Study On The Metal Ion Doping And Metal Oxide Composites Nano-TiO₂ Gas Sensors

The pulp and paper industry is a heavily polluting industry that emits a large amount of exhaust gas into the environment for a long time.This paper is mainly aimed at the NH₃ and H₂S appeared in the industrial environment in pulp and paper mills.It is based on the anatase nano-TiO₂ colloid synthesized by a low-temperature liquid phase method.In order to solve the the disadvantages of pure nano-TiO₂ gas sensor,such as high operating temperature and low sensitivity,it is modified by metal ion doping and metal oxide composite.At last,the gas sensing mechanisms are studied.The main research contents and results are as follows:（1）Different concentrations of Fe³⁺,Cu²⁺,Ni²⁺and Co²⁺were doped into the nano-TiO₂colloid by ultrasonic doping to improve the gas response of nano-TiO₂ to NH₃.The results showed that the response of the TiO₂ gas sensor with concentration of 20%Co²⁺was up to12.171,which realized the detection of NH₃ at room temperature,and its response reached3.259-12.171 to 1-50 ppm NH₃,while the response/recovery time of the gas sensor were less than 19 s and 38 s,respectively,which achieved rapid detection of NH₃ at room temperature.In addition,the gas sensor had excellent selectivity,repeatability and stability to NH₃.（2）A high performance H₂S gas sensor based onα-Fe₂O₃/TiO₂ nanocomposite was developed by a liquid phase reaction.With the determined optimal conditions for gas sensing,50 mol%α-Fe₂O₃ doping amount and operating temperature of 120°C,the following gas sensing performance were obtained:The response of theα-Fe₂O₃/TiO₂ composite sensor to 50ppm H₂S was 7 times higher than that of the pure TiO₂,and achieved the responses of 3.4-15.6when the sensor was exposed to H₂S of 1-50 ppm.The response/recovery time of the gas sensor to 50 ppm H₂S were acceptable as 25 s and 48 s,respectively;the gas sensor demonstrated an excellent selectivity,repeatability and stability to H₂S.Compared with the other reported H₂S sensor of operating temperature of 300°C,its operating temperature dropped by 60%to 120°C,which could prolong the service life of the gas sensor and reduce energy consumption.（3）Based on the previous metal oxide composite could improve the gas sensing performance of TiO₂ nanoparticles gas sensor,the NH₃ sensors of metal oxide composites were prepared.Firstly,CuO nanoparticles,NiO nanoparticles,and Co₃O₄ nanoparticles were synthesized by hydrothermal method,and then combined with TiO₂ nanoparticles.The results showed that the NiO/TiO₂ nanocomposite gas sensor with 50 mol%NiO doping amount had the best gas sensing performance and realized the detection of NH₃ at room temperature.The gas sensor achieved the response of 1.438-10.168 to 1-50 ppm NH₃.The gas sensor had a fast response/recovery time,which were less than 60 s and achieved rapid detection of NH₃ at room temperature.In addition,the gas sensor had excellent selectivity,repeatability and stability to NH₃.（4）Finally,the mechanisms of metal ion doping and metal oxide composites on the gas sensing performance of the sensor were studied.The mechanism of the influence of metal ion doping on the gas sensing performance of the sensor was mainly attributed to the lattice replacement of metal ion and the change of the forbidden band width of TiO₂.The mechanism of the influence of metal oxide composites on the gas sensing performance of the sensor could be attributed to the effects of heterojunctions of two metal oxides,which include the potential barrier modulation and Fermi-level mediated charge transfer effects,the change of width of the conduction channel for the electron transportation and a synergistic effect of two metal oxides.