Quantitative evaluation of the responses of a gravimetric gas sensor based on mesoporous functionalized silica: Application to 2,4-DNT and TNT detection

The literature reports several attempts to predict the responses of gas sensors using as only input the molecular structures of the analyte and sensing material. However, these are restricted to relatively simple and homogeneous materials. The present paper reports for the first time the semiquantitative estimation of the sensing responses of quartz crystal microbalance sensors based on a complex material, taking relative humidity into account. The sensing material is methylated mesoporous silica, and the analytes are vapors of the nitroaromatic compounds 2,4-dinitrotoluene (2,4-DNT) and trinitrotoluene (TNT). Our approach is based on molecular dynamics simulations. The amount of vapor (water, 2,4-DNT or TNT) adsorbed on the sensing surfaces is obtained as a function of their partial pressure by simulating adsorption isotherms at high temperature and extrapolating the results to ambient conditions. Furthermore, a correction factor is introduced to account for the role of residual water within the mesoporous silica. The order of magnitude of the simulated sensing responses to 2,4-DNT and TNT is found to be consistent with experimental data.