Selective Adsorption Research Articles

Adsorption of fluorine from lepidolite hydrometallurgy wastewater by aluminum modified zeolite.

Fluoride contamination is a serious environmental problem in lepidolite hydrometallurgy wastewater. The treatment of fluoride-bearing wastewater is challenging because of the presence of coexisting ions including lithium (Li+), rubidium (Rb+), silicate (SiO32-), sulfate radical (SO42-). However, aluminum-modified zeolite (Al@zeolite) with sufficient hydroxyl groups and high adaptability has unique advantages for eliminating fluoride from lepidolite hydrometallurgy wastewater. Al@zeolite was prepared on natural zeolite by an atmospheric process and then used for the adsorption of fluorine from fluoride-bearing wastewater produced by the lepidolite hydrometallurgy process. The results of material characterization confirmed the successful immobilization of aluminum within the zeolite pores and indicated the formation of zeolite-Al-OH. The zeolite host significantly enhanced the chemical stability of Al@zeolite against pH changes for a wide pH range of 2.0-10.0. The adsorbent had a surface area of 33.46m2/g and demonstrated excellent capacity and selectivity for fluoride adsorption. Notably, a maximum adsorption of 98.6% was observed at a pH value of 6.0 for a duration of 20min with a fluoride content of 20mg/L, and the equilibrium concentration decreased to 0.4mg/L. The results of fluorine adsorption showed that fluoride uptake onto Al@zeolite agreed well with the pseudo-second-order kinetic model and the Langmuir isotherm model. The reusability of the substance was evaluated for up to eight cycles following consecutive regeneration with 0.2mol/L AlCl3. The exhausted Al@zeolite was effectively regenerated through simple alkaline treatment for recycling. The above results verified that Al@zeolite is a new kind of efficient defluoridation adsorbent for lepidolite hydrometallurgy wastewater with practical application prospects.

Preparation of High‐Selectivity Li+ Adsorbents Based on Bauxite via Liquid‐Phase Alkaline Thermal Activation

ABSTRACTBauxite, as the main aluminium‐bearing mineral in China, is a crucial resource for the industrial production of aluminium and aluminium‐related products. In this study, bauxite‐based aluminium composite Li+ adsorbents were prepared using a liquid‐phase alkaline thermal activation—acid in situ method. The effects of various factors on Li+ adsorption from brine were investigated through single‐factor experiments. Multiple techniques, such as scanning electron microscopy (SEM), energy dispersive x‐ray spectroscopy (EDS), x‐ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method, Fourier transform infrared spectroscopy (FT‐IR), and x‐ray photoelectron spectroscopy (XPS), were employed to characterise and analyse the microstructure, pore size distribution, chemical element distribution, and mineral structure of the adsorbents. In addition, the changes in bauxite structure and properties before and after functionalization were investigated. Results indicate that the adsorption capacity of LATA‐AIS‐LDH‐BX adsorbent prepared by the acid in situ method reached 1.15 mg/g at pH = 7; the adsorption capacity of LATA‐Al‐LDH‐BX adsorbent prepared by the aluminium salt conversion method reached 2.16 mg/g. The adsorption behaviour of both adsorbents followed the pseudo‐second‐order kinetic model and the Langmuir model. In the presence of interfering ions (Na+, K+, SO24+, Mg2+), the composite adsorbents showcased strong selective adsorption capacity for Li+. After five cycles of adsorption–desorption, the adsorption rates decreased by 12.19% and 11.48%, respectively, demonstrating good recycling stability. Furthermore, the Li+ adsorption capacities in salt lake brine reached 0.82 mg/g and 1.48 mg/g, indicating promising potential for industrial application.

Fluorinated Conjugated Microporous Polymers Based on Pillar[n]arenes for Removal of Water Pollutants and Their Cation Selective Adsorption.

Organic dyes are widely used in many applications. However, the leakage of organic dyes into the natural environment has become a severe and worldwide problem owing to their high toxicity and nonbiodegradability. Therefore, the development of effective removal technologies for organic dyes is required. In this article, we report the synthesis and adsorption properties of highly fluorinated conjugated microporous polymers based on pillar[n]arenes. The polymers exhibited large Brunauer-Emmett-Teller surface areas of up to 1063 m2 g-1 and selective adsorptive removal of cationic organic dyes from aqueous solutions. Comparison with the nonfluorinated polymers indicated that the adsorption mechanism mainly relies on the fluorine-cation electrostatic interaction. The maximum adsorption capacity reached 313 mg g-1 for crystal violet, which is higher than those of conventional adsorbents. Additionally, the fluorinated polymers could function as proton channels when they were embedded into lipid membranes.

Removal of Trace Benzene from Cyclohexane Using a MOF Molecular Sieve.

Cyclohexane (Cy), commonly produced by the catalytic hydrogenation of benzene (Bz), is used in large quantities as a solvent or feedstock for nylon polymers. Removing trace unreacted Bz from the Cy product is technically difficult due to their similar molecular structures and physical properties. Herein, we report that a metal-organic framework (MOF) adsorbent shows a molecular sieving effect for Bz and Cy with record-high Bz/Cy adsorption selectivities (216, 723, and 1027) in their liquid mixtures (v/v = 1:1, 1:10, and 1:20), and traps Bz molecules effectively even at low partial pressure in the vapor phase (e.g., 2.49 mmol/g at 8.2 Pa) or at low content in liquid-phase Cy (e.g., 128 mg/g at 20 ppm). Over 99% removal of trace Bz (1000 ppm) from liquid Cy could be achieved in one simple stripping step at room temperature using this sorbent, producing a Cy with >99.999% purity. Single-crystal structure analyses for guest-free and Bz-loaded phases of the MOF disclosed that a narrow slit-like pore aperture and the strong uniting of multiple weak host-guest and guest-guest interactions are the co-origin of its distinct adsorption property for Bz and Cy.

Surface Hydroxyl Groups Functionalized Porous CeO2 for Enhanced Selective Adsorption of As(III).

The adsorption technique has been considered as one of the promising methods to remove arsenic ions in aqueous systems. However, the adsorbents are usually poorly selective and have low capacity. Herein, a kind of porous CeO2 containing surface hydroxyl group which synthesized facilely possesses the great performance of selective adsorption of As(III) with 98.57% removal against 14 other coexisting metal ions. The results showed that the processes of As(III) and As(V) uptake were heterogeneous monolayer adsorptions and included external and intraparticle diffusions. The adsorption capacities at pH 2.5 reached 111.24 and 56.89 mg/g for As(III) and As(V), respectively. In addition, it also showed that As(III) could be oxidized to As(V) in the adsorption process. Density functional theory calculations revealed that the OH group in H3AsO30 and the As atom in H3AsO40 have affinity with lattice oxygen (O2-) in CeO2, while the O atom in H2AsO4- preferred the Ce atom in CeO2. This study provides a novel porous CeO2 containing hydroxyl groups for selective and efficient removal of arsenic and elucidates the mechanism of As(III) and As(V) adsorptions.

Economically Scalable Cu-based MOFs: Vital Role of Structural Integrity towards Selectivity on Azeotropic Ethanol Dehydration.

A facile, green, and economical method for the scalable synthesis of hydrophilic copper-triazole metal-organic frameworks (Cu-trz) is demonstrated. Numerous open metal sites within the highly crystalline porous structure of Cu-trz are generated through mild thermal activation, enabling its application in liquid-phase ethanol dehydration under ambient conditions. The frameworks with distinct crystallinity and particle sizes were achieved by modifying the synthesis process. The high crystallinity of the framework plays an exclusive role in enhancing water adsorption capacity. With selective water adsorption comparable to commercial zeolite 3A, Cu-trz MOF emerges as a promising candidate for cost-effective water-ethanol separation.

Divergent Adsorption Regulation in Metal-Organic Frameworks for Highly Efficient CF4/C2F6 Separation.

The efficient removal of low-concentration components from homologous mixtures is often hampered by the co-directional effect of traditional thermodynamic regulation approaches, typically leading to a trade-off between adsorption capacity and selectivity. Focusing this challenge on the critical task of purifying perfluorocarbons in electronics industry, a divergent regulation strategy is reported that significantly improves the separation efficiency of low-concentration hexafluoroethane (C2F6) from tetrafluoromethane (CF4). This approach involves the selective shielding of open metal sites and the modulation of channel geometry within an electron-deficient ligand-based pore environment, thereby facilitating a C2F6 dense-packing accommodation mode while weakening the CF4 affinity due to the reduced host-guest interactions. Simultaneously enhanced C2F6 adsorption and reduced CF4 adsorption are achieved, resulting in record-high low-pressure C2F6 uptake and C2F6/CF4 selectivity. Comprehensive insights into the unique separation mechanism are illustrated through a combination of solid-state MAS nuclear magnetic resonance(SSNMR), molecular simulations, and meticulously designed comparative experiments. As a result, benchmark C2F6/CF4 separation performance is achieved, as demonstrated by the unprecedented electronic-grade (over 99.999%) CF4 productivity (401 L kg-1) obtained from an industrially relevant C2F6/CF4 (3:97) mixture, as well as the excellent water/air/heat stability and recyclability.

A Flexible Metal‐Organic Framework for the Removal of Propyne from Propylene

AbstractEfficient removal of propyne impurities from propylene is essential for producing high‐purity propylene. In this study, we utilize the flexible metal‐organic frameworks (MOFs) material, MOF‐508, for C3H4/C3H6 separation. Propyne (C3H4) induces a “Gate‐opening” effect in MOF‐508, transitioning it from a narrow‐pore phase to a large‐pore phase at low pressure. In contrast, propylene (C3H6) only triggers this effect at a higher pressure of 0.55 bar. Notably, at 298 K and 0.5 bar, MOF‐508 adsorbs 71.9 cm3/g of C3H4, compared to just 7.9 cm3/g of C3H6. This selective adsorption significantly enhances C3H4/C3H6 separation (50/50, v/v), as further demonstrated by dynamic breakthrough experiments.

Self‐adaptive Coordination Evolution Mediated Pore‐Space‐Partition in Metal–Organic Frameworks for Boosting SF6/N2 Separation

AbstractThe controllable and precise structural regulation of metal–organic frameworks (MOFs) based on isoreticular chemistry is an effective strategy for creating functional material platforms, such as efficient porous adsorbents. Herein, for the first time, mediated by an unprecedented self‐adaptive coordination evolution (SACE) on pseudo‐D2h‐symmetric [M4(μ3‐O)2(COO)6] (M=Mn/Fe) clusters, two pore space partitioned MOFs (CTGU‐47‐Mn/Fe, CTGU=China Three Gorges University) have been successfully constructed. Owing to the more confined adsorption space and dense binding sites produced by pore space partitioning (PSP), the CTGU‐47‐Mn/Fe exhibit significantly enhanced performance in the capture or recovery SF6 (greenhouse/electronic specialty gas) from SF6/N2 mixture compared to their non‐partitioned homologous structures (CTGU‐46‐Mn/Fe) with adsorption selectivity increased from 37/72 to 634/157 (v/v, 10/90, 100 kPa). The theoretical calculations also elucidated that the implementation of PSP within CTGU‐47‐Mn/Fe leads to dramatically strengthened binding affinity for SF6 over N2 through extra multiple F⋅⋅⋅H interactions. This study represents a valuable advance in crystal engineering field: the SACE of polynuclear metal clusters is expected to be useful in the structural regulation of MOFs and the fabrication of advanced porous adsorbents.

An Adaptive Metal-Organic Framework Discriminates Xylene Isomers by Shape-Responsive Deformation.

The separation of xylene isomers, especially para-xylene, is a crucial but challenging process in the chemical industry due to their similar molecular dimensions. Here, a flexible metal-organic framework, Ni(ina)2, (ina = isonicotinic acid) is employed to effectively discriminate xylene isomers. The adsorbent with adaptive deformation accommodates the shapes of isomer molecules, thereby translating their subtle shape differences into characteristic framework deformation energies. Through a combination of multiple local flexibility behaviors, Ni(ina)2 exhibits guest-specific structural transformations that energetically favor para-xylene over other isomers. Single-crystal X-ray diffraction, in situ powder X-ray diffraction, and theoretical investigations validate this "adaptive fitting" mechanism, where the degree of structural deformation scales with the mismatch between the molecular shape and pore geometry. As a result, Ni(ina)2 achieves exceptional para-xylene selectivity in both liquid and vapor phase separations, maintaining a high para-xylene purity and productivity. This work demonstrates a novel strategy of exploiting framework flexibility to address challenging molecular separations and provides fresh insights into the design of selective adsorbents.

Mn-doped SrTiO3 perovskite: Synthesis and characterisation of a visible light-active semiconductor

This study focuses on the synthesis and characterisation of Mn-doped SrTiO3 using the citric method. As-prepared samples featured a non-porous microstructure with a mean particle size of approximately 5 μm, composed of sintered submicron crystallites. Manganese was successfully incorporated into the perovskite structure as Mn4+, with a homogeneous distribution across the Sr and Ti positions. The doping induced a distinctive dark brown hue, indicating significant visible light absorption. A pronounced band gap shift from 3.32 to 2.92 eV was revealed via Tauc analysis of the Kubelka-Munk function. Both the SrTiO3 and Mn-doped SrTiO3 samples demonstrated a high adsorption capacity exclusively for cationic dye (Methylene Blue) at pH 10, with the Mn-doped sample showing slightly enhanced removal efficiency, reaching a maximum adsorption capacity of 310.7 mg g−1. The selective adsorption at high pH can be attributed to electrostatic interactions between the perovskite surface and MB molecules. This combination of high adsorption capacity and a reduced band gap highlights the material’s potential for photocatalysis applications.

Selective Gas Adsorption in Permanently Microporous Coordination Cages with Exposed Metal Sites.

Porous coordination cages (PCCs), molecular analogs of metal-organic frameworks, offer modular platforms for studying the adsorption properties of small molecules, with coordinatively unsaturated metal centers playing a pivotal role in tuning these behaviors. In this work, we present the synthesis, activation, and detailed gas adsorption studies of second-row transition metal-based M24L24 cuboctahedral cages, specifically Mo24(bdc)24, Rh24(bdc)24, and [Ru24(bdc)24]Cl12. These materials represent rare examples of Mo-, Rh-, and Ru-based hybrid porous solids. The synthesis and activation of these cages were optimized to maximize porosity, yielding BET surface areas of up to 832 m2/g. Gas adsorption studies with CO2 and CO reveal distinctive uptake behaviors linked to the metal cations, with Mo24(bdc)24 demonstrating the highest gravimetric CO2 uptake (2.12 mmol/g at 298 K) and [Ru24(bdc)24]Cl12 exhibiting the strongest CO binding (-75 kJ/mol). Additionally, we explore the selective adsorption of unsaturated hydrocarbons, such as ethylene and propylene, revealing strong binding interactions at low pressures as a result of strong metal-hydrocarbon interactions based on pi-backbonding interactions.

Underlying mechanism of electrospun starch-based nanofiber mats to adsorb the key off-odor compounds of oyster peptides

The solid-phase adsorption principles and fundamental mechanism of isobutyric acid, 1-octen-3-ol, and octanal (three key off-odor compounds of oyster peptides) were explored using electrospun octenyl succinylated starch-pullulan (OSS-PUL) nanofiber mat. The nanofiber mats had selective adsorption behaviors as indicated by the selective adsorption rates of isobutyric acid, 1-octen-3-ol, and octanal, which were 94.96 %, 85.03 %, and 65.36 %. The contents of the II-type inclusion complexes (ICs) formed with the nanofiber mats by the three off-odor compounds mentioned above were significantly different. The mean fiber diameter of the octanal/nanofiber mat IC with the highest content of II-type IC was significantly decreased (p < 0.05). In contrast, the isobutyric acid/nanofiber mat IC did not significantly change. The findings suggested that nanofiber mats interacted most strongly with octanal and weakly with isobutyric acid. This study will provide the theoretical foundation for deodorizing aquatic products using electrospun starch-based nanofiber mats.

Two novel 3D polyoxometalate-based metal–organic frameworks for structure-directed selective adsorption and photodegradation of organic dyes

Degradation of organic dyes from industrial wastewater is crucial for human health and ecological balance. Synergy adsorption and photodegradation is one of the effective methods to degrade organic dyes at present. The former is usually limited by the challenge of its the recovery and the poor adsorption capacity of the adsorbent, whereas the latter frequently suffers from sluggish reaction kinetics. Herein, the introduction of the unique electron-rich Keggin polyoxometalates (CuW12 and SiW12) into electron-deficient metal photosensitive viologen framework to construct two polyoxometalate(POM)-based metal organic frameworks (POMOFs) of 3D porous layered structures, namely [Cu2(ipbp)2(H2O)2][CuW12O40]·3H2O (1) and [Co2(H2ipbp)3(H2O)2(CoO6)2][SiW12O40]·H2O (2); (H2ipbp·Cl = 1-(3,5-dicarboxyphenyl)-4,4′-bipyridinium), which enable selective adsorption of methylene blue (MB) and effectively photocatalytic degradation cationic dyes. In addition, POMs and metal-organic frameworks act in synergy to result in much improved adsorption of certain cationic dyes as well as enhanced photocatalytic activity that allow the catalyst to show better excellent reusability and stability. The adsorption degradation rate of MB and rhodamine B (RhB) of 2 is faster than that of 1 because of the lower Zeta potential of 2 suggesting that there are electrostatic interactions in the adsorption process. This work adopted a novel view to comprehening the technology.

A novel recyclable surface ion-imprinted graphene aerogels for high selective adsorption of lithium in salt lake brine

To mitigate the growing pressure of lithium resource supply and requirement, the exploration of abundant lithium from salt lake brine has emerged as a novel avenue for lithium resource acquisition. Surface ion imprinting technology with specific recognition could achieve selective lithium adsorption. However, existing Li+-imprinted adsorption materials exhibit poor adsorption performance and difficult recovery. To address these issues, the novel recyclable Li+-imprinted graphene aerogels were synthesized by using graphene oxide as the skeleton material, and thiourea dioxide as the reducing agent, assisted by DMF and NH3·H2O. The imprinted aerogels demonstrate excellent structural stability (bearing 10000 times of its weight), superior adsorption capacity (31.66 mg g−1), high selectivity and good regeneration performance (91.0% after six cycles). The selection factors for Li+ over Na+, K+ and Mg2+ reach 10.00, 5.71 and 4.00, respectively. This is attributed to the strong metal coordination interreaction between 2-Hydroxymethyl-12-crown-4 and Li+, thereby specifically recognizing and adsorbing Li+. This research offers a fresh material for the enrichment and recovery of lithium resources in salt lake brine.

Selective adsorption and photodegradation of potentially hazardous salicylic acid by a novel magnetic surface molecularly imprinted photocatalyst (SMIP-Fe0@b-TiO2/CQDs)

Selective adsorption and photodegradation of potentially hazardous salicylic acid by a novel magnetic surface molecularly imprinted photocatalyst (SMIP-Fe0@b-TiO2/CQDs)

Novel honeycomb 3D Co/In-MOF with rigid ligand are used for efficient C1-C3 light hydrocarbons adsorption separation, fluorescence sensing and selective dye adsorption

Gas adsorption and separation, fluorescence sensing and dye adsorption have always attracted much attention and discussion as hot areas of applied research on metal–organic frameworks (MOFs). In this study, two structurally distinct three-dimensional (3D) MOFs, {[NH2Me2]2[Co3(L1)2]·6DMA·8H2O}n (Co-1) and {[NH2Me2]2[In2(L1)2]·7DMF·4H2O}n (In-1), were successfully synthesized by the reaction of rigid ligand L1 (L1 = 4-(2,6-bis(4′-carboxy-[1,1′-biphenyl]-4-yl)pyridin-4-yl)isophthalic acid) with Co2+ and In3+ under solvent-heated conditions, both of which have unique honeycomb structures. Co-1 exhibits high adsorption capacity for C3H6 and C3H8 (298 K: C3H6, 142.88; C3H8, 136.66 cm3·g−1). Meanwhile, it shows selective adsorption properties as high as 39.63, 42.94, 9.07, 4.12 and 3.04 for C3H6/CH4, C3H8/CH4, C2H2/CH4, CO2/CH4 and C2H2/CO2. The C2H2/CO2 breakthrough experiment has validated the practical separation potential of Co-1 for binary mixtures, with a dynamic separation coefficient reaching up to 2.34. Furthermore, the intrinsic mechanism for the differences in the adsorption and separation properties caused by the framework structures on the microscopic scale are revealed by the density functional theory (DFT). In-1 is a bifunctional MOF capable of rapidly and accurately detecting CrO42− and Cr2O72− ions in water via fluorescence sensing, and selectively adsorbing the cationic dye methylene blue (MB) through electrostatic interaction with high efficiency. 21.74 mg·g−1 of MB (10 mg·L−1, 24 mL) is adsorbed by 10 mg In-1 in 50 min. Kinetic, adsorption isotherm and thermodynamic analyses show that the adsorption process of MB on In-1 is mainly driven by chemisorption, which exhibits a homogeneous monomolecular layer adsorption, and that the process is a spontaneous and heat-absorbing reaction

Flotation separation of ilmenite and titanaugite by sodium oleate (NaOL)/cetyltrimethylammonium bromide (CTAB) mixed collectors: Selectivity and synergistic adsorption mechanism

Flotation separation of ilmenite and titanaugite by sodium oleate (NaOL)/cetyltrimethylammonium bromide (CTAB) mixed collectors: Selectivity and synergistic adsorption mechanism

Highly selective adsorption of MoS2/ZnO heterojunctions for SO2 and H2S gas molecules: A DFT study

Highly selective adsorption of MoS2/ZnO heterojunctions for SO2 and H2S gas molecules: A DFT study

Selective adsorption of arsenic by water treatment residuals cross-linked chitosan in co-existing oxyanions competition system

Selective adsorption of arsenic in co-existing oxyanions competition systems remains a significant challenge in water treatment due to the limitations of adsorbent materials that often overlook competitive adsorption, resulting in an overestimation of their actual purification potential for target contaminants. In this study, a novel hydrogel bead adsorbent, composed of water treatment residuals (WTRs) and chitosan (Chi), was developed to selectively remove arsenic, while minimizing the interference from phosphate, which is the strongest and most representative competitor in multi-oxyanion systems. The WTRs-Chi beads (WCB) adsorbents were optimized by adjusting the ratios of WTRs:Chi, with characterization results indicating that increased WTR doping improved the degree of crosslinking and the formation of bidentate complexes with enhanced electrostatic selectivity. Importantly, the co-existence of phosphate had minimal adverse effects on arsenic removal compared to other reported adsorbents. The maximum adsorption capacity for As (Ⅴ) in the binary system was 34.12 mg/g, and the adsorption behavior was fitted well by the pseudo-second-order kinetic model and the extended Langmuir isotherm model. The experimental results, supported by X-ray photoelectron spectroscopy analysis (XPS), revealed that both As (Ⅴ) and P (Ⅴ) adsorption in the single system were driven by electrostatic attraction and ligand exchange. However, in the binary system, the inhibition of P (V) adsorption was attributed to competitive desorption caused by electrostatic repulsion, which hindered the formation of inner-sphere complexes. This study provides a practical approach for developing selective adsorbents to address arsenic contamination in complex water environments and promotes the recycling of municipal solid waste.