Low temperature CO and CH4 dual selective gas sensor using SnO2 quantum dots prepared by sonochemical method

Abstract

Abstract In this study, a low temperature sensor with a dual function property is fabricated by using 3–4 nm SnO 2 quantum dots (QDs) prepared by sonication-assisted precipitation. The sensor shows high selectivity to CO in the presence of methane below 375 °C. SnCl 4 aqueous solution was precipitated by ammonia under sonication, which continued for 1, 2 and 3 h. A part of the sample was then dried and calcined at 400 °C for 1.5 h and characterized by XRD and BET. UV–vis analyses were carried out for band gap measurements. The average particle size and the specific surface area of the SnO 2 QDs as well as their sensing properties were compared with the SnO 2 nano-particles prepared by conventional sol–gel method. The BET surface area of sonochemically as-prepared product after 2 h sonication and the one calcined at 400 °C after 1.5 h are 257 and 212 m 2 /g, respectively while the specific surface area for SnO 2 prepared by conventional sol–gel method is about 80 m 2 /g. XRD spectra revealed pure crystalline phase of SnO 2 is formed for both as-prepared and calcined samples of SnO 2 QDs. However, for the sample prepared by sol–gel method and calcined at 400 °C, SnO crystals are detected along with the SnO 2 crystals. Band gap measurements for the sample fabricated by sonochemical method and calcined at 400 °C indicated band gap energy of 5.7 eV which shows 2.1 eV blue-shift (shift into smaller wave lengths) from that of the bulk SnO 2 which was reported earlier by others. Quantum dots of SnO 2 show exceedingly high response to different concentrations of 100, 300 and 1000 ppm of CO in a temperature range of 25–350 °C. At about 50 °C a response of 27 was obtained for 1000 ppm CO, which increases to a maximum of 147 at 225 °C and then decreases whereas the maximum of 47.2 was detected for the SnO 2 sample prepared by the sol–gel method occurred at about 300 °C. At the same time no response to methane is observed in the whole range of temperatures for SnO 2 QDs. On the other hand the response to methane is higher than that to CO at above 375 °C.