Synergism between few-layer black phosphorus and graphitic carbon nitride enhances the photoredox C-H arylation under visible light irradiation

The development of solar-driven chemical transformations is one of the most attractive research interests as they lay the groundwork for a more sustainable future. To reach this target, efficient photocatalysts, particularly metal-free photocatalysts, should be designed and fabricated. For the design of efficient photocatalysts in terms of optical, chemical/thermal properties, and long-term stability, constructing heterojunctions of two-dimensional (2D) materials consisting of earth-abundant elements is one of the most environmentally friendly options. In this study, a highly efficient photoredox catalyst was developed by combining few-layer black phosphorus (FLBP) and graphitic carbon nitride (g-CN) binary heterojunctions, which build up a synergistic effect at the heterojunction interfaces. As-prepared FLBP/g-CN heterojunctions were tested in photoredox C-H arylation of heteroarenes with diazonium salts under visible light irradiation and showed excellent activity, with the product yields reaching up to 94% under ambient conditions. The activity of FLBP/g-CN heterojunctions showed a volcano-shaped relation with respect to the BP loading ratios, where the FLBP/g-CN with 35 wt% FLBP provided the best performance. The substrate scope of FLBP/g-CN heterojunctions was investigated over a variety of heteroarenes (furan, thiophene, and N -Boc pyrrole) with diazonium salts bearing electron-donating (ED) and electron-withdrawing (EWD) groups (29 examples in total). Moreover, a suitable band diagram showing a unique electron-hole migration between g-CN and FLBP, which is different from anticipated type-I heterojunction in the heterojunction structure, was proposed by the mechanistic studies and charge migration experiments. A volcano-shaped relation between the amount of FLBP in the FLBP/g-CN heterojunctions in the photoredox C-H arylation was exhibited. To understand the activity of 35 wt% FLBP/g-CN, band alignments of heterojunction was studied in detailed.