Surface defects in anatase TiO₂ on graphene for LPG sensing: From molecular adsorption to electrical response

The reliable detection of liquefied petroleum gas (LPG) is essential for safety in domestic and industrial environments due to its high flammability and the risks of accidental leakage. However, the role of specific surface defects in graphene-supported TiO₂ sensing materials remains poorly understood. Here, we combine density functional theory (DFT) with experimental characterization to investigate surface defects in a graphene–TiO₂ (GR–TiO₂) hybrid architecture for LPG sensing. At the atomic scale, oxygen vacancies and step-edge configurations on anatase TiO₂(101) modify the adsorption behavior of representative LPG components: methanethiol exhibits the most favorable interaction, particularly at under-coordinated and oxygen-deficient Ti sites, whereas propane and butane interact predominantly through weaker dispersion-driven contributions. These results identify surface coordination and oxygen deficiency as key factors governing molecular adsorption. Experimentally, a ~10 nm TiO₂ coating was deposited on hydroxylated graphene by atomic layer deposition. XPS revealed predominantly Ti⁴⁺ together with a Ti³ ⁺ contribution associated with locally reduced Ti environments, providing complementary evidence of oxygen-deficient TiO₂ consistent with the defect-related cathodoluminescence emission, while XRD confirmed that the employed ALD growth conditions produced the anatase TiO₂ phase. Under LPG exposure, the GR–TiO₂ device showed normalized current suppressions of ~97% and ~90% at + 3 V over two sequential exposures, with ~89% of the exposure-induced change recovered after a fixed 60 s interval. By linking defect-dependent adsorption to the measured electrical response, this study provides molecular-level insight into surface-defect engineering for GR-TiO₂ LPG sensors.