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

Graphene oxide nanosheets (GO) are promising noble-metal-free catalysts. But, the catalytic activity and selectivity of GO is still very low. Herein, GO is firstly 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 is responsible for absorbing light to produce charge carriers, on A-GO to fabricate a CdS/A-GO photocatalyst without noble metals for photoreducing CO2 by H2O. CdS/A-GO exhibits a higher photoreduction efficiency than CdS/GO and CdS/P-GO. The main carbon-based photoreduction product on CdS/A-GO is CH3OH, whereas that on CdS/GO and CdS/P-GO becomes CO. The more conductive and hydrophilic A-GO triggers 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.