Metal Oxide Nanoparticles: A Comprehensive Review of Recent Advances in Synthesis Strategies, Characterization and Multifunctional Applications

The metal oxide nanoparticles have been the subject of intense research interest because of their remarkable physicochemical properties such as high surface area, particle size tunability, outstanding chemical stability, optical activity, catalytic efficiency, and antimicrobial behavior. These properties make them very useful in environmental, biomedical, energy, sensing, agricultural and industrial applications. The synthesis method is important to control the morphology, crystallinity, surface charge, band gap and overall performance of metal oxide nanoparticles. They have been prepared by various physical, chemical and biological means such as solgel, co-precipitation, hydro/solvothermal, microwave assisted, sonochemical, combustion and green synthesis. Of these, the green synthesis is gaining more interest as it employs plant extract, microorganisms, and other biological materials as reducing agents, stabilizing agents and capping agents that make the process more eco-friendly and cost-effective.Recent advancements in the synthesis and application of metal oxide nanoparticles are discussed. It emphasizes major synthesis routes, main factors that influence the formation of nanoparticles, characterization techniques and structure–property relationships. A special focus is on the influence of synthesis parameters like type of precursor, pH, temperature, reaction time, solvents and capping agents on the properties of nanoparticles. In addition, the uses of metal oxide nanoparticles in photocatalysis, wastewater treatment, antimicrobial activity, drug delivery, biosensing, energy storage, gas sensing, and agriculture are also included. Finally, present challenges, toxicity issues, problems of large-scale production, and future research directions are discussed, to support the practical and sustainable use of metal oxide nanoparticles.