Table 2. Brief summary of MOS gas sensors.

Material	Target gas	Opt (°C)	T res	T rec	Synthesis method	Con (ppm)	Res	Ref.
Ag/ZnO	Ethanol	325	NA	NA	Sol–gel	50	32.5	38
Eu/SnO2	Acetone	280	4	3	Electrospinning	100	32.2	39
Ni/ZnO	H2S	215	50	124	Electrospinning	50	474	40
Mo/SnO2	Ethanol	220	7	103	Electrospinning	100	46.8	41
Co/ZnO	Acetone	370	60	77	Hydrothermal	5	18.5	42
Cr/ZnO	Ethanol	300	NA	NA	Hydrothermal	400	45	43
Dy/In2O3	Ethanol	250	5	248	Hydrothermal	100	85	43