Multifunctional silver nanoparticles supported on ZnAl-LDH and ZnNiAl-LDH: Applications in reduction and ozonation reactions, and biological activity

Doping silver metallic nanoparticles AgNPs onto a porous solid results in an ultrafine size and good dispersion. This improves stability and avoids aggregation problems, enabling the design of an efficient, reusable nanocatalyst for wastewater treatment. This work focuses on the doping of Layered Double Hydroxides (LDHs) with silver metallic nanoparticles. The effect of the LDHs structure on the dispersion of AgNPs was investigated using bimetallic (ZnAl-LDH) and trimetallic (ZnNiAl-LDH) LDHs. The obtained materials were characterized using XRD, XRF, FTIR, TGA, XPS, SEM/EDS (mapping and spectral), TEM/SAED, zeta potential and nitrogen sorption measurements. Then these solids were used as catalysts for catalytic reduction, catalytic ozonation, and antimicrobial activities using several strains. The results showed good stability of LDHs after NaBH₄ treatment, subsequently giving good dispersion of AgNPs on their surfaces with ultrafine sizes. The application of different solids in dye reduction revealed that only the AgNPs-doped materials exhibited catalytic activity. Under the optimized conditions, Ag@ZnNiAl-LDH was identified as the most effective catalyst, exhibiting rate constants of 0.013, 0.0113, and 0.0019 s−1 for MB, MO, and 4-NP, respectively. In the binary system containing MO and MB the catalyst was more selective via the cationic dye MB following electrostatic attractions between them as confirmed by zetametry analysis. The MB dye ozonation reaction was selected as the model reaction, and several parameters were optimized, including pH, catalyst mass, and catalyst chemical composition. The best catalyst was found to be ZnNiAl-LDH under the following conditions: a catalyst mass of 70 mg, a pH of 11, and [MB] of 0.025 mM. The rate constant recorded under these conditions was 0.1248 min−1. Reuse of the catalysts in both catalytic applications yielded good results, and they demonstrated good stability after characterization with slight Ag leaching during MB reduction. The antibacterial tests on the different samples showed promising results, particularly against gram-negative bacteria.