Biosynthesis of gold nanoparticles by a mining- adapted bacterial consortium: Physicochemical properties and environmental applications

Biological synthesis of gold nanoparticles (AuNPs) offers an eco-friendly alternative to conventional synthesis methods. A bacterial consortium (comprising Klebsiella pneumoniae , Stenotrophomonas maltophilia , Acinetobacter bereziniae , and Bacillus cereus) was used for AuNPs biosynthesis. Physicochemical characteristics and functional properties of AuNPs were evaluated. Techniques including UV-Vis spectroscopy, Transmission Electron Microscopy (TEM), Fourier Transform Infrared (FTIR) spectroscopy, Dynamic light scattering (DLS), and X- ray diffraction (XRD) were used to characterize the AuNPs. Results showed that particle size distribution, surface charge, and crystallinity were influenced by biomolecular capping. When applied in antimicrobial activity against Enterococcus spp. and Klebsiella pneumoniae inhibition was significant at 25 μg/mL and most pronounced at 50 μg/mL. TEM analysis confirmed cell membrane rupture as the primary antimicrobial mechanism. AuNPs were incorporated into TiO 2 (Degussa P25) to form a composite (TiO 2 /0.5 wt% AuNP). Scanning electron microscopy (SEM, UV-Visible Diffuse Reflectance Spectroscopy (UV–Vis DRS) and Brunauer-Emmett-Teller (BET) analysis were employed to characterize the composite. The composite showed enhanced surface reactivity and reduced band gap (from 3.1 to 2.7 eV) when compared with pristine TiO 2 . The composite exhibited enhanced Rhodamine B degradation under both visible light and sunlight. First-order photocatalytic kinetics was confirmed with high correlation coefficients (R 2 ≥ 0.92), validating the model. Enhanced reaction rates for the composite were noticed under visible light, the rate constant increased by 1.67-fold (0.0025 vs. 0.0015 min -1 ), and under sunlight (R 2 ≥ 0.96), by 2.5-fold (0.019 vs. 0.0075 min -1 ). Results highlight the importance of biosynthesized nanomaterials and their role in targeted applications in catalysis and environmental remediation.