Hybrid of graphene with ZnO as NO2 gas sensor: a brief review

Purpose The purpose of this paper is to review recent advancements in reduced graphene oxide–zinc oxide (rGO–ZnO) hybrid nanostructure-based nitrogen dioxide (NO2) gas sensors, focusing on their potential for sensitive, real-time environmental monitoring and mitigation of health risks. Design/methodology/approach The method includes a litreature-based comparative analysis of recent studies on rGO–ZnO NO2 gas sensors, covering synthesis techniques, structural configurations, operating conditions and performance metrics such as response time, detection limit and recovery efficiency. Findings Hybrid rGO–ZnO sensors fabricated mainly through hydrothermal and chemical synthesis methods demonstrate high sensitivity, with room-temperature operation, rapid response times (seconds to minutes) and detection limits down to parts-per-billion. Key challenges include low recovery efficiency, humidity interference and substrate limitations. Originality/value This paper provides a cohesive evaluation of synthesis methods, performance characteristics and design strategies for rGO–ZnO NO2 gas sensors, highlighting both technological advancements and unresolved challenges, and suggesting future directions such as green synthesis, flexible substrates and Internet of Things-enabled applications.