Photoactivated Graphene Oxide to Enhance Photocatalytic Reduction of CO2.

Graphene oxide (GO) is commonly used in photocatalytic reactions but mainly as a cocatalyst. Limited information is available on the intrinsic ability of GO to photocatalytically reduce CO2 as a sole photocatalyst and the activation of light irradiation. In this study, simulated sunlight (SS) and UV-irradiated GO (GOSS and GOUV, respectively) showed enhanced efficiency of photocatalytic reduction of CO2 compared to pristine GO, with a CO yield (4 h) ratio of GOSS/GOUV/GO of 2.7:2.1:1. Here, irradiation plays two important roles: (1) irradiating GO to eliminate CO released under photolysis from photocatalytic reactions and (2) activating GO to create defects and restore the large π-conjugated network, obtaining photolysis-saturated and photoactivated GO for photocatalytic reduction of CO2. The increasing defect density and π conjugation of irradiated GO, as supported by X-ray photoelectron and Raman spectroscopy, improve the yield of photoelectrons and prolong the lifetime of photogenerated charge carriers, as supported by electron spin resonance and transient absorption spectroscopy. This results in an enhanced photocatalytic efficiency of irradiated GO. The higher CO yield of GOSS compared to GOUV indicates that simulated sunlight irradiation is more favorable for GO activation. Our results show that activating GO under irradiation enhances the photocatalytic reduction of CO2.