Study On Humidity Sensing Properties Of Metal-organic Frameworks Materials Of ZIF-8（I₂）

Three-quarters of the area is occupied by the ocean on the earth. The water willevaporate and exist in form of water vapor everywhere. It has great influence on ourproduction and life. So testing humidity is crucial for us. Humidity sensor is the devicewhich can convert water to electrical signal of easy handling according to certain rule.The principle is that the electrical characteristics of humidity sensor change with themoisture absorption such as resistors and capacitors. With the rapid development ofscience and technology, people need higher performance and better stability humiditysensor increasingly. Finding new humidity materials take more and more attention toresearchers. Metal-Organic Frameworks materials become more and more popularbecause of the large specific surface area, large adsorption capacity and excellent stabilitycharacteristics. The channel structure also can be designed. By changing the structure orcomponent can change the performance, so there is a wide prospect in the aspect ofhumidity sensor by using Metal-Organic Frameworks compounds.In this paper, the concept of humidity representations, the classification of humiditysensor, the humidity characteristic parameters and the development of humidity sensorwere included comprehensively. And we introduced the metal-organic frameworkscompounds briefly. The experiments included: ZIF-8（Zeolitic Imidazolate Frameworks）nanocrystals were synthesized by a solvothermal method, of which pores wassuccessfully doped in with I₂.The crystal structures of ZIF-8and ZIF-8（I₂） werecharacterized by X-ray diffraction （XRD）, the morphologies of ZIF-8and ZIF-8（I₂）（ZIF-8doped with I₂） were observed by scanning electron microscope （SEM）. ThenZIF-8（I₂） humidity sensor was fabricated by coating the nanocrystals materials on Ag-Pdinterdigitated electrodes by coating methods. Besides, complex impedance property atdifferent RH （Relative Humidity） was analysed to study sensing mechanism of ZIF-8（I₂）. The results show that:1) ZIF-8（Zeolitic Imidazolate Frameworks） nanocrystals were synthesized by asolvothermal method, of which pores was successfully doped in with I₂.Theproportion of the quality of ZIF-8and the quality of I₂is respectively0.5：1,1：1,1.5：1. We write as ZIF-8（50%I₂）, ZIF-8（100%I₂）, ZIF-8（150%I₂）.2) ZIF-8（50%I₂）, ZIF-8（100%I₂）, ZIF-8（150%I₂） humidity sensors were respectivelyfabricated by coating method. The results indicate that the materials show highsensitivity at high relative humidity. There are two orders of magnitude with thechange of resistance. The response time of ZIF-8（50%I₂） humidity sensor is2min,recovery time is40s，the humidity hysteresis is about6%RH; The response time ofZIF-8（100%I₂） is1min, recovery time is2min, and the humidity hysteresis is about7%RH. The response time of ZIF-8（150%I₂） is40s, recovery time is3min, and thehumidity hysteresis is about8%RH。3) Above all we found that: the quality of I₂which is doped in can affect the humidityproperties of humidity sensor. The device doped in100%I₂is the best.Besides, complex impedance property at different RH was analysed to study sensingmechanism of ZIF-8（I₂）. The results show that Metal-Organic Frameworks materials willbe very important in humidity sensor applications.