In situ synthesis of metal (Bi0)–semiconductor [BiOX (X = Cl, Br, and I)] nanocomposites as a highly effective catalyst for the reduction of 4-nitrophenol to 4-aminophenol†
Abstract
The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) has been efficiently catalyzed by in situ generated Bi0–BiOX (X = Cl, Br, I) nanocomposites in the presence of sodium borohydride (NaBH4). The hierarchical 3D arrays of precursors (BiOCl, BiOBr, and BiOI) have been synthesized by a facile co-precipitation method at ambient temperature. The metallic Bi0 is generated in situ by partial reduction of the Bi3+ ions in BiOX (X = Cl, Br, and I) mediated by NaBH4 during the conversion of 4-NP to 4-AP. In situ generated Bi0–BiOX shows better catalytic activity than Bi0–BiOX composite formed by mixing individually synthesized metallic Bi0 particles with semiconducting BiOX nanoparticles. The Bi0–BiOI nanocomposite demonstrated higher catalytic activity (kapp = 0.529 min−1) compared to Bi0–BiOCl (kapp = 0.095 min−1) and Bi0–BiOBr (kapp = 0.098 min−1) due to its efficient conversion into metallic Bi0. The approximate percentage composition of in situ generated metallic Bi0 on the surface of BiOCl, BiOBr, and BiOI is nearly 10, 17, and 25%, respectively. Further, the reduction of 4-NP has been completed within 24, 22, and 6 minutes by in situ generated Bi0–BiOCl, Bi0–BiOBr, and Bi0–BiOI nanocomposites from BiOCl, BiOBr, and BiOI, respectively. Extensive studies have been conducted to generate a better understanding of the actual catalytic sites present on the surface of the catalysts.