High Adsorption Uptake Research Articles

Formation of a N/O/F-Rich and Rooflike Cluster-Based Highly Stable Cu(I/II)-MOF for Promising Pipeline Natural Gas Upgrading by the Recovery of Individual C3H8 and C2H6 Gases.

Due to the ultralow amounts of C3H8 and C2H6 gases, to design and synthesize water-stable MOFs that are promising for real-world efficient pipeline natural gas (NG) upgrading by the recovery of individual C3H8 and C2H6 gases is still a great challenge. Here, a N/O/F heteroatom-rich and rooflike [Cu(II)4Cu(I)2(COO)4(tetrazolyl)6] cluster-based ultra-microporous tsi-MOF (SNNU-Bai68) was afforded as a multiple heteroatom-rich and curved-surface-shaped cluster-based ultra-microporous MOF and the first porous MOF based upon such rooflike [Cu(II)xCu(I)y(tetrazolyl)z](2x+y-z)+ cluster. In SNNU-Bai68, the rooflike cluster was further assembled into a 1D chain secondary building block (SBB), which led to a high density of accessible potential adsorptive sites. Very interestingly, it exhibited the most promising balance of high gas adsorption uptakes at 0.01, 0.03, and 0.05 bar, high C3H8/CH4, C3H8/C2H6, and C2H6/CH4 adsorption selectivities, moderate adsorption enthalpies, and high water and chemical stability for pipeline natural gas upgrading by the recovery of individual C3H8 and C2H6 gases, which was further confirmed by the breakthrough experiments of the gas mixtures with/without 74% RH. Furthermore, the SC-XRD and GCMC studies revealed that the successful separation of C3H8, C2H6, and CH4 gases in SNNU-Bai68 is due to different synergistic effects of H-bonds between the frameworks at three adsorptive sites around each rooflike cluster and those different gas molecules, which were initially described systematically by the number of H atoms from the gas molecules, the total number of H-bonds within the synergistic H-bonds, and the binding energy of the framework at an adsorption site toward the gas molecules. In addition, this work may provide a method for the construction of a multiple heteroatom-rich and curved-surface-shaped cluster-based ultra-microporous MOF as a novel approach to build MOFs with polar pore surfaces, suitable pore sizes, and unique pore shapes to maximize the synergistic H-bonds between the framework and guests.

Application of Mn-Fe Layered Double Hydroxide as an Adsorbent for the Removal of Arsenic from Synthetic Acid Mine Drainage

The Mn-Fe layered double hydroxide using chloride in the interlayer anion was successfully synthesized using chemical co-precipitation methods. The Mn-Fe LDH was then applied as adsorbent for arsenic removal from synthetic acid mine drainage. The adsorbent characterizations of SEM and XRD analysis showed that the Mn-Fe LDH had many different functional groups and a high specific surface area for the adsorption processes. The morphological structure of Mn-Fe LDH by the SEM-EDS analysis method shows a round shape structure with a particle size of about 1 μm, and the XRF analysis method shows that the Mn and Fe elements dominate more than other components. Batch adsorption experimental conducted using the Mn-Fe LDH with the interlayer anion of chloride as an adsorbent to study the effect of contact time, equilibrium pH, and temperature on the arsenic removal. The Mn-Fe LDH showed high adsorption uptake capacity and selectivity for the arsenic in the synthetic acid mine drainage. The adsorption and ion exchange between interlayer chloride anions in Mn-Fe LDH and As (V) solution was the main adsorption mechanism. Therefore, the Mn-Fe LDH can be used as an adsorbent in water and wastewater treatment. In contrast, this research has the potential to be processed and developed into advanced materials.

In silico design of a new Zn-triazole based metal-organic framework for CO2 and H2O adsorption.

In search for future good adsorbents for CO2 capture, a nitrogen-rich triazole-type Metal-Organic Framework (MOF) is proposed based on the rational design and theoretical molecular simulations. The structure of the proposed MOF, named Zinc Triazolate based Framework (ZTF), is obtained by replacing the amine-organic linker of MAF-66 by a triazole, and its structural parameters are deduced. We used grand-canonical Monte Carlo (GCMC) simulations based on generic classical force fields to correctly predict the adsorption isotherms of CO2 and H2O. For water adsorption in MAF-66 and ZTF, simulations revealed that the strong hydrogen bonding interactions of water with the N atoms of triazole rings of the frameworks are the main driving forces for the high adsorption uptake of water. We also show that the proposed ZTF porous material exhibits exceptional high CO2 uptake capacity at low pressure, better than MAF-66. Moreover, the nature of the interactions between CO2 and the MAF-66 and ZTF surface cavities was examined at the microscopic level. Computations show that the interactions occur at two different sites, consisting of Lewis acid-Lewis base interactions and hydrogen bonding, together with obvious electrostatic interactions. In addition, we investigated the influence of the presence of H2O molecules on the CO2 adsorption on the ZTF MOF. GCMC simulations reveal that the addition of H2O molecules leads to an enhancement of the CO2 adsorption at very low pressures but a reduction of this CO2 adsorption at higher pressures.

One-Pot Synthesis of Novel Porous Carbon Adsorbents Derived from Poly Vinyl Chloride for High Methane Adsorption Uptake

One-Pot Synthesis of Novel Porous Carbon Adsorbents Derived from Poly Vinyl Chloride for High Methane Adsorption Uptake

A Series of Mesoporous Metal‐Organic Frameworks with Tunable Windows Sizes and Exceptionally High Ethane over Ethylene Adsorption Selectivity

AbstractThe NIIC‐20 (NIIC stands for Nikolaev Institute of Inorganic Chemistry) is a family of five isostructural metal‐organic frameworks (MOFs) based on dodecanuclear wheel‐shaped carboxylate building blocks {Zn12(RCOO)12(glycol)6} (glycol is deprotonated diatomic alcohol: ethylene glycol, 1,2‐propanediol, 1,2‐butanediol, 1,2‐pentanediol or glycerol), quantitatively crystallized from readily available starting chemicals. The crystal structures contain large mesoporous cages of 25 Å connected through {Zn12} rings, of which inner diameter and chemical nature depend solely on the chosen glycol. The NIIC‐20 compounds feature high surface area and rarely observed inversed adsorption affinity for saturated hydrocarbon (ethane) over the unsaturated ones (ethylene, acetylene). The corresponding IAST (Ideal Adsorbed Solution Theory) adsorption selectivity factors reach as much as 15.4 for C2H6/C2H4 and 10.9 for C2H6/C2H2 gas mixtures at ambient conditions, exceeding those for any other porous MOF reported so far. The remarkable combination of high adsorption uptakes and high adsorption selectivities makes the NIIC‐20 series a new benchmark of porous materials designed for ethylene separation applications.

A Series of Mesoporous Metal-Organic Frameworks with Tunable Windows Sizes and Exceptionally High Ethane over Ethylene Adsorption Selectivity.

The NIIC-20 (NIIC stands for Nikolaev Institute of Inorganic Chemistry) is a family of five isostructural metal-organic frameworks (MOFs) based on dodecanuclear wheel-shaped carboxylate building blocks {Zn12 (RCOO)12 (glycol)6 } (glycol is deprotonated diatomic alcohol: ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol or glycerol), quantitatively crystallized from readily available starting chemicals. The crystal structures contain large mesoporous cages of 25 Å connected through {Zn12 } rings, of which inner diameter and chemical nature depend solely on the chosen glycol. The NIIC-20 compounds feature high surface area and rarely observed inversed adsorption affinity for saturated hydrocarbon (ethane) over the unsaturated ones (ethylene, acetylene). The corresponding IAST (Ideal Adsorbed Solution Theory) adsorption selectivity factors reach as much as 15.4 for C2 H6 /C2 H4 and 10.9 for C2 H6 /C2 H2 gas mixtures at ambient conditions, exceeding those for any other porous MOF reported so far. The remarkable combination of high adsorption uptakes and high adsorption selectivities makes the NIIC-20 series a new benchmark of porous materials designed for ethylene separation applications.

Protein adsorption to (3-acrylamido propyl) trimethyl ammonium chloride-grafted Sepharose gel: Charge density reduction via copolymerizing with electroneutral monomer drastically increases uptake rate.

Polymer-grafting to porous materials is an effective way to create protein ion-exchangers of high capacity and uptake rate because the 3D architecture of the polymeric ion exchange groups provides high binding space and facilitated transport of the bound protein. Herein, a new anion exchanger was fabricated by grafting (3-acrylamide propyl) trimethyl ammonium chloride (APTAC) onto Sepharose FF gel for protein adsorption and chromatography. The ion exchanger, denoted as FF-pAPTAC, presented high capacity but limited uptake rate in bovine serum albumin (BSA) adsorption due to the high charge density of the cationic polymer chains. To solve the problem, we proposed to copolymerize APTAC with an electroneutral monomer, acrylamide (AM), onto Sepharose FF to modulate the charge density of the grafted polymer chains. By decreasing the feeding molar ratio of APTAC to AM, the ionic capacity (IC) of the copolymerized resins, FF-p(AM-APTAC)n (n denotes IC in mmol/L), decreased, but the chain length could be remained almost unchanged due to the similar reactivity ratios of the two monomers. With decreasing IC, the static adsorption capacity (qm) of FF-p(AM-APTAC)n decreased gradually because of the decline of protein binding sites. The uptake rate, however, represented by the ratio of effective pore diffusivity to the free solution diffusivity (De/D0), exhibited a strong uptrend with decreasing IC, reaching ~2.5-fold of the maximum observed with FF-pAPTACn. It is considered that the decrease of charge density weakened protein binding strength to the chains and increased the chain flexibility, which consequently facilitated the transport of bound proteins on the chains. Moreover, at the same IC, each FF-p(AM-APTAC)n displayed similar adsorption capacity but high uptake rate as compared with its FF-pAPTACn counterpart mainly due to the longer chain length of the copolymer. Particularly, ~6.5-fold enhancement of De/D0 was observed at IC=50±2mmol/L. Both high adsorption capacity and uptake rate made FF-p(AM-APTAC)n exhibit superior dynamic binding performance. The findings proved that reducing chain charge density by copolymerizing an electroneutral monomer was promising for fabrication of high-performance protein ion exchangers.

Surface trace doping of Na enhancing structure stability and adsorption properties of Li1.6Mn1.6O4 for Li+ recovery

Li1.6Mn1.6O4 (LMO) is a dominant adsorbent for lithium recovery from solutions resulted from its high theoretical adsorption uptake and a low loss rate of Mn, which can potentially be further improved by trace doping. We achieve stable cycling and high adsorption capacity of Li1.6Mn1.6O4 from aqueous lithium resources by Na doped (LMO-Na). The Mn dissolution is decreased from 5.4% (bare adsorbent) to 4.4%, and the uptake is increased from 33.5 mg/g to 33.9 mg/g (CLi+: 24 mmol/L). Furthermore, DFT calculations predict that Na replace for Li at 16d sites, result in an enhancement of the Li+ adsorption rate and structure stability of LMO. The loss rate of Mn in cycling process is restrained by Na doped, which may result from reducing the content of low valent Mn3+ and improving the structural stability of material. The effect of Na substitution on adsorption capacity and structure stability is discussed.

Porous carbon nanotube networks and pillared graphene materials exhibiting high SF6 adsorption uptake and separation selectivity of SF6/N2 fluid mixtures: A comparative molecular simulation study

Abstract SF6 and SF6–N2 gas mixtures are well known insulators used in industry applications, but SF6 has to be recovered due to its high global warming potential. In this study, the adsorption of the pure SF6 and N2 fluids and the separation of their mixture with SF6:N2 = 1:9 composition, using three-dimensional porous carbon nanotube networks and pillared graphene materials has been studied by employing Monte Carlo and Molecular Dynamics simulations at ambient temperature and pressure up to 20 bar. The results obtained reveal a significant SF6 uptake and high adsorption selectivity for SF6 over N2, compared to the best performing materials in the literature. The selectivity for SF6 decreases in the case of pillared graphene and strongly depends on the nanotube pillar and graphene layer distances. The saturation capacity of the investigated materials is also achieved at very different pressure ranges, as it has been reflected on the calculated adsorption isotherms. Due to this fact, the translational diffusion coefficients of the adsorbed SF6 and N2 molecules in each material are significantly different at ambient conditions. The results obtained might be used as a springboard towards the rational design of carbon-based materials for the capture of the very potent greenhouse gas SF6.

Implications from γ-globulin adsorption onto cation exchangers fabricated by sequential alginate grafting and sulfonation

Abstract Our previous work proved that high adsorption capacity and uptake rate of lysozyme were achieved on alginate (Alg)-grafted resin with an ionic capacity (IC) of 240 mmol·L−1 (Alg-FF-240). Moreover, the salt-tolerant feature of Alg-FF-230 was improved by using sequential alginate grafting and sulfonation strategy. Inspired by the enhanced adsorption performance of lysozyme, we have herein proposed to investigate the static and dynamic adsorption behaviors of γ-globulin on a series of Alg-grafted resins with different grafting densities and sulfonation degrees. The adsorption capacity of γ-globulin decreased with increasing alginate-grafting density (IC) from 160 to 230 mmol·L−1 at 0 mmol·L−1 NaCl because of the steric hindrance caused by the alginate-grafting layer. Effects of ionic strength (IS) indicated that the adsorption capacities of the resins with the IC value of 230–370 mmol·L−1 were much higher than CM Sepharose FF at 50–100 mmol·L−1 NaCl, and the uptake rate of Alg-FF-230 was about twice as much as that of CM Sepharose FF. This work demonstrated the important effects of alginate-grafting layer and IS in γ-globulin adsorption behavior, which would be helpful in the design of Alg-grafted resins and the selection of proper IS condition for protein purification.

The treatment of Raw Water Sources of Drinking Water using Chitosan/Mg/Al–LDH Composites: Problem cases in Municipal Waterworks in Banjarmasin

A study was done on treatment of raw water sources for drinking water using chitosan/Mg-Al LDH (CS/Mg/Al–LDH) composites by adsorption process. An analysis on the adsorbent characterizations of FTIR, SEM and XRF showed that the CS/Mg/Al–LDH had many different functional groups and a high specific surface area for adsorption processes. The CS/Mg/Al–LDH showed high adsorption uptake capacity and selectivity for iron (Fe), turbidity, and colour in the raw water sources for drinking water in Municipal Waterworks in Banjarmasin. Therefore, the CS/Mg/Al–LDH composites have the potential to be used as an adsorbent in water and wastewater treatment.

Adsorption of the inhalation anaesthetic isoflurane by activated carbon fibres with reference data on non-porous carbon

Activated carbon fibres with a range of pore sizes, prepared from pre-oxidized acrylic fibre by physical activation in CO2 at different temperatures and times, were investigated as adsorbents for the inhalation anaesthetic isoflurane (2-chloro-2-(difluoromethoxy)-1,1,1-trifluoroethane). Adsorption–desorption isotherms of isoflurane were determined at 293 K and were analysed by the αS method using reference adsorption data, determined also at 293 K, on non-porous carbon. One of the samples obtained showed a much higher adsorption uptake at 100 mbar than reported in previous studies on different materials, while another sample not only showed a higher adsorption uptake than reported previously, but also a higher adsorption uptake at a pressure as low as 1 mbar showing potential for the capture of isoflurane. The results indicate that isoflurane does not adsorb in fine ultramicropores, of width less than about 0.5 nm. Comparison of the pore size distributions of these materials indicated that the presence of supermicropores, as well as ultramicropores, is relevant for the adsorption of isoflurane even at trace levels. Reference adsorption data for isoflurane on non-porous carbon is also presented.

Implications from the grafting density and ionic capacity effects on protein adsorption to poly (N,N-dimethylaminopropyl acrylamide)-grafted sepharose FF

Our previous study reported a novel protein ion-exchanger, N,N-dimethylaminopropyl acrylamide (DMAPAA)-grafted Sepharose FF, of very high protein adsorption capacity and uptake rate. To gain new insight into the polymer grafting effects on protein adsorption and chromatography, 18 DMAPAA-grafted anion exchangers of four grafting densities and various chain lengths (i.e., ionic capacities, ICs) were prepared and named as FF-Brx-pDMAPAAn (x represents grafting density and n stands for IC in mmol/L). It was found that an optimal IC existed at each grafting density to present a maximal capacity. Of the four optimal-IC resins, FF-Br3-pDMAPAA587 showed the highest capacity (377 mg/mL), but the protein uptake rate, defined as the ratio of effective pore diffusivity to free diffusivity (De/D0), was smaller than the resin of a similar ionic capacity but lower grafting density (FF-Br2-pDMAPAA592). Consequently, the dynamic binding capacity (DBC) of FF-Br2-pDMAPAA592 was higher than that of FF-Br3-pDMAPAA587 at flow velocities higher than 450 cm/h. Moreover, FF-Br3-pDMAPAA587 showed higher adsorption capacity than FF-Br2-pDMAPAA592 at 0−150 mmol/L NaCl, leading to its higher DBC values as compared to FF-Br2-pDMAPAA592 in the same salt concentration range. Taken together, DMAPAA-grafted resins of different grafting densities would be useful for purifying feedstocks of different ionic strengths.

Effective adsorption of metronidazole antibiotic from water with a stable Zr(IV)-MOFs: Insights from DFT, kinetics and thermodynamics studies

The adsorptive removal of antibiotics, emerging organic pollutants in water is very important but challenging. In this work we report a series of eight water stable metal-organic framework (MOFs), which are methodically screened for the removal of metronidazole (MNZ) from water. It was found that two isostructural Zr(IV)-MOFs (UiO-66 and UiO-66-NH2) showed adsorption capacities of around 200.2 mg g−1 and 265.5 mg g−1, respectively, which are higher than the experimental values of reported porous materials used for MNZ removal so far. The MOFs were characterized by Powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy, Thermogravimetric analysis (TGA), Scanning electron microscope (SEM), Energy-dispersive X-ray elemental analysis (EDX), BET isotherm, UV–vis (UV–vis) spectrophotometer and NICOMP™ 380 ZLS. The effects of various parameters including time, concentration, temperature and pH were investigated. The adsorption mechanism of UiO-66-NH2 for MNZ has also been explored through computational simulations. The results showed that MNZ molecules are mainly locate at around the -NH2 functional groups in pore surfaces of UiO-66-NH2, with the increase of molecular level of the amino groups, the affinity of the framework to MNZ could be significantly increased. The results demonstrated that highest adsorption uptake by UiO-66-NH2 was attributed to -NH2 functional group including with (hydrogen bonding interactions, electrostatic interaction and larger pHpzc). The adsorption process of the two MOFs fitted the pseudo-second-order kinetic model and Langmuir isothermal model, whilst the adsorption was endothermic, with the confirmation by thermodynamic studies.

Room temperature phosphorescent determination of aflatoxins in fish feed based on molecularly imprinted polymer - Mn-doped ZnS quantum dots

Possibilities of room temperature spectrometry based on Mn-doped ZnS quantum dots coated with a molecularly imprinted polymer based nanosensor have been explored for the sensitive and selective determination of aflatoxins. Synthesized polymeric nanoparticles exhibit intense room temperature phosphorescence (total decay time of 0.004 s) and aflatoxins quench the room temperature phosphorescence when interact with the recognition cavities of the molecularly imprinted polymer attached to the phosphorescent quantum dots. Room temperature phosphorescence was recorded by scanning from 520 nm to 720 nm (maximum peak intensity at 594 nm) after excitation at 290 nm. The prepared imprinted material was found to have higher adsorption capacity than those based non-imprinted quantum dots, demonstrating high adsorption uptake for aflatoxins. In addition, selectivity studies have demonstrated that the material offers a specific recognition for aflatoxins. Room temperature phosphorescence quenching by aflatoxins was found to be linear within the 2–20 μg L−1 range, and a limit of detection of 3.56 μg kg−1 was obtained. This value was lower than the maximum acceptable/residual level (aflatoxins in feeds) published by the European Commission. The results indicate a simple room temperature phosphorescence nanosensor for aflatoxins detection in fish feed as a versatile tool having excellent sensitivity and selectivity.

Protein cation exchangers derived by charge reversal from poly(ethylenimine)-Sepharose FF: Comparisons between two derivatization routes

It has been known that anion exchangers prepared by grafting poly(ethyleneimine) (PEI) onto Sepharose FF (PEI-Sepharose) at ionic capacities (IC) over 600 mmol/L show both high protein adsorption capacity and uptake kinetics, and charge reversal of PEI-Sepharose by modification with succinic anhydride can produce protein cation exchangers of high capacity and uptake rate. Previously, a Charge Reversal-then-Reduction procedure (route A) was studied for preparation of cation exchangers of different IC values from PEI-Sepharose. In this work, we proposed a new route, that is, Charge Reduction-then-Reversal route (route B), to develop cation exchangers of different IC values from PEI-Sepharose FF with an IC of 700 mmol/L (FF-PEI-L700) as the starting resin. The two kinds of cation exchangers (route A, PEI-L700-CRn; route B, PEI-Rm-Cn) are compared for lysozyme (Lys) adsorption and chromatography. The two modification routes result in the difference in the ligand structures that significantly affect protein adsorption equilibrium and kinetics. Route A introduces long electroneutral groups that hinder protein adsorption and reduce equilibrium capacity. Moreover, charge reversal by reaction with succinic anhydride could cause diamide formation, which reduces remaining carboxyl groups or the IC. In the charge-reduced FF-PEI-Rm resins of the lowest IC (394 mmol/L) prepared in route B, the diamide formation was little due to the lack of primary and secondary amine groups, so its charge reversal makes a higher-IC cation exchanger. This makes PEI-Rm-Cn show a higher IC (589 mmol/L) than PEI-L700-CRn (463 mmol/L) in which De/D0 jumps about four times. The differences in the adsorption equilibrium and kinetics make the two kinds of resins behave distinctly in dynamic adsorption and chromatography. Namely, PEI-Rm-Cn resins display obviously higher dynamic binding capacities than PEI-L700-CRn resins in the IC range studied. For instance, the DBC (at 10% breakthrough) of PEI-R590-C680 (192 mg/mL) is 33% higher than that of PEI-L700-CR680 (144 mg/mL). This is proved by the purification of Lys from chicken egg white solution, in which the PEI-R590-C680 column purified Lys with a recovery yield 14% higher than the PEI-L700-CR680 column. This research thus demonstrated that Charge Reduction-then-Reversal route is superior over Charge Reversal-then-Reduction route in fabricating a high-capacity cation exchanger from PEI-Sepharose.

Rational Design of Nanoporous MoS2 /VS2 Heteroarchitecture for Ultrahigh Performance Ammonia Sensors.

2D transition metal dichalcogenides (TMDs) have received widespread interest by virtue of their excellent electrical, optical, and electrochemical characteristics. Recent studies on TMDs have revealed their versatile utilization as electrocatalysts, supercapacitors, battery materials, and sensors, etc. In this study, MoS2 nanosheets are successfully assembled on the porous VS2 (P-VS2 ) scaffold to form a MoS2 /VS2 heterostructure. Their gas-sensing features, such as sensitivity and selectivity, are investigated by using a quartz crystal microbalance (QCM) technique. The QCM results and density functional theory (DFT) calculations reveal the impressive affinity of the MoS2 /VS2 heterostructure sensor toward ammonia with a higher adsorption uptake than the pristine MoS2 or P-VS2 sensor. Furthermore, the adsorption kinetics of the MoS2 /VS2 heterostructure sensor toward ammonia follow the pseudo-first-order kinetics model. The excellent sensing features of the MoS2 /VS2 heterostructure render it attractive for high-performance ammonia sensors in diverse applications.

Preparation of carbon nanofiber with multilevel gradient porous structure for supercapacitor and CO2 adsorption

In this work, we demonstrate a simple method to prepare carbon nanofiber (CNF) with multilevel gradient porous structure derived from polyvinylidene fluoride (PVDF)- polyvinyl pyrrolidone (PVP) /PVP core-shell nanofiber. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have confirmed that the as-prepared CNF contains a hollow channel embraced by mesoporous and microporous structures. Its specific surface area reaches to 1084 m2/g with the mesoporous volume contribution of 59%. The as-prepared porous CNF shows a high capacitance of 331 F/g at 1 A/g and 99.6% capacitance retention after 10,000 cycles at 5 A/g, which is better than the corresponding CNF with irregularly arranged hierarchical pores. The all-solid-state symmetric supercapacitor assembled using the as-prepared porous CNF as electrodes exhibits an excellent high specific capacitance of 147.4F/g at 1 A/g with a high energy density of 13.1 W h/kg. The capacitance retention still maintains at 89.2% after 2000 cycles at a current density of 5 A/g. Meanwhile, the as-prepared porous CNF also shows a high CO2 adsorption uptake, 5.08 mmol/g at 0 °C and 1 bar. The possible reason and mechanism have been discussed.

Metal–Organic Framework-74 for Ultratrace Arsenic Removal from Water: Experimental and Density Functional Theory Studies

This study investigates and compares arsenic, As(V), removal from aqueous media using the water-stable zinc metal–organic frameworks (Zn-MOF-74) prepared via room-temperature precipitation (RT-Zn-MOF-74) and a solvothermal procedure (HT-Zn-MOF-74). The Zn-MOF-74 crystals possess average particle sizes of 66 nm and 144 μm for RT-Zn-MOF-74 and HT-Zn-MOF-74, respectively. Moreover, nanosized RT-Zn-MOF-74 exhibited a superior performance to HT-Zn-MOF-74. While the Brunauer–Emmett–Teller surface area of RT-Zn-MOF-74 was smaller than that of HT-Zn-MOF-74, higher adsorption uptake took place on the room-temperature-synthesized ones because of their small particle size and better dispersion. Adsorption isotherm studies showed that the Langmuir isotherm was effective for the adsorption of As(V) onto RT-Zn-MOF-74 and HT-Zn-MOF-74 with maximum adsorption uptake (qmax) values of 99.0 and 48.7 mg g–1, respectively. These values exceed most reported maximum adsorption capacities at neutral pH. The thermodynamics of ads...

Characterization of new polymer-grafted protein cation exchangers developed by partial neutralization of carboxyl groups derivatized by modification of poly(ethylenimine)-Sepharose with succinic anhydride

Previously, we have studied protein adsorption and chromatographic behaviors on poly(ethylenimine) (PEI)-grafted Sepharose FF anion-exchange resins, and found that protein uptake rates increased greatly when PEI grafting density reached over a critical ionic capacity (cIC) due to the occurrence of the “chain delivery” effect. Moreover, by partial charge neutralization of starting resin FF-PEI-L740 (IC = 740 mmol/L, larger than the cIC) with sodium acetate to FF-PEI-R440, it exhibited a three-fold increase in uptake rate over FF-PEI-L740. In this work, to take the advantages of PEI and extend the applications of the PEI-grafted resins in cation-exchange chromatography, a series of cation exchangers of five different ICs were developed. First, the charged of FF-PEI-L740 was reversed from positive to negative by reaction with excess succinic anhydride, which created a cation-exchanger with an IC of 970 mmol/L (FF-FEI-C970). FF-PEI-C970 was further modified with ethanolamine for partial charge neutralizations, leading to the preparation of four charge-reduced cation exchangers with IC values (in mmol/L) of 780, 630, 560 and 430, which were denoted as FF-PEI-CR780, −CR630 −CR560 and −CR430, respectively. Protein adsorption and chromatographic behaviors were investigated using lysozyme (Lys) as the model protein. It was found that, the resins of high and moderate IC values (IC ≥ 560 mmol/L) afforded adsorption capacities up to over 230 mg/mL. Besides, the uptake rate, represented by the effective pore diffusivity (De/D0), exhibited significant increase from 0.067 (FF-PEI-C970 and FF-PEI-CR780) to 0.343 (FF-PEI-CR630 and FF-PEI-CR560) and then to 1.035 (FF-PEI-CR430) with decreasing IC. It was considered that decreasing IC led to the decreased protein binding sites (binding strength), which encouraged the occurrence of the “chain delivery” effect. Moreover, the resins of high and moderate IC values, particularly, the resins of moderate IC values (FF-PEI-CR630 and FF-PEI-CR560), presented both high adsorption capacities and uptake kinetics at 0–100 mmol/L NaCl. Besides, dynamic binding capacity achieved 150 mg/mL for the resins of moderate IC values at 0 mmol/L NaCl concentration, and afforded >110 mg/mL for the resin of high IC values at 0–100 mmol/L NaCl concentration. The results proved the excellent IEC performance of the PEI-derived cation exchangers.