The effect of N-vacancy on the photocatalytic activity of graphitic carbon nitride in the oxidative Mannich reaction

Abstract

Graphitic carbon nitride (g-CN) has been the focus of attention for sustainable solutions in diverse photocatalytic chemical transformations. However, the relatively low surface area and high recombination of photogenerated charge carriers of g-CN have hindered its wider application in photocatalysis. To eliminate these drawbacks, certain modifications on g-CN have been explored in the last decade. In this study, we present a simple calcination method to create nitrogen (N) defects in the g-CN structure, increasing the specific surface area and resulting in new mid-gap states among the energy band levels, lowering the absorption energy barrier and preventing charge recombination. The annealed g-CN with N-vacancies, denoted as A-g-CN, was characterized by using advanced instrumental techniques, and the nature of the induced modification was revealed by studying its morphological structure, chemical composition, and optoelectronic properties. The photocatalytic activity of the as-prepared A-g-CN was studied on a model reaction, namely the oxidative Mannich reaction under ambient conditions, resulting in drastically high conversion yields of up to 99%. The reaction mechanism of photoredox C–H (sp³) functionalization was also suggested by experimental studies.