Phyto-mediated synthesis of M-ZT/bentonite nanocomposite using Hagenia abyssinica for synergistic photocatalytic and antimicrobial efficacy

In this study, single-phase nanoparticles (ZnO, Mg-ZnO (M-Z), TiO₂) and multiphase nanocomposite (M-Z/TiO₂ (M-ZT), M-Z/TiO₂/Bentonite (M-ZTB)), were synthesized via a green method using Hagenia abyssinica (H. abyssinica) leaf extract. Comprehensive characterization confirmed the formation of a stable heterostructure with superior physicochemical properties, including a small crystallite size (22.98 nm) and a narrowed optical bandgap (2.95 eV), enabling efficient visible-light-driven applications. Under optimal conditions (pH 9, 15 mg catalyst dose, 15 ppm methylene blue (MB), the M-ZTB nanocomposite achieved 96% dye degradation following pseudo-first-order kinetics (R² > 0.99) and maintained over 94% efficiency after four reuse cycles, demonstrating excellent structural stability. The M-ZTB nanocomposite exhibited strong antibacterial effects against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, producing inhibition zones of 22.7 mm and 22.2 mm, respectively, at a concentration of 100 µg/mL. It also demonstrated very low Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values, with MIC/MBC of 0.813 and 1.625 µg/mL for S. aureus, and 1.625 and 3.125 µg/mL for E. coli, respectively. The enhanced photocatalytic and antibacterial performance is attributed to synergistic effects among the Mg-ZnO/TiO₂ heterojunction and bentonite support, promoting effective charge separation, surface reactivity, and metal ion release.