Photoreduction of carbon dioxide of atmospheric concentration to methane with water over CoAl-layered double hydroxide nanosheets

Abstract

The photoreduction of CO₂ to carbon energy sources over catalysts is of great interest and significance. However, though many studies have been conducted at high CO₂ concentrations, research on CO₂ photoreduction at atmospheric concentrations remains rare. Herein, CoAl-layered double hydroxide (CoAl-LDH) nanosheets have been synthesized as a platform to explore low-concentration CO₂ photoreduction. The CoAl-LDH nanosheets exhibited efficient photocatalytic activity for CO₂ photoreduction to CH₄ at atmospheric concentration (400 ppm) under simulated solar light, and the reaction proceeded without deactivation for 55 hours. A CH₄ production rate of 4.3 μmol g⁻¹ h⁻¹ was achieved without the assistance of any sacrificial agent or noble metal. CO₂ adsorption experiments showed that the CoAl-LDH nanosheets exhibited an adsorption capacity of 2.95 cm³ g⁻¹, which was about twice that of P25 with a comparable specific surface area. XPS analysis indicated that CH₄ generation was closely related to the divalent cobalt, and the CH₄ yield decreases sharply when the divalent cobalt is oxidized, which was ascribed to the dissociation of water to release H for the hydrogenation of intermediates through further experimental analysis. This work emphasizes the importance of the alkaline OH group for the efficient adsorption of low-concentration CO₂ and reveals the unique property of divalent cobalt for CO₂ photoreduction.