Table 1.

Toluene sensing using resistive gas sensor with different sensing materials.

Sensing Materials	Additives/Catalysts	Resistance (R) in Presence of Analyte	Detection Range	Operating Temperatures	Sensitivity*	Ref.
Nanoporous TiO2	Pd	decreases	50–200 ppm	RT	1.85 for 200 ppm	[12]
WO3 microtubes	Carbon	decreases	50–500 ppb	90 °C	39 for 500 ppb	[13]
ZnO and TiO2-doped ZnO nanostructures	TiO2	decreases	1–3000 ppm	160–390 °C	16.10 for 100 ppm (at 290 °C)	[7]
TiO2 nanostructured films by hydrothermal method	–	decreases	50 ppb	450–550 °C	24 for 50 ppm for 10 min exposure (at 500 °C)	[14]
WO3 using cotton fibers as templates	Carbon	decreases	100 ppb–1000 ppm	190–370 °C	0.8 for 100 ppb for 40 sec exposure (at 320 °C)	[15]
TiO2 nanotubular films by hydrothermal method	–	decreases	50 ppm	500 °C	51% for 50 ppm toluene (at 500 °C)	[6]
Pure and Sn-, Ga- and Mn-doped ZnO nanoparticles	Sn, Ga and Mn	decreases	5000 ppm	200–600 °C	1050 to 5000 ppm for Mn-doped ZnO (at 400 °C)	[16]
NiO crystallites by hydrothermal method	–	increases	3–1100 ppm	350 °C	1.28 for 11 ppm and 2.2 for 1100 ppm	[17]
Tetrapod-shaped ZnO nanopowders	–	decreases	100 ppm	180–480 °C	11 for 100 ppm (at 320 °C)	[18]
Carbon nanoparticles (CNP)/N,N,- dimethyl-1,3-propanediamine-copolymer	Carbon black	increases	<550 ppm	30 °C	0.04 for 200 ppm	[11]
Hybrid film of chemically modified graphene and vapor-phase-polymerized PEDOT	Graphene	increases	Fully saturated	RT	0.3 for fully saturated	[9]

^*As definition of sensitivity varies in these studies, the sensitivity is normalized as (R_final–R_base)/R_base.