Noble-Metal-Free CdS Nanoparticle-Coated Graphene Oxide Nanosheets Favoring Electron Transfer for Efficient Photoreduction of CO2

Graphene oxide (GO) nanosheets are promising noble-metal-free catalysts. However, the catalytic activity and selectivity of GO are still very low. Herein, GO is first functionalized via noncovalent interactions by an aspartic acid modified anhydride having COOH groups to form A-GO. A-GO is more conductive and hydrophilic than GO and P-GO synthesized via functionalizing GO by a COOH-free anhydride. Then, we load CdS nanoparticles, which are responsible for absorbing light to produce charge carriers, on A-GO to fabricate a CdS/A-GO photocatalyst without noble metals for the photoreduction of CO2 by H2O. CdS/A-GO exhibits a higher photoreduction efficiency than that of CdS/GO and CdS/P-GO. The main carbon-based photoreduction product of CdS/A-GO is CH3OH, whereas that of CdS/GO and CdS/P-GO is CO. The more conductive and hydrophilic A-GO triggers a more efficient electron transfer, CO2 adsorption, and production of hydrogen atoms from H2O dissociation, thus leading to the higher photoreduction efficiency and product change on CdS/A-GO. Besides, the COOH groups of the aspartic acid modified anhydride supply their hydrogen atoms to promote the conversion from CO2 to CH3OH on CdS/A-GO. Therefore, noncovalently functionalizing GO with different active species can efficiently improve the catalytic performance of GO. This opens a new way to design and construct noble-metal-free catalysts with enhanced activity and selectivity.