Gas adsoprtion phenomenon in microporous zeolite adsorbent

Gas adsorption on zeolites gains remarkable attention in this new era of nanotechnology since it has industrial importance in many process industries. Efforts of chemists during the past few decades have advanced the field of synthesis and accelerated the development of zeolites with different physicochemical properties for specific application. New technologies involving gas separation, gas purification, gas storage, high temperature gas sensor, semiconductor material hold a great promise for industrial applications. In order to develop and design an efficient and economically feasible industrial adsorption process, it is important to understand the adsorption phenomena between solid and gas phases. The presence of metal cations in the extra-framework structure determines the accessibility of gas molecules into the zeolite framework. In addition, the selectivity and capacity of adsorption is also being influenced by the adsorbate-adsorbent interactions. The molecules may interact through dispersion, induction, field-quadrapole and/or repulsion forces. Hence, information on physicochemical properties of zeolites as well as the properties of adsorbent is equally important in order to understand gas adsorption phenomena in zeolite microstructures. Results of this study show that structural properties and adsorbate-adsorbent interactions affect gas adsorptive characteristics of zeolites

Gas adsorption isotherm, pore size distribution, and free volume fraction of polymer-polymer mixed matrix membranes before and after thermal rearrangement

Producción CientíficaIn this work, CO2 adsorption at 273.15 K and N2 adsorption at 77 K of mixed matrix membranes has been studied, as a method to directly determine their fractional free volume (FFV). These membranes consist of a continuous phase of copoly(o-hydroxyamide)s (HPA) or copoly(o-hydroxyamide-amide)s (PAA) and a relatively highly porous polymer network filler (PPN1). Both the pure copolymers and the mixed matrix membranes (MMMs) have been analyzed before and after a thermal rearrangement (TR) process. The CO2 adsorption results have allowed characterizing the pore size distribution of the studied membranes in the 3–15 Å range, by using the Non-Local Density Functional Theory (NLDFT). Whereas the N2 adsorption has allowed determining the pore size distributions in the range between 20 and 250 Å. The experimental determination of the pore volume and the density allows the direct calculation of the membranes’ free volume fractions, which were in good agreement with the most usual FFV evaluation methods. In addition, part of the pore volume detected by N2 adsorption was associated with defects and poor integration of the membrane components. This correction has allowed us to make a new evaluation of the density of these materials.Gobierno de España (AEI) proyects (PID2019-109403RB-C21/AEI/10.13039/501100011033 y PID2019-109403RB-C22/AEI/10.13039/501100011033)Junta de Castilla y León - EU-FEDER (CL-EI-2021-07, UIC082

Improving gas sensing properties of graphene by introducing dopants and defects: a first-principles study

The interactions between four different graphenes (including pristine, B- or N-doped and defective graphenes) and small gas molecules (CO, NO, NO2 and NH3) were investigated by using density functional computations to exploit their potential applications as gas sensors. The structural and electronic properties of the graphene-molecule adsorption adducts are strongly dependent on the graphene structure and the molecular adsorption configuration. All four gas molecules show much stronger adsorption on the doped or defective graphenes than that on the pristine graphene. The defective graphene shows the highest adsorption energy with CO, NO and NO2 molecules, while the B- doped graphene gives the tightest binding with NH3. Meanwhile, the strong interactions between the adsorbed molecules and the modified graphenes induce dramatic changes to graphene's electronic properties. The transport behavior of a gas sensor using B- doped graphene shows a sensitivity two orders of magnitude higher than that of pristine graphene. This work reveals that the sensitivity of graphene-based chemical gas sensors could be drastically improved by introducing the appropriate dopant or defect

Computer program calculates and plots surface area and pore size distribution data

Computer program calculates surface area and pore size distribution of powders, metals, ceramics, and catalysts, and prints and plots the desired data directly. Surface area calculations are based on the gas adsorption technique of Brunauer, Emmett, and Teller, and pore size distribution calculations are based on the gas adsorption technique of Pierce

Gas adsorption in active carbons and the slit-pore model 2 : mixture adsorption prediction with DFT and IAST

We use a fast density functional theory (a 'slab-DFT') and the polydisperse independent ideal slit-pore model to predict gas mixture adsorption in active carbons. The DFT is parametrized by fitting to pure gas isotherms generated by Monte Carlo simulation of adsorption in model graphitic slit-pores. Accurate gas molecular models are used in our Monte Carlo simulations with gas-surface interactions calibrated to a high surface area carbon, rather than a low surface area carbon as in all previous work of this type, as described in part 1 of this work (Sweatman, M. B.; Quirke, N. J. Phys. Chem. B 2005, 109, 10381). We predict the adsorption of binary mixtures of carbon dioxide, methane, and nitrogen on two active carbons up to about 30 bar at near-ambient temperatures. We compare two sets of results; one set obtained using only the pure carbon dioxide adsorption isotherm as input to our pore characterization process, and the other obtained using both pure gas isotherms as input. We also compare these results with ideal adsorbed solution theory (IAST). We find that our methods are at least as accurate as IAST for these relatively simple gas mixtures and have the advantage of much greater versatility. We expect similar results for other active carbons and further performance gains for less ideal mixtures

Gas adsorption in active carbons and the slit-pore model 1 : pure gas adsorption

We describe procedures based on the polydisperse independent ideal slit-pore model, Monte Carlo simulation and density functional theory (a 'slab-DFT') for predicting gas adsorption and adsorption heats in active carbons.A novel feature of this work is the calibration of gas-surface interactions to a high surface area carbon, rather than to a low surface area carbon as in all previous work. Our models are used to predict the adsorption of carbon dioxide, methane, nitrogen, and hydrogen up to 50 bar in several active carbons at a range of near-ambient temperatures based on an analysis of a single 293 K carbon dioxide adsorption isotherm. The results demonstrate that these models are useful for relatively simple gases at near-critical or supercritical temperatures

Modeling of gas adsorption on graphene nanoribbons

We present a theory to study gas molecules adsorption on armchair graphene nanoribbons (AGNRs) by applying the results of \emph{ab} \emph{initio} calculations to the single-band tight-binding approximation. In addition, the effect of edge states on the electronic properties of AGNR is included in the calculations. Under the assumption that the gas molecules adsorb on the ribbon sites with uniform probability distribution, the applicability of the method is examined for finite concentrations of adsorption of several simple gas molecules (CO, NO, CO$_2$, NH$_3$) on 10-AGNR. We show that the states contributed by the adsorbed CO and NO molecules are quite localized near the center of original band gap and suggest that the charge transport in such systems cannot be enhanced considerably, while CO$_2$ and NH$_3$ molecules adsorption acts as acceptor and donor, respectively. The results of this theory at low gas concentration are in good agreement with those obtained by density-functional theory calculations.Comment: 7 pages, 6 figure