Few Layer Phosphorene/Reduced Graphene Oxide/Graphitic Carbon Nitride Ternary Heterojunctions for Sustainable Photoredox C-H Functionalization of Heteroarenes

Abstract

Building upon our research in the rational design of metal-free heterojunctions as multifunctional photocatalysts, we report herein a novel ternary heterojunction comprising few-layer phosphorene (FLP), reduced graphene oxide (rGO), and graphitic carbon nitride (g-CN) (FLP/rGO/g-CN) for the visible-light-driven C-H arylation of heteroarenes. Comprehensive characterization techniques confirmed the successful integration of FLP, rGO, and g-CN into a well-defined heterostructure with intimate interfacial contact. Optimization studies on the photoredox C-H arylation of heteroarenes revealed that 30 wt% FLP within rGO/g-CN exhibited superior performance, outperforming individual constituents and binary heterojunction (rGO/g-CN). Under the optimized reaction conditions, the FLP/rGO/g-CN heterojunction efficiently mediated the arylation of furan derivatives with aryldiazonium salts, achieving yields up to 94%, while thiophene derivatives furnished moderate yields (up to 84%) with electron-deficient aryl groups. Solid-state NMR (ssNMR) analysis reveals strong interactions between the central nitrogen atoms of the tri-s-triazine units and the FLP species as well as rGO, leading to increased local electron density that synergistically enhances photocatalytic activity compared to the pristine materials. Mechanistic studies, including radical scavenger experiments and charge transfer analysis, revealed a synergistic nonclassical type-I heterojunction mechanism that promotes efficient spatial separation and directional migration of photogenerated charge carriers, thereby minimizing their recombination. Furthermore, the FLP/rGO/g-CN heterojunction demonstrated excellent recyclability, maintaining its high activity over five consecutive cycles without significant loss, underscoring its robustness and high chemical stability. This study highlights the potential of rationally engineered 2D-based ternary heterostructures as sustainable and high-performance photocatalysts for solar-driven C-H functionalization, offering insights into the design of advanced metal-free catalytic systems for organic transformations.