| Summary: | In this work, we have synthesized BiOCl nanoplates (diameter 140−220 nm, thickness 60−70 nm) via a co-precipitation method, and then created Bi nanoparticles (diameter 35−50 nm) on the surface of BiOCl nanoplates via a NaBH<sub>4</sub> reduction method. By varying the NaBH<sub>4</sub> concentration and reaction time, the evolution of Bi nanoparticles was systematically investigated. It is demonstrated that with increasing the NaBH<sub>4</sub> concentration (at a fixing reaction time of 30 min), BiOCl crystals are gradually reduced into Bi nanoparticles, and pure Bi nanoparticles are formed at 120 mM NaBH<sub>4</sub> solution treatment. At low-concentration NaBH<sub>4</sub> solutions (e.g., 10 and 30 mM), with increasing the reaction time, BiOCl crystals are partially reduced into Bi nanoparticles, and then the Bi nanoparticles return to form BiOCl crystals. At high-concentration NaBH<sub>4</sub> solutions (e.g., 120 mM), BiOCl crystals are reduced to Bi nanoparticles completely with a short reaction time, and further prolong the treatment time leads to the transformation of the Bi nanoparticles into a two-phase mixture of BiOCl and Bi<sub>2</sub>O<sub>3</sub> nanowires. The photodegradation performances of the samples were investigated by choosing rhodamine B (RhB) as the model pollutant and using simulated sunlight as the light source. It is demonstrated that an enhanced photodegradation performance can be achieved for the created Bi@BiOCl hybrid composites with appropriate NaBH<sub>4</sub> treatment. The underlying photocatalytic mechanism was systematically investigated and discussed.
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