Controlled growth of ZnS/ZnO heterojunctions on porous biomass carbons via one-step carbothermal reduction enables visible-light-driven photocatalytic H2 production

Abstract

For visible-light-driven H₂ production, rational design of heterojunction photocatalysts might be a feasible strategy to achieve enhanced H₂ evolution efficiency. Herein, we prepared ZnS/ZnO heterojunctions highly dispersed on porous biomass carbons (ZnS/ZnO@C) through a one-step carbothermal reduction process at elevated temperatures. By means of the proposed synthetic pathway, the ZnS/ZnO@C composites were enabled with visible-light-driven photocatalytic capacity, despite either ZnS or ZnO being catalytically inactive for H₂ production under visible irradiation. The as-prepared photocatalyst with a 1 : 1 mole ratio of zinc and carbon sources at 800 °C displayed an optimal H₂ production rate of ca. 37.1 μmol h⁻¹ g⁻¹. TEM images and UV–DRS spectra suggested that the formation of ZnS/ZnO heterojunctions would induce the generation of oxygen defects in ZnO to greatly promote visible light adsorption. Electrochemistry analyses and time-resolved photoluminescence spectra demonstrated that more efficient separation of photo-induced carriers took place via the interfaces of ZnO/ZnS heterojunctions, prolonging the charge separation lifetime. Moreover, porous biomass carbons would serve as electron conductors to efficiently improve the photo-induced electron transfer from the bulk of ZnS/ZnO to surfaces for boosting the reduction of H₂O to H₂. The ZnS/ZnO heterojunctions with oxygen defects coupled with porous biomass carbons jointly achieved highly efficient H₂ production under visible irradiation. This work thus provided a facile means by using low-cost porous biomass carbons to design robust and flexible photocatalysts for visible-light-driven H₂ production with high efficiency.