Metal oxide/g-C3N4 nanocomposites chemiresistive gas sensors: A review on enhanced performance

Metal-oxide-semiconductors (MOS) gas sensors are widely used for detecting and measuring the concentration of various gases in different applications. Changing the electrical resistance when the MOS surface reacts with a specific gas is the basis of the operation of the gas sensor of MOS. They offer versatility in detecting various gases and fabricating them suitable for supervising energy efficiency, monitoring health and safety, and controlling hazardous emissions. However, traditional MOS sensors suffer from poor selectivity and usually require high operating temperatures. To overcome these limitations, researchers have explored strategies such as doping, bimetallic/co-doping, and composite structures with conductive polymers and 2D materials such as polyaniline (PANI), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), reduced graphene oxide (rGO), graphitic carbon nitride (g-C₃N₄), and graphene. Among the 2D materials, g-C₃N₄ stands out due to its distinct characteristics, including chemical stability, porosity structure, abundance, lack of toxicity, and numerous surface defects. The exfoliated structure and surface defects of g-C₃N₄ provide active sites for adsorbing atmospheric oxygen and facilitating reactions with specific gas molecules. This review introduces MOS gas sensors, covering their fabrication methods and electrical measurements. It then attentions on the properties of g-C₃N₄, synthesis methods, and its potential for composition with the MOS. The review highlights the enhanced gas sensing performance achieved by MOS/g-C₃N₄ nanocomposites to detect different gases.