Material Screening for Gas Sensing using an Electronic Nose: Gas Sorption Thermodynamic and Kinetic Considerations

Abstract

To detect multiple gases in a mixture, one must employ an electronic nose or sensor array, composed of several materials as a single material cannot resolve all the gases in a mixture accurately. Given the many candidate materials, choosing the right combination of materials to be used in an array is a challenging task. In a sensor whose sensing mechanism depends on a change in mass upon gas adsorption, both the equilibrium and kinetic characteristics of the gas-material system dictate the performance of the array. The overarching goal of this work is two-fold. First, we aim to highlight the impact of thermodynamic characteristics of gas-material combination on array performance and to develop a graphical approach to rapidly screen materials. Second, we aim to highlight the need to incorporate the gas sorption kinetic characteristics to provide an accurate picture of the performance of a sensor array. To address these goals, we have developed a computational test bench that incorporates a sensor model and a gas composition estimator. To provide a generic study, we have chosen, as candidate materials, hypothetical materials that exhibit equilibrium characteristics similar to metal organic frameworks (MOFs). Our computational studies led to key learnings, namely: (1) exploit the shape of the sensor response as a function of gas composition for material screening purposes for gravimetric arrays; (2) incorporate both equilibrium and kinetics for gas composition estimation in a dynamic system; and (3) engineer the array by accounting for the kinetics of the materials, the feed gas flow rate, and the size of the device.

Simultaneous Estimation of Gas Adsorption Equilibria and Kinetics of Individual Shaped Adsorbents

“…Irrespective of the technique, the discrete experimental data is always converted to a functional form using thermodynamically consistent or empirical isotherm and kinetic models to facilitate incorporation of adsorption characteristics of a given material into process or sensor models. 6,13 Over the past few years, there has been a strong momentum toward developing robust and practical approaches to rapidly characterize the adsorption behavior of gases in porous materials. The overarching goal of this work is to propose a technique�drawing inspiration from the DCB and the ZLC techniques�to address the challenge related to rapid and accurate characterization of both adsorption equilibrium and kinetics using small amounts of sample (<100 mg).…”

Airborne Toluene Detection Using Metal–Organic Frameworks

“…22,23 The detection mechanism proceeds via the capture, either through chemical or physical sorption, of the analyte on the layer at the surface of the oscillating quartz crystal, with the mass alteration inducing a shift in the piezoelectric quartz resonant frequency. 24 As a consequence, the sensing performance in terms of sensitivity, selectivity, response/recovery time, reproducibility, repeatability, and stability is mainly driven by the physicochemical interaction between the surface coated material and the target molecule. In this context, a variety of traditional adsorbents has been explored as toluene-sensitive films, including organic 25 and organosilicate polymers, 19,26 porous silica, 27 and diverse carbons.…”

Simultaneous Estimation of Gas Adsorption Equilibria and Kinetics of Individual Shaped Adsorbents

“…[1][2][3] The prediction of the performance of these porous materials in these applications is typically carried out using optimization of computational models that simulate the respective processes that can then be validated with experiments. [4][5][6][7][8][9][10][11][12][13][14][15][16] The reliability of the results obtained from these simulations is contingent on the accurate determination of the textural characteristics, e.g., skeletal density and porosity, and of the adsorption behaviour, i.e., equilibrium adsorption capacity and kinetics for the relevant gases on the porous material. Recent advances in material science and computational methods has led to an increase in the rate of material discovery for various applications.…”

“…Irrespective of the technique, the discrete experimental data is always converted to a functional form using thermodynamically consistent or empirical isotherm and kinetic models to facilitate incorporation of adsorption characteristics of a given material into process or sensor models. 6,16 Over the last few years there has been a strong momentum toward developing robust and practical approaches to rapidly characterize the adsorption behavior of gases in porous materials. The overarching goal of this work is to propose a technique -drawing inspiration from the DCB and the ZLC techniques -to address the challenge related to rapid and accurate characterization of both adsorption equilibrium and kinetics using small amounts of sample (< 100 mg).…”