Acetone Sensing Performance Of Three-dimensional Ordered Macroporous C-doped WO₃ Materials And Ni/c-codoped 3DOM WO₃ Materials

Acetone is a commonly used volatile organic solvent and industrial raw material.Inhaling acetone may cause headaches,coma and even damage the nervous system function.It is also a biomarker for diabetes,which can be diagnosed by measuring the concentration of acetone in the breath.Metal oxide semiconductor gas sensors have been widely used in gas detection due to their fast response,simple operation and real-time analysis.However,WO₃ material still has some problems such as poor stability at high temperature,unsatisfactory detection of trace acetone and acetone in complexgasenvironment.Consideringthethree-dimensionalordered macroporous/mesoporous（3DOM）material with porous structure and large specific surface area,which very beneficial to gas adsorption and transport,is likely to solve the current problems of WO₃.And ion doping may increase the density of oxygen vacancy and change the phase to enhance the gas-sensing properties.In this paper,WO₃ with 3DOM morphology is synthesized by template method,and Ni²⁺doped3DOM WO₃ is synthesized on the basis of previous work to improve the responsiveness,selectivity and stability of acetone.The main results are as follows:1.Taking polystyrene spheres with highly regular arrangement as the template,three-dimensional ordered macroporous C-doped WO₃ material was obtained by the impregnation and calcination processes,and the influence of pore size on gas sensitivity was studied.XRD and Raman spectra show that when the calcination temperature is 400oC,WO₃ phase is hexagonal phase and monoclinic phase,but when the calcination temperature is higher than 450oC,WO₃ is transformed into monoclinic phase.XPS indicates that there were W-C bond exists in the material,proving that carbon is doped into the WO₃ lattice.SEM and TEM results showed that the five samples had macropore diameters of 205,340,410,520,730 nm and window diameters of 77,98,120,180,195 nm,respectively,and presented highly ordered three-dimensional structures.BET indicates that the specific surface area is about 12m²·g^-1,and there are also mesopores exists in the material.2.According to the gas sensing test,the best calcining temperature and working temperature of the samples with different pore sizes were optimized.The response performances to acetone were investigated under the optimal conditions.All of which were much higher than that of unshaped pure WO₃,and the gas-sensitive performance first increased and then decreased with the increase of pore diameter.Among them,the response value of W3-450 with 410 nm macropore diameter was the highest,which to 10 ppm acetone was 13.5.The humidity test showed that the response of W3-450 to 10 ppm acetone at the relative humidity of 90%was 8.The selectivity test showed that the response values of sample W3-450 to 10 ppm ethanol,methanol,NH₃,formaldehyde and CO were all lower than 4,and the selectivity of sample to acetone was very good.The stability test showed that the gas sensitivity of sample was stable in three consecutive months,and the response value of 10 ppm acetone was always around 13.3.The PS sphere with optimal diameter was used as the template to synthesize Ni/C co-doped 3DOM WO₃ with different doping amounts（1%-10%）by adjusting W/Ni atom ratio in the precursor,and the influence of doping on the physical phase and morphology of the material was studied,and a series of characterization methods were used to characterized.XRD,Raman spectra showed the phases of pure sapmple and 1%doped sample was pureγ-WO₃,ε-WO₃ appears when the amount of Ni doping turns 3%.The lattice distortion increases with the increase of doping amount.SEM shows that the pore sizes of a series of samples after calcining are all around405 nm.XPS indicated that Ni-O-W bond and W-C bond were formed after doping,indicating that both Ni²⁺and C were doped into WO₃ lattice.UV-vis indicates that WO₃ band gap becomes narrow and defect density increases after doped.4.All the 3DOM Ni-WO₃ samples show higher sensing performence and lower optimum working temperature（370oC）than undoped samples according to the gas sensing test（390oC）.The sample showed the highest response to acetone when it turns to Ni doping amount 5%（WN3）,it is 18 to 10 ppm acetone and the undoped WO₃ was 13,then the performance decreased to 15 when it turns 10%.It was turns out the sensing performance to acetone was first increased and then decreased with the amount of Ni doping increased.Humidity test showed that WN3 had a good response to 10 ppm acetone even at 90%humidity.The selective test showed that under the same conditions,the sensitivity of WN3 to acetone was much higher than that of other gases with the same concentration,about 6 times that of methanol and 9times that of ethanol,showing good selectivity.