N4-TiO2) heterojunction and even though initial stages of the mechanism seems to differ a bit for the semiconductors, there is a hydrogen production value from which mechanism is apparently the same on both solids.