Table 2.

Materials based on TiO₂ used in gas sensor applications.

Year	Material	Method	Substrate	Gas Detected	Main Results	Refs.
2018	Soot template TiO2 fractals	Chemical vapor deposition (CVD)	Deposited soot template (a layer of candle soot was deposited on Ti/Pt electrodes)	Acetone vapour	Novel structural design/diabetic concentrations in the breath.	[134]
2018	TiO2 films	Atomic layer deposition (ALD)	Alumina sensors and microscope slides	NH3 and CH4	Sensitivity toward NH3 varied with thickness.	[135]
2019	TiO2 NP	Bar coating	Alumina	H2S	Works at RT under UV.	[136]
2019	MgO:TiO2 thin films	Co-sputtering (confocal sputtering)	Pt/SiO2/Si	CH4	All the results showed that the dopant can improve the electrical performance and sensor properties.	[137]
2019	Nanostructured TiO2	Molecular layering (ML)	Al2O3 substrates with platinum electrodes	O2	ML-deposited TiO2 film shows good selectivity to oxygen.	[138]
2021	TiO2 thin film	Pulsed laser deposition (PLD)	-(100) silicon (Si/SiO2) -(100) SrTiO3 (STO) -polycrystalline Al2O3	H2S	The surface of PLD TiO2 film on Si/SiO2 has a higher roughness than that on the STO substrate.	[139]
Composite heterostructure
2018	p-copper oxide thin film/n-TiO2Nts heterostructure	Anodization/ oxidation	Ti foil	H2, ethanol, acetone, chloroform, and NO2	The improvement in the sensing properties is attributed to the heterojunction between the CuO thin film and the TiO2 NTs.	[140]
2018	TiO2 + SnO2 NPs	SG+	Glass	NH3	The improvement in the sensor performance is due to the increased active surface area and the efficient electron–hole charge separation and transfer.	[141]
2019	Pd/Al2O3/TiO2 thin film heterostructure	Atomic layer deposition (ALD)	Quartz	H2	Development of flexible gas sensors.	[142]
2019	TiO2/perovskite heterojunctions	Electrochemical method, Sol–gel	Ti foil	CO	The heterojunction is more sensitive than a single film and could operate at lower temperatures.	[143]
2019	TiO2 film/carboxyl PP film/MWCNTs	ALD/CCVD	Si/SiO2	CO, H2, and NH3	Better sensor response, lower detection limit, and lower operation temperature against H2 compared to the separate sensors.	[144]
2019	Polyaniline (PANI)/TiO2 core–shell nanofibers	In situ chemical polymerization on electrospun TiO2 nanofibers	Glass	NH3	Under UV at RT at different humidity levels.	[145]
2019	TiO2/SnO2 and TiO2/CuO thin film nano-heterostructures	Reactive magnetron sputtering	Metallic target and a-SiO2	NO2	The response of TiO2/SnO2 to NO2 at 150 °C is double than in the case of pure SnO2.	[146]
2019	ZnO (n-type)-TiO2 (n-type)-PANI (p-type) Micro/nanoballs	Chemical deposition technique	Glass	LPG, NO2, acetone, NH3, and CO2	Very good selectivity.	[130]
2020	TiO2 decorated with Au NPs	Irradiation with laser	Si and interdigital electrodes	Volatile organic compounds	Very selective and stable over time; works at RT.	[147]
2022	Pd doped CoTiO3/TiO2 (Pd-CTT)	HT	Interdigital electrodes	Benzene	Works at RT; good resistance to humidity interference.	[148]