Study On Photoelectrical Sensitivity Of Formaldehyde Based On Modified ZnO Nanomaterials

Excessive indoor formaldehyde has become a problem that people can not ignore.Long-term exposure to this environment will cause people to suffer from diseases such as nasopharyngeal cancer and leukemia.Therefore,we need a low-cost,rapid and accurate method to detect formaldehyde gas.At present,the most commonly used is metal oxide semiconductor gas sensor,among which gas-sensitive materials are particularly important for formaldehyde detection.ZnO nanomaterials have the advantages of wide band gap（3.4 e V）and high mobility.Therefore,ZnO is selected as the core material in this paper,but a single ZnO nanomaterial still has the disadvantages of poor stability and low responsiveness in practical application.Therefore,the photoelectric performance of ZnO nanomaterials and the responsiveness and sensitivity of photoelectric gas sensors are improved by metal ion doping and heterojunction of single ZnO nanomaterials in this paper.The research content of this thesis mainly includes the following two aspects:1.A series of Cu-ZnO nano-hollow spheres with different concentrations were prepared by oil bath method.The characteristics of ZnO nanoparticles were analyzed by TEM and XPS,and it is proved that Cu⁺is successfully doped on zno surface,and there are Cu₂O nanoparticles at high concentration.The photoelectric test results show that Cu-ZnO-3（1 m M）material has the best gas sensitive property.Under UV irradiation,the response to 100 ppm formaldehyde gas is 181.84%,which is 16 times that of pure ZnO.Moreover,the detection limit of the nanomaterial can reach 20 ppb.In addition,the sensor has excellent recovery performance and long-term stability.The improvement of gas-sensitive performance of Cu-ZnO nano-hollow spheres is mainly due to the p-type doping of Cu⁺and the formation of p-type semiconductor Cu₂O nanoparticles,which increases the surface resistance of the nano-spheres and leads to the obvious decrease of current.2.Through SEM,XRD and XPS tests,it is proved that we have successfully prepared porous flower-like ZnO and Cu O-ZnO nanomaterials.The photoelectric sensitivity test of the two materials shows that Cu O-ZnO nanocomposites have better performance in detecting formaldehyde than pure ZnO nanomaterials.When formaldehyde concentration is 2 ppm and 100 ppm,the response of Cu O-ZnO samples is 5.59 and 6.51 times that of pure ZnO samples.In addition,the sensor also has a good selectivity,at the same concentration of its response to formaldehyde is 50 times that of ammonia.The influence of heterojunction formation on the gas sensitivity of HCHO was investigated by surface photovoltage test,and the gas sensitivity mechanism of Cu O-ZnO sensor was discussed.