Adsorption最新文献

We report a molecular simulation study on the adsorption-based trapping of different gaseous contaminants using nanoporous materials. In more detail, in the context of gas decontamination for space applications, we focus on adsorption from low pressures up to larger pressures of specific molecules ranging from water, hydrocarbons, and siloxanes. As far as the nanoporous adsorbents are concerned, we restrict the present study to a set of prototypical materials: an active carbon, a zeolite and a metal-organic framework. In addition to discussing the ability of each material type to adsorb specific gas molecules, we illustrate how simple descriptors such as Henry’s constant in the low-pressure range (K_text {H}) and the pressure (alpha) at which half the nanoporosity gets filled can be used to rationalize and design molecular “getters” for space decontamination. Finally, by considering a specific yet representative binary gas mixture, we show that the adsorption of hydrophilic molecules– water– and hydrophobic molecules– siloxane– occurs without competitive/collective adsorption effect (provided adsorption occurs at low to moderate pressures).

The Redlich-Peterson isotherm is widely used in liquid phase adsorption studies but the combination with the Ideal Adsorbed Solution Theory is hampered by the fact that an analytical expression for the reduced grand potential does not exist in the range of low pressures or concentrations. In this contribution we demonstrate an efficient approach to approximate the reduced grand potential using a Padé approximant allowing to perform the calculations with the Fast-IAS algorithm leading to execution times that are slightly slower but comparable to a dual site Langmuir/Fast-IAS combination. While the non-autonomous initial value approach remains a simpler method for this isotherm, the proposed method is recommended when execution times have to be minimized.

This work outlines the foundations for conducting a first-principle study of the adsorption process using the steepest-entropy-ascent quantum thermodynamic (SEAQT) framework, a method capable of predicting the unique non-equilibrium path a system follows from an initial state to stable equilibrium. To account for multi-component adsorption, the SEAQT framework integrates the particle number operator for each adsorbed species directly into its equation of motion. The framework is a unified approach for describing both adsorption kinetics and equilibrium isotherms. At equilibrium, it aligns well with classical isotherm models, while out of equilibrium, it provides a consistent description of adsorption kinetics in terms of grand potentials. The theoretical predictions are validated through initial comparisons with experimental data from the literature and show good agreement. Furthermore, the SEAQT framework achieves this without requiring a priori knowledge of specific adsorption mechanisms. Additionally, it reveals the relationship between intensive thermodynamic properties during kinetic change to out-of-equilibrium fluctuations, underscoring the relevance of non-equilibrium thermodynamics to measurable physical quantities. : .

Organic pollution is a major environmental issue that requires the deployment of steps to lower the organic content of water. In this study, Glycidyl methacrylate (GMA) functionalized Zr-MOF was fabricated and employed as a selective adsorbent in PW to reduce COD level. XRD, EDX, BET, PSA and FT-IR were employed to investigate the properties of the synthesized MOF. The synthesized MOF has an enormous surface area of 1144 m^2/g, a mean pore diameter of 2.84 nm, and an overall pore volume of 0.37 cm³/g. Investigating the effects of pH (2–12), contact time (10–120 min), and adsorbent dose (0-2000 mg/L) on COD % removal allowed us to assess the effectiveness of UiO-66-GMA. The results demonstrated that at pH 8 and a 500 mg/L dose of MOF, COD removal efficiency increased from 35.2 to 94.67%. Additionally, as contact time was extended from 10 to 50 min, the removal efficiency improved from 52.78 to 92.4%. Adsorption isotherm analysis revealed that the pseudo-second-order kinetic and Freundlich isothermal models provided a very good match to the adsorption data (R² = 0.98). A maximum COD removal efficiency of 96.12% was reported. Based on the current research, it is feasible to draw the conclusion that Zr-functionalized MOFs are an efficient adsorbent for the adsorption of organic contaminants.

Automated sorption balances are widely used for characterizing the interaction of water vapor with hygroscopic materials. This paper is part of an interlaboratory study investigating the stability and performance of automated sorption balances. A previous paper in this study investigated the mass, temperature, and relative humidity (RH) stability of automated sorption balances by looking at the mass change of a non-hygroscopic sample over time. In this study, we examine the mass stability of wood samples held at constant RH for seven to ten days after a step change. The reason for the long hold times was to collect data to “operational equilibrium” where the change in mass is on the order of the inherent operational stability of the instrument. A total of 80 datasets were acquired from 21 laboratories covering absorption with final RH levels ranging from 10 to 95%. During these long hold times, several unusual behaviors were observed in the mass-vs-time curves. Deviations from expected sorption behavior were examined by fitting the data to an empirical sorption kinetics model and calculating the root mean square error (RMSE) between the observed and smoothed behavior. Samples that had a large RMSE relative to the median RMSE of the other datasets often had one of several types of errors: abrupt disturbances, diurnal oscillations, or long-term mass decline during an absorption step. In many cases, mass fluctuations were correlated with changes in the water reservoir temperature of the automated sorption balance. We discuss potential errors in sorption measurements on hygroscopic materials and suggest an acceptable level of RMSE for sorption data.

Adsorption kinetics has been regarded as one of the most critical factors determining the productivity and economic feasibility of direct air capture (DAC) of CO₂, but has received relatively little attention compared with adsorption thermodynamics. One commonly used method for kinetics investigation is thermogravimetric analysis (TGA) which suffers from gas diffusion limitations and often underestimates adsorption rates. Here, a modified TGA system equipped with a porous self-made crucible was employed to address the gas diffusion challenges and analyze the kinetic behaviors of three polymeric chemisorbents, including Lewatit VP OC 1065, for DAC. The obtained adsorption kinetics were successfully applied to simulate and describe the breakthrough behaviors in a fixed-bed column. The CO₂ adsorption/desorption kinetics of chemisorbents with different amine structures or loadings were measured at various temperatures and described through the linear driving force model. The present work offers a reliable and fast kinetics analysis approach for DAC, paving the way for accurately collecting the kinetics parameters used for guiding further adsorbent and process design.

Graphic abstract

Metal-organic frameworks (MOFs) are 3-dimensional coordination polymers which contain metals and organic linkers. MOFs are of strong interest in the fields of separation, catalysis, chemo-sensing, and pollution remediation. MOFs are highly desired, which have complex and controlled composition, structure and functional properties. Here, we report the copper porphyrin aluminum MOF (actAl-MOF-TCPPCu) denoted compound 4, and mechanistic and kinetic studies of adsorption of volatile organic sulfur compound, diethyl sulfide (DES) by it. The characterization is conducted by qualitative and quantitative methods, structural analysis with the Rietveld crystal lattice refinement, and complementary microscopy and spectroscopy. Then a comprehensive study of mechanism and kinetics of DES sorption is presented, under the dynamic conditions in the flow of air. The latter is conducted by a novel method of in-situ time-dependent ATR-FTIR spectroscopy in the controlled environment. The binding sites of DES include the µ(O–H), the COO⁻ group, phenyl and pyrrole groups and they are ranked by the strengths of bonding. The kinetics of sorption obeys the Langmuir model of the pseudo-first order rate law with effective rate constant k_eff = 0.95 ± 0.05 min^− 1. Moreover, the linear dependence of kinetic rate constant on concentration of DES suggests that the sorption is diffusion limited. The sorption of DES in the static equilibrium conditions results in the binary stochiometric adsorption complex with formula (Al-MOF-TCPPCu)₂(DES)₇. Finally, a facile regeneration of the adsorption complex was achieved, without using chemicals. The copper-containing porphyrin aluminum MOF and related materials are promising for the removal of volatile organic sulfur compounds from air.

Towards the beneficiation of agricultural waste for water treatment and energy, Hura crepitans pods (HC), pyrolysed at 500, 600 and 700 °C with holding times of 30 and 60 min, were modified with chitosan and used for the adsorption of methylene blue. The biochar was characterised using pH of point of zero charge (pHpzc), elemental analysis, BET, FTIR spectroscopy, XRD and SEM–EDX. The pHpzc of HC was 9.2 and elemental analysis showed that the % carbon of the biochar was higher than that of the feedstock. The higher heating value of HC biochar was greater than 20 MJ kg⁻¹; projecting it as alternative solid-fuel source. The biochar appeared in the region for anthracite on van Krevelen diagram. Modification of the biochar with chitosan decreased the BET surface area. The FTIR spectra showed distinctive functional groups responsible for adsorption, XRD depicted the amorphous nature of the biochar. The adsorption capacity of HC biochar increased as the pyrolytic temperature and holding time increased from 500 to 700 °C and 30 to 60 min, respectively. Langmuir isotherm and pseudo-second order kinetic models gave the best fit to the experimental data. The monolayer adsorption capacity of HC7B biochar was 48.78 mg g⁻¹. Thermodynamic parameters showed that the adsorption process was endothermic, disorderly and spontaneous. The mechanism of adsorption was mainly by non-electrostatic interaction such as π-π interaction. The highest percentage desorption was achieved with 0.1 M H₂SO₄ and HC biochar was successfully regenerated after 5 cycles. Hura crepitans pod biochar was effective in the adsorption of MB from aqueous solution and modification with chitosan improved its adsorption capacity.

This Density Functional Theory (DFT) study, utilizing the B3LYP-D3 functional with a 6-311+ +G(d,p) basis set, explores the efficacy of B₁₂N₁₂ and B₁₂P₁₂ nanocages for detecting Bromochlorodifluoromethane (BCF), a potent greenhouse gas and ozone-depleting substance. Our investigations reveal that both B₁₂P₁₂ and B₁₂N₁₂ nanocages show a notable affinity for BCF. Specifically, B₁₂P₁₂ nanocage demonstrates a stronger interaction with BCF, evidenced by an interaction energy of − 23.89 kJ mol⁻¹ compared to − 20.17 kJ mol⁻¹ for BCF@B₁₂N₁₂. The interaction energy, along with charge transfer and non-covalent interaction (NCI) analyses, confirms the physisorption nature of the BCF adsorption on the nanocages. UV/Vis spectroscopy predicts significant bathochromic shifts upon BCF adsorption, indicating potential for optical sensing. Moreover, BCF adsorption significantly reduces the HOMO-LUMO gap by 43.9% for BCF@B₁₂P₁₂ and by 22.3% for BCF@B₁₂N₁₂, thereby enhancing conductivity. This increased conductivity can be converted to an electrical signal, that correlates with the presence of BCF in the environment, affirming the potential of these nanocages as effective BCF detectors.

In the field of chemical engineering, achieving deep thiophene removal from coked benzene is a formidable challenge. This, coupled with the limitation of low sulfur capacity, has been major obstacle to the large-scale application of adsorption desulphurisation technology. In this study, Ni-Pt/Al₂O₃-CA adsorbent was prepared. The citric acid treated γ-Al₂O₃ was used as the carrier, and Ni-Pt bimetal as the active component. The relationship between the microstructure and adsorption performance of the adsorbent was investigated by BET, XRD, SEM, TEM, TPR, XPS and Py-FTIR. The results showed that the Ni-Pt/Al₂O₃-CA adsorbent could not only reduce the thiophene content in benzene to less than 10 ppb but also had sulfur capacity of 2.73 mg S/g compared with the monometallic adsorbent. The adsorption performance of the Ni-Pt/Al₂O₃-CA adsorbent was restored to 95% of the initial one after three repetitive experiments. Meanwhile, based on the kinetic modelling results, the quasi-secondary kinetic model fitted the adsorption data of thiophene on Ni-Pt/Al₂O₃-CA adsorbent better. And the process of thiophene adsorption was described in depth in the diffusion model.