The Study On Gas And Humidity Sensitivity Of QCM Modified By Metal Organic Framework Materials

Quartz Crystal Microbalance?QCM?is a gas sensor with many advantages,such as low cost,simple structure,high sensitivity,real-time monitoring and measurement accuracy at room temperature.Metal Organic Frameworks?MOFs?are a class of micro-/mesoporous hybrid materials with high specific surface area,high porosity and adjustable pore size,which have already shown a variety of applications.In recently,MOFs have gradually begun to be used in the field of sensors.Therefore,this paper is mainly about the combination of MOFs and QCM sensors for HF and humidity detection.The main contents and conclusions of this paper mainly include three parts are as followed:?1?MIL-101?Cr?and NH₂-MIL-101?Cr?materials were prepared by a simple hydrothermal method.The materials synthesized were characterized by different analytical techniques including SEM,FT-IR,XPS,XRD,TEM,BET and TGA,etc.Then,the QCM gas sensors based on MIL-101?Cr?and NH₂-MIL-101?Cr?materials were constructed to detect HF gas,and a series of detecting HF gas experiments were performed.The experimental results show that the NH₂-MIL-101?Cr?material exhibits a higher response to HF gas than MIL-101?Cr?material,and the NH₂-MIL-101?Cr?thin film modified gas sensors have a response is 464 Hz for 2.5 ppm HF.NH₂-MIL-101?Cr?has a rapid response and recovery dynamics,the response time is 4 s and the recovery time is 12 s.NH₂-MIL-101?Cr?also exhibits a good repeatability and stability for detecting HF gas,and when the concentration range of HF is confined from 50 ppb to500 ppb,the QCM sensors all exhibit almost good linear frequency responses towards HF gas.The NH₂-MIL-101?Cr?gas sensor also exhibits a good selectivity for HF gas.In addition,in order to make a thorough inquiry for the sensing mechanism of HF and NH₂-MIL-101?Cr?,we employ Gaussian 09 as a tool to simulate the adsorption energy change of HF molecular on NH₂-MIL-101?Cr?,and found that the adsorption energy??H?between HF gas molecules and NH₂-MIL-101?Cr?was-47.32 kJ mol^-1.It is indicated that the interaction between NH₂-MIL-101?Cr?and HF gas is chemisorption,and this material is suitable for detecting HF gas.In addition,the HF adsorption isotherm was obtained by microgravity method,and then the adsorption enthalpy between NH₂-MIL-101?Cr?and HF molecules was 48.60 kJ mol^-1,which also indicates that the interaction between two materials is reversible chemical adsorption.?2?MIL-125?Ti?and NH₂-MIL-125?Ti?materials were synthetized by solvothermal method.The prepared materials were characterized by XRD,FT-IR,SEM and BET.The humidity sensing performances of the two materials based QCM sensors were studied by exposed to humidity range of 11%⁹7%RH?relative humidity?.The experimental results show that the MIL-125?Ti?and NH₂-MIL-125?Ti?sensors have some advantages,such as high sensitivity,good repeatability,fast response/recovery and etc.Compared with MIL-125?Ti?,the sensor modified by NH₂-MIL-125?Ti?exhibited higher response to humidity.when the indoor humidity was about 52%,the frequency shift of the NH₂-MIL-125?Ti?sensor to a 11%relative humidity was 57 Hz higher than MIL-125?Ti?,indicating that the amino-functionalized material had a certain enhancement to the response of the humidity sensor.Furthermore,the adsorption enthalpy between water molecules and MIL-125?Ti?or NH₂-MIL-125?Ti?was obtained by Materials Studio,which proved that the amino functionalization could enhance the humidity sensitivity of MIL-125?Ti?.?3?GO/NH₂-MIL-125?Ti?composites decorated with different content of graphene oxide?GO?were prepared by solvothermal method.The materials were characterized by XRD,SEM,TEM,TG,BET and FTIR.It can be seen from the XRD pattern that when the amount of graphene oxide added is 1%,the peak intensity is the strongest and the peak shape is relatively sharp.When the GO is added in excess,the intensity of the diffraction peak of PXRD is became weak,indicating that the excess of GO leads to limitation of NH₂-MIL-125?Ti?crystal growth.The SEM and TEM images show that as the amount of GO added increases,the average diameter of the particles gradually decreases,and the particles gradually break and the size gradually becomes uneven.The BET test indicated that the prepared GO/NH₂-MIL-125?Ti?composite material showed a significant increase in specific surface area.The results of humidity sensitivity test showed that the response of 1%GO/NH₂-MIL-125?Ti?sample to 97%RH relative humidity was 807 Hz,which was much higher than NH₂-MIL-125?Ti?.In addition,the humidity sensor constructed by GO/NH₂-MIL-125?Ti?has good reproducibility,long-term stability,fast response-recovery and low hysteresis.