Nanostructured Metal Oxides for Environmental Sensing: Synthesis, Properties, and Applications

Abstract

The increasing presence of environmental contaminants poses significant threats to ecosystems and human health, necessitating the development of advanced sensing technologies. Nanostructured metal oxides (NMOs) have emerged as promising materials for electrochemical sensing applications due to their unique physicochemical properties, including high surface area, tunable band gaps, enhanced electron transfer kinetics, and excellent biocompatibility. This review comprehensively examines the synthesis strategies, fundamental properties, and sensing applications of two important NMOs—hafnium oxide (HfO₂) and zinc oxide (ZnO)—for environmental contaminant detection. The article discusses various fabrication approaches including hydrothermal, sol-gel, precipitation, and microwave-assisted methods, highlighting their influence on morphological characteristics and sensing performance. Special emphasis is placed on the role of surface capping agents in stabilizing NMOs and enhancing their selectivity toward specific analytes. The electrochemical sensing mechanisms, detection limits, and linear dynamic ranges of HfO₂- and ZnO-based sensors for various environmental pollutants are critically evaluated. Additionally, the antimicrobial properties and biocompatibility aspects of these NMOs are discussed, supporting their potential as environmental safeguards. Computational studies employing density functional theory that elucidate the interactions between capping agents and NMO surfaces are also reviewed. This comprehensive analysis demonstrates that NMOs, particularly when surface-engineered with appropriate capping agents, offer significant potential for developing sensitive, selective, and cost-effective environmental monitoring platforms.