Research On H₂S-Sensing Properties And Mechanism Of Nanocrystalline WO₃ Films

Metal oxide semiconductor gas sensors have been widely applied in the detection of various toxic gases,household gases,air-pollution gases and industrial smoke,due to the advantages of high sensitivity,low cost,fast response and long serving life.WO₃ is one of the most widely used metal oxide gas-sensing materials,some of its advantages include abundant resources,low cost,stable physical and chemical properties,and large number of detectable gases.However,there were still faced many problems such as high working temperature and poor selectivity.The small size colloidal nanocrystals have become a current research hotspot because of their large specific surface area,high surface activity and excellent film-forming ability at room temperature.It is an ideal candidate for gas sensors with low power consumption,high sensitivity and fast recovery/response.Here,WO₃ colloidal nanocrystals were synthesized by solvothermal method,and we studied the H₂S-sensing properties and mechanism of nanocrystalline WO₃ films which were prepared by coating the sensing materials on ceramic substrate at room temperature.First,the effect of reaction time on the materials morphologies was studied.WO₃nanocrystals?³ nm in grain size?,nanowires,larger size nanoparticles?⁶ nm in length and².5 nm in width?were obtained at the reaction time of 3 h,12 h,24 h,respectively,when the solvothermal synthesis temperature was 180°C.The gas-sensing films were fabricated by spin-coating followed by CuCl₂ ligand exchange at room temperature,the nanocrystalline WO₃ with a grain size of 3 nm have the best gas-sensing performance,the sensor has a high response of 57 to 50 ppm H₂S,the response and recovery time was 46 s and 126 s,respectively,and excellent selective properties toward H₂S,its theoretical limit of detection is estimated to be 46 ppb at 80°C.In addition to the classical gas-sensing mechanism model of oxide semiconductors,we studied the adsorption behavior of both H₂S and O₂ on the reductive and oxidative surface of nanocrystalline WO₃ films through the first-principles calculations based on density functional theory.The result indicates the adsorption of H₂S on WO₃ induced an n-type doping effect.The WO₃ gains electrons and its resistance decreased due to the adsorption of H₂S,leading to gas sensing response.Finally,WO₃ colloid nanocrystal gas sensors were fabricated on the basis of commercial chip sensor substrate.The sensors were treated by in situ annealing at different temperatures.And we studied the sensors H₂S-sensing properties under different annealing temperature and heating voltage.The H₂S gas sensor based on the WO₃ nanocrystals preliminarily shows a good potential application due to its low power consumption.