Adsorption最新文献

The selective capture of volatile organic compounds (VOCs) is a significant challenge in environmental remediation. In this study, we explore how MOF structural flexibility and the electronic properties of VOCs influence their adsorption by comparing two functionalized zeolitic imidazolate frameworks: the flexible ZIF-8_CH₃ and the rigid ZIF-8_Br. Using benzene and hexafluorobenzene as probe molecules with contrasting quadrupole moments, we demonstrate that ligand functionalization significantly impacts both structural dynamics and adsorption/separation performance. ZIF-8_CH₃ exhibits higher overall uptake capacities, reaching up to 7.3 mmol/g for hexafluorobenzene. In contrast, ZIF-8_Br shows superior separation capabilities, with IAST selectivity values reaching 17.1 for benzene/hexafluorobenzene mixtures at low pressures. Our experimental and computational analyses reveal that aromatics with negative quadrupole moments more readily appear to trigger the gate-opening phenomenon, establishing a potential correlation direct correlation between electron density distribution and molecular sieving efficiency. These findings offer new insights into the rational design of functionalized frameworks for selective VOC capture, highlighting the crucial role of electronic effects in determining host-guest interactions and separation performance.

Graphical abstract

In this study, the adsorption and sensing capabilities of the recently introduced B₂C₃N nanosheet toward several typical hazardous heavy metals including Cu (0), Cu (I), Cu (II), As (0), As (III), and V (0) were systematically investigated using density functional theory (DFT) at the B3LYP/6-311G(d, p) level. The optimized geometries, adsorption energies, electrical conductivities, and recovery times were thoroughly analyzed to evaluate the selectivity and stability of the nanosheet-metal complexes. Our results reveal that B₂C₃N exhibits strong and selective adsorption toward Cu (II) and As (III) species, with significant changes in electrical conductivity serving as reliable sensing signals. The calculated recovery times indicate practical potential for reusability and efficient desorption of certain metals. This computational insight provides a theoretical foundation for the application of B₂C₃N nanosheets in environmental remediation and heavy metal sensing. Limitations of the current gas-phase model and suggestions for future experimental validation and extended theoretical studies are also discussed to guide further research.

Fast pressure swing adsorption (FPSA) is an adsorption-based separation process with cycle durations ranging from a few to tens of seconds. While widely used in small-scale oxygen generators, FPSA still holds significant potential for improvement. In this study, we propose and demonstrate a novel rapid vacuum swing adsorption (FVSA) cycle, where adsorption occurs at atmospheric pressure and desorption under vacuum, to enhance small-scale oxygen production from air. A simulated air mixture, containing 78% nitrogen (N₂), 21% oxygen (O₂) and 1% argon (Ar), was processed through a dual-column FVSA system using LiLSX zeolite as the adsorbent. A numerical model was developed on Aspen Adsorption and validated against previously reported results. A parametric study was conducted to assess the effects of various operating conditions on separation performance. The results indicate that a low feed flow rate, low desorption pressure, and an optimal length-to-diameter (L/D) ratio improve the separation efficiency. Under operating conditions of 101.1 kPa adsorption pressure, 40.3 kPa desorption pressure, and a feed rate of 47 L/min, the system achieved a 91% O₂ product stream with a 5 L/min flowrate and 44% O₂ recovery. Compared to traditional FPSA, FVSA reduced energy consumption by 13% (39.24 vs. 33.99 kJ·mol⁻¹O₂) and lowered the air-to-oxygen ratio by 25% (14.4 vs. 10.8) while maintaining comparable O₂ purity, demonstrating its potential for more efficient oxygen production.

This study reports an anionic metal-organic framework (iMOF-A), {(H₂pa)₃[Co₃(BTCA)₃].6H₂O}_n, where H₂pa. is 1,3-propylenediamonium and BTCA is 1,2,3,4-butanetetracarboxylate. The compound, based on Co²⁺, crystallizes in a monoclinic system, (space group I2/a) with a non-interpenetrated three-dimensional pts topology. Its charge balancing is achieved by H₂pa cations located in the framework’s pores, which can be exchanged with Ni²⁺ ions. The compound was characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis, and ultraviolet-visible absorption spectroscopy. The ion-exchange properties were evaluated by substituting the propanediammonium cations with Ni²⁺ from aqueous solution. Batch experiments assessed the framework’s effectiveness in selectively adsorbing Ni²⁺, considering variables like initial metal ion concentration and contact time. The results show a high affinity for Ni²⁺ ions, attributed to the unique polymer’s structural features. This work expands the library of anionic metal-organic frameworks and provides insights into the tunable ion-exchange properties of such frameworks.

Graphical abstract

A new metal-organic framework {(H₂pa)₃[Co₃(BTCA)₃].6H₂O}_n exhibits ion exchange between pore diammonium cations and hard metals in aqueous solution, supported by structural and spectroscopic studies.

Accurate experimental adsorption equilibrium measurements are necessary for benchmarking adsorbents, validating molecular simulations and setting up process simulations. Although many sources of errors in these measurements have been reported in the literature, the purity of the gas used is generally not considered a major problem as long as research grade gases are used. In this work, we propose that significant deviations in the measured isotherms can potentially arise due to the accumulation of impurities in the measurement cell, especially in the low-pressure region, which is important for systems dealing with low partial pressure, such as (hbox {CO}_2) direct air capture (DAC). We conduct numerical studies to highlight this issue. The first part of our analysis uses the Langmuir isotherm equation to generate baseline isotherms representative of adsorbents with varying affinities for (hbox {CO}_2), enabling a parametric assessment of impurity effects. This is followed by a material-specific study examining the influence of impurities on isotherms for several zeolites and metal-organic frameworks (MOFs).

Monolithic adsorbents offer an opportunity to intensity cyclic adsorption processes, but uniformity of channel size and flow distribution have a detrimental effect on separation performance. Mathematical modelling and optimisation techniques require repeated process simulations up to cyclic steady state but the real monolith model representing the response of a distribution of channels is computationally expensive. This study explores the possibility of employing the ideal single channel monolith model to do an initial search, followed by a secondary search with the computationally more complex and more accurate real monolith model. Two case studies have been considered here to cover the different nature of the product of interest (i.e., heavy or light), and whether the optimisation is constrained or unconstrained. For unconstrained optimisation, the optimum decision variable values found with the ideal monolith model are similar to those obtained when only the real monolith model is used for all the functional evaluations (i.e., the real optimum). However, the corresponding objective function values were not the same due to the ideal and real monolith model predictions differing for certain combinations of decision variables. In this case, a quick secondary refinement search with the real monolith model yielded the real optimum objectives. In the case of constrained optimisation, the optimum objective and decision variable values predicted from the initial search differed substantially from the real optimum. Optimum values close to the real optimum could still be obtained with the two-step search strategy. The two-step search strategy required approximately half the computational effort, compared to the approach where only the real monolith model was used for all the evaluations.

Materials capable of effectively storing (hbox {H}_{2}) and (hbox {CH}_{4}) are essential for the enhancement of hydrogen and methane-based transportation. Metal-Organic Frameworks (MOFs) are strong contenders for meeting the gas storage targets of the Department of Energy (DOE). Many Cu(I)-based MOFs degrade in air and moisture. NU-2100, a newly developed Cu(I)-based MOF, shows air stability. The total and usable (hbox {H}_{2}) and (hbox {CH}_{4}) storage capacities of NU-2100 at 298.15 K and 0.5–35 MPa are calculated and analyzed by means of Grand Canonical Monte Carlo (GCMC) studies. A comparative assessment is performed, including MOFs with similar metal compositions, pore size, density and porosity at 298.15 K and 25 MPa. The findings demonstrate that NU-2100 exhibits storage capacities that match or outperform the MOFs included in this investigation. The origin of these higher capacities is that the molecules interact with the atoms of NU-2100 in wider regions or pores than in the other MOFs. The autonomy range of a hydrogen and a methane vehicle containing NU-2100 are also calculated. A hydrogen or a methane vehicle storing the gas on this new material would reach the same autonomy as a vehicle storing the gas by compression, using a larger tank volume and lower pressures.

Efficiently recovering the natural gas from the gas mixture is crucial to its application. Grand Canonical Monte Carlo (GCMC) molecular simulations were performed to screen MOFs from 100 samples covering four typical kinds of MOFs based on the selective performance of methane and carbon dioxide mixtures at 298 K and 0–0.1 MPa. Incorporation was introduced to ameliorate the performances of the selected MOFs, and the effect of mixing carbon molecular sieve (CMS), activated carbon and graphene oxide (GO) on the structure, the adsorption selectivity as well as the adsorbent performance score (APS) for carbon dioxide was also evaluated. Researches were conducted on the samples by performing the structural characterization, microscopic morphology observation and the measurements of the adsorption isotherms of methane and carbon dioxide. It shows that, at 298 K under pressure 0.1 MPa, the adsorption selectivity coefficient for the gas mixture contained the equal molar volume fraction of methane and carbon dioxide on Ni-MOF-74 is about 60 and the APS is larger than 500; within the range of incorporated amount 1–15 wt%, only the sample prepared by 5 wt% GO respectively obtained 15.4% and 47.9% increment in the adsorption selectivity coefficient and the adsorption capacity of CO₂. Results also reveal that, during three adsorption and desorption cycles, the fluctuation amplitude of the adsorption capacity, adsorption selectivity coefficient, APS on the sample can all be kept within 0.03%, and the largest adsorption selectivity coefficient is about 25.65 with 4.1% increment in APS within the molar volume fraction range of methane 50–90%. It suggests that the composite of Ni-MOF-74 incorporated by 5 wt% GO is suitable for separating the natural gas from the mixture of methane and carbon dioxide.

Nutrient recovery from sewage wastewater through nanomaterial adsorbents is a promising method for reducing environmental pollution and recycling essential nutrients. In this study, various adsorbents, specifically Chitosan (CHI), Ceramic-based Zeolite nanomaterial (N-Zs), and Silica-assisted Nano hemicellulose (Si-NHC), were prepared to analyze their capacity to adsorb NH₄⁺ and PO₄³⁻ from synthetic and real wastewater sources. The study revealed a notable adsorption capacity of 84.734 ± 10.165 mg/g and 0.192 ± 0.024 mg/g for NH₄⁺ and PO₄³⁻, respectively, by Si-NHC. The hydrothermally synthesized N-Zs show poor efficiency compared to other adsorbents. Optimal conditions for NH₄⁺ adsorption were identified at a pH of 5.5, utilizing 0.1 g of Si-NHC per 50 ml of solution, with a contact time of 2.5 h. An economic analysis of NH₄⁺ recovery from treated wastewater indicated advantages due to its lower cost and higher adsorption capacity. The higher adsorption capacity and degradable nature position Si-NHC as a viable candidate for use as a fertilizer. The detailed adsorption and desorption cycle durability and efficiency of the Si-NHC were also evaluated.