Design And Preparation Of Sensitive Membranes Of VOCs Sensor And Sensing Analysis Of Chloroform

The detection of Volatile Organic Compounds（VOCs）plays an important role in environmental protection,hazard warning,and health care.In view of the demand for sensitive,simple and portable detection modes,VOCs sensors are currently the most commonly used detection methods,but there are still problems in that sensitivity,selectivity,stability and other performances are inadequate.The sensitive membranes that adsorb VOCs are a key component of sensors,the design,preparation and adsorption properties and mechanisms of VOCs sensitive membranes are beneficial to the application and development of sensors,and new ideas for VOCs detection will be provided.The main research work and results are as follows:（1）Construction of gas testing system.Quartz crystal micro-balance（QCM）oscillator circuit is designed and produced,QCM,vector network analyzer,gas sealed box are connected to construct a gas testing system,the vector network analyzer were debugged.The parameters were set to the Starting frequency:8.8 MHz,Termination frequency:9.2 MHz,Number of points:1601,Avg:1 kHz;Average:on,Smooth:on.Graphene oxide film was prepared by cyclic voltammetry on QCM and used in gas testing system to test VOCs such as ethanol,chloroform and so on.The oscillation frequency of QCM conforms to Sauerbrey equation with quick response.Therefore,the gas testing system can be used for detection of QCM gas sensor which is the foundation of VOCs test.（2）Synthesized and sensing analysis of foamed TiO₂ material.The foamed TiO₂film was prepared on QCM sensor by drop-coating.The parameters such as solvent,concentration and dosage of the film were optimized:10μL 0.5μg/μL foamed TiO₂film was prepared by using ethanol as solvent.Under the conditions,the VOCs such as chloroform and benzene in ppm were adsorbed obviously,and the foamed TiO₂ film was compared with the film made of nano-particle TiO₂.The SEM graph showed that the foamed TiO₂ was more uniform,and it was found that the frequency of QCM sensor with foamed TiO₂ film to chloroform decreased to a greater extent.On the basis of this,p-tert-butylcalix[8]arene was spin-coated on QCM to form foam TiO₂/Calix[8]composite sensitive film,and the concentration and dosage of the composite film were optimized.The structure was characterized by FTIR,Raman spectroscopy and sensitive mechanism was analyzed.Chloroform were selectivity adsorbed by foam TiO₂/Calix[8]composite membrane.The frequency value of QCM decreased linearly when 60-300ppm of chloroform were absorbed by QCM,the linear regression equation is-△f=0.4430 C+5.489（R²=0.9778）,and the detection limit of QCM to chloroform is 60ppm.It can be completely desorbed within 5-10 min,and the QCM frequency is recovered after the test is completed.（3）Synthesized and sensing analysis of metal-organic frameworks（MOFs）based on p-tert-butylcalix[8]arene.The MOFs material was firstly synthesized with p-tert-butylcalix[8]arene as organic ligands and Fe³⁺as metal links.The structures of the synthesized MOFs were characterized by SEM,EDS and FTIR,and sensitive films are prepared on QCM by spin coating.The parameters of concentration,dosage and spin-coating rate and were optimized:the film was prepared by spin coating with 8μL of 1μg/μL MOFs solution,the speed of the spinning was slowly increased from 100rps/min to 1000 rps/min.The VOCs such as chloroform and benzene in ppm level can be adsorbed by the MOFs film,the response time is 3-5 min,and the chloroform can be selectively adsorbed.The minimum detection limit is 30 ppm,and the frequency value of QCM decreased linearly when 30-200 ppm of chloroform were absorbed by QCM,and the linear regression equation is-Δf=0.6731 C-2.488（R²=0.9735）.VOCs were desorbed within 3-5 min after the test,and the frequency of QCM basically recovered to the frequency value before the adsorption of VOCs.The SEM and other characterization methods were used to analyze the sensitive mechanism of sensitive membranes.The effects of sensitive membranes dissolved by different solvents（chloroform,ethanol,acetone）on the selectivity were analyzed.It was found that the sensitive membrane prepared by chloroform dissolution had the best selectivity to chloroform.Compared with p-tert-butylcalix[8]arene,the detection limit of the QCM sensor was reduced by this way,selectivity to chloroform was improved,and this QCM sensor can stably work within 1-3 months.It provides a new approach to the development of VOCs sensitive membranes and sensors.