Ion-imprinted Membranes Research Articles

A DFT-designed neodymium ion-imprinted membrane with fouling resistance and high flux

The rare earth metal neodymium (Nd) is widely used in advanced industries such as hybrid cars and aerospace. Therefore, recovering neodymium from wastewater presents valuable opportunities for secondary recycling. The recovery of Nd3+ from wastewater using ion imprinting technology (IIT) for efficient selective separation holds significant importance. In this study, hydrophilic Nd(III) ion-imprinted membranes, termed Nd(III)–P/P/TIIM, were synthesized using the IIT technique. Nd(III)–P/P/TIIM exhibited efficient and selective separation capabilities for Nd3+ with a remarkable retention rate of 95.68 % and a high water flux reaching up to 636.94 L·m−2·h−1. Additionally, its relative selectivity coefficients for interfering ions (KLa, KEu, KCu) were 3.9, 29.5, and 37.9, respectively. Various analyses, including DFT calculations, HOMO and LUMO calculations, MEP images, and XPS spectroscopy, confirm that the mechanism of selective retention of Nd3+ by Nd(III)–P/P/TIIM in solution is due to Coulombic adsorption between the –COO− anion and Nd3+ as well as an imprint memory effect. Even after undergoing three water-BSA cycles, the membrane maintained a water flux of 357.96 L·m−2·h−1. The antifouling principle of Nd(III)–P/P/TIIM was investigated by XDLVO theory, attributed to the increase of electron donor tension (γ−) and Lewis acid-base interactions (ΔGAB) at the membrane surface. This work provides an insightful guidance for engineering high-performance membranes and has the potential to provide an alternative method for recycling neodymium.

Adsorption performance and mechanism of TiO2/PVDF-based lithium-ion imprinted membrane in leaching solution of spent lithium-ion batteries

Efficient recycling of spent lithium-ion batteries (LIBs) is particularly important for the sustainable development of energy metal resources. A lithium ion-imprinted membranes (LIIMs) was synthesized by environmentally friendly hydrolysis polymerization. Its adsorption performance and mechanism in a simulated spent LIBs leaching solution was investigated. The Li+ adsorption of the LIIMs conformed to a pseudo-second-order kinetic model and occurred with a fast adsorption rate. The activation energy was associated with chemical adsorption. Thermodynamic results confirmed that Li+ adsorption was exhibited by the LIIMs as spontaneous exothermic behavior. The LIIMs showed a satisfactory affinity for lithium in simulated leaching solution (SLS), and the selective separation factors of Li+ for Fe2+, Cu2+, Ca2+, Zn2+, Mn2+, K+, and Na+ were 10.93, 19.30, 22.66, 23.49, 26.14, 27.57 and 39.00, respectively. The selective adsorption mechanism of LIIMs mainly occurred through coordination between Li+ and the oxygen on the crown ether at the surface active adsorption sites. The results proved that the LIIMs as a highly selective green adsorbent material has a broad application prospect in the recycling of spent LIBs. Importantly, the elucidation of the adsorption performance and the revelation of the adsorption mechanism provide the theoretical support for the future commercialization of LIIMs.

Bis-terpyridine imprinted nanocage in the confined two-dimensional lamellar membrane for selective adsorption of Nd(III)

Nd is a strategic metal, but its extraction and separation process remains a challenging task. Here, ion-imprinted membranes with six-coordinated and semi-rigid imprinted nanocage structure were developed by self-assembling terpyridine monomers in the confined reduced graphene oxide (rGO) nanochannels. The obtained membranes displayed excellent Nd(III) adsorption capacity of 20.6 mg g−1 in the solution including seven rare earth elements (REEs), together with a 7.68 times higher selectivity to Y(III). Experimental measurements and theoretical calculations revealed that Nd(III) was well coordinated to the six pyridine-nitrogen in the nanocage, which showed shorter average coordination bond (0.77 Å) and stronger binding energy (-10.52 eV) than other REEs. These were mainly attributed to the rigid symmetrical crab-type architecture and specific cavity size of bis-terpyridine nanocage. Meanwhile, the limited decomposition of these metastable nanocage derived from 2D confined effect and nanochannel walls with few groups reduced the interference of groups at non-imprinted sites on selective adsorption. The excellent anti-swelling property of rGO framework endowed 7 static adsorption cycles and maintained high selectivity (K'(Nd/Y) > 7). Integrated into account the well-defined semi-rigid sites constituted by non-covalent interactions, this strategy provided a new idea for facile synthesis of imprinted sites with higher selectivity.

Highly efficient separation and enrichment of hafnium from zirconium oxychloride solutions by advanced ion-imprinted membrane separation technology

Hafnium (Hf) is an important strategic material for the semiconductor, aerospace and nuclear industries. In this paper, an advanced ion-imprinted membranes (IIMs) separation system was prepared for the first time to achieve efficient separation and enrichment of Hf ions from zirconium oxychloride solutions. IIMs were constructed by a keyhole complex imprinting method with N, N-di-2-ethylhexyl diglycolamic acid (D2EHDGAA) as the carrier molecule, cellulose triacetate (CTA) as the base polymer and Hf ions as the template ion. In addition, amide acid driven IIMs were coupled with aspartic acid in the feed phase, which changes from preferential extraction of Zr to preferential extraction of Hf. To characterize it, we used Fourier transform infrared (FT-IR) spectroscopy and scanning election microscopy (SEM). The results showed that IIMs can increase CHf/CZr from 2.33:100 to 33.33:100 within 1 h compared with polymer inclusion membranes (PIMs) and ionic liquid supported liquid membranes (SLMs), which increased by 3.33 and 3.67 times. The selectivity and enrichment performance for the enrichment of Hf ions from Zr solution were significantly improved due to the high recognition selectivity of ion imprinting. Therefore, IIMs, as an advanced membrane separation system, may have good potential for industrial application in the field of efficient separation and enrichment of Hf ions.

A novel lithium ion-imprinted membrane with robust adsorption capacity and anti-fouling property based on the uniform multilayered interlayer

Effective modification strategies contribute to high adsorption capacity, separation efficiency and anti-fouling properties of ion-imprinted membranes. The design of a homogeneous and hydrophilic interlayer between the substrate membrane and ion-imprinted layer is crucial factor for the excellent performance of ion-imprinted membranes. In this study, a novel multilayered interlayer (SiO2@SP-PDA) was developed and uniformly coated on the substrate surface (PVDF membrane). The polydopamine (PDA) prepared via oxidation of sodium periodate (SP-PDA) increases the uniformity of SiO2@SP-PDA modification, which reduces the agglomeration of the ion-imprinted layer, and thereby boosts the adsorption capacity to 231.77 mg·g−1. The prepared ion-imprinted membrane (SiO2@SP-PDA-IIM) exhibits a favorable anti-fouling property due to the incremental hydrophilicity and the presence of SiO2 nano interlayer. Based on the XDLVO theory, it can be deduced that the SiO2 modification increases the membrane surface electron donor tension (γ−), which plays an essential role in enhancing the anti-fouling property of SiO2@SP-PDA-IIM. In this paper, the design of multilayered structure is of great significance to make the ion-imprinted membrane be a potential candidate for Li+ efficient separation in natural water.

An effective lithium ion-imprinted membrane containing 12-crown ether-4 for selective recovery of lithium

The high lithium content in spent lithium ion batteries (LIBs) and a large number of spent LIBs generation shift the target of lithium recovery to solid waste. Adsorption separation is of great application value for lithium recovery. There is still a lack of a lithium adsorption material with excellent properties. Herein, an environmental hydrolytic polymerization to prepare lithium ion-imprinted membranes (LIIMs) with high adsorption capacity and selectivity is presented. The LIIMs can reach adsorption equilibrium in 40 min, showing fast adsorption kinetics. The optimal adsorption capacity of the LIIMs for Li+ was 132.00 mg g−1 after immersing in a 300 mg L−1 LiCl solution based on ample binding sites and a strong affinity force. Langmuir isothermal adsorption results proved that the imprinting sites on LIIMs were homogeneous. The selective separation factors (α) of Li+ to Mg2+, K+, Ca2+, Na+ were 6.80, 17.00, 21.30, and 24.60, respectively, which implies the superior selectivity LIIMs toward Li+. The adsorption capacity of LIIMs remained about 97 % after six cycles. Due to the suitable cavity, abundant rebinding sites, and strong affinity, the LIIMs have a good selective adsorption ability to Li+. Therefore, the LIIMs would have potential applications for separating Li+ from spent LIBs.

Preparation of a novel ion-imprinted membrane using sodium periodate-oxidized polydopamine as the interface adhesion layer for the direction separation of Li+ from spent lithium-ion battery leaching solution

In this paper, a novel ion-imprinted membrane (SP-IIM) was prepared by combining graft polymerization with chemical modification and from polydopamine (PDA) oxidized by sodium periodate (SP-PDA) as the interface adhesion layer. The PDA was oxidized by sodium periodate at pH 5.0, causing it to undergo extensive cross-linking within the adhesion layer to provide better chemical stability for improving the reusability of the membrane. The flaky microstructure of the SP-PDA provided more surface area for the loading of 12-Crown-4 (12C4). The optimal adsorption capacity of the SP-IIM for Li+ was 42.58 mg·g−1 after incubating the membrane in a 200 mg·L–1 solution of Li+ for 180 min. The kinetics and isotherm data of the adsorption of Li+ onto the SP-IIM were fitted to pseudo-second-order kinetics and Langmuir model, respectively. Through selective adsorption experiments, the optimal selective separation factors of Li+/Mn2+, Li+/Co2+, Li+/Ni2+ were 6.71, 5.84 and 3.03, respectively. Density functional theory (DFT) calculations were performed on the coordination of metal cations (Li+, Mn2+, Co2+, and Ni2+) by 12C4, the results of which showed that the weak binding of Li+ to 12C4, as well as the favorable dehydration of Li+, made it easier for Li+ to be coordinated by 12C4 in a multicomponent solution containing Li+, Mn2+, Co2+, and Ni2+. The oxidation of the PDA by sodium periodate caused significant intermolecular cross-linking within the SP-PDA layer to reduce the possibility of the ion-imprinted layer detaching from the membrane, thereby increasing the reusability of the SP-IIM. After five repeated adsorption–desorption cycles, the adsorption capacity of the SP-IIM only decreased by 4.6%, which indicated that the SP-IIM was highly reusable. This work improved the adsorption capacity and reusability of ion-imprinted membranes by changing the microstructure of the interface adhesion layer, which was of great significance to the further development of ion-imprinted membranes.

Insights into ion imprinted membrane with a delayed permeation mechanism for enhancing Cd2+ selective separation

Ion imprinted polymers exhibit great potential in ion separation from wastewater. However, the difficulty of ion separation by membrane is proverbial, which severely restricts the application of membrane in metal resource recovery from industrial wastewater. Herein, a rational molecular-level design approaches for membrane fabrication was developed to modify a layer of ion imprinted polymer onto the PVDF membrane. Batch rebind and permeation experiments suggest that specific host-guest binding sites had been fabricated along the membrane pore in ion imprinted membranes (IIM). A higher monomer dose leads to a higher rejection of Cd2+, and the more bind sites in IIM. The binding of IIM to Cd2+ was 1.84 times that of non-ion imprinted membranes (NIM). Permselectivity factors (γ) of IIM are larger than 5.39 in mixture ions solutions. Chemical characterization and density functional theory (DFT) calculation reveal that the Cd2+ recognition sites of functional groups are C−S and C˭S. Cd2+ mass transport in IIM suggest that the imprint effects provide a binding force that would delay Cd2+ to permeate through IIM, so as to selectively separate Cd2+ with other ions. The imprint effects may enlighten a novel molecular-level design approaches for membrane fabrication to enhance the selectivity of ion-ion.

Fabrication of a novel and highly selective ion-imprinted PES-based porous adsorber membrane for the removal of mercury(II) from water

Herein, poly(ether sulfone) based ion imprinted membranes (IIM) were prepared through phase inversion, using ion imprinted polymer (IIP) particles obtained by radical copolymerization of acrylamide, acrylonitrile and ethyleneglycoldimethacrylate along with a template of Hg(II) complexed with bathophenanthroline (BPh). Optimization of the ability for Hg(II) removal from water and pure water flux of the IIM were investigated through Central Composite Design (CCD) combined with Response Surface Methodology (RSM). Accordingly, the optimized factors were obtained as IIP percentage of 2.5 wt% used in membrane preparation, as well as trans-membrane pressure of 0.19 bar, pH 7.95 and Hg(II) concentration of 4 ppm during filtration through the membrane. Using the optimum parameters, the removal percentage and flux of IIM were about 98.1% and 37.5 kg/m2 h, respectively. The maximum adsorption capacity of IIM was 432 mg/m2 (or 21.6 mg/g), almost four times higher than that of non-imprinted membrane (NIM; 105 mg/m2) (or 5.25 mg/g) which was prepared using copolymer particles prepared without the Hg(II) template. The IIM showed a high selectivity toward Hg(II) ions compared to other metal ions and could be effectively recycled for at least 6 times without any major loss of adsorption capacity. The synthesized imprinted membranes have demonstrated considerable potentials to selectively separate mercury(II) from simulated industrial wastewater.

Stable, regenerable and 3D macroporous Pd (II)-imprinted membranes for efficient treatment of electroplating wastewater

Pd (II) from release-unbridled electroplating wastewater is causing great challenges, which is unfavourable either to human health or resource reutilization. Ion-imprinted membranes (IIMs) have recently drawn attentions for selective separation of specific ions from analogues. In this context, we have developed a facile strategy for fabrication of Pd (II)-imprinted membranes (Pd-IIMs) for the selective separation of Pd (II). The enhanced flux was obtained by three-dimensional macroporous structure on polydimethylsiloxane (PDMS). Then the Pd-IIMs were synthesized by a modification-imprinting strategy based on PDMS substrates. With the existence of Co (II), Cu (II), Cd (II) and Ni (II), the as-obtained Pd-IIMs showed superior adsorptive selectivity (3.32–5.06) and perm-selectivity (2.34–4.04) towards Pd (II), as well as the satisfactory regeneration performance (more than 92% of the initial rebinding capacities after 5 cycles of adsorption/desorption). Moreover, the as-prepared Pd-IIMs also displayed stability on separation factors even under ultrasonic treatment. Notably, the overused Pd-IIMs after applications for selective separation of Pd (II) showed a satisfactory performance for the treatment of methylene blue (99.87%), which displayed potentials for the “further applications”. The Pd-IIMs and preparationstrategy developed in this work have shown a positive opportunity for the efficient treatment of electroplating wastewater and organic dyes.

Recent advances in ion-imprinted membranes: separation and detection via ion-selective recognition

Ionic selectivity is achieved based on ion-imprinted membranes.

Multilayered ion-imprinted membranes with high selectivity towards Li+ based on the synergistic effect of 12-crown-4 and polyether sulfone

High-selective multilayered Li+-imprinted membranes (Li-IIMs) with enhanced hydrophilicity and stability were developed based on polyether sulfone substrate membranes. The multilayered structure was prepared with polydopamine (pDA) as the interfacial adhesion layer, SiO2 nanoparticles as the hydrophilic layer and Li+-imprinted polymers as the imprinted layer. The selective “Li+-recognition sites” were formed using 12-crown-4 (12C4) as the adsorbing units. The optimal relative selectivity coefficients (α) of Li+/Na+ and Li+/K+ reached up to 1.85 and 2.07 with the imprinting factor (β) of 2.51, and the high permselectivity factors (γ) of Na+/Li+ (7.39) and K+/Li+ (9.86) were achieved on Li-IIMs. The Langmuir isotherm model and the pseudo-second-order kinetics model best fitted the rebinding data of Li-IIMs, as well as the rebinding capacities reached up to 90.3% of initial binding after 5 cycles of adsorption/desorption and just declined to 88.1% after another 5 cycles a month later. Therefore, the as-prepared Li-IIMs would have potential applications for the separation of lithium ions from salt lake brines.

Application of diffusive transport model for better insight into retardation mechanisms involved in ion-imprinted membrane transport

Heavy metal removal from water is a great concern for environmentalists and engineers. Ion-imprinted membranes are among the state of the art technologies for selective adsorption of heavy metals from aqueous environment. Dialysis permeation of nickel ions through Ni(II)-imprinted membranes has been thermodynamically studied in our prior work. In current study, the diffusive transport model was developed and then applied for better insight into the retardation mechanisms involved in the ion-imprinted membrane transport. The Sips isotherm model was coupled with the transport model to obtain the governing equation. Chemisorption and physical interactions (bulk diffusion and pore-clogging) were the most probable retardation mechanisms according to the modeling results. Relative retardation factor (η) was also defined as; transport-rate controlled by chemical adsorption to that controlled by physical interactions. With the help of the retardation factor, it was understood that the membrane behavior gradually changes from chemisorption to facilitated transport during permeation time. Effect of important operating parameters such as time, temperature and concentration on transport behavior was also investigated. Results indicated that chemisorption rate is rather higher at lower concentrations, early permeation times and reduced temperatures. In addition, η tabulated greater values for Ni(II) compared to Co(II) due to the imprinting effect.

Electrochemical sensor based on in situ polymerized ion-imprinted membranes at graphene modified electrode for palladium determination

In this work, an amperometric sensor was developed for the selective recognition and sensitive determination of palladium in complex matrices using a glassy carbon electrode (GCE) modified with a novel ion-imprinted membrane (IIM) and graphene. Graphene enhanced the sensor's electron transfer and sensitivity. The electrode surface was first directly modified with graphene through the electrodeposition of graphene oxide. An ion-imprinted polymer membrane was subsequently synthesized on this modified surface via in situ polymerization in acetonitrile using allylurea (NAU) as a functional monomer, ethylene glycol dimethacrylate (EGDMA) as cross-linking agent, and azobisisobutyronitrile as an initiator at a molar ratio of template (PdCl2) to NAU to EGDMA of 1:4:40. Amperometric i-t curves were measured for the determination of palladium. The designed modified electrode was shown a linear response to Pd(II) ions in the range of 2.0×10−8–2.0×10−4molL−1 of Pd(II) ion with a detection limit of 6.4×10−9molL−1. Metal ions present at concentrations 15 times higher than that of Pd(II) did not interfere with the determination of Pd(II). The sensor was successfully applied to determine palladium in catalyst and plant samples with a relative standard deviation (RSD) of less than 3.3% (n=5) and recoveries in the range of 99.2–106.5%.

An Ion-Imprinted Microporous Polypropylene Membrane for the Selective Removal of Cu(II) from an Aqueous Solution

An ion-imprinted microporous polypropylene membrane for the selective removal of Cu(II) from an aqueous solution was successfully prepared by combining graft polymerization with chemical modification. The chemical and physical changes of the ion-imprinted membranes surface were characterized by Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (FESEM-EDX), and water contact angle (WCA). The adsorption behaviors of the ion-imprinted membranes towards Cu(II) were investigated in detail using batch experiments. The equilibrium was achieved in approximately 60 min, and the experimental kinetic data fitted the pseudo second-order model better. The maximum adsorption capacity was 183.49 µg/cm2, and the Langmuir equation fitted the adsorption isotherm data. The results of competitive adsorption experiments indicated that the ion-imprinted membranes had high selectivity towards Cu(II), and the selectivity coefficients with respect to Zn(II), Ni(II) and Pb(II) were 60.40, 68.80, and 70.64, respectively. Permeation experiments showed that the ion-imprinted membranes exhibited good permeability and permselectivity towards Cu(II). Furthermore, the ion-imprinted membranes could maintain almost the same adsorption capacity towards Cu(II) even after ten adsorption-desorption cycles.

Development of ion imprinted technique for designing nickel ion selective membrane

An ion imprinted membrane with a porous polyvinylidene fluoride (PVDF) support was prepared by surface ionic imprinting technology. Ion imprinted membranes possess artificial recognition sites, which are able to specifically rebind a target ion in the presence of other similar compounds. In this study, Ni(II) ion imprinted membrane (IIM) was synthesized by copolymerization of Ni(II) ion (or without it for non-imprinted membrane) and dithizone as chelating ligand in the presence of methacrylic acid (MAA), ethyleneglycol dimethacrylate (EGDMA) as monomer and cross-linker, respectively using 2,2-azobisisobutyronitrile (AIBN) as initiator. Dithizone was selected as complex agent to show the capability of using a non-special ligand for synthesis of selective ion imprinted membrane. The affecting parameter such as pH and concentration of Ni 2+ ion solution on the loading capacity of membrane were investigated. To obtain the maximum adsorption efficiency of Ni, pH of the sample solution should be carefully adjusted at 8. In addition, the effect of imprinting technique on the selective recognition of Ni(II) ion towards Co(II) ions through the modified imprinted membrane was studied in the permeation experiments. The results of permeation and adsorption experiment indicated that, the Ni(II) ion imprinted membrane has the ability of specificity and recognition towards the imprinted nickel ion compared to the non-imprinted polymer membrane. The separation factor ( α) of the imprinted membrane for the Ni 2+ ion versus Co 2+ ions was 2.6, whereas the non-imprinted and control membrane (without dithizone ligand) did not show any selectivity.

Molecular Recognition Based Iron Removal from Human Plasma with Imprinted Membranes

The aim of this study is to prepare ion-imprinted poly(2-hydroxyethyl methacrylate) (HEMA) based membranes which can be used for the selective removal of Fe3+ ions from Fe3+-overdosed human plasma. N-methacryloyl-(L)-glutamic acid (MAGA) was chosen as the ion-complexing monomer. In the first step, Fe3+ was complexed with MAGA and then, the Fe3+-imprinted poly(HEMA-MAGA) membranes were prepared by UV-initiated photo-polymerization of HEMA and MAGA-Fe3+ complex in the presence of an initiator (benzoyl peroxide). After that, the template (i.e., Fe3+ ions) was removed by using 0.1 M EDTA solution at room temperature. The specific surface area of the Fe3+-imprinted poly(HEMA-MAGA) membranes was found to be 49.2 m2/g and the swelling ratio was 92%. According to the elemental analysis results, the polymeric membranes contained 145.7 micromol MAGA/g polymer. The maximum adsorption capacity was 164.2 micromol Fe3+/g membrane. The relative selectivity coefficients of ion-imprinted membranes for Fe3+/Zn2+ and Fe3+/Cr3+ were 12.6 and 62.5 times greater than the non-imprinted matrix, respectively. The Fe3+-imprinted poly(HEMA-MAGA) membranes could be used many times without decreasing their Fe3+ adsorption capacities significantly.