Table 2. Sensing Parameters of Different CO₂ Sensors Based on MOX Semiconductors.

sensing material	synthesis route	operating temperature [°C]	response at concentration [ppm]	operating condition	reference
ZnO/CuO nanorods	hydrothermal	RT	0.09 at 1000a	dry	(16)
5wt%Sn-CdO nanopowders	co-precipitating	250	1.18 at 5000b*	dry	(17)
CuO@1wt%Ag-BaTiO3 spheres decorated	mixing	120	0.60 at 1000a*	dry	(18)
CeO2 yolk-shell nanospheres	solvothermal	100	3.98 at 2400c	negligible response below 70 RH%	(19)
Nd2O2CO3 nanoparticles	sol–gel	350	4.00 at 1000d	negligible response below 50 RH%	(20)
CaO-In2O3 mesoporous	impregnation	230	1.80 at 2000d	dry	(21)
N-ZnO nanoparticles	sol–gel	250	4.50 at 2000d*	dry	(61)
Na:In2O3 nanoparticles	sol–gel	200	7.10 at 1000e	uniform response above 15 RH%	this work

^a, where R is the resistance (R_gas, resistance in CO₂ atmosphere; R_air, resistance in carrier gas). The asterisk denotes a value not explicitly stated in the study but approximated from a graphical plot.

^b, where R is the resistance (R_gas, resistance in CO₂ atmosphere; R_air, resistance in carrier gas).

^c, where R is the resistance (R_gas, resistance in CO₂ atmosphere; R_air, resistance in carrier gas).

^d, where R is the resistance (R_gas, resistance in CO₂ atmosphere; R_air, resistance in carrier gas). The asterisk denotes a value not explicitly stated in the study but approximated from a graphical plot.

^e, where G is the conductance (G_gas, conductance in CO₂ atmosphere; G_air, conductance in carrier gas).