A stage-by-stage phase-induction and nucleation of black phosphorus from red phosphorus under low-pressure mineralization
In the preparation of black phosphorene (BP) by means of low-pressure mineralization, the complex temperature program makes the synthesis mechanism complicated and confusing. Herein, orthorhombic BP crystals were successfully synthesized by low-pressure mineralization and the phase transitions at every stage were revealed systematically and were accurately confirmed via a series of interference experiments and supported by structure characterization. Additionally, the nucleation agents and nucleation sites were systematically investigated. Based on this, we found that the synthesis of BP is a process of stage-by-stage phase-induction. At first, red phosphorus (RP) is transformed to Hittorf's phosphorus (HP) without the assistance of mineralizers. Subsequently, HP is transformed into BP at the cooling stage. Moreover, Sn24P19.3I8 should work as the sole nucleation agent, and leads to BP crystal nucleation and growth to form large crystals in the subsequent heat preservation stage. Also, the nucleation site lies in the product region opposite the source region. In addition, the radial morphology of the BP crystal bunches under an RP/SnI4/Sn (granule) system was revealed firstly, and taking the straps out from the BP bunches is convenient for exfoliating.