Tailoring the redox ability of carbon nitride quantum dots/reduced graphene oxide-black phosphorus (CNQDs@rGOBP) ternary heterojunctions for photodegradation of organic pollutants

Abstract

The direct utilization of solar energy in chemical transformations has paved the way for widespread use of photocatalysis for degradation. However, the state-of-the-art photocatalytic systems for various applications have not yet reached the desired level due to poor visible-light absorption and the high-cost requirements of the developed photocatalysts. Recently, the combination of different semiconductors via band engineering has been regarded as a highly efficient strategy to construct metal-free photocatalysts. In this study, a novel ternary heterojunction photocatalyst was fabricated by decorating reduced graphene oxide/black phosphorus binary heterojunctions (rGOBP) with carbon nitride quantum dots (CNQDs) via the ultrasound-assisted liquid exfoliation method. Different ratios of rGOBP binary and CNQDs@rGOBP ternary heterojunctions were prepared to investigate how the content is correlated synergistically to the coupling of the materials at their interfaces, thus possessing a superior photophysical properties. Combining the polar functional groups of as-synthesized rGO and CNQDs with the non-bonding electrons of BP on the surface led to the formation of a chemically stable photocatalyst with high catalytic performance. Harmonizing the salient features of each material boosted the degradation efficiency of organic pollutants 2.5 times in aqueous media compared to their pristine components. The photocatalytic performance of CNQDs@rGOBP heterojunctions was screened by studying different pollutants and catalyst concentrations. Moreover, the photogenerated charge migration pathway was proved by considering the results of the scavenger experiments and changes in the work functions of materials. A nonclassical type-I heterojunction, occurring at the farthest charges of band edges, was proposed as the underlying mechanism behind the superior photocatalytic activity of CNQDs@rGOBP ternary heterojunctions.