Preparation Of NO₂ Gas Sensor Based On TiO₂ Nanotubes

With the rapid development of industry,air pollution has generated worldwide public concern.Especially,the increasing emission of NO₂ becomes a most hot environmental issue. Therefore,gas sensor serve as analytical tools with reliable accuracy are needed for in-situ and real-time detection.The semiconducting metal oxides have a promising prospect of practical applications because of their high sensitivity,low cost,facile fabrication technique and easy conduction.However,the high conduct temperature,low selectivity and poor stability of the traditional semiconducting metal oxides restrict their applications. 1-dimensional or qusia-1-dimensional nanomaterials with unique properties make it possible to achieve gas sensor with excellent activity under room conduct temperature.In this work,a system controlled via program for measuring the property of gas sensor was designed and established to decrease the operation error,so that the accuracy and facile measurements for gas sensor can be achieved.The performance of NO₂ gas sensor based on 1-dimensional unordered and ordered TiO₂ nanotubes were tested under the same conduct conditions using this system.Conventional thin film gas sensor was fabricated by dip-coating using a mixture of unordered TiO₂ nanotubes and TiO₂ nanoparticles on Si substrate.The mixed powder was prepared by hydrothermal technique.The SEM and TEM images shown that the unordered TiO₂ nanotubes have tube diameter of ca.15nm and the length of the nanotube was ca. several micrometer;the XRD pattern indicated that the crystal structure of TiO₂ nanotubes obtained via hydrothermal technique was convert from titanate to anatase through second hydrothermal process;the performance of NO₂ gas sensing property demonstrated that the resistance of sensor is as high as the order of 10⁷Ωat 80℃in air,and sensitivity is 0.28 to 12.5ppm NO₂ under the same condition.Besides,the sensor exhibited poor recovery property.In the second part,highly ordered TiO₂ nanotube arrays were prepared by anodization fabricated as NO₂ gas sensor.The SEM images shown the TiO₂ nanotube arrays have average diameter of ca.100nm,wall thickness of ca.10nm,nanotube length of ca.700nm and were grown vertically on the substrate.The spectrum of XRD indicated that the crystal structure of the sample was dominantly anatase phase after annealing at 500℃.It can be found the ordered TiO₂ nanotube arrays have distinct response signal to the.NO₂ gas.The response signal increased with the increment of NO₂ concentration at 80℃;the sensitivity of ordered TiO₂ nanotube arrays for 2.5ppm NO₂ was up to 130 at the same operation temperature.With the increasing of the operation temperature,sensitivity drop quickly.Besides,the response time rise slightly and recovery time drop dramatically.