Evolution of Bi Nanowires from BiOBr Nanoplates Through a NaBH4 Reduction Method with Enhanced Photodegradation Performance

In this work, we have adopted a coprecipitation method to synthesize BiOBr nanoplates with diameter of 150-450 nm and thickness of 40-80 nm, and then created Bi nanowires (diameter: 6 nm) on their surface through a NaBH4 reduction method. Evolution of Bi nanowires was systematically investigated by varying the concentration of NaBH4 solution and reaction time. It is demonstrated that with increasing the NaBH4 concentration (2 h reaction), Bi nanowires are gradually evolved from BiOBr crystals, and in particular treatment by 110 mM NaBH4 solution leads to the complete evolution of BiOBr nanoplates to Bi nanowires. At a low-concentration NaBH4 solution (30 mM), BiOBr crystals are partially reduced to Bi nanowires with increasing reaction time, and then the Bi nanowires are recrystallized into BiOBr nanowires/nanoparticles on the surface of BiOBr nanoplates. At a high-concentration NaBH4 solution (110 mM), BiOBr nanoplates are easily reduced to Bi nanowires with a short reaction time, and further prolonging the reaction time leads to the gradual transformation of Bi nanowires into Bi4O5Br2 nanoparticles/nanowires. Photocatalytic performances of the samples were evaluated by eliminating rhodamine B from aqueous solution under simulated sunlight illumination. It is demonstrated that the creation of Bi nanowires (an appropriate content) on the surface of BiOBr nanoplates can produce excellent Bi@BiOBr composite photocatalysts with enhanced photodegradation performances. The underlying enhanced photocatalytic mechanism was investigated and discussed.