Construction of graphene oxide-coated zinc tetraphenyporphyrin nanostructures for photocatalytic CO2 reduction to highly selective CH4 product.

The zinc-based photocatalysts for CO2 reduction have attracted increasing attention, however, usually exhibit low CO2-to-CH4 selectivity. Here, the graphene oxide (GO)-coated zinc tetraphenylporphyrin (ZnTPP/GO) nanocomposites are successfully synthesized through a simple method. It is found that with the increase of GO content, the crystallinity of ZnTPP nanocrystals enhances with the size decrease, and then the light absorption can easily match with the solar spectrum. The optimal ZnTPP/GO sample exhibits the CH4 evolution rate of 41.6 μmol g-1 h-1 and CH4 selectivity of >95%, which are higher than those of ZnTPP nanocrystals (7.8 μmol g-1 h-1 and 50.3%). The systematic characterizations confirm that the generation of axial coordinated ZnOC bonds between ZnTPP and GO plays a key role in the formation of ZnTPP/GO nanostructure and their synergic effect on photocatalytic CO2 reduction. The encapsulation of GO on ZnTPP nanocrystals not only promotes the CO2 adsorption, interfacial reaction, and stability, but also accelerates the separation of photoinduced carriers on ZnTPP (0.1 ps vs. 425.9 ps), the transportation from ZnTPP to GO (2.3 ps vs. 83.6 ps), and their final enrichment on GO. This work provides a new strategy to apply graphene and organic nanomaterials in artificial photosynthesis.