Novel surface ionic imprinting materials prepared via couple grafting of polymer and ionic imprinting on surfaces of silica gel particles

In this paper, a new surface molecular imprinting technique is put forward, and a kind of novel ion-imprinted polymers (IIPs) were prepared through a new approach: firstly functional macromolecule polyethyleneimine (PEI) was grafted onto the surfaces of silica gel particles via the coupling grafting method (“grafting to” method) and the composite material PEI/SiO₂ with chemical linking was formed; secondly the ionic imprinting was carried out towards the macromolecule PEI grafted on the surface of silica particles using Cu²⁺ or Cd²⁺ ion as a template, epichlorohydrin (ECH) as a crosslinking agent and by coordination linkage actions, and Cu²⁺ ion (or Cd²⁺ ion)-imprinted material IIP-PEI/SiO₂ was prepared. The binding characteristics of IIP-PEI/SiO₂ for Cu²⁺ ion (or Cd²⁺ ion) were studied in detail by adopting both static and dynamic methods. The experimental results show that the ion-imprinting material IIP-PEI/SiO₂ has specific recognition ability for the template ions, and this character displays mainly in two aspects: (1) it has high affinity for the template ions, its binding amounts for the template ions are much greater than that of the non-imprinted composite material PEI/SiO₂, and the adsorption capacity enhances nearly two times compared to PEI/SiO₂; (2) it has excellent selectivity for the template ions, for the IIP-PEI/SiO₂ by using Cu²⁺ as template ion, its selectivity coefficients relative to Zn²⁺ and Ni²⁺ are 80.21 and 86.08, respectively, and for the IIP-PEI/SiO₂ by using Cd²⁺ as template ion, its selectivity coefficients relative to Cr³⁺ and Pb²⁺ are 77.05 and 88.22, respectively. Besides, the imprinting material IIP-PEI/SiO₂ has a fine elution property using HCl solution as eluent. The obtained imprinting material by using the new surface molecular imprinting techniques possesses superexcellent binding property for template molecules or ions because of the distribution of imprinted cavities in a thin polymer layer and smaller diffusion barrier.     

Reversible immobilization of glycoamylase by a variety of Cu2+‐chelated membranes

Glycoamylase (AMG) is an γ‐amylase enzyme which catalyzes the breakdown of large α(1,4)‐linked malto‐oligosaccharides to glucose. It is an extracellular enzyme and is excreted to the culture medium. In this study, AMG was immobilized on a variety of metal affinity membranes, which were prepared by chelating Cu²⁺ ions onto poly(hydroxyethyl methacrylate) (PHEMA) using N‐methacryloyl‐(L )‐histidine methyl ester (MAH), N‐methacryloyl‐(L )‐cysteine methyl ester (MAC), and N‐methacryloyl‐(L )‐phenylalanine methyl ester (MAPA) as metal‐chelating comonomers for reversible immobilization of AMG. The PHEMAH, PHEMAC, PHEMAPA membranes were synthesized by UV‐initiated photo‐polymerization and Cu²⁺ ions were chelated on the membrane surfaces. Cu²⁺‐chelated membranes were characterized by swelling tests, SEM, contact angle measurements, elemental analysis, and FTIR. AMG immobilization on the Cu²⁺‐chelated membranes was performed by using aqueous solutions of different amounts of AMG at different pH values and Cu²⁺ loadings. Durability tests concerning desorption of AMG and reusability of the Cu²⁺‐chelated membranes yielded acceptable results. It was computationally determined that AMG possesses four likely Cu²⁺/Zn²⁺ binding sites, away from the catalytic site, to which the metal‐chelated membranes can be efficiently used. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Selective separation of some heavy metals by poly(vinyl alcohol)‐grafted membranes

A poly(vinyl alcohol) membrane (PVA) was modified by radiation graft copolymerization of acrylic acid/styrene (AAc/Sty) comonomers. The Cu and Fe ion‐transport properties of these membranes were investigated using a diaphragm dialysis cell. In the feed solution containing CuCl₂ or a mixture of CuCl₂ and FeCl₃, the PVA‐g‐P(AAc/Sty) membranes showed high degrees of permselectivity toward Cu²⁺ rather than toward Fe³⁺. The permeation of Cu²⁺ ions through the membranes was found to increase with decrease in the grafting yield. However, as the content of Cu²⁺ ions in the Cu/Fe binary mixture feed solutions decreased, the rate and the amount of transported Cu²⁺ through the grafted membrane decreased, with no appreciable permselectivity toward Fe³⁺. When Fe²⁺ ions were used instead of Fe³⁺ ions in the feed solution containing Cu²⁺, the transport of both Cu²⁺ and Fe²⁺ through the membrane was observed. The rate of transport of Fe²⁺ was higher than that of Cu²⁺. In addition, it was found that the selective transport of ions was significantly influenced by the pH difference between both sides of the membranes. As the pH of the feed or the received solution decreased, both Cu²⁺ and Fe³⁺ passed through the membrane and were transported to the received solution. The role of carboxylic acid and the hydroxyl groups of the grafted membranes in the transportation process of ions is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 125–132, 2000     

Tetraamminezinc complex integrated interpenetrating polymer network nanocomposite membrane for phosphorous recovery

Phosphorous recovery from wastewater by nanofiltration (NF) is a feasible and sustainable approach, but challenges still exist in the development of highly efficient membranes for the selective permeation of phosphorus. Herein an interpenetrating network (IPN) of crosslinked polyvinyl alcohol (PVA) is integrated with Zn²⁺ moieties through coordination with the amino groups of crosslinked polyethyleneimine (PEI) and deposited on borate crosslinked polydopamine-grafted carbon nanotubes (B-PDA-CNT) intermediate layer incorporated into the microfiltration substrate to form the composite membrane. The positively charged membrane in acidic conditions affords good rejection (>85%) of heavy metals ions including Cd²⁺, Cu²⁺, Zn²⁺, Pb²⁺, and Ni²⁺. Meanwhile, a low phosphorus rejection of <15% is realized with the application of a relatively low transmembrane pressure. This presupposes that the developed approach achieves selective removal of heavy metals from a phosphate solution and is attractive for low pressure recovery of phosphorus. © 2018 American Institute of Chemical Engineers AIChE J, 65: 755–765, 2019     

Synthesis,characterization, metal sorption,and biological activity of poly(N‐heterocylic acrylamide)

N‐heterocyclic acrylamide monomers were prepared and then transferred to the corresponding polymers to be used as an efficient chelating agent. Polymers reacted with metal nitrate salts (Cu²⁺, Pb²⁺_, Mg²⁺, Cd²⁺, Ni²⁺, Co²⁺_, Fe²⁺) at 150°C to give metal‐polymer complexes. The selectivity of the metal ions using prepared polymers from an aqueous mixture containing different metal ion sreflected that the polymer having thiazolyl moiety more selective than that containing imidazolyl or pyridinyl moieties. Ion selectivity of poly[N‐(benzo[d]thiazol‐2‐yl)acrylamide] showed higher selectivity to many ions e.g. Fe³⁺, Pb²⁺, Cd²⁺, Ni²⁺, and Cu²⁺. While, that of poly[N‐(pyridin‐4‐yl)acrylamide] is found to be high selective to Fe³⁺ and Cu²⁺ only. Energy dispersive spectroscopy measurements, morphology of the polymers and their metallopolymer complexes, thermal analysis and antimicrobial activity were studied. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42712.     

Adsorption and desorption properties of grafted polyethylene films modified with polyethylenimine chains

The chelating membranes for adsorption of metal ions were prepared by the bonding of linear and branched polyethylenimines (LPEI and BPEI) on the glycidyl methacrylate (GMA) photografted porous polyethylene (pPE) (pPE‐g‐PGMA) films. The adsorption and desorption properties of LPEI and BPEI‐bonded pPE‐g‐PGMA (LPEI‐(pPE‐g‐PGMA) and (BPEI‐(pPE‐g‐PGMA)) films to Cu²⁺ ions were investigated as a function of the grafted amount, amount of bonded PEI, molecular mass of PEI, pH value, and temperature. The amounts of LPEI and BPEI bonded to the pPE‐g‐PGMA films increased over the reaction time, and the bonding of LPEI and BPEI offered the water‐absorptivity to the pPE‐g‐PGMA films. The amount of adsorbed Cu²⁺ ions at pH 5.0 had the maximum value at the grafted amount of 10 mmol/g for the (LDPEI‐(pPE‐g‐PGMA) and (BPEI‐(pPE‐g‐PGMA) films with a constant amount of bonded PEI. The amount of adsorbed Cu²⁺ ions for the LPEI‐(pPE‐g‐PGMA) films was higher than that for the BPEI‐(pPE‐g‐PGMA) films. The amount of Cu²⁺ ions desorbed from the LPEI‐(pPE‐g‐PGMA) and BPEI‐(pPE‐g‐PGMA) films increased with an increase in the HCl concentration. The quantities of Cu²⁺ ions of about 100% were desorbed in the aqueous HCl solutions of more than 0.1M for the LPEI‐(pPE‐g‐PGMA) films and more than 0.05M for the BPEI‐(pPE‐g‐PGMA) films. The amounts of adsorbed Cu²⁺ ions were almost the same in each adsorption process at pH 5.0. This indicates that the LPEI‐(pPE‐g‐PGMA) and BPEI‐(pPE‐g‐PGMA) films can be applied to a repeatedly generative chelating membrane for adsorption and desorption of metal ions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5965–5976, 2006     

Nickel(II)‐imprinted monolithic columns for selective nickel recognition

Ni²⁺‐imprinted monolithic column was prepared for the removal of nickel ions from aqueous solutions. N‐Methacryloyl‐L ‐histidine was used as a complexing monomer for Ni²⁺ ions in the preparation of the Ni²⁺‐imprinted monolithic column. The Ni²⁺‐imprinted poly(hydroxyethyl methacrylate‐N‐methacryloyl‐L ‐histidine) (PHEMAH) monolithic column was synthesized by bulk polymerization. The template ion (Ni²⁺) was removed with a 4‐(2‐pyridylazo) resorcinol (PAR):NH₃? NH₄Cl solution. The water‐uptake ratio of the PHEMAH–Ni²⁺ monolith increased compared with PHEMAH because of the formation of nickel‐ion cavities in the polymer structure. The adsorption of Ni²⁺ ions on both the PHEMAH–Ni²⁺ and PHEMAH monoliths were studied. The maximum adsorption capacity was 0.211 mg/g for the PHEMAH–Ni²⁺ monolith. Fe³⁺, Cu²⁺, and Zn²⁺ ions were used as competitive species in the selectivity experiments. The PHEMAH–Ni²⁺ monolithic column was 268.8, 25.5, and 10.4 times more selective than the PHEMAH monolithic column for the Zn²⁺, Cu²⁺, and Fe³⁺ ions, respectively. The PHEMAH–Ni²⁺ monolithic column could be used repeatedly without a decrease in the Ni²⁺ adsorption capacity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of support layer on gas permeation properties of composite polymeric membranes

PES/Pebax and PEI/Pebax composite membranes were prepared by coating the porous PES and PEI substrate membranes with Pebax-1657. The morphology and performance of the prepared membranes were investigated by SEM and CO₂ and CH₄ permeation tests. The CO₂ permeances of 28 and 52 GPU were achieved for PES/Pebax and PEI/Pebax composite membranes, respectively, with CO₂/CH₄ selectivities almost equal to that of Pebax (26). The experimental data were further subjected to a theoretical analysis using the resistance model. It was found that the porosity and the thickness of the dense section of PES substrate were an order of magnitude higher than those of PEI substitute. The porosity/thickness ratio of PEI substrate was, however, higher than PES, explaining the higher permeance of PEI/Pebax composite membrane. Substrates with porosities much higher than the Henis-Tripodi gas separation membrane were used in this work, aiming to achieve the selectivity of Pebax, rather than those of the substrate membrane materials.     

Preparation and Characterization of Cellulose Acetate/Aminated Polysulfone Blend Ultrafiltration Membranes and their Application Studies

Abstract

Ultrafiltration membranes are largely being applied for heavy metal ion separations from aqueous streams. Cellulose acetate (CA) and aminated polysulfone (APSf) based membranes are prepared in the absence and presence of the polymeric additive, polyethylene glycol, PEG 600, in various compositions. The effects of polymer blend composition and additive concentration on compaction, pure water flux, membrane hydraulic resistance, water uptake, and contact angle has been investigated to evaluate the performance of the membranes and the results are discussed. Surface and cross-sectional morphologies of membranes were also analyzed using scanning electron microscopy. Toxic heavy metal ions such as Cu²⁺, Ni²⁺, Cd²⁺, and Zn²⁺ were separated by the blend membranes using polyethyleneimine (PEI) as polymeric ligand. The rejection and permeate flux efficiencies of the blend membranes are compared with pure cellulose acetate membranes.     

Removal of Ag(l), Cu(II) and Zn(ll) ions with a supported liquid membrane containing cryptands as carriers

The interface behaviour in the facilitated co-transport of Ag(I), Cu(II) and Zn(II) ions through supported liquid membranes (SLMs) made of a flat-sheet polypropylene membrane support containing cryptands (2.2.2 or 2.2.1) as carriers was studied. The liquid-liquid extraction tests showed a maximum distribution coefficient when the carrier concentration was greaterthan 10⁻⁴M. In transport experiments the transmembrane flux increased with increasing carrier concentration reaching a limiting value at greater than 10⁻³M concentration. The calculation ofthe diffusion coefficients in membranes showed ahigherdiffusivityof2.2.2-metal complexes with respect to 2.2.1-metal complexes for silver ions. A sequence of diffusivity D(Ag+)>D(Cu²⁺)>D(Zn²⁺) was obtained, but carrier 2.2.1 showed a higher selectivity through copper ions. A sequence of diffusivity D(Cu²⁺)>D(Zn²⁺)>D(Ag⁺) was obtained. The diffusivity was significantly higher when using Celgard 2500 support compared to Celgard 2400 or 2402. Variable metal ion concentrations in the feed phase fluxes almost zero, at less than 10⁻² M concentration, were obtained. In the transient state of the transport through the SLM, different molar flow rates at the feed-membrane and membrane-strip interfaces were observed. The selectivity of the interfaces containing 2.2.2 in the separation binary mixtures of ions showed the following separation factors: SF_AgZn = 2.50, SF_AgCu = 1.64, SF_cuZn = 1.42.     

Highly Copper(II) Ion‐Selective Transport Through Liquid Membrane Containing N,N′‐bis(salicylidene)‐1,2‐phenyldiamine

Abstract

N,N′‐bis(salicylidene)‐1,2‐phenyldiamine was synthesized for examining their ability to extract and transport Cu²⁺ through a liquid membrane. By using hydrazine sulfate and potassium thiocyanate as reducing agent and acceptor respectively in the receiving phase at the optimum pH of 1.5, the amount of copper transported across the liquid membrane after 3.5 hours was 96%. The selectivity and efficiency of copper transport from aqueous solution containing various metal ions were investigated.     

Conversion of soybean oil into ion exchange resins: Removal of copper (II), nickel (II), and cobalt (II) ions from dilute aqueous solution using carboxylate‐containing resin

An ion‐exchange resin containing carboxylic acid groups was prepared by reaction of epoxidized soybean oil with triethylene tetramine, followed by hydrolysis of glycerides by using sodium hydroxide solution. The cation exchange capacity of the resins was determined to be 3.50 mequiv/g. The adsorption capacity for Cu²⁺, Ni²⁺, and Co²⁺ on the obtained resin at pH 5.0 was found to be 192, 96, and 78 mg/g, respectively. Effect of pH on the adsorption capacity for copper (II), nickel (II), and cobalt (II) ions were also studied. Cu²⁺, Ni²⁺, and Co²⁺ were adsorbed at a pH above 3. These metal ions adsorbed on the resin are easily eluted by using 1N HCl solution. The selectivity of the resin for Cu²⁺ from mixtures containing Cu²⁺/Co²⁺/Ni²⁺ ions in the presence of sodium chloride was also investigated © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2386–2396, 2002     

Separation of co2-ch4 and co2-n2 systems using ion-exchanged fau-type zeolite membranes with different si/al ratios

FAU-type zeolite membranes with different Si/Al ratios were hydrothermally synthesized on the outer surface of a porous α-Al₂O₃ support tube. The permeances of the membranes to CO₂, CH₄ and N₂ were then measured at 308 K for single-component and equimolar binary systems. The separation properties were dependent on both the Si/Al ratio and the ion-exchange treatment. For single-component systems, a lower Si/Al ratio resulted in the incorporation of a larger number of Na⁺ ions. For a CO₂-CH₄ mixture, both CO₂ permeances and CO₂/CH₄ selectivities were approximately half the values obtained for a binary CO₂-N₂ mixture. The highest selectivities, obtained using the NaX(1) zeolite membrane, were 28 for CO₂/CH₄ and 78 for CO₂/N₂. The RbY, RbX(1) and RbX(2) zeolite membranes showed larger CO₂ permeances, compared with those of the original Na-type membranes. Ion-exchange with K⁺ ions was the most effective for the NaY zeolite membrane in that both the CO₂ permeance and the CO₂/CH₄ selectivity were increased.     

Effects of crosslinking modification on the O2/N2 separation characteristics of poly(phenyl sulfone)/poly(bisphenol A‐co‐4‐nitrophthalic anhydride‐co‐1,3‐phenylenediamine) blend membranes

A series of blend membranes of poly(phenyl sulfone) (PPSU) with poly(bisphenol A‐co‐4‐nitrophthalic anhydride‐co‐1,3‐phenylenediamine) (PBNPI) were prepared through a solution casting method. This was done to examine the permeation characteristics of oxygen and nitrogen. The effect of the PPSU/PBNPI ratio on the membrane structure and O₂/N₂ separation performance were investigated. The results show that the permeability increased remarkably with the content of PPSU, whereas the selectivity decreased slightly. To enhance the selectivity of O₂/N₂, the blend membranes were further crosslinked with a p‐xylylenediamine agent via the immersion method. According to the Fourier transform infrared analysis, the N? H group was formed on the imide group of PBNPI. Therefore, we suggest that during the crosslinking modification, the PBNPI served as a crosslinkable polymer; this resulted in increased crosslinking efficiency with PBNPI content. The high‐resolution X‐ray diffraction and melting point method results show that crosslinking modification improved the selectivity with an acceptable loss in permeability along with increased crystallinity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dehydration of tetrahydrofuran by pervaporation using crosslinked PVA/PEI blend membranes

Dense blend membranes were prepared by blending hydrophilic polymers poly(vinyl alcohol) (PVA) and poly(ethyleneimine) (PEI), which were then crosslinked by glutaraldehyde (GA) in a mixture of solvents under the catalysis of hydrochloric acid (HCl) for the dehydration of tetrahydrofuran (THF) by pervaporation. The effect of experimental parameters such as feed water concentration, permeate pressure, and membrane thicknesses on permeate parameters, i.e., flux and selectivity were determined with feed water concentration less than 40 wt %. The membranes were found to have good potential for breaking the azeotrope of 94 wt % THF with a flux of 1.072 and 0.376 kg/m² h for plane PVA/PEI and crosslinked PVA/PEI blend membrane, which exhibited high selectivity of 156 and 579 respectively. Selectivity was found to improve with decreasing feed water concentration and increasing membrane thickness, whereas flux decreased correspondingly. High permeate pressure causes a reduction in both flux and selectivity. These effects were clearly elucidated with the aid of the known relationship among plasticization effect, degree of swelling, permeate pressure, and feed water concentration. These blend membranes were also subjected to sorption studies to evaluate the extent of interaction and degree of swelling in pure as well as binary feed mixtures. Further ion exchange capacity studies were carried out for all the crosslinked and uncrosslinked membranes to determine the total number of interacting groups present in the membranes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1152–1161, 2006     

Preparation of functionalized ion‐imprinted phenolic polymer for efficient removal of copper ions

In this work, an ion‐imprinted polymeric material based on functionalized phenolic resin was developed for the efficient selective removal of Cu²⁺ ions from aqueous solution. p‐Aminophenol‐isatin Schiff base ligand (HPIS) was first synthesized and combined with Cu²⁺ ions to prepare the corresponding complex [Cu(PIS)₂]. The Schiff base ligand along with its copper complex was fully investigated and characterized before anchoring in a base‐catalyzed condensation copolymerization with formaldehyde and resorcinol. The Cu²⁺ ions were removed from the obtained resin construction and the resulting Cu²⁺ ion‐imprinted material (Cu‐PIS) was employed for the selective extraction of Cu²⁺ ions under different pH values, initial concentrations and contact time conditions. The optimum pH for the removal process was chosen as 6 and the maximum adsorption capacity was 187 ± 1 mg g^–1. Also, the kinetics showed a better fit with the pseudo‐second‐order equations. The selectivity of the prepared Cu‐PIS was also evaluated in a multi‐ionic species containing Ni²⁺, Cd²⁺, Pb²⁺, Co²⁺ besides Cu²⁺ ions and the determined parameters confirmed a superior recognition capability toward the imprinted Cu²⁺ ions. © 2019 Society of Chemical Industry     

Physicochemical investigation of radiation‐grafted poly(acrylic acid)‐graft‐poly(tetrafluoroethylene–ethylene) copolymer membranes and their use in metal recovery from aqueous solution

ET‐g‐PAAc membranes were obtained by radiation grafting of acrylic acid onto poly(tetrafluoroethylene–ethylene) copolymer films using a mutual technique. The ion selectivity of the grafted membranes was determined toward K⁺, Ag⁺, Hg²⁺, Co²⁺, and Cu²⁺ in a mixed aqueous solution. The ion‐exchange capacity of the grafted membranes was measured by back titration and atomic absorption spectroscopy. The Hg²⁺ ion content of the membrane was more than that of either the K⁺ or Ag⁺ ions. The presence of metal ions in the membranes was studied by infrared and energy‐dispersive spectroscopy measurements. Scanning electron microscopy of the grafted and metal‐treated grafted membranes showed modification of the morphology of the surface due to the adsorption of K⁺ and Ag⁺ ions. No change was observed for the surface of the membrane that was treated with Hg²⁺ ions. The thermal stability of different membranes was improved more with Ag⁺ and Hg²⁺ ions than with K⁺ ions. It was found that the modified grafted membranes possessed good hydrophilicity, which may make them promising candidates for practical applications, such as for cation‐exchange membranes in the recovery of metals from an aqueous solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2692–2698, 2002     

Effects of halloysite nanotubes on the morphology and CO2/CH4 separation performance of Pebax/polyetherimide thin-film composite membranes

Enhancing the performance of gas separation membranes is one of the major concerns of membrane researchers. Thus, in this study, poly(ether-block-amide) (Pebax)/polyetherimide (PEI) thin-film composite membranes were prepared and their CO₂/CH₄ gas separation performance was investigated by means of pure and mixed gases permeation tests. To improve the properties of these membranes, halloysite nanotubes (HNT) were added to Pebax layer at different loadings of 0.5, 1, 2, and 5 wt % to form Pebax-HNT/PEI membranes. Scanning electron microscopy, gas sorption, X-ray diffraction, Fourier-transform infrared, and differential scanning calorimetry tests were also performed to investigate the impact of HNT on structure and properties of prepared membranes. Results showed that both CO₂/CH₄ selectivity and CO₂ permeance increased by adding HNT to Pebax layer up to 2 wt %. By increasing HNT loading to 5 wt %, the CO₂/CH₄ selectivity decreased from 32 to 18, while CO₂ permeance increased from 3.25 to 4.2 GPU. Pebax/PEI and Pebax-HNT/PEI membranes containing 2 wt % of HNT were tested using CO₂/CH₄ gas mixtures at different feed CO₂ concentrations and feed pressure of 4 bar. The results showed that with increasing CO₂ concentration from 20 to 80 vol %, CO₂/CH₄ selectivity of Pebax/PEI composite membranes increased by 19%, while, in Pebax-HNT/PEI membrane, CO₂/CH₄ selectivity decreased by 40%. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48860.     

Direct and transfer hydrogenation of furfural over MOF-derived Pd-Cu@C catalysts

Owing to the self-reducing ability of palladium acetate in solutions, an ethanol solution containing Pd⁰ particles was prepared and coated in-situ into copper metal–organic framework (Cu-MOF), forming Pd@Cu-MOF in a coated structure. The Pd@Cu-MOF was reduced under N₂ or H₂ to form carbon-coated Pd-Cu@C. The pyrolysis and carbonization of Cu-MOF and the reduction of Cu²⁺ were studied. The Cu-MOF under either N₂ or H₂ was pyrolyzed and carbonized, but the Cu²⁺ reduction mechanisms were different. The high-temperature carbothermic reduction of Cu²⁺ under N₂ produced Cu⁰, but during low-temperature reduction under H₂, the reducing H₂ reduced Cu²⁺ to Cu⁰. Furfural hydrogenation experiments showed that compared with H₂, the Pd-Cu@C prepared under N₂ reduction displayed higher furfural hydrogenation activity. The catalytic activity of Pd-Cu@C prepared from in-situ Pd⁰ coating was higher than the Pd/Cu@C prepared from the impregnation method. With i-propanol as the solvent, the catalytic hydrogenation of furfural under H₂ consisted of direct catalytic hydrogenation with molecular hydrogen as the hydrogen source and catalytic transfer hydrogenation with i-propanol as the hydrogen donor. The catalytic activity of direct catalytic hydrogenation is higher than the catalytic transfer hydrogenation.     

Preparation of a Facilitated Transport Membrane Composed of Carboxymethyl Chitosan and Polyethylenimine for CO2/N2 Separation

The miscibility of carboxymethyl chitosan/polyethylenimine (CMCS/PEI) blends was analyzed by FT-IR, TGA and SEM. Defect-free CMCS/PEI blend membranes were prepared with polysulfone (PSf) ultrafiltration membranes as support layer for the separation of CO₂/N₂ mixtures. The results demonstrate that the CMCS/PEI blend is miscible, due to the hydrogen bonding interaction between the two targeted polymers. For the blended membrane without water, the permeability of CO₂ gas is 3.6 × 10⁻⁷ cm³ cm⁻² s⁻¹ cmHg⁻¹ and the corresponding separation factor for CO₂ and N₂ gas is about 33 at the pressure of 15.2 cmHg. Meanwhile, the blended membrane with water has the better permselectivity. The blended membrane containing water with PEI content of 30 wt% has the permeance of 6.3 × 10⁻⁴ cm³ cm⁻² s⁻¹ cmHg⁻¹ for CO₂ gas and a separation factor of 325 for CO₂/N₂ mixtures at the same feed pressure. This indicates that the CO₂ separation performance of the CMCS/PEI blend membrane is higher than that of other facilitated transport membranes reported for CO₂/N₂ mixture separation.