| SnO2is a typical n-type semiconductor gas sensing material. It is widely used due to its high conductivity, stable crystal structure and low cost. The surface properties of SnO2have great influence on its sensing properties. The hot research area in improving the gas sensing properties is to find a proper preparation method to synthesize novel micro structure material with high specific surface area. Meanwhile, doping and compositing are significantly effective.The SnO2-based hierarchical nano-materials were synthesized by sintering precursors got from a facile solvothermal process. The structures of the materials were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectrometry (EDS), BET and X-ray photoelectron spectroscopy (XPS). The gas sensors were fabricated by coating the sensing materials on alumina ceramic tubes. And the gas sensing properties were tested in a static state gas-sensing test system. The growth mechanism of hierarchical structure was analyzed. The influences of the incorporations of other metal oxides on morphology and gas sensing properties were studied. And the sensing mechanism of the sensors was discussed.The experimental results indicated that the undoped SnO2hierarchical nano-materials had better responses to acetone than to other VOCs gases, such as:ammonia, benzene, toluene, methanol, formaldehyde. Experiments about SnO2preparation conditions were performed from four aspects:sintering temperature, the choice and quantity of solvent, the reaction time in the reaction still and the concentrations of the sulfur source. Comparisons were made to find the influence of different preparation conditions on the morphology and acetone sensing properties of SnO2. Choosing12h as the reaction time, using30mL ethylene glycol as organic solvent,1mmol SnCl2·2H2O and1.4mmol thiourea as solutes, the "0-2-3" hierarchical SnO2material synthesized by sintered under620℃showed the best acetone sensing properties.Pd-loaded SnO2hierarchical materials had better sensing properties to toluene. The doped materials were synthesized by solvothermal method. Various concentrations of Pd dopant (0mol%,0.5mol%,1.2mol%,2mol%,2.3mol%) were added into precursors. It was found that Pd atoms in the as-prepared samples are present as PdO surface species (as deduced from XPS results). And the Sn3d and O1s binding energies of1.2mol%are the lowest in all tested samples, respectively. The sensor fabricated by using1.2mol%Pd-doped SnO2exhibited higher response to toluene at operating temperature250℃than other sensors at their best operating temperatures. A model based on spill-over effect was built to explain the resistance change with Pd concentration, and then help to analysis the sensing mechanism.A certain amount of Zn powder was added into the solvothermal precursor by using the ultrasonic dispersion. After the solvothermal and sintering process, hierarchical ZnO/SnO2composite was synthesized. The sensor fabricated by using the composite material showed better response to ammonia than to other gases at room temperature. The XRD result showed that the composite material was composed by ZnO and SnO2. ZnO is uniformly distributed in the composite sample proved by EDS result. And the ratio of ZnO to SnO2is0.248. The resistance of the sensor is super high at room temperature. The recovery of the sensor after testing ammonia sensing properties need thermal desorption. The sensing mechanism of the composite material was discussed. |
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