Zinc gallate-based gas sensors for toxic gas detect-ion: From theoretical aspects to material design and applications – A critical review

Rising environmental pollution and the severe health risks caused by toxic and flammable gases necessitate the development of highly sensitive, selective, and reliable gas sensors. Zinc gallium oxide [ZnGa₂O₄-ZGO], a wide-bandgap spinel oxide semiconductor, is a promising material for advanced gas sensing due to its excellent chemical stability, tunable surface characteristics and high sensitivity at relatively low operating temperatures. This review provides a focused and dedicated overview of ZGO-based gas sensors systematically compiling the diverse experimental and theoretical studies reported to date, and critically discussing synthesis strategies, structural and morphological optimization, and their impact on sensing performance. It addresses the detection of key hazardous gases, including carbon monoxide (CO), nitrogen oxides (NOₓ), hydrogen sulfide (H₂S), sulfur dioxide (SO₂), ammonia (NH₃) and flammable gases like liquefied petroleum gas (LPG), highlighting their environmental and health impacts, underscoring the need for real-time monitoring. Moreover, sensitivity, selectivity and operating temperatures of ZGO-based gas sensors have been compared with other metal oxide-based sensors’ (i.e., ZnO, SnO₂, or In₂O₃) performances in detecting NO 2 , H 2 S and LPG. Additionally, challenges such as device miniaturization, humidity interference, and selectivity are discussed alongside innovative strategies involving nanostructuring, doping, and composite materials. Also, chemiresistive ZGO-based gas sensors dominate existing literature, while photoluminescence-based sensing remains largely unexplored, presenting a gap to be addressed. Future efforts should focus on leveraging luminescent properties of this spinel oxide, for advanced gas detection and integrating it into smart and wearable sensor platforms. Investigations on reducing gases and volatile organic compounds (VOCs) should also be prioritized, as there is scope for improvement. • Critically reviews zinc gallate-based gas sensors’ fabrication and applications • Covers both experimental and theoretical studies on zinc gallate -based gas sensors since 1998 • Highlights an in-depth analysis of oxidizing/reducing/volatile organic compounds sensing using zinc gallate -based gas sensors. • Identifies key research gaps as their application is still limited—especially for photoluminescence and reducing gas sensing • The need for low-cost synthesis methods, expanded gas testing, structural optimization, and real-world validation is imminent.