Adsorption最新文献

Abstract

The carbonization temperature of carbon precursors before their activation is an important factor affecting the porous structure and properties of the resulting activated carbons. In this work сorrelation between the textural and adsorption properties of asphalt-based porous carbons and the carbonization temperature has been found. Additionally, the optimal carbonization temperature, and reasons why the carbonization temperature affects the main textural characteristics of the activated carbon were established. A series of porous carbons has been prepared from petroleum asphalt by a two-stage method, including carbonization of asphalt at different temperatures from 450 to 800 °C and KOH activation. To reveal the reasons of the correlation the carbonized samples were studied by TG-DTG, IR-Fourier, TEM methods. It is shown that the carbonization temperature effects on the structural defects, distance between the graphene layers, the reactivity and thermal stability of the carbonized asphalts. These specificities contribute to formation of porous structures of the activated carbons. The carbonization temperature 500–600 °С of the petroleum asphalt is found to be the optimal for further activation. The KOH activation of the petroleum asphalts carbonized at 500–600 °С provides microporous carbon with the high specific surface area (about 2000 m²g^-1) and the CO₂ uptake (3.3 mmolg^-1). Additionally, the specific surface area of the activated carbons is shown can be predicted from the temperature of 50% (T_50%) mass loss of the carbonized petroleum asphalt. The linear dependence of the T_50% on BET surface area can be fitted by T_50%=640–0.424S_BET with determination coefficient R² equal to 0.96.

Abstract

Water adsorption capacities of various adsorbents reported in the literature were investigated to define a hydrophobicity index that was plotted vs. water capacity. In this plot, logarithmic curves were proposed to be used as indicators of performance limits of adsorbents, especially for adsorption heat pumps. In spite of their useful adsorption properties, zeolites generally exhibited quite low hydrophobicity, remaining well below the logarithmic curve. In this study, the use of composites of zeolite NaY was examined both theoretically and experimentally for improvements in the water capacity and hydrophobicity. Salt impregnation and hydrothermal synthesis experiments were performed to prepare composites of zeolite NaY with LiCl/MgCl₂ salts and activated carbon, respectively. Water capacity and hydrophobicity of zeolite NaY composites were generally superior to those of pure zeolite. Zeolite composites may be advantageous for enhancing adsorption capacity and hydrophobicity of zeolites while eliminating low stability and slow adsorption kinetics of other adsorbents. Interface between two different phases might indicate another opportunity to provide improved adsorption properties for zeolite composites.

Ion exchange is the reversible exchange of ions in which there is no significant change in the solid structure. Zeolites are aluminosilicates with a defined structure, including cavities occupied by cations and water molecules, both with great freedom of movement, which makes cation exchange possible. In this study, small-pore zeolites chabazite (CHA) and clinoptilolite (CLI) were ion-exchanged with potassium. Then, the samples were characterized by N₂ isotherms at 77 K, CO₂ adsorption microcalorimetry at 298 K, and water vapor isotherms at 313 K. A mathematical model was applied to evaluate the adsorption kinetics for water vapor uptakes. Textural analysis showed that the ion exchange with potassium decreased the porosity of both zeolites, but CO₂ microcalorimetric data showed that these samples had higher CO₂ adsorption enthalpy, indicating a greater sorbate-sorbent interaction as compared to the pristine zeolites. Uptake rate curves suggest water diffusion is not appreciably altered after ion exchange. Interestingly, despite the larger size of K⁺ cations as compared to Na⁺, effective diffusion time constant is on order of magnitude larger for the potassium-loaded CLI very likely due to the leaching of other contaminants upon ion-exchange.

Abstract

Desulfurization is a necessary process to reduce the corrosiveness of natural gas. In this regard, H₂S adsorption on porous materials has gained attention in the development of new eco-friendly technologies. Although there are many experimental and theoretical studies about gas adsorption on MOFs, so far, there has been no theoretical work about desulfurization of natural gas or biogas through H₂S adsorption on MOF BTC. Therefore, the objective of this study was to preselect by ab initio calculations which metal center M²⁺, such as Co²⁺, Ni²⁺, Cu²⁺, or Zn²⁺, has the highest potential for selective desulfurization of natural gas. DFT calculations were performed at B3LYP-D3/6-311++G(2d,p)+LanL2DZ level for H₂O, H₂S, COS, CO₂, and CH₄ adsorption on M-BTC MOF clusters in order to obtain adsorption complex equilibrium geometries, adsorption energies and thermodynamic properties. It was found that Zn-BTC MOF cluster has the highest potential for selective H₂S removal from dry natural gas streams, since its adsorption energy is −79.4 kJ mol⁻¹, which is 2.4 times higher than CH₄. Furthermore, H₂S adsorption on Zn-BTC MOF is an exothermic process and thermodynamically favorable. Through NBO and EDA analyses, it was found that d electrons transfer from adsorbate to metal center unoccupied orbitals contributes mainly to a possible H₂S chemisorption on Zn-BTC and Co-BTC, while for CO₂ and CH₄ adsorption, non-bonded interactions predominate. Most of the gases coordinate to coordinatively unsaturated site of BTC MOF cluster at axial position, indicating a stronger interaction with metal center compared to linkers.

Abstract

Organic azo-dyes, including Congo Red, present a significant environmental concern due to their widespread industrial usage and resistance to biodegradation, leading to severe contamination of effluents. This study explores the efficacy of two basic perovskites (MSnO₃, where M = Ca and Sr) in removing Congo Red by adsorption, offering a potential solution for wastewater treatment. The synthesis of the adsorbents was performed by a coprecipitation technique, an effective and no-waste producing method. By adjusting reaction conditions, the physical-chemical characteristics of the perovskites, including crystallinity, morphological features, surface area and porosity, were controlled. Adsorption studies conducted across a range of Congo Red concentrations (10–100 mg L^− 1) at pH 10 revealed MSnO₃ to possess exceptional adsorption capacity exceeding 100 mg per gram. The results indicate irreversible adsorption and potential adsorbent regeneration by thermal treatment. Slow kinetics also suggest strong binding forces aligned with the fundamentals of pseudo-second-order adsorption kinetic model. Regarding the impact of the synthesis parameters, while the precipitation conditions may not significantly influence adsorption performance, perovskite samples synthesized at higher temperatures are considered more suitable for this application due to their enhanced stability and regenerative capabilities for repeated use. Estimated correlations between sample parameters and adsorption efficiency provide a valuable insight for the practical application of oxide perovskites in addressing dye contamination issues.

Abstract

Emissions of carbon dioxide (CO₂) from fossil fuel usage continue to be an incredibly challenging problem to the attainment of CO₂ free global economy; carbon Capture and Storage (CCS) and the substitution of fossil fuel with clean hydrogen have been identified as significant primary techniques of achieving net zero carbon emissions. However, predicting the number of gases trapped in the geological storage media effectively and safely is essential in attaining decarbonization objectives and the hydrogen economy. Successful underground storage of carbon dioxide and hydrogen depends on the wettability of the storage/cap rocks as well as the interfacial interaction between subsurface rocks, the injected gas, and the formation of brine. A key challenge in determining these factors through experimental studies is the presence of conflicting contact angle data and the difficulty of accurately replicating subsurface conditions in the laboratory. To address this issue, molecular dynamics simulations offer a microscopic approach to recreating subsurface conditions and resolving experimentally inconsistent results. Herein, we report the molecular dynamics simulation results for hydrogen (H₂) and cushion gas (e.g., CO₂ and N₂) on quartz surfaces to understand the capillary and trapping of these gases in sandstone formations. The results of these three gasses were compared to one another. The simulation predictions showed that the intermolecular interactions at the CO₂-quartz surface area are more substantial than at the N₂ and H₂-quartz interface, suggesting that the quartz surface is more CO₂-wet than N₂ and H₂-wet under the same circumstances. In addition, it was found that CO₂ has a substantially higher adsorption rate (∼ 65 Kcal/mol) than N₂ (∼ 5 Kcal/mol) and H₂ (∼ 0.5 Kcal/mol). This phenomenon can be explained by the fact that CO₂ density is substantially larger than N₂/H₂ density at the same geo-storage conditions. As a result, CO₂ could be the most favorable cushion gas during underground hydrogen storage (UHS) because a higher CO₂ residual is expected compared to H₂. However, due to the Van der Waal Interaction force with quartz, only a small amount of H₂ can be withdrawn.

Abstract

Dynamic adsorption is important for evaluating the Volatile Organic Compounds (VOCs) adsorption performance. During adsorption process, the exothermal characteristic could lead to an increase of the column temperature, which might cause bed combustion and is negative to the adsorption efficiency. In present study, we chose graphene oxide(GO) as adsorbent, comparing with hypercrosslinked polymeric adsorbent(HPA), and conducted the dynamic adsorption experiment of ethanol, n-hexane and cyclohexane at 308 K, 318 and 328 K with different adsorbent column height. The results showed that the temperature had linear and negative influence on breakthrough capacity for three VOCs on two adsorbents. And the breakthrough adsorption capacity of ethanol, n-hexane and cyclohexane on two adsorbents were as follows: ethanol > cyclohexane > n-hexane, closely related with physical parameters of VOCs. But the physical properties of ethanol, n-hexane and cyclohexane have little influence on dynamic adsorption rate in this paper. In addition, for n-hexane and cyclohexane, the breakthrough adsorption capacity on HPA were higher than that on GO, but their k values were similarity on HPA and GO. While for ethanol, the breakthrough capacity and k value on GO were higher than HPA. Most important of all, the negative effect of temperature on VOCs adsorption on GO was lower than HPA. Therefore, GO is a good alternative adsorbent for VOCs recovery. Furthermore, with higher column height, the dynamic adsorption capacity was higher but the adsorption rate was lower. While the influence of temperature on dynamic adsorption capacity and rate were relative independent with column height of adsorbent.

Density functional theory (DFT) calculations were utilized to evaluate the adsorption of cyano radical (^.C≡N) on H-capped (5, 0), (6, 0), and (8, 0) zigzag aluminum nitride nanotubes (AlNNTs) and the results were compared to the adsorption on a (6, 0) zigzag aluminum phosphide nanotube (AlPNT). The most stable configuration (C-side) involves the attachment of CN to the outer surfaces of pure AlPNT and AlNNT via a covalent bond. The adsorption energy of^.CN on the (5, 0) AlNNT surface, with a tube diameter of 4.82 Å and length of 16.4 Å, was found to be -253.17 kJ mol⁻¹ through N-side (IV) and -259.12 kJ mol⁻¹ through C-side (V), indicating a chemisorption process. The adsorption of^.CN through the C-side on (5, 0) AlNNT is more stable than through the C-side on (6, 0) and (8, 0) AlNNTs. Natural bond orbital (NBO) revealed that in these configurations, there was a charge about 0.254 (C-side) and 0.357 (N-side) |e| transferred from the (5, 0) AlNNT to the^.CN as an electron acceptor, demonstrated by a strong orbital hybridization during the adsorption process. The decrease in softness, energy gap, and electrophilicity of^.CN-adsorbed AlNNT can indicate a shift toward enhanced stability and reduced reactivity. Increasing the diameter and length of AlNNTs leads to significant alterations in the structural and electronic features of the nanotubes, as suggested by our findings. The analysis of the total density of states (DOS) illustrated the interaction between^.CN and the nanotube surfaces resulted in alterations in the electronic structure of the nanotubes.

The sorption of Zr(IV) and Y(III) was examined using an iron-tin silicate (FeSnSi) composite prepared by the co-precipitation technique. The analytical tools that characterize prepared composite are FT-IR, SEM, EDX, XRD, and XRF. The effects of temperature, pH, ion concentrations, and shaking time are all considered in the sorption studies conducted on Zr(IV) and Y(III). The sorption of studied metal ions depends on pH, and the pseudo-2nd-order model governs the kinetics of reactions. Negative Gibbs energy values confirmed the excellent feasibility and spontaneity of the sorption process. Positive enthalpy values indicate that this process was endothermic. Positive entropy values demonstrated that the disorder between the solid and liquid phases was enhanced during adsorption. Freundlich and Langmuir models are used to study isotherms. The results of the binary system verify that Zr(IV) may be separated from the Zr-Y system at various pHs. According to the findings, the produced composite may effectively remove Zr(IV) and Y(III) from aqueous solutions. It may also be viable for purifying wastewater contaminated with these metal ions.

Adsorption is the most efficient technique for the removal of toxic organic dyes and metal ions from wastewater and it demands efficient, low-cost, environment friendly and collectable adsorbents. In this study, a one-pot strategy has been developed for the crosslinking of chitosan and carboxymethyl cellulose with citric acid to form the cross-linked hydrogel. The synthesized biosorbent hydrogel was characterized by FTIR, XRD and SEM that have confirmed the successful crosslinking. The batch adsorption experiments were performed to examine the capacity of hydrogel for the adsorption of Cu(II). The optimization of the adsorption process was carried out on the basis of various factors including; metal ion concentration, time, temperature, pH, agitation speed and adsorbent dose. Different isothermal and kinetic models were applied to interpret the data. The thermodynamic studies revealed that Langmuir model was the best fit with > 90% Cu(II) removal at pH 6. The kinetic studies confirmed the suitability of pseudo-second-order kinetics with correlation coefficient (R²) value 1. Several adsorption–desorption cycles were performed to check the recovery and reusability of hydrogel without the loss of maximum adsorption capacity.