Morphological effect of green and chemically synthesized nano-ZnO for evaluation of antimicrobial and photo-catalytic activity

Abstract

The growing threat of multidrug-resistant bacteria and water pollution from textile industries necessitates the synthesis of more effective ZnO nanoparticles (ZnO NPs) with enhanced antimicrobial and dye degradation capacities. Their biocompatibility, photocatalytic activity, and antimicrobial properties make them particularly promising for environmental and biomedical applications. This article reviews the latest advancements in the production of ZnO NPs using various capping/stabilizing agents and organic extracts, with a focus on their antibacterial properties and their ability to degrade dyes under visible light exposure. Zinc oxide (ZnO) structures with diverse morphologies can be synthesized through various methods involving vapor, liquid, and solid phases. Among these, liquid-phase synthesis is commonly employed for photocatalytic applications. Hydrothermal synthesis has been found to produce the smallest nanoparticles, which demonstrated remarkable antibacterial efficacy, exceeding 90 % against both Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli) and Gram-positive strains (Bacillus subtilis, Staphylococcus aureus). The average degradation rate of textile dyes exceeds 98 %, with commonly used dyes such as Congo red, methylene blue, and methyl orange being effectively degraded. This review highlights ZnO synthesis, particularly focusing on various liquid-phase methods, including precipitation, green synthesis, sol-gel, and hydrothermal techniques. Special attention is given to the specific synthesis parameters employed in each method to control and modify the desired morphology. Analyzing the morphologies of ZnO, those with the smallest size, structural defects, and high surface area, such as flower, nanosheet, and nanorod shapes, exhibit the highest photocatalytic and antimicrobial activity.