Metal-free heterojunction of black phosphorus/oxygen-enriched porous g-C3N4 as an efficient photocatalyst for Fenton-like cascade water purification

It is significant to directly use solar energy for selective H2O2 production and subsequent water purification through a Fenton reaction that converts H2O2 into highly active free radicals. Nevertheless, the efficiency of such a promising route is still unsatisfactory due to the low sunlight utilization, poor selectivity towards H2O2 production, and the requirement of additional Fe-based co-catalysts in the Fenton reaction. Here we present a fascinating design to synthesize a metal-free photocatalyst for highly selective H2O2 production and efficient water purification via a Fenton-like cascade reaction. A BP/OPCN heterojunction is constructed for the first time by assembling 2D oxygen-enriched porous g-C3N4 (OPCN) with 2D black phosphorus (BP), which can effectively promote the visible light response and charge separation. Further investigation reveals that the surface oxygen groups and nanopores of the OPCN are critical both in increasing the active sites and in enhancing the selectivity of H2O2 production. The highest H2O2 production rate of BP/OPCN reaches a remarkable value of 3463 μmol h−1 g−1, which is much higher than that of reported g-C3N4-related materials. The large amount of H2O2 produced in situ over BP/OPCN can subsequently undergo a Fenton-like cascade reaction to degrade organic pollutants in wastewater in only one step. This work demonstrates an efficient photocatalytic approach to produce H2O2 and purify wastewater, while discovering the fundamental roles of the surface chemistry and physical structure of the photocatalyst.