Rational Design of S-Scheme Heterojunction toward Efficient Photocatalytic Cellulose Reforming for H2 and Formic Acid in Pure Water.

Abstract

Photocatalytic cellulose reforming usually requires harsh conditions due to its sluggish kinetics. Here, a hollow structural S-scheme heterojunction of ZnSe and oxygen vacancy enriched TiO2 , namely, h-ZnSe/Pt@TiO2 , is designed and fabricated, with which the photocatalytic reforming of cellulose for H2 and formic acid is realized in pure water. H2 and formic acid productivity of 1858 and 372µmol g-1 h-1 and a steady H2 evolution for 300 h are achieved with α-cellulose. Comparable photocatalytic activity can also be achieved using various cellulose sources. It is experimentally proven that the photogenerated charge transfer follows an S-scheme mechanism, which not only promotes the charge separation but also preserves the higher reductive and oxidative abilities of the ZnSe and TiO2 , respectively. Furthermore, the polyhydroxy species produced during cellulose degradation are favored to adsorb on the oxygen vacancy enriched TiO2 surface, which promotes the photocatalytic reforming process and is accounted to the preservation of formic acid as the major solution-phase product. In addition, sequential reactions of oxidation of aldehydes and elimination of formic acid of the cellulose degradation process are revealed. This work provides a photocatalytic strategy to sustainably produce hydrogen and value-added chemicals from biomass under the most environmentally benign condition, i.e., pure water.