Green synthesis of ZnO/catechin nanocomposite: Comprehensive characterization, optical study, computational analysis, biological applications and molecular docking

Abstract

Herein, a green and cost-efficient approach was employed to develop the ZnO/Catechin nanocomposite. Margosa leaf extract was utilized as a reducing and capping agent in the fabrication of ZnONPs. Catechin extracted from green tea was employed to modify the ZnONPs, and various conjugation strategies between ZnONPs and extracted catechin were explored. Comprehensive characterization techniques including SEM, elemental mapping, EDX, UV–vis spectroscopy, FT-IR, and XRD were employed to validate the successful formation of the ZnO/Catechin nanocomposite, revealing an average crystal size of 49.37 nm. In vitro antimicrobial assessment was conducted on green-synthesized ZnONPs (A), extracted catechin (B), and the nanocomposite (C) against both gram-positive bacteria (Bacillus cereus, Staphylococcus aureus) and gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa). Minimum inhibitory concentration (MIC) testing highlighted the robust inhibitory effects of the nanocomposite (C) at notably lower concentrations (10–60 μg/mL), surpassing the efficacy of precursor compounds (A and B), which necessitated higher concentrations (20–600 μg/mL) for moderate effectiveness. Components (A-C) exhibited enhanced antibacterial efficacy, yielding inhibitory zones ranging from 9 ± 0.01 to 13 ± 0.22 mm against the tested pathogens, outperforming Azithromycin as a positive control. Exploration of Frontier molecular orbitals (FMOs) unveiled smaller band gap energies (Eg) of 1.86, 0.49, and 2.14 eV for the prepared nanocomposites (C1-3) in contrast to precursor compounds (A = 4.04 eV, B = 4.03 eV).