Synthesis And Gas Sensing Performance Of Tungsten Trioxide With Hierachical Porous Structures

Semiconductor metal oxides gas sensors get a great deal of attention for gas detection and breath analysis,considering the high reliability,rapid analysis,small size and simple operation.Tungsten trioxide?WO₃?has great application value in gas sensor owing to its wide band gap width and low resistivity.However,it is still need to improve the sensitivity,selectivity and stability for WO₃ based gas sensing materials.Hierarchical porous structures are excellent structural candidates to endow metal oxides based gas sensing materials with high selectivity and stability,compared with those of the monomorphological structures and non-porous metal oxide material.In order to improve the sensitivity and stability for detecting acetone in breath environments,the hierarchical porous 3DOM WO₃ materials were synthesized.3DOM materials have high degree of well-ordered porous architecture as well as open inner surface,which can provides high gas accessibility for analyte gas molecules and more active sites for redox reaction.All these merits improve the gas sensing properties of sensitivity and stability for 3DOM WO₃ materials effectively.Inorder to improve the sensitivity and selectivity for monitoring toluene,the hierarchical Au-loaded WO₃ hollow microspheres were synthesized.The hierarchical hollow structures can enhance the speed of gas diffusion.Meanwhile,the“sensitization” effects noble metal nanoparticles speeds up the formation of electron charge transfer dynamics.Considering this,Au-decorated WO₃ hollow microspheres were synthesized for detecting acetone effectively.The main contents are as follows:1.A series of 3DOM WO₃ were synthesized by a simply PS template with post-heat treatment method.Also,they were characterized by XRD,TEM,SEM,XPS and N2 adsorption desorption.Results show that the multilayer and ordered porous architecture can be obtained when the precursor concentration is 9.6 mol/L.Also,when the size of PS template was 340 nm?560 nm?860 nm,the corresponding size of macropores of WO₃ was 240 nm?360 nm and 540 nm,the corresponding size of mesopores was 30 nm?20 nm and 18 nm.2.The effect of working temperature on the sensitivity of the 3DOM WO₃ was discussed.Results show that the optimal operating temperatures are confirmed at340? for acetone.The response can achieve 10 when 10 ppm gaseous acetone wasintroduced.The selectivity of tungsten trioxide was also studied.Under the same conditions,the response is below 2.5 for these gas molecules,including methanol,ethanol,ammonia,NO and CO,while the response towards acetone can reach 10.0,indicating the the materials possessed high selectivity to acetone.The stability of tungsten trioxide was studied.After 80 days,the responses to acetoe of 10 ppm?5ppm?3 ppm?1 ppm?0.5 ppm and 0.3 ppm still maintain 10.0?8.1?6.9?4.3?3.1?2.3,which are the same as the initial value.Moreover,the effect of the relative humidity on the acetone responses was further investigated.The response to 2 ppm acetone is 3.2,while that to 0.9 ppm acetone is 2.0 at 90% RH,indicating the the materials is still sufficient to separate diabetic patients from healthy persons.3.Au-decorated hierarchical WO₃ hollow microspheres were synthesised by hydrothermal and wet impregnation method.Also,The materials were characterized by XRD,TEM,SEM,XPS and N2 adsorption desorption.The results of XRD indicate that Au-WO₃ materials were comprised of orthorhombic tungsten oxide and cubic gold.The results of SEM,TEM and N2 adsorption desorption reveal that WO₃ hollow microspheres,composed of particles with irregular shapes,has a double pore structure,including 300 nm macropore and 40 nm mesopore.The results of TEM EDX elemental mapping images show that Au nanoparticles are homogeneously distributed throughout the whole microspheres.4.The effect of working temperature on the sensitivity of the Au-WO₃ material was discussed.Results show that the optimal operating temperatures are confirmed at340 ? for tolene.The effect of different Au weight ratios on the gas sensing properties of WO₃ were investigated.When the theoretical content of Au reach 1.5%,the response gets the maximum value.The sensitivity towards 10 ppm toluene can achieve 6.3 which is almost 3 times higher than the bare WO₃ sensor.The selectivity of tungsten trioxide was also studied.Under the same conditions,the response is below 2.2 for these gas molecules,including benzene,methanol,ethanol,ammonia,NO?CO and acetone,while the response towards acetone can reach 6.3,indicating the the materials possessed high selectivity to toluene.The response and recovery time of materials was studied.The tests show that the response time and recovery time of WO₃ sensor is 31 s and 12 s under 5 ppm toluene at 340 ?,while for1.5-Au-WO₃ sensor,is 31 s and 12 s.At last,the stability of tungsten trioxide was studied.After 40 days,the responses towards toluene of 10 ppm?5 ppm?3 ppm?1ppm?0.8 ppm?0.5 ppm?0.3 ppm still maintain 6.5?5.5?4.7?4.3?4.0?3.2?2.4,which are almost same as 40 days ago.