Construction of Carbon Nitride Based Intramolecular D–A System for Effective Photocatalytic Reduction of CO2

Photocatalytic technology provides a new strategy for mitigating energy crisis. The development of photocatalytic materials with high efficiency and stable visible light response has always been the direction of researchers in the field of photocatalysis. Graphite carbon nitride (g-CN) has attracted ever increasing attention in the field of photocatalysis due to its special characteristics (such as visible light response, high stability, and low cost). However, the low separation efficiency of photogenerated electrons and holes limits its catalytic activity. In this paper, a novel g-CN-based intramolecular donor–acceptor (D–A) system was prepared to promote the separation efficiency of light-induced charge carriers. The catalyst is prepared from g-CN and 1,2-dibromobenzene (Bz) through a simple calcination method. Characterization results confirmed that Bz was successfully introduced into the g-CN (g-CN-Bz (x)) framework. The formation of the D–A structure leads to the spatial separation of electrons and holes pairs, which significantly accelerates the separation efficiency of charge carriers. Moreover, the D–A structure plays an important role in adjusting the width of band gap, which can increase the light absorption capacity of the catalyst. The D–A system also leads to the formation of a built-in electric field, which significantly accelerates the migration speed of electrons. Among the prepared catalysts, g-CN-Bz (0.01) has the best photocatalytic CO2 reduction performance, and the evolution rate of CO is 5.2 times higher than that of CN (3.64 μmol g−1). In addition, the reaction is carried out in water without any sacrificial agent, which makes it green and environmentally friendly. The charge carrier excitation-recombination process between donor and acceptor, and photocatalytic reduction of CO2 to CO over the CN based DA composites.