Semiconducting Metal Oxide Gas Sensors for VOCs, N2O, and Organophosphorus Compounds: Materials Design, Operando Mechanistic Insights, and Data-Driven Selective Detection.

Semiconductor metal oxide (SMOX) gas sensors are attractive platforms for detecting volatile organic compounds, greenhouse gases, and hazardous organophosphorus compounds owing to their low cost, structural simplicity, miniaturization potential, and high sensitivity. However, their practical application remains limited by high operating temperatures, poor selectivity, humidity interference, and an incomplete understanding of surface reaction mechanisms. This review discusses recent advances in resistance-change-type SMOX gas sensors from the integrated viewpoints of materials chemistry, operando mechanistic analysis, and data-driven gas identification. Representative n-type oxides, including ZnO, SnO2, WO3, In2O3, and TiO2, are considered, with ZnO highlighted as a model system for examining crystal-facet engineering, oxygen-vacancy regulation, nanostructure design, noble-metal modification, and heterojunction formation. Particular attention is given to the detection of ethanol, acetone, toluene, nitrous oxide, and dimethyl methylphosphonate as chemically distinct target analytes. Operando spectroscopy and density functional theory (DFT) calculations are discussed as powerful tools for clarifying adsorbed species, reaction intermediates, lattice oxygen participation, and electronic-structure evolution under working conditions. Finally, machine learning (ML)-assisted analysis of multidimensional sensing signals is reviewed as an emerging strategy for improving selectivity and quantitative recognition. This review provides a unified chemical perspective for the rational design of next-generation SMOX gas sensors.