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

Trung, Do Dang, Toan, Le Duc, Hong, Hoang Si, Lam, Tran Dai, Trung, Tran, Van Hieu, Nguyen
Talanta 2012 v.88 pp. 152-159
air quality, ammonia, aqueous solutions, carbon dioxide, coatings, gases, hydrogen, liquid petroleum gas, monitoring, nanowires, nitrogen dioxide, semiconductors, temperature
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 (250–4000ppm) and interference gases (100ppm CO, 100ppm H₂, 250ppm LPG, 10ppm NO₂ and 20ppm 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.