Benzoxazine hierarchical porous carbon spheres as metal-free photocatalysts for efficient CO2 reduction

Photocatalytic reduction of CO 2 is a promising strategy for the conversion of high value-added chemicals, but the difficulty lies in the design of photocatalysts that combine high electron transfer efficiency, activity and stability. In this paper, the pore structure and the number of active sites of carbon spheres were modulated to promote the adsorption and reduction of CO 2 . MBZCSs-40 achieved a CO yield of 28.23 μmol g -1 for 8 h. N 2 adsorption and desorption and SEM confirmed the existence of a hierarchical pore structure. XPS showed that the ratio of the introduced pyridine nitrogen groups was well linearly correlated with the reducing properties and was hypothesized to be the main active centers. CO 2 adsorption isotherms revealed that MBZCSs-40 had the highest adsorption capacity of 1.86 g. In situ infrared detected that CO 2 was adsorbed on the nitrogen active sites and converted to CO 2 *, followed by the generation of the key intermediate COOH* in the presence of e - and H + . The moderate amount of nitrogen doping promoted micropores generation and thus exposed more active sites. Pyridine nitrogen enhanced the adsorption and activation of CO 2 and promoted the generation of COOH*. This study provides a new perspective for the design of nitrogen-doped metal-free photocatalysts.