Recent progress of theoretical and experimental studies on semiconductor-nanostructured NO2 gas sensors

The presence of NO 2 in the atmosphere is a dangerous air pollutant, which reacts with other substances and causes severe health risks. Accurate real-time detection systems are necessary for the environment due to severe pollution. Because of high chemical stability and adjustable electrical characteristics, semiconductor-based chemiresistive gas sensors that use metal oxides as their sensing materials have emerged as promising platforms for NO 2 detection. The study examines how different synthesis techniques affect the performance characteristics, including sensitivity, selectivity, response and recovery time, temperature range, and durability. Theoretical DFT studies enable scientists to understand how NO 2 molecules bind to surfaces by showing the relationship between adsorption energy and charge transfer and changes in electronic structure at the Fermi level, which links to sensor performance. Dopant engineering, defect control, and heterostructure synthesis enable enhanced signal transduction and improved reversibility by creating new electronic states that support orbital hybridization with NO 2 . The experimental work demonstrates that carbon/oxide hybrids and MOF-derived porous oxides and nanostructuring, together with catalytic decoration and designed junctions, operate to improve system performance by accelerating charge transport and adsorption–desorption kinetics. The research shows that surface modification methods successfully reduce humidity-based drift because their effectiveness is demonstrated through photo-activation studies, which show that UV, visible, and NIR light sources can lower operational temperature while boosting recovery performance. The study demonstrates that theoretical models together with empirical results can improve predictive modelling while reducing the need for trial-and-error testing.