Well-designed 3D/2D/2D WO3/Bt/g-C3N4 Z-Scheme heterojunction for tailoring photocatalytic CO2 methanation with 2D-Layered Bentonite-clay as the electron moderator under visible light

Abstract

Photocatalytic CO2 reduction to renewable hydrocarbon fuels is a promising strategy to address global energy issues; however, producing fuels like CH4 is highly challenging under visible light. In this work, fabrication of a two-dimensional bentonite (2D-Bt) nanosheet mediated WO3/g-C3N4 Z-scheme heterojunction for highly selective photocatalytic CO2 reduction to CH4 under visible light has been investigated. The photocatalytic performance of the newly developed WO3-embedded 2D pillared Bt with 2D g-C3N4 composite for selective photocatalytic CO2 reduction to methane was studied using H2O as the reducing agent under visible light. WO3/Bt/g-C3N4 (WBCN) exhibits the highest photocatalytic activity for CH4 production, which was 6.01, 6.76, and 25.30 times higher than using WO3/g-C3N4, Bt/g-C3N4, and g-C3N4 samples, respectively. Noticeably, WO3-coupled with g-C3N4 was favorable for CO production; however, introducing Bt layered clay was in favor of methane formation during the CO2 reduction process. Additionally, the Z-scheme of the WO3/g-C3N4 composite with Bt as the electron moderator could promote photoinduced charge separation and redox ability of the separated charge carriers, resulting in excellent CO2 reduction to CH4. The rate of reaction was dependent only on the external mass transfer due to surface reactions over the WBCN composite catalyst. With increasing photon flux, methane production was further enhanced due to the thermodynamically favorable process for the activation of CO2 methanation reaction. Besides, good cycling ability was observed due to the presence of a layered clay structure, which was sustained in multiple cycles without obvious deactivation. This study provides a green clay based noble-metal-free approach to construct a structured composite photocatalyst with a Z-scheme charge carrier and would be beneficial for CO2 reduction and other solar energy applications.