| The gas sensitivity of the gas sensor depends primarily on the performance of its gassensing material.The modified of metal oxide semiconductor gas film which used in production and life has been rarely reported.In this paper,SnO2 gas sensing film,WO3 gas sensing film and Pd-SnO2 gas sensing film have been selected as the modified modification materials.The SnO2 gas-sensing film and WO3 gas-sensing film are modified by organic small molecule semiconductor Copper phthalocyanine,and the Pd-SnO2 gas-sensing film was modified by polyvinylidene fluoride microporous membrane.The main contents of this paper are as follows:CuPcTS/SnO2 composite films were prepared by simple impregnation and assembly.P-type CuPcTS molecules are uniformly adsorbed on the surface of the ntype SnO2 film and form a p-n heterojunction.The high gas permeability of CuPcTS /SnO2 composite membrane was significantly improved dur to the combine of the high adsorption capacity of CuPcTS molecule to NO2 at low temperature and the stability of SnO2 film.The response value of CuPcTS/SnO2 composite film to 1 ppm NO2 is 2400,which is almost 24 times that of the original SnO2 film.Based on the linear relationship fitted by the least squares method,the detection limit of the CuPcTS / SnO2 composite film（signal to noise ratio 3）is close to 40 ppb.In addition,the NO2 selectivity of CuPcTS/SnO2 composite films was also significantly improved.The response of the pure SnO2 film to 1 ppm NO2 was 5 times and 10 times the 50 ppm CO and SO2,respectively.However,the response values of the composite membranes were 60 and 50 times,respectively,at the same concentration.The sensitivity and selectivity of CuPcTS/SnO2 composite film to ppb grade NO2 shows the bright prospect of air pollution in indoor and outdoor detection of NO2 concentration.CuPcTS/WO3 composite films were prepared by simple impregnation and assembly.The gas sensitivity of CuPcTS/WO3 composite membrane showed a significant improvement compared with CuPcTS/SnO2 composite membrane,and had high sensitivity and high selectivity to ppb grade NO2.The CuPcTS/WO3 composite membrane’s response to 0.1 ppm NO2 is 92 which is 5.4 times to original WO3 film.Based on the linear relationship fitted by the least squares method,the detection limit of the CuPcTS/WO3 composite membrane（signal to noise ratio 3）is close to 70 ppb.The NO2 selectivity of CuPcTS/WO3 composite membranes was also significantly improved.The sensitivities of WO3 film to 0.1 ppm NO2 were 13 times and 10 times of 50 ppm CO and SO2 respectively,but the response of CuPcTS/ WO3 composite film at the same concentration was 83 and 90 times,respectively.It can be seen that Cu Pc can significantly improve the sensitivity and selectivity of ntype metal oxide semiconductors to NO2 at room temperature by the modified of SnO2 film and WO3 film.This selective enhancement is due to the formation of electron transfer channels on the surface of the metal oxide with the metal oxide,which will lead the electron transfer between the metal oxide surface and Cu Pc when the NO2 adsorption and desorption on the Cu Pc surface.The Pd-SnO2 nanoparticles were prepared by ultrasonic assisted method.The results showed that the material had good H2 detection performance at 0 RH% humidity and 150℃,but the gas-sensing performance of Pd-SnO2 decreased with the increase of air humidity.At 100 RH%,Pd-SnO2 gas sensor will lose 70% sensitivity to 50 ppm H2,and with the detection of gas concentration increases,the sensitivity loss increased to 82% when the gas concentration is 500 ppm.A porous PVDF film was deposited on the surface of Pd-SnO2 gas-sensing film by phase separation to improve its performance in high humidity air.The sensitivity of the PVDF-Pd-SnO2 gas-sensing membrane is better than that of the Pd-SnO2 gas-sensing membrane,and its sensitivity loss is 22% at 100 RH% and its sensitivity loss decreases to 12% with the H2 concentration decreased to 500 ppm,but the PVDF-Pd-SnO2 gas-sensing film also has a low overall sensitivity,which is lower than that of the Pd-SnO2 gassensitive film in a dry environment. |
