Gas-sensing Properties Of Nano-WO₃ And WO₃/SiO₂ Composite Films Prepared By Solution Method

Recently,detecting and controling toxic and harmful gases timely and effectively is vital for people to provide a clean and healthy living environment since the exhaust emission of factories and automobiles is harmful to the human's health.Gas sensor has been widely used as a functional device for detecting harmful gases.Therefore,exploring the gas sensor with low-cost,high sensitivity and simple is the current research focus,and the research on metal oxide semiconductor gas sensor is most popular.Currently,common semiconductor gas sensors are mostly based on SnO₂,ZnO,WO₃ and Fe₂O₃ materials,WO₃ as an n-type semiconductor material attracts great attention due to its distinctive electrochromic,photocatalytic and gas sensing properties.In this paper,the gas sensing properties of WO₃ were investigated,and the main research contents and results are as follows:Firstly,nano-sized WO₃ films and powder were prepared by solution method using oxalic acid as morphology control agent.The composition and microstructure of WO₃ were analyzed by X-ray diffraction?XRD?and scanning electron microscopy?SEM?,respectively.Initial WO₃precursor powder was composed of WO₃·2H₂O and WO₃·H₂O and then transformed into monoclinic WO₃ phase while calcining at 400oC.The microstructures showed that there are cross-arranged nanosheets structure and the existence of gaps between those nanosheets in WO₃film,and that there are smaller nanosheets structure and the disordered stacking arrangement in WO₃ powder.Compare with the gas sensing properties of WO₃ powder,the sensitivity of WO₃film to NO₂ gas is higher,and the value of sensitivity reaches the maximum of 6.72 when the holding time is 90 min.Then,nano-sized WO₃ film and powder were prepared by solution method using citric acid as morphology control agent.WO₃ precursor powder was a mixture of WO₃·2H₂O and WO₃·H₂O,and can be converted into triclinic WO₃ phase after calcining at 400oC.WO₃ film presents a nanosheets structure with the staggered arrangement,gaps between sheets and a large number of cracks on the surface.Nevertheless,WO₃ powder presents microspheres structure composed of the nanosheets.And the gas sensing properties of WO₃ film is better than that of WO₃ powder,but the poor stability of film needs to be further improved.Finally,SiO₂ films with different layers were superposed on WO₃ film by sol-gel method.It is concluded that WO₃ film with two layers of SiO₂ films?WS-2?has excellent gas sensing properties,and the sensitivity of WS-2 to H₂S gas exceeds 100 at 250oC.Furthermore,the WS-2can detect 10 ppm H₂S gas effectively,and the sensitivity of WS-2 can maintain⁷5%after 50days.