Selective detection of carbon dioxide using LaOCl-functionalized SnO2 nanowires for air-quality monitoring

In spite of the technical important of monitoring CO2 gas by using a semiconductor-type gas sensor, a good sensitive and selective semiconductor CO2 sensor has been not realized due to the rather unreactive toward CO2 of conventional semiconductor metal oxides. In this work, a novel semiconductor CO2 sensor was developed by functionalizing SnO2 nanowires (NWs) with LaOCl, which was obtained by heat-treating the SnO2 NWs coating with LaCl3 aqueous solution at a temperature range of 500–700 °C. The bare SnO2 NWs and LaOCl–SnO2 NWs sensors were characterized with CO2 (250–4000 ppm) and interference gases (100 ppm CO, 100 ppm H2, 250 ppm LPG, 10 ppm NO2 and 20 ppm NH3) at different operating temperatures for comparison. The SnO2 NWs sensors functionalized with different concentrations of LaCl3 solution were also examined to find optimized values. Comparative gas sensing results reveal that LaOCl–SnO2 NWs sensors exhibit much higher response, shorter response–recovery and better selectivity in detecting CO2 gas at 400 °C operating temperature than the bare SnO2 NWs sensors. This finding indicates that the functionalizing with LaOCl greatly improves the CO2 response of SnO2 NWs-based sensor, which is attributed to (i) p–n junction formation of LaOCl (p-type) and SnO2 nanowires (n-type) that led to the extension of electron depletion and (ii) the favorable catalytic effect of LaOCl to CO2 gas.