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The unique electronic properties (electron mobility and carrier lifetime) are key factors for metal oxide semiconductor devices that directly determine the device's performance and application. Electron mobility of metal oxide semiconductor has a certain impact on response and operating temperature of gas sensor. Heterojunction composites of carbon quantum dots (CQDs) and perovskite materials have attracted much attention due to their great potential for gas sensors. In this paper, a gas sensor for monitoring methanol gas was developed based on nitrogen-doped carbon quantum dot/Ag-LaFeO3 (NCQDs/Ag-LaFeO3) p-n heterojunction materials (NALPN). NCQDS and Ag-LaFeO3 form a heterojunction, which improves the carrier transport ability and separation of electron-hole pairs. The surface of NCQDs contains COOH, optimize the selectivity of Ag-LaFeO3 to methanol gas. Gas sensitivity test results show that the NALPN to 5 ppm methanol gas possessed high response (73), low operating temperature (92 °C) and good selectivity. These excellent properties prove that NALPN materials are the main competitors for future gas sensitive materials.

Highly sensitive and selective detection against toluene gas remains a tremendous challenge in gas sensor applications. In this work, a series of molecular imprinted Ag-LaFeO3 nanoparticles (IAL NPs) were synthesized in a microwave-assisted colloidal route. Especially, the one prepared with optimal amount of imprint molecules (IAL-2 NPs) have a response of 24.0 to 5 ppm toluene at the optimum working temperature of 215 °C with negligible responses to the other test gases, exhibiting enhanced gas sensing properties for toluene gas at a relatively low working temperature. The improved performance can be attributed to the favorable effect of microwave radiation, the molecular imprinting structure and the sensitization of Ag, which illuminates that IAL-2 NPs is a potential candidate for toluene detection.

Xylene is a hazardous volatile organic compound, however, the selective detection of ppm-level xylene using oxide semiconductor gas sensor remains a challenging issue. In this study, Ag-LaFeO 3 was modified with molecular imprinting technique, in which methacrylic acid and hydroxyethyl methylacrylate are used as functional monomers, respectively. Based on XRD, EDS, XPS, SEM, TEM, BET nitrogen adsorption observations, the structure and morphology of the samples are characterized. The as-prepared molecularly imprinted nanoparticles with methacrylic acid as functional monomer exhibit high selectivity and response to xylene gas, and the response is dependent on the type and content of the functional monomer. To 5 ppm xylene, the optimal response is 36.2 at the operating temperature of 99 °C. In addition, low cross-responses to the other test gases were observed. The remarkable enhancement in the gas-sensing properties of the samples is attributed to their high specific surface area and molecular imprinting structure.