Preparation And Humidity Sensitive Properties Of MOFs/Silicon Nanoporous Pillar Arrays

Because humidity control and detection are playing an increasingly important role in industrial and agricultural production,medical and health care,meteorological monitoring,storage and People’s Daily life,the design and development of high-performance humidity sensor has become a research hotspot.As the soul part of the moisture sensitive sensor,the moisture sensitive material directly determines the performance of the moisture sensitive sensor.Therefore,the development and research of new humidity sensitive materials is the primary task to prepare high performance humidity sensitive sensors.Because of their large specific surface area and high porosity,metal-organic framework materials（MOFs）are considered as strong candidates for the next generation of moisture sensors.These sensors have fast response speed but poor desorption performance.Si-NPA is composed of micrometer-scale porous silicon column array and porous layer supporting the silicon column,which has multi-level microstructure and large specific surface area.The channel network composed of silicon column and porous layer facilitates the transport of water molecules,improves the response/recovery speed,and is a suitable material for preparing moisture sensor or substrate of moisture sensor.Therefore,the combination of the above two materials is expected to improve the deficiency of a single material as a sensor,further increase the specific surface area and adsorption site of the new humidity sensor,improve the response/recovery speed and long-term stability of the device.Based on the above research background,this paper constructed three kinds of moisture sensors based on MOFs/Si-NPA.The specific research work is as follows:1.ZIF-8/Si-NPA humidity sensor was prepared by solvothermal method.The results show that the ZIF-8/Si-NPA humidity sensor has good humidity sensitivity in the whole humidity range.When the test frequency is 20 Hz,the capacitance value increases from0.85 n F to 1500 n F,and the capacitance value spans four orders of magnitude.The capacitance responsiveness is 186047%,the response/recovery time is 21/9 s,the wet hystericity is small（2.27%）,and the repeatability and stability are good.Complex impedance analysis showed that the rich hydrophilic groups on the outer surface of ZIF-8 and the Si-O-H bond of Si-NPA accelerated the chemisorption process.Therefore,the device has the shortest response recovery time and the highest capacitance response,such as excellent humidity sensitivity.2.The NH₂-MIL-125（Ti）/Si-NPA humidity sensor was prepared by in-situ hydrothermal method.The results show that the humidity sensor has good humidity sensitivity in the range of 11%RH to 75%RH.When the test frequency is 20 Hz,the capacitance responsiveness of NH₂-MIL-125（Ti）/Si-NPA is 5397%,the response/recove-ry time is 70 s and 6 s respectively,and the wet hystericity is very small,only 1.95%.After 1 year of storage,the capacitance of the device fluctuates very little and has good long-term stability.The analysis shows that the extremely short recovery time and small wet lag are mainly attributed to the channel network formed by Si-NPA.3.MIL-101（Cr）/Si-NPA moisture sensor was prepared by hydrothermal method combined with spin coating technology.The results show that at 300 Hz test frequency,in the range of 11%-75%RH humidity,the capacitive responsiveness of the humidity sensor can reach 20,729.2%,and the response/recovery time is long（82/25 s）,and the wet hysteria is large（7.08%）,but the linearity is good.Then,the wet sensor of Fe Cl₃/MIL-101（Cr）/Si-NPA was made by mixing Fe Cl₃ into MIL-101（Cr）.It is found that the moisture sensitivity of the sensor can be significantly improved by adding an appropriate amount of Fe Cl₃,and the optimal amount of Fe Cl₃ is 8 wt.%.The capacitance responsiveness of the 8 wt.%doped sample is 2.2 times that of the undoped sample,the response/recovery time is reduced to 46/6 s,the wet hysteresis is reduced to 5.23%,the linear correlation coefficient is increased to 0.991,and the stability is also improved.Finally,the mechanism of its moisture sensitivity was analyzed by complex impedance spectroscopy.These results indicate that the addition of Fe Cl₃ is an effective way to improve the moisture sensitivity of MIL-101（Cr）/Si-NPA.There are 85 figures,4 tables and 106 references.