Recent advances in the synthesis and applications of zinc oxide nanomaterials for healthcare energy and environmental systems

Zinc oxide (ZnO) nanomaterials have emerged as multifunctional materials with wide-ranging applications in healthcare, energy, and environmental technologies. This review provides a comprehensive and critical overview of recent advances in ZnO nanomaterial synthesis, including physical, chemical, biological, and green approaches, with special attention to eco-friendly and scalable methods. The work further correlates structural, optical, and catalytic properties of ZnO nanoparticles with their performance in biomedical systems, photocatalysis, gas sensing, dye degradation, and energy conversion devices. Recent developments (2020–2025) are summarized to highlight trends in surface modification, hybrid nanocomposites, and biocompatibility enhancement. Particular emphasis is placed on the limitations of current synthesis strategies, such as non-standardized plant extract preparation in green routes and issues of reproducibility in large-scale production. The review concludes with future prospects for standardizing synthesis protocols, improving nanotoxicity evaluation, and integrating ZnO-based nanostructures into sustainable industrial and biomedical systems. This work thus provides a unified, sustainability-focused perspective that bridges synthesis innovations with practical applications of ZnO nanomaterials across interdisciplinary domains.