A review on black-phosphorus-based composite heterojunction photocatalysts for energy and environmental applications

In the past decades, using semiconductor-based photocatalytic technology to accomplish solar-to-chemical energy conversion has been a potential strategy for simultaneously mitigating the severe environmental and energy crises. Black phosphorus (BP) is a promising nonmetal photocatalyst with numerous advantages, such as an adjustable direct band gap, a wide light absorption range, and ultrahigh charge carrier mobility. However, pure BP photocatalysts exhibit unsatisfactory performance because of poor ambient stability and fast recombination of the photogenerated electrons and holes. To overcome these obstacles, much research has focused on constructing BP-based heterojunction photocatalysts by combining BP with other catalytic materials. In this review, a brief introduction of the crystal structure, optical absorption, and electrical properties of BP photocatalysts is firstly presented. Then, the common preparation methods of BP with different dimensions are addressed. In accordance with the separation and migration path of the photogenerated electron-hole pairs at the interface, BP-based heterojunction photocatalysts are classified into Type I, Type II, Z-scheme, and S-scheme heterojunctions. In addition, three modification strategies for synergistically enhancing the ambient stability and catalytic performance of BP-based heterojunctions are presented, including modification with metal nanoparticles, in situ growth of metal phosphides, and combination with carbon-based materials. Thereafter, a series of applications in energy and environmental fields is illustrated. Finally, some personal perspectives are given on future directions for developing BP-based heterojunction photocatalysts.