Linking Fluid Densimetry and Molecular Simulation: Adsorption Behavior of Carbon Dioxide on Planar Gold Surfaces

Abstract

Phase equilibria of fluid substances and their mixtures are important in numerous scientific as well as industrial applications and are, therefore, a major focus of thermophysical property research. For the development and improvement of thermophysical property models, reliable experimental data are crucial. However, measurements of thermophysical properties in the vicinity of the dew line can be substantially distorted by surface phenomena such as adsorption and capillary condensation on the quasi nonporous metal surfaces of the experimental apparatuses. To support the qualitative understanding of these phenomena on an atomistic level and to estimate their impact on experiments, we performed classical molecular dynamics (MD) simulations. As a first proof-of-concept investigation, we focused on pure CO2 on an idealized face-centered cubic (fcc) {111} gold surface. The results, in the form of an adsorption isotherm at T = 283.15 K, are compared to sorption measurements using a specially designed gold sinker incorporated in an optimized gravimetric sorption analyzer. This first comparison between atomistic MD simulations and gravimetric experiments helps in assessing the applicability of our simulation technique and paves the way for a deeper understanding of the relevant surface phenomena occurring in our apparatus.

Net, Excess, and Absolute Adsorption of N2, CH4, and CO2 on Metal–Organic Frameworks of ZIF-8, MIL-101(Cr), and UiO-66 at 282–361 K and up to 12 MPa

“…Adsorption measurements were carried out with a gravimetric sorption analyzer (Rubotherm, Germany; since 2016, TA instruments, USA) incorporating a magnetic-suspension balance. This type of instrument has been widely used for accurate adsorption measurements at high pressures, ,, and it is able to measure the adsorption of nonporous materials after improvements in accuracy. , The key information of our measurement system was summarized previously. , The measurement system operates over the temperature range from 263 to 423 K and pressures up to 35 MPa with expanded measurement uncertainties ( k = 2) being 0.30 K in temperature, 4.1 kPa in pressure, and 90 μg in mass.…”

Adsorption of CO2 at T = 298 K and Pressures up to 6 MPa on Quasi Nonporous Al13Fe4

“…Apart from aluminum, other prominent examples include industrially important metals such as zinc, chromium, nickel, and titanium. , In general, the oxide layers of these metals are mainly terminated by OH-groups, which can undergo condensation reactions with a variety of reagents. , However, the increased specific surface area of the material due to surface oxidation comes with an increase of adsorption capacity of atmospheric components or solvents used during fabrication processes (e.g., storage and cleaning) at ambient temperature. As well, irregularities in the surface structure may lead to a superposition of adsorption and capillary condensation in pore-like formations. , We hypothesize that, the unknown consequences of sorption effects and contamination layers may result in a change of adhesion mechanisms and material composition at the surface.…”

“…Common commercial instruments usually cannot achieve such accuracy, therefore, measurements were conducted using an optimized gravimetric sorption analyzer based on a magnetic suspension balance. This apparatus, already presented and tested in previous works, , allows measurements of very small adsorption capacity. In the present work, the experimental adsorption capacity ranges between (0.002 and 0.632) with combined expanded uncertainties ( k = 2) in the range of (0.001 to 0.025) , which is almost an order of magnitude smaller compared to a common commercial instrument …”

“…As well, irregularities in the surface structure may lead to a superposition of adsorption and capillary condensation in pore-like formations. 9,10 We hypothesize that, the unknown consequences of sorption effects and contamination layers may result in a change of adhesion mechanisms and material composition at the surface.…”

“…10.1021/acs.jced.1c00897. Chemical processes, graphical results of XRD analysis, mass calibration and BET-multipoint description, tables and figure reporting the volumetric data, and tables and figure reporting the gravimetric measurements and the uncertainty analysis results (PDF) Machine readable data (ZIP)…”