Aminated metal-free red phosphorus nanosheets for adsorption and photocatalytic reduction of Cr(VI) from water

The pollutant of hexavalent chromium (Cr(VI)) threats to the environment as well as to the human beings due to its strong toxicity, carcinogenicity, mobility and undegradability. Herein, a novel porous aminated red phosphorus (RP) nanosheet photocatalyst was synthesized to remove Cr(VI) from water through adsorption and in-situ photocatalytic reduction. The introduction of –NH₂ on the surface of RP nanosheet could effectively improve adsorption and photocatalytic reduction performance for Cr(VI) removal during visible light irradiation. As a result, the optimized RP-AP-0.5 (AP: 3-aminopropyltriethoxysilane) nanosheet displays the apparent reaction rate constant of 0.0190 min⁻¹, which is 5.5 times higher than that of pure RP (0.0035 min⁻¹), the 96.5% reduction efficiency for Cr(VI) within 120 min at pH = 4.8 ± 0.1 and still exhibits more than 95% removal efficiency after 5 cycles at the same condition. The enhanced Cr(VI) removal performance of the aminated RP nanosheet can be assigned to accelerating the interfacial reaction dynamics and more effective electron-hole separation owing to the presence of –NH₂ groups. This study provides a new method to develop high-efficiency metal-free photocatalysts with –NH₂ modification for Cr(VI) removal.