Synthesis, Structural Evolution and Antimicrobial Properties of Thermally Treated Zinc–Chromium Layered Double Hydroxide-Derived Nanostructured Oxides toward Wastewater Treatment

This paper investigates the rational design, structural evolution and antimicrobial activity of nanostructured zinc–chromium Layered Double Hydroxides (Zn/Cr-LDHs) and their thermally produced Mixed Metal Oxide (MMO) phases. Zn/Cr-LDHs were synthesized using a simple co-precipitation method and then calcined at 100[Formula: see text]C and 300[Formula: see text]C to induce phase transformations into ZnO and ZnCr 2 O 4 crystalline phases, confirmed by XRD. Field-emission scanning electron micrographs revealed significant changes in morphology and crystallite size as the calcination temperature increased. Optical analysis revealed that the bandgap energy increased steadily from 1.98 eV for the original LDHs to 2.11 eV for Zn/Cr-MMO@300[Formula: see text]C, indicating enhanced electronic properties suitable for photocatalytic applications. Notably, the material demonstrated strong antibacterial activity against Escherichia coli, Staphylococcus aureus and two fungi,Candida albicans and Penicillium digitatum, with inhibition zones reaching 18 mm for bacteria and 15 mm for fungi after 48 h, exceeding the results for MMO@500[Formula: see text]C and MMO@700[Formula: see text]C. The combination of tunable structure, visible-light activity and high biocidal efficacy highlights the potential of these nanostructures as antimicrobial agents with optical and structural features suitable for future photocatalytic wastewater treatment.