Facile Synthesis of Crystalline Bismuth Nanoparticles Using Orange Peel Extract: Concurrent Antibacterial and...

This study presents an innovative and environmentally friendly synthesis of bismuth nanoparticles (BiNPs) using orange peel extract (OPE), highlighting its potential for antibacterial and catalytic applications. By fine-tuning the reaction conditions, such as temperature and time, it was determined that at 100 °C with a reaction time of 8 h, the best quality BiNPs were achieved. XRD analysis confirmed the rhombohedral crystalline structure of the BiNPs, with an average crystallite size of 29 nm. Morphological evaluation via electron microscopy revealed a predominantly spherical population ranging from 10 to 80 nm, with 60% of the particles concentrated between 10 and 30 nm and a mean diameter of 28 nm. FTIR and TG analyses demonstrated that phytochemicals from the OPE facilitate the stabilization of the nanoparticles. The DLS results further support the presence of an organic corona, yielding a hydrodynamic diameter (D _h ) between 100 and 150 nm (average 122 nm); the discrepancy between the TEM and DLS values is attributed to the hydration layer and the bulky stabilizing ligands on the particle surface. The BiNPs showed significant antibacterial activity against E. coli, S. aureus, V. cholerae, and S. typhi. The study also demonstrated the potential of the BiNPs in the catalytic reduction of 4-nitrophenol to 4-aminophenol, achieving a competitive normalized rate constant of 8.76 s^-1g^-1. Furthermore, the BiNPs exhibited significant catalytic activity in the degradation of organic pollutants, specifically methyl orange and methylene blue. These findings establish OPE-mediated BiNPs as effective, "green" heterogeneous catalysts with high potential for addressing environmental challenges through the remediation of industrial dyes and nitro-aromatic compounds. This confirms the efficiency of the sustainable approach and brings future directions for nanotechnology and ecological applications.