Table 2.

Advantages and disadvantages of functionalized materials. Note that the response of pure metal oxide nanofibers (Table S2 in Supporting Information File 1) is taken as the reference point.

Material	Advantages	Disadvantages	References
pure MOx	minimal response/recovery time	minimal sensitivity, high operating temperature, low detection limit	[100,105,115,118] [119,144,282–284]
functionalized MOx	high sensitivity, lower detection limit, short response/recovery time	slightly lower operating temperature	[10–11,104,175,178–179] [188,200,209,215,220]
MOx–MOx composites	enhanced selectivity, short response/recovery time, improved operating temperature	slightly improved response, slightly improved detection limit	[222,224–228,230] [235,285–287]
conjugated polymer–conjugated polymer composites or conjugated polymer/non-conjugated polymer–MOx composites	low operating temperature, high selectivity, minimal detection limit, minimal response/recovery time	minimal response	[87,238,241,248,258] [278–279,288–294]
graphene–MOx, CNTs–MOx	lower operating temperature, minimal response/recovery time, minimal detection limit,	minimal response	[89,243–244,246,252] [268,295–296]