Quartz crystal microbalance adsorption apparatus for high pressure gas adsorption measurements in nanomaterials
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The primary objective of this study was to develop a sensitive and cost-effective sorption system to analyze adsorption and diffusion of different gases on micro porous materials and nanotubes. A high pressure Quartz Crystal Microbalance (QCM) based adsorption apparatus for single-component gas was developed. A QCM is an acoustic-wave resonator in which the acoustic wave propagates through the crystal. Therefore, it is highly responsive to addition or removal of small amounts of mass adsorbed or deposited on the surface of the crystal. This mass sensitivity makes the QCM an ideal tool for the study of gas adsorption. The QCM-based adsorption apparatus is advantageous over the commercialized none-gravimetric and gravimetric equipment in a way that it is low-cost, highly sensitive and accurate for mass sorption applications, satisfactorily stable in a controlled environment, and can be used for thin films. The high pressure apparatus was calibrated using Matrimid 5218, whose thermodynamic properties and adsorption parameters are known. The Matrimid was spin-coated onto a 14 mm-diameter QCM, and sorption equilibrium data for were obtained for CO₂ gas at 25, 30, 48, and 52 ºC and partial pressure range between 0 to 4 bar. In order to compare the experimental data with available literature data, the experimental data was fitted into a dual-mode adsorption model. The model results from Henry's law and a Langmuir mechanism. Comparison of the experimental adsorption isotherm of Matrimide for CO₂ gas with literature data showed reasonable agreement between the experimental and literature data. In this study, the adsorption parameters of aluminosilicate nanotubes are observed. Aluminosilicate nanotubes are ideal materials for chemical sensing, molecule separation, and gas storage; hence, there is a need for adsorption and diffusion data on this material. The adsorption of CO₂, N₂, and CH₄ gases on aluminosilicate nanotubes samples has been studied in the temperature range of 20° to 120° Celsius and pressure range of 0 to 8 bar. The experimental results yield the CO₂ and N₂ heat of adsorptions of -32.9 and -28.1 kJ/mol respectively.