Preparation And Gas-sensing Properties Of Pn-type SnO₂ Composite Material

Volatile organic compounds?VOCs?are a major group of air pollutants,and potentially lead to photochemical smog,carcinogenesis,teratogenesis,and mutagenesis,which endanger both ecological environment and human health.To detect VOCs effectively in real time is urgent.Therefore,the research and development of appropriate gas sensors has significant scientific meaning and practical application value.At present semiconductor SnO₂ has been widely used in gas sensors,however,SnO₂ gas sensor shows high working temperature,inferior selectivity and other problems in practical application.For the past researches,it is found that building heterostructure on the surface of SnO₂ nanomaterial will improve response and alter selectivity notably of gas sensors.In this article,p-n type NiO-SnO₂ composite material was successfully prepared by hydrothermal treatment.The response of sensors based on NiO-SnO₂ composite with different Ni content were examined.Main research contents and conclusions are as follows:1.C@SnO₂ was synthesized by hydrothermal method first,then C@Ni?OH?₂-SnO₂ was synthesized by chemical precipitation using tetraethyl ammonium hydroxide as the precipitant.The final NiO-SnO₂ composites were obtained after calcination.The prepared composite materials were charactered by XRD,BET.The result showed that the nickel doping tin oxide materials were nanocrystals with the grain size less than 10 nm.The tin oxide sensor with 10 mol% nickel doping concentration exhibited good gas-sensing properties,and the sensitivity of the sensor to 100 ppm toluene is 18.1 at the optimum operating temperature?400 ??,which increases one time compared with the pure SnO₂ sensor?8.7?.The gas sensing properties of Ni doping composite with other concentration were not improved yet.2.C@SnO₂ was synthesized by hydrothermal method first,then C@NiO-SnO₂ was synthesized by second step hydrothermal treatment with urea used as homogeneous phase precipitator and finally NiO-SnO₂/SnO₂ heterostructure composites were obtained by calcinations.The structure and morphology of NiO-SnO₂/SnO₂ composites were characterized by XRD,TEM and BET.Composite are polycrystalline tetragonal SnO₂ nanostructures with high specific surface area and average grain size of about 10 nm.The gas sensing properties of the Ni doping SnO₂ were improved with low Ni doping concentration?1-2 wt %?but further increase of Ni-doping concentration resulted in deteriorated response by low conductivity.The sensor based on 1 mol% Ni doping SnO₂ and the sensor based on 2 mol% Ni doping SnO₂ show ultrahigh response to n-butanol and formaldehyde at low temperature,respectively,with good selectivity.3.C@NiO was prepared by hydrothermal treatment using urea as the homogeneous phase precipitator first,then C@Ni O-SnO₂ was synthesized by second step hydrothermal treatment with urea,and finally NiO-SnO₂ composites were obtained by calcinations.The prepared samples are characterized and analyzed by XRD,SEM,EDS,and BET,and its gas sensing properties are studied.The result showed that Ni²⁺ of composite materials?25 mol% Ni doping SnO₂ and 33 mol% Ni doping SnO₂?replaced the Sn⁴⁺ and entered the lattice,which formed a solid solution,so there is no NiO characteristic peak.The specific surface area of the composite material range from 70.1 to 104.5 m2/g,and its specific surface area increases gradually with Ni doping.The sensor based on 25 mol% Ni doping SnO₂ has good selectivity to n-butanol.