Effects of temperature on methanol adsorption on functionalized graphite: Saturation of functional groups

Abstract

Grand Canonical Monte Carlo simulation of methanol adsorption on a graphite model with two hydroxyl groups grafted on the surface has been carried out to investigate the effects of temperature in the range of 278-360K. The spacing between the OH groups was chosen so that two hydrogen bonds could be formed with the first methanol molecule. In the Henry law region, the isosteric heat at zero loading is greater than the condensation heat. When the loading is increased, the isosteric heat at low temperatures decreases slightly and exhibits a shoulder, which is associated with the formation of a cluster of methanol molecules around one OH group. On further increase in loading, the adsorbate-adsorbate interactions decrease because methanol begins to adsorb on the other OH group, resulting in a sharp decrease in the isosteric heat to a minimum, at which point both OH groups are covered with methanol molecules. At higher temperatures the isosteric heat at zero loading decreases but remains higher than the condensation heat. The shoulder heat is progressively diminished with temperature because methanol molecules are distributed over the two OH groups, due to the entropic effects. Interestingly, the minimum heat still occurs when the functional groups are covered and is even more pronounced at high temperatures.

Molecular Insights into the Effect of Temperature and Functional Groups on the Nonwetting, Prewetting, Partial Wetting, and Complete Wetting Transitions of Ethanol on Graphite

“…We modeled graphite as a homogeneous substrate with a constant surface density of 38.2 nm –2 , and the potential energy between an LJ site and graphite was modeled with the Steele 10-4-3 potential equation, with the molecular parameters for the carbon atom in a graphene layer taken from Steele, σ i (s) = 0.34 nm and ε i (s) / k B = 28 K. The interlayer distance between the two graphene layers was 0.3354 nm. The homogeneous solid model was used since it was used in previous studies and gave consistent results with experimental data for a wide variety of fluids, including ethanol and methanol. − …”

Design and Synthesis of a Water-Resistant Mesoporous Silica Gel for the VOC Adsorption–Desorption Treatment

“…Volatile organic compounds (VOCs) are harmful to the human body and the environment. These chemicals come from a vast range of sources, such as exhaust emissions, painting, textile printing, petrochemical, coal chemical industry, etc. − VOCs are of various types and can be categorized into polar and nonpolar VOCs according to the degree of polarity of molecules. − Up to date, many different technologies have been proposed to eliminate VOC emissions, including adsorption, , condensation, catalytic oxidation, biodegradation, and other recovery and removal methods. In these processes, adsorption–desorption has been considered the most efficient method of removing and recovering organic pollutants .…”

Atomic Heat Contributions for Carbon Dioxide Adsorption in IRMOF-1

“…In cooperation with experiments, computer simulation has been widely used and plays an important role in revealing both macroscopic and microscopic behavior as well as details of the adsorption on a atomistic level and can serve as a large-scale prescreening tool. , The grand canonical Monte Carlo (GCMC) simulation technique is commonly used in studying gas adsorption. Several GCMC studies of total isosteric heat for CO 2 adsorption in IRMOF-1 have been reported in the literature, − and a few papers have appeared which distinguish the fluid–fluid (F–F) and fluid–solid (F–S) interactions for CO 2 adsorption on other MOFs. , It has been noted that the isosteric heat of adsorption at low loadings (in the Henry Law region) can be attributed to the interaction energy between an adsorbate molecule and the most favorable binding sites in the adsorbent. − Although the heat data are essential in the design of adsorbent materials, to the best of our knowledge, the separate heat contributions between CO 2 or other adsorbates and each atom type in IRMOF-1 and other MOFs have not been explored.…”