Understanding the Intrinsic Reactivity of Black Phosphorus

Abstract

Black phosphorus (BP), a rediscovered two-dimensional (2D) material, has garnered significant interest due to its unique structure and physicochemical characteristics, including adjustable direct bandgaps, high carrier mobility, large specific surface area, and pronounced chemical reactivity. Distinct from the flat atomic structure of graphene, BP features a puckered honeycomb-like structure derived from sp³ hybridization. In addition to the three-coordination, each phosphorus atom possesses a lone pair of electrons, leading to an electron-rich nature. A variety of nanostructures such as nanosheets, nanoribbons, and quantum dots are developed from the bulk crystal of BP. The large surface area of nano BP provides numerous reactive sites that augment intralayer chemical interactions. Therefore, nano BP serves as a versatile scaffold for materials engineering, with potential applications across chemistry, catalysis, energy, and biomedicine. It is crucial to have a deep and systematic understanding of the hybridization interactions between BP and diverse molecules or materials, which is essential for functional design of BP-based materials for target applications.

Researchers have witnessed a surge in discussions surrounding the structure, physical properties, and synthesis methods of BP in recent years. However, the intrinsic reactivity of BP has received limited attention. The chemical properties of BP are usually associated with its environmental instability or degradation, and the main efforts are focused on its passivation rather than its exploitation. The intrinsic reactivity of BP facilitates a range of emerging applications including biomedicine, reducing agents, and composite construction. Notably, the controllable biodegradation of BP nanosheets can inhibit tumor growth, a phenomenon that has inspired the development of “bioactive phospho-therapy” as a cancer treatment strategy both in vitro and in vivo. In this Account, we first discuss the origin of BP’s chemical reactivity, and then categorize the typical types of chemical reactions, including redox reactions, covalent bonding, and noncovalent interactions. Each section is dedicated to a specific interaction type and is accompanied by relevant applications. These applications, which include catalysis, ion storage, sensors, and drug delivery, effectively demonstrate the structure–property–function relationships inherent in BP-based functional materials. Finally, a forward-looking perspective on the reactivity of BP is presented in the conclusion, which attempts to address the fundamental scientific questions and current technical challenges in this field. This Account is expected to encourage researchers to further explore the multifaceted potentials of BP across various areas.