Engineering Planar Crystallinity in Nitrogen-Vacancy-Incorporated Carbon Nitride for Efficient Photoredox Catalysis

Abstract

The concurrent evolution of value-added benzimidazole compounds and hydrogen within the domain of chemical synthesis is of paramount importance. The utilization of photocatalysis enhances both the efficiency and environmental benignity of the synthetic process. However, it is profoundly challenging within a photocatalytic system to simultaneously augment the number of active sites and the internal transport rate of photogenerated charge carriers. To address this issue, a template-free, step-by-step assembly strategy has been proposed for the synthesis of planar crystalline carbon nitride (CCN) incorporated with a nitrogen vacancy (Nv). In contrast to the simultaneous assembly method, the sequential assembly process encompasses a progressive crystallization mechanism. This method is conducive to the mitigation of the incidence of structural disarray, thereby precluding the genesis of non-ordered defects throughout the whole bulk phase. The ordered in-plane arrangement facilitates the spatial segregation of electrons and holes, thereby decoupling the redox active sites. This separation minimizes the likelihood of back reactions and suppresses the recombination process, which is advantageous for the efficiency of photocatalytic coupling reactions. Certified by multiscale characterization and theoretical simulations, the incorporation of Nv enhances the energy band structure and provides sites with unsaturated coordination for the adsorption and activation of ethanol molecules. This interfacial synergistic effect of Nv and co-catalyst Pt as the Lewis site achieves efficient activation of both coupling partners. The obtained CCN demonstrates significant bifunctional photocatalytic activity, achieving a yield of benzimidazole at 5.0 mmol g^–1 with a conversion and selectivity rate of 99%. Simultaneously, the hydrogen evolution rate of CCN is measured at 9.1 mmol g^–1 within 4 h. The template-free, step-by-step assembled strategy utilized in this study provides new perspectives on developing highly efficient photocatalysts at the molecular level.