High-Pressure Studies on the Transition from Red Phosphorus to Black Phosphorus
Abstract
Black phosphorus (BP) is a promising material in many research fields. However, the transition process from amorphous red phosphorus (ARP) is elusive and hence hinders large scale synthesis and applications. This work describes the application of the high-pressure method to study the transition process from ARP to BP.
In this thesis, the following three objectives were achieved: (1) to understand the mechanism of the transition, (2) to facilitate the synthesis of BP by taking the advantage of less pure ARP, (3) to propose new methods of synthesizing BP-based materials, such as the moderately oxidized BP and the black phosphorus/ amorphous red phosphorus (BP/ARP) heterostructure.
The pressure-induced crystallization of ARP to BP was investigated by in-situ Raman spectroscopy and high-resolution transmission electron microscopy (TEM). Raman measurements revealed slow crystallization kinetics. TEM analyses provided information supporting the crystallization mechanism of structural rearrangement and oriented attachment of phosphorus atoms.
Under this mechanism, the impure ARP was demonstrated to be a suitable raw material with lower cost in synthesizing BP. According to energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy (XPS), no metal elements are chemically bonded with the phosphorus in either ARP or as-made BP, resulting in an unaffected transformation and providing a low cost alternative raw material for the scale-up synthesis of BP. Nevertheless, a moderately oxidized BP was first and successfully prepared using slightly oxidized ARP under high pressure as evidenced by the Raman and XPS results. Also according to the infrared spectroscopy and XPS, the phosphorus-oxygen bonds in both ARP and converted BP showed reversible changes after compression. This finding provides a new route to directly prepare BP with native oxidized phosphorus endowing unexplored features to the BP.
The BP/ARP heterostructure featuring very small nanocrystals and the well-defined crystalline regions of BP exhibit increased reactivity in visible-light-driven hydrogen production from water than pure ARP and BP, suggesting a new metal-free photocatalyst for producing hydrogen from water. Moreover, by applying pressure, we found that the rate of the photo-driven chemical reaction could be further increased in terms of hydrogen production and irradiation time.