Recoverable Detection of Dichloromethane by MEMS Gas Sensor Based on Mo and Ni Co-Doped SnO2 Nanostructure
HighlightsWhat are the main findings?The problem of dichloromethane “poisoned” MOS materials was well solved.Gas sensing mechanism of dichloromethane on the MOS material was elucidate.What is the implication of the main finding?The best performance of significant response and excellent recoverability by the MEMS sensor to dichloromethane is attributed to a synergetic effect from Mo and Ni co-doping into SnO2.Kinetically, the transportation of dichloromethane molecules onto the surface determines the response process. Thermodynamically, the output steady electronic signal of the MEMS sensor follows the equations newly derived by statistical mechanics.The challenging problem of chlorine “poisoning” SnO2for poorly recoverable detection of dichloromethane has been solved in this work. The materials synthesized by Ni or/and Mo doping SnO2were spread onto the micro-hotplates (<1 mm3) to fabricate the MEMS sensors with a low power consumption (<45 mW). The sensor based on Mo·Ni co-doped SnO2is evidenced to have the best sensing performance of significant response and recoverability to dichloromethane between 0.07 and 100 ppm at the optimized temperature of 310 °C, in comparison with other sensors in this work and the literature. It can be attributed to a synergetic effect of Mo·Ni co-doping into SnO2as being supported by characterization of geometrical and electronic structures. The sensing mechanism of dichloromethane on the material is investigated. In situ infrared spectroscopy (IR) peaks identify that the corresponding adsorbed species are too strong to desorb, although it has demonstrated a good recoverability of the material. A probable reason is the formation rates of the strongly adsorbed species are much slower than those of the weakly adsorbed species, which are difficult to form significant IR peaks but easy to desorb, thus enabling the material to recover. Theoretical analysis suggests that the response process is kinetically determined by molecular transport onto the surface due to the free convection from the concentration gradient during the redox reaction, and the output steady voltage thermodynamically follows the equation only formally identical to the Langmuir–Freundlich equation for physisorption but is newly derived from statistical mechanics.
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