| Metal oxide type semiconductor gas sensors have played important role in the fields of atmospheric monitoring,industrial safety production,indoor environmental quality inspection,etc.WO3 is an excellent n-type semiconductor sensitive material with high sensitivity and good stability,However,the detection range,sensitivity,and response speed could be further improved.Therefore,it is of great significance to prepare,study the structure and improve the sensing properties of WO3.In order to improve the sensitivity to reducing gas acetone,WO3 with different crystal phases and Ag loaded WO3?Ag/WO3?were firstly prepared by microwave hydrothermal method.Then,the as-prepared materials were characterized by XRD,SEM,TEM,XPS,etc.After that,the response to acetone vapor,dynamic response/recovery,detection of concentration range,optimal working temperature,selectivity and anti-interference capability,long-term stability were examined to show the sensing properties of WO3 and Ag/WO3.The effect of preparation parameters on structure and gas sensitivity of different WO3 and Ag/WO3 were investigated to reveal the gas sensing mechanism.The main achievements are summarized below.?1?Monoclinic WO3 was prepared by microwave hydrothermal method using sodium tungstate as tungsten source.The effects of hydrothermal temperature and precursor solution p H on the composition,structure and gas-sensitive properties of the material were investigated.The results show that the monolinic WO3 was obtained from a precursor with p H=0.5 and microwave hydrothermal treated at 180°C.Due to the high specific surface area and abundant oxygen vacancies,the chemical adsorption of gas on the surface of the material is significantly improved.The optimum working temperature of monoclinic WO3 is 320°C.The acetone detection range concentration is 0.25ppm100 ppm.And the detection limit of monoclinic WO3 is as low as 7.5 ppb,indicating a very sensitive behavior to acetone.Besides,the monoclinic WO3 has a response/recovery time of less than 5 s in the 0.25 ppm to 100 ppm acetone concentration range,and has high stability and selectivity.?2?The hexagonal phase WO3 was prepared by microwave hydrothermal method using ammonium metatungstate as tungsten source.The phase composition,morphology and gas sensitivity were improved by adjusting the precursor p H and the addition of oxalic acid.The results showed that the microsphere-shaped hexagonal phase WO3 was formed from self-assembled nanorods with precursor p H=1 and the oxalic acid dosage was 1 g.The obtained WO3 showed?001?growth orientation.There are more micropores on the surface,and the specific surface area was increased significantly.Therefore,the material exhibits enhanced gas sensing property.The optimal working temperature of hexagonal WO3 is 340°C,and the response to 100 ppm acetone is 39.1,the response/recovery time is 6 s/7 s,respectively.?3?Photochemical deposition method was used to reduce Ag from AgNO3solution by UV irradiation and in-situ loading on the surface of WO3.By controlling the dosage of AgNO3,WO3 with different content of Ag were obtained.It was found that the Ag loading content has a great influence on the sensitivity of WO3.When the loading amount of Ag is 2.12%,the optimum working temperature was reduced to 280?,the response to 100 ppm acetone gas was increased to 44,and the response recovery time was 3 s and 4 s,respectively.?4?The monoclinic phase WO3 has more oxygen vacancies on the surface,which enhances the sensitivity and decrease the detection limit to ppb level.Due to the?001?growth orientation,the adsorption and reaction ability of the hexagonal phase WO3 are increased.As a result,the sensitivity is higher than that of the monoclinic phase.As for Ag/WO3,Ag plays an important role in catalyzing adsorption/desorption of gas molecules,as well as the acetone oxidation-reduction process.As a result,the response increased and the optimal working temperature decreased.The sensitivity of the material was further enhanced. |
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