Research On The Development And Performance Improvement Of Nanomaterials Coated QCM Gas Sensors

Quartz crystal microbalance,(QCM)is a kind of gravimetric sensor using quartz resonator as the core sensing device.Based on the positive-inverse piezoelectric effect of quartz crystal and the specific adsorption of the analyte by the coating film,a QCM sensor can convert the component information such as mass and concentration of the analyte into a frequency signal for measurement.In this paper,by combining QCM and nano materials,we applied QCM method to gas detection field to fabricate sensors for trace gas detection at room temperature.Besides,considering the deficiencies of QCM gas sensors in sensing materials,detection methods,gas sensing mechanism and in practical applications,our work is mainly focused on the development of a QCM sensor coated with nano materials and the studies concerning the improvement of its gas sensing properties.The sensitivity of the sensor can be effectively enhanced by noble metals addition method,and the selectivity can also be significantly improved through functionalized composition.By correcting the linear solvation energy relationship(LSER)model with the hydrophilicity parameters,an approach to quantitatively investigate the gas sensing mechanism was obtained and utilized.The main research contents and results are as follows:On the basis of our existing research,the whole QCM gas sensor system was improved and optimized centering three key parts including the detection circuit,the sensor fabrication and the test chamber,and was finally constructed.Then,nano Ni(OH)2 material synthesized using a low-temperature template-free hydrothermal method was used as the sensing film to modify a QCM sensor and the fabricated sensor was employed to detect low-volatility dibutyl phthalate(DBP).When tested at room temperature,the sensor achieved high sensitivity for DBP at low concentration of ppb level and maintained good repeatability as well as stability.Besides,the sensor exhibited superior response and selectivity to DBP over other plasticizers and possible interferences.The study on the improvement of gas sensing properties especially for sensitivity and selectivity,which are the two key performances of a QCM gas sensor,was conducted.For sensitivity enhancement,we mainly focused on the noble metals addition method.Accordingly,Au-functionalized ZnO porous microspheres was prepared for QCM modification.In detection of ultra-low concentration of DBP,the ZnO-Au coated QCM sensor achieved a 1.62-time enhancement in sensitivity and the selectivity was also improved.As to selectivity improvement,functionalized modification and composition method was deeply investigated,based on which,graphene oxide/chitosan(GO/CS)nanocomposite was synthesized and firstly introduced as the sensing material of a QCM sensor.Due to the extraordinary affinity to amine vapors inherited from CS,the GO/CS coated sensor also performed favorable selectivity for methylamine(MA),dimethylamine(DMA)and trimethylamine(TMA),which was greatly improved over GO.On the other hand,compared with CS,the response amplitudes increased 3 times or more after composed with GO.The GO/CS nanocomposite was finally obtained as a better sensing material for selective detection of amine vapors,possessing the merits of both GO and CS.All the results above confirmed the effectiveness of the two methods in improving the sensitivity and selectivity of a sensor,and also provided feasible ideas and methods for related research.When it comes to the sensing mechanism,the performances of QCM gas sensors coated with simple nano metal oxide,noble metal doped nano metal oxide and functionalized nanocomposite were compared and analyzed.Based on this,a qualitative investigation of the sensing properties was reached considering the microstructures,physicochemical properties as well as functional groups of the sensing film.Furthermore,by analyzing the selectivity and sorption properties of the GO/CS coated QCM sensor based on the responses,partition coefficients and affinity values,the original LSER model was revised combining the hydrophilicity parameter.The corrected model gave a quantitative approach to investigate the gas sensing mechanism of GO/CS towards amine vapors.This method is able to obtain a more objective and more reasonable investigation for sensing and adsorption mechanism of nano materials,and thus provide a more rational theoretical basis for the selection,modification and development of sensing materials for a QCM-like sensor.