Preparation and characterization of Co(II) ion-imprinted composite membrane based on a novel functional monomer

In this paper, a novel functional monomer, N-(pyrrolidin-2-ylmethyl) methacrylamide (PMMA), was synthesized. Using Co(II) ions as the template, 2,2-azoisobutyronitrile (AIBN) as the initiator, ethylene glycol dimethacrylate (EDGMA) as the crosslinking agent, twenty-seven Co(II) ion-imprinted composite membranes (Co(II)-PMMAIICM1~27) and their corresponding non-imprinted composite membranes (PMMA-NICM1~27) were prepared.

Microporous and Mesoporous Materials 334 (2022) 111707 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso Preparation and characterization of Co(II) ion-imprinted composite membrane based on a novel functional monomer Li Zhao b, 1, Deqiong Hu a, c, 1, Huiling Cheng a, * a Faculty of Science, Kunming University of Science and Technology, Kunming, Yunnan, 650500, China Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming, Yunnan, 650051, China c Yunnan Chihong Resources Comprehensive Utilization Co Ltd, Qujing, Yunnan, 655000, China b A R T I C L E I N F O A B S T R A C T Keywords: Novel functional monomer Ion-imprinted composite membrane Membrane selectivity permeation Cobalt In this paper, a novel functional monomer, N-(pyrrolidin-2-ylmethyl) methacrylamide (PMMA), was synthesized Using Co(II) ions as the template, 2,2-azoisobutyronitrile (AIBN) as the initiator, ethylene glycol dimethacrylate (EDGMA) as the crosslinking agent, twenty-seven Co(II) ion-imprinted composite membranes (Co(II)-PMMAIICM1~27) and their corresponding non-imprinted composite membranes (PMMA-NICM1~27) were prepared Additionally, the related parameters of the imprinting system were systematically optimized Co(II) ionimprinted composite membranes (Co(II)-PMMA-IICM16) were prepared using Nylon-6 as the supporting mem­ brane, which was soaked in a pre-polymerized solution of N,N-dimethylformamide and water (DMF: H2O (v/v) = 1: 1) for 180 s, using a molar ratio of template, monomer, and crosslinker of 1: 4: 50 The obtained material had a higher adsorption capacity (Qe = 428.24 mg g− 1) and imprinting factor (IF = 2.36) The surface and internal porosity of Co(II)-PMMA-IICM16 were characterized by scanning electron microscopy and a nitrogen adsorption apparatus In addition, it was found that the adsorption process of Co(II)-PMMA-IICM16 prepared under optimal conditions was better described by a Langmuir isotherm adsorption model, which verified that the adsorption involved monolayer adsorption The kinetics data was more closely fit by a pseudo-second-order kinetics model, indicating that this adsorption process proceeded via chemisorption The permeation experiments indicated that a “delayed” permeation mass transfer mechanism also occurred (β(Co(II)/Cd(II)) = 2.11 and β(Co(II)/Cu(II)) = 1.55) The Co(II) ion-imprinted composite membrane prepared in this paper demonstrated a relatively better imprinting effect, a specific recognition ability for template ions, and good selective permeability These results validated that the design of this novel functional monomer was reasonable, and that it has potential applications in various fields where adsorption is necessary Introduction Cobalt (Co) is a naturally occurring heavy metal that exists in three oxidation states (0, +2, and +3), the most of which is +2 Co(II) is highly susceptible to corrosion by alkali, water, and air, and as a result, it has been widely used in various applications including electroplating, mineral processing, and forging [1,2] Along with economic develop­ ment and social progress, significant amounts of Co(II) have been released into the environment At low levels, Co(II) ion acts as a nutrient and has benefits for both humans and plants [3] In contrast, beyond permissible levels, it may lead to various acute or chronic reactions such as those affecting the gastrointestinal tract, asthma, pneumonia and so on [4–6] Therefore, the effective treatment and removal of Co(II) ions from wastewater is still highly important Ion imprinting technology is derived from molecular imprinting technology, which is also a biomimetic recognition technology that can introduce ion recognition sites into some polymeric materials [7–10] Ion-imprinted polymers prepared by ion imprinting have high affinities and selectivity for template ions [11] Membrane separation technology is one of the most promising separation techniques due to its many advantages such as continuous operation, easy amplification, and low energy consumption However, current commercially-available ultra­ filtration, microfiltration, and reverse osmosis membranes lack pre­ determined selectivity, and it is difficult to achieve the selective * Corresponding author E-mail address: ynchenghl@163.com (H Cheng) These authors contributed to the work equally and should be regarded as co-first authors https://doi.org/10.1016/j.micromeso.2022.111707 Received 18 December 2021; Received in revised form 11 January 2022; Accepted 14 January 2022 Available online 24 January 2022 1387-1811/© 2022 The Authors Published by Elsevier Inc This is an open (http://creativecommons.org/licenses/by-nc-nd/4.0/) access article under the CC BY-NC-ND license L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 separation of individual substances [12,13] Membranes prepared via a combination of ion imprinting techniques allow for the simple, fast, and effective separation of specific ions Ion-imprinted composite membranes (IICMs) are comprised of an ion-imprinted polymer layer on either the surface or pores of an existing membrane, which combines the advantages of an ion-imprinted poly­ mer with the stability of a membrane The recognition ability of IICMs is closely related to the properties of the complexes formed between template ions and functional monomers Therefore, selecting functional monomers that match the functional groups and structures of template ions is the key to preparing IICMs with good performance [14–17] Suitable functional monomers can be selected according to the structure of the template ions Acidic template ions can be selected for basic functional monomers, and mixed functional monomers can also be considered for some complex template ions Acrylic acid, acrylamide, and vinyl pyridine are the mostly common functional monomers used to prepare IICMs [18–23] However, these functional monomers and template ions only weakly bind to each other, so it is difficult to use them for ion imprinting Therefore, much research has focused on designing new functional monomers which possess strong ionic bonding abilities with the template ions for ion imprinting In recent years, some studies have reported the development of novel functional monomers For example, Betra et al [24] synthesized a novel polymerizable functional monomer containing three functional groups, which was then poly­ merized with styrene to prepare a molecular-imprinted polymer mem­ brane which selectively recognized imprinted molecules Fang et al [25] designed and synthesized a heterocyclic compound containing a positively-charged imidazole moiety, tetra-bromine-bi-4,5-2 (methylene bi-imidazole) acridine This compound was used as a functional mono­ mer, antimony potassium tartrate as a template, and bulk polymeriza­ tion was used to successfully prepare a novel Sb(III)-ion-imprinted polymer (CFM-IIP) Xu et al [26] synthesized thymine-isocyanate trie­ thoxysilane (T-IPTS) as a functional monomer to successfully prepare mercury-imprinted polymers capable of specifically recognizing mer­ cury ions Some studies have made progress by synthesizing novel functional monomers with different target ions, as well as analyzing the feasibility, recognition mechanism, and new characterization methods Additionally, identifying and pioneering a new research field using novel functional monomers for ion imprinting has promising prospects In this paper, an absorbent material, Co(II) ion-imprinted composite membranes (Co(II)-PMMA-IICMs) was prepared by Co(II) ion as the template, N-(pyrrolidin-2-ylmethyl) methacrylamide (PMMA) as the novel function monomer, a commercial membrane as the support membrane Additionally, the related parameters of the influence factors were systematically optimized The surface morphology, internal structure, adsorption characteristics, and mass transfer mechanism of the optimal imprinted composite membrane were studied The results showed that the membrane had good specific adsorption recognition and permeation selectivity for Co(II) template ions, and it is expected that the membrane can be used for the removal of Co(II) from aqueous solutions methacrylamide (PMMA) is detailed in the Supplementary Materials Document Ultraviolet–visible spectrophotometry (UV–Vis) (UV-2500, Shi­ madzu, Japan) was used to obtain the UV–Vis spectra of Co(II)-IICMs and NICMs An N2 adsorption apparatus (MFA-140, Builder) and scan­ ning electron microscopy (SEM, Nova Nano SEM 450FEI-IMC, USA) were employed to characterize the surface area and porosity of Co(II)IICMs and NICMs, respectively Inductively coupled plasma optical emission spectroscopy (ICP-OES) (Avio 500, PerkinElmer, America) was used to analyze the concentration of metal ions 2.2 Synthesis of N-(pyrrolidin-2-ylmethyl) methacrylamide The synthetic method of N-(pyrrolidin-2-ylmethyl) methacrylamide is shown in Fig 1, whose steps are detailed below A mixture of N-Boc prolinol (10.05 g, 50 mmol) and anhydrous potassium carbonate (6.9 g, 50 mmol) was formed in a round bottom flask, and anhydrous dichloromethane (150 mL) was used to dissolve the mixture P-toluene sulfonyl chloride (11.5 g, 60 mmol) was added to the mixed solution in batches, and the reaction was carried out for 24 h Once the TLC indicated the disappearance of the reagents, the reaction solution was poured into cold water (200 mL) and stirred for 30 min, and the methylene chloride layer was washed three times with water (50 mL × 3) After drying with anhydrous sodium sulfate, the organic phase was concentrated in vacuo, and compound was obtained without additional purification Compound and sodium azide (6.5 g, 100 mmol) were dissolved in dry DMF in an oil bath at 92 ◦ C, and the reaction was allowed to proceed for 24 h After the reaction was completed, the mixture was cooled to room temperature and dissolved in ethyl acetate (200 mL) Then, after washing the organic layer times with water and drying and concen­ trating with anhydrous sodium sulfate, compound was obtained Compound and palladium on carbon (0.1 g) were dissolved in methanol (100 mL) and allowed to react at room temperature under a hydrogen atmosphere for days After the TLC indicated the disap­ pearance of the reactants, the solution was filtered, and compound was obtained Next, anhydrous dichloromethane (100 mL) was used to dissolve a mixture of anhydrous potassium carbonate (6.9 g, 50 mmol) and methacryloyl chloride (5 mL) with magnetic stirring in an ice bath The dichloromethane solution containing compound was added into the mixture, and the reaction was allowed to proceed overnight Once the TLC indicated the disappearance of the raw materials, the reaction mixture was poured into cold water (200 mL) and stirred for h Then, the methylene chloride layer was washed three times with water (50 mL × 3) After drying with anhydrous sodium sulfate, the organic phase was concentrated in vacuo, and compound was obtained Finally, anhydrous dichloromethane (30 mL) was used to dissolve a mixture of compound and trifluoroacetate (20 mL), and the reaction proceeded for 24 h After the TLC indicated the consumption of reagents, saturated sodium carbonate solution was slowly added dropwise to the mixture until no more gas evolution was observed Then, the solution was stirred for h, and dichloromethane (50 mL × 3) was used to extract the solution After drying with anhydrous sodium sulfate, the organic phase was concentrated in vacuo Light-green oily compounds (3.19 g) were obtained by column chromatography using dichloromethane as the eluent The total yield of the five-step sequence was 38% The intermediates involved in the synthesis process were reported according to Refs [27,28], and final product N-(pyrrolidin-2-ylmethyl) methacrylamide was characterized as follows: H NMR (400 MHz, CDCl3, ppm) δ: 5.21 (s, 1H), 5.10 (s, 1H), 4.96 (brs, 1H), 4.17 (d, J = 7.3 Hz, 1H), 3.55–3.63 (m, 3H), 3.35–3.41 (m, 1H), 2.07 (d, J = 5.2 Hz, 1H), 1.90 (s, 3H), 1.85 (d, J = 6.0 Hz, 2H), 1.70–1.74 (m, 1H), 1.51–1.60 (m, 1H); 13C NMR (100 MHz, CDCl3, ppm) δ: 173.09, 141.33, 116.67, 66.95, 60.99, 50.20, 28.42, 24.78, 19.77 Experimental 2.1 Materials and instruments Analytically pure reagents used in this experiment, including cobalt chloride hexahydrate (CoCl2⋅6H2O), were purchased from Fangchuan Chemical Reagent Technology (Tianjin, China) Ethylene glycol dime­ thacrylate (EDGMA), 2,2-azoisobutyronitrile (AIBN), NaOH, HCl, and CH3CH2COOH were purchased from Aladdin Industrial Corporation (Shanghai, China) and used as received Polyvinylidene fluoride (PVDF), Nylon-6, and polytetrafluoroethylene membrane (PTFE), with pore sizes of 0.45 μm and thicknesses of 125 μm, were obtained from Shanghai Yadong Heji Rosin Co., Ltd, (Shanghai, China) and used to produce adsorbent The synthetic procedure of N-(pyrrolidin-2-ylmethyl) L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 Fig Synthetic method of N-(pyrrolidin-2-ylmethyl) methacrylamide 2.3 Preparation of Co(II) ion-imprinted composite membrane room temperature After 12 h, the solution was analyzed by UV–Vis to determine the concentration of Co(II) ions The adsorption capacity Q (mg.g− 1) of Co(II)-PMMA-IICM16 and PMMA-NICM16 and the imprinting factor IF at equilibrium were calcu­ lated by the following equations: Co(II)-PMMA-IICM were prepared according to the procedure shown in Fig The detailed procedure is as follows: First, 0.0238 g CoCl2⋅6H2O and different amounts of functional monomer N-(pyrrolidin-2-ylmethyl) methacrylamide (PMMA) were mixed and dissolved in solvents, and then shocked for h at 25 ◦ C Then, the crosslinker, ethylene glycol dimethacrylate (EGDMA), and 10.00 mg initiator, 2,2-azoisobutyronitrile (AIBN), were added into this mixture After being ultrasonicated for min, a pre-polymerization complex was formed Next, different support membranes were soaked in a prepolymerization solution for a certain period of time at room tempera­ ture The polymerization was carried out for about 24 h at 60 ◦ C Finally, the obtained Co(II)-PMMA-IICM were washed by a mixture of methanol and acetic acid in a volume ratio of 9: The as-prepared membranes were dried for 24 h after the template ions were completely removed using Soxhlet extraction Non-imprinted composite membranes (PMMA-NICM) were prepared according to the abovementioned method, but the template (CoCl2 6H2O) was absent (1) Q = (C0 − C).V / m IF = QCo(II)− / PMMA− IICM QPMMA− NICM (2) where C0 and C (mg.mL− 1) are the initial and equilibrium concentra­ tions of the Co(II) ions, respectively, V (mL) is the volume of the solu­ tion, and m is the mass of the Co(II)-PMMA-IICM16 2.4.1 Adsorption isotherms The adsorption behavior of Co(II)-PMMA-IICM16 was described by the Langmuir and Freundlich models: 2.4 Batch adsorption experiments Langmuir ⋅ model:⋅C/Q = KL /qm + C/qm (3) Freundlich ⋅ model:⋅lnQ = lnC/n + lnKF (4) where Q (mg⋅g− 1) is the amount of Co(II) ions on Co(II)-PMMA-IICM16 at equilibrium, C (mg⋅mL− 1) is the concentration of the Co(II) ions at equilibrium, qm (mg⋅g− 1) is the maximum adsorption capacity, KL (mL⋅mg− 1) and KF (mg⋅g− 1) represent the equilibrium constants of the First, 20.0 mg Co(II)-PMMA-IICM16 and 10.00 mL Co(II) solution with a fixed initial concentration were added into a stoppered 25.00 mL Erlenmeyer flask Then, the flask containing Co(II) ions was shocked at Fig Schematic of the preparation process of Co(II)-PMMA-IICM L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 Langmuir and the Freundlich models, respectively the left cell, and an identical volume of deionized water was placed into the right cell Then, competitive penetration experiments were carried out using a mechanical stirrer with a fixed speed at 25 ◦ C The amount of metal ions in the receiving solution was determined via ICP-OES The permeation flux J (mg⋅cm− s− 1), permeability coefficient P (cm2⋅s− 1), and permeation selectivity factor β were obtained from the following equations: 2.4.2 Adsorption kinetics Pseudo-first-order and pseudo-second-order kinetic models were used to study the adsorption kinetics of Co(II) on Co(II)-PMMA-IICM16, as shown in equations (5) and (6): Pseudo − first − order ⋅ kinetic ⋅ model: ⋅ ln(Q − Qt ) = − k1 t + lnQ (5) Pseudo − second − order ⋅ kinetic⋅ / / / model:⋅t Qt = t Q + Q2 k2 (6) − where Qe (mg⋅g ) is obtained from the abovementioned contents, Qt (mg⋅g− 1) is the amount of Co(II) adsorbed at time t, K1 (min− 1) and K2 (g⋅mg− 1⋅min− 1) are the rate constants of the pseudo-first-order, and pseudo-second-order kinetic models (7) ΔGθ = ΔH θ − TΔSθ (8) / / lnK = − ΔH RT + ΔSθ R (9) θ / / ln(Q / C) = ΔSθ R − ΔH θ RT (11) P = Ji d/(CFi − CRi ) (12) / βCo2+ /j = PCo2+ Pj ⋅j = ⋅Cu(II)⋅or⋅Cd(II) (13) where A (cm2), d (cm), and V (mL) represent the effective membrane area, membrane thickness, and the volume of the feeding and receiving solutions, respectively ∇Ci/∇t represents the changes in the concen­ trations in the receiving solution, and CFi and CRi are the corresponding ion concentrations in the feeding and receiving pools, respectively 2.4.3 Adsorption thermodynamics The thermodynamic parameters, including the enthalpy change (ΔHθ ), Gibbs free energy change (ΔGθ ), and entropy change (ΔSθ ), were calculated by using the following Van’t Hoff expressions: ΔGθ = − RT lnKd Ji = ΔCi V/ΔtA⋅i = Co(II), ⋅Cu(II), ⋅or⋅Cd(II) Results and discussion 3.1 Effects of various parameters during the preparation of Co(II)PMMA-IICM 3.1.1 Effects of support membrane species The properties of the supporting membrane are one of the important factors affecting the selectivity and permeability of ion-imprinted composite membranes To obtain a better Co(II)-PMMA-IICM, a series of (Co(II)-PMMA-IICM1~3) and corresponding non-imprinted mem­ branes (PMMA-NICM1~3) were prepared using polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and Nylon-6 microfiltration membranes The properties of these composites were tested using Co(II) solutions It can be seen from Fig that the Co(II)-PMMA-IICM3 had a better adsorption capacity (692.89 mg g− 1) than PMMA-NICM3, and its imprinting factor (IF) reached 1.24 This may be due to the fact that the Nylon-6 membranes are more hydrophilic than the PTFE and PVDF membranes That is, the Nylon-6 membrane pores were more easily filled with solvent and solute molecules because they were more easily adsorbed onto the membranes, which increased the adsorption capacity of the Nylon-6 membrane [29] Therefore, the following experiments used Nylon-6 as the support membrane (10) where R (8.314 J mol− K− 1) is the universal gas constant, T (K) is the absolute temperature, and Kd is the thermodynamic equilibrium constant 2.5 Permeation experiments Competitive penetration tests were used to test the selective permeation performance of Co(II)-PMMA-IICM16 First, Co(II)-PMMAIICM16 was fixed on an H-shaped permeation device (Fig 3), with a total volume of 200 mL and an area of 1.5 cm2 at the joint of the two cells Then, 100.00 mL of an aqueous solution containing Co(II), Cd(II), and Cu(II) ions with identical concentrations of 25 mg mL− was added into 3.1.2 Effects of functional monomer dosages To investigate the effect of functional monomer dose during poly­ merization on Co(II)-PMMA-IICMs, several Co(II)-PMMA-IICM3~6 were fabricated using template-to-monomer ratios of 1:2, 1:4, 1:6, and 1:8 to identify the appropriate ratio As shown in Fig 5, when too little or too much was used, the adsorption of the Co(II)-PMMA-IICMs depended on the amount of functional monomer due to the specific recognition ability of the imprinted membrane majority When an insufficient amount of functional monomer was used, it is difficult to form stable complexes with imprinted ions In contrast, excessive functional monomer can produce many non-specific binding sites in the membrane, which can reduce the recognition ability and selectivity of the membrane [30,31] According to the imprinting factor and adsorption capacity of the imprinted composite membranes, the optimal amount of functional monomer was mmol Therefore, the molar ratio of the template ion to functional monomer was 1:4 3.1.3 Effects of the amount of cross-linker Effects of the amount of cross-linker (EGDMA) on the adsorption capacity was also investigated The crosslinking agent is the main component in ion-imprinted composite membranes and can fix template-monomer complexes in the polymer matrix The amount of Fig Schematic of the H-Shape permeation device L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 Fig The adsorption capacity of support membrane species (mCo(II)-PMMA-IICM = 20 mg; CCo(II) = 25 mg mL− 1; t = 12 h; pH = 7; T = 25 ◦ C) Fig The adsorption capacity of functional monomer dosages (mCo(II)-PMMA-IICM = 20 mg; CCo(II) = 25 mg mL− 1; t = 12 h; pH = 7; T = 25 ◦ C) crosslinking agent can also affect the structural integrity, accessibility, and quantity of recognition sites, thereby changing the mesh structure and adsorption properties of composite membranes [32] Fig shows the adsorption capacity of Co(II)-IICM3,7~12 and NICM3,7~12 prepared from different molar ratios of template ions and crosslinking agents (1:10, 1:20, 1:30, 1:40, 1:50, 1:60, and 1:70, respectively) Fig shows that the maximum amount of adsorbed Co(II) ion (625.84 mg g− 1) was obtained when using Co(II)-PMMA-IICM12 pre­ pared with a 1:50 M ratio of Co(II) ion to EGDMA This material had a better imprinting factor (1.40) If too little crosslinking agent was used, the template-monomer chelate structure did not form during prepolymerization, Moreover, the lack of a crosslinking agent was not helpful for forming imprinted sites [33], which gave the imprinted composite membrane a poor selectivity However, the use of excessive crosslinking agent increased the rigidity of the membrane, and made the substrate close to the imprinting site As a result, a template: functional monomer: crosslinker ratio of 1:4:50 was selected to prepare the Co (II)-PMMA-IICM L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 Fig The adsorption capacity of amount of cross-linker (mCo(II)-PMMA-IICM = 20 mg; CCo(II) = 25 mg mL− 1; t = 12 h; pH = 7; T = 25 ◦ C) 3.1.4 Effects of solvent ratio Co(II) ions are water-soluble, while cross-linking agents and func­ tional monomers are hydrophobic To maintain the binding spaces of Co (II) ions during polymerization, the imprinting process requires a ho­ mogenous mixture of Co(II) ions, functional monomers, and crosslinking agents Therefore, the pore-forming solvent must be mixed with water and an organic solvent [34] In this work, organic solvents (CH3OH, CH3CH2OH, (CH3)2CHOH, and CH3CH2CN) and H2O at a volume ratio of 1:1 (v/v) were used Additionally, different volume ra­ tios of N, N-dimethylformamide (DMF) and H2O (1:1, 1:3, 2:3, 3:1, 3:2, 3:7, 7:3) were used during preparation The results in Table show that the optimal solvent composition was 1:1 (v/v) DMF:H2O, and the experiment achieved a better imprinting factor of 2.36 using Co(II)-PMMA-IICM16 (428.24 mg g− 1), compared with PMMA-NICM16 (181.68 mg g− 1) The influence of solvent composition on the imprinting factor was greater than that on the adsorption amount The imprinting factor is used as the main means to evaluate adsorption Therefore, Co(II)-PMMA-IICMs using an optimum volume ratio (v/v) of DMF:H2O 1:1 was used in the following experiments 3.1.5 Effects of soaking time on membrane In the pre-polymerization system, a short soaking time was not favorable for the deposition of the imprinted polymer, making it difficult for the membrane to be covered However, excessive soaking times resulted in the formation of thick imprinted polymer deposits on the composite membrane Under these conditions, it is difficult for the substrate to access the recognition sites in the imprinted membrane interior, which is not conducive to the adsorption and recognition of the substrate by the membrane [35] Therefore, soaking times of 30 s, 60 s, 180 s, 360 s, 1800 s, and 3600 s were selected for the study, as shown in Fig It is evident from Fig that the adsorption ability of Co(II) ions increased with soaking times less than 180 s The better adsorption ca­ pacity of Co(II)-PMMA-IICM16 and PMMA-NICM16 were 428.24 and 181.68 mg g− separately, and the imprinting factor is calculated to be 2.36 from these two values After 180 s, the adsorption of Co(II) ions decreased to 324.42 mg g− The ion-imprinted composite membrane showed the best affinity and specific recognition to Co(II) ions when the base membrane was soaked for 180 s The optimized Co(II)-PMMA-IICM16 had a relatively good adsorption capacity and high imprinting factor when the following preparation conditions were used: a Nylon-6 microporous membrane as the sup­ porting membrane, a solvent volume ratio of 1:1 (v/v) of DMF: H2O, a molar ratio of template ions, functional monomer, and cross-linker of 1:4:50, and a membrane soaking time of 180 s Table The adsorption capacity of various solvent ratios (mCo(II)-PMMA-IICM = 20 mg; CCo − ◦ (II) = 25 mg mL ; t = 12 h; pH = 7; T = 25 C) Membrane Solvent ratio (v:v) Q (Co(II)-PMMA-IICM) (mg.g− 1) Q (PMMA-NICM) (mg.g− 1) IF 12 13 CH3OH: H2O (1: 1) CH3CH2OH: H2O (1: 1) (CH3)2CHOH: H2O (1: 1) CH3CH2CN: H2O (1: 1) DMF: H2O (1: 1) DMF: H2O (1: 3) DMF: H2O (2: 3) DMF: H2O (3: 1) DMF: H2O (3: 2) DMF: H2O (3: 7) DMF: H2O (7: 3) 625.84 672.34 447.03 560.29 1.40 1.20 689.66 538.79 1.28 512.40 413.22 1.24 428.24 639.48 344.46 243.75 301.17 379.30 251.89 181.68 586.94 268.24 233.98 229.26 292.92 179.46 2.36 1.09 1.28 1.04 1.31 1.29 1.40 14 15 16 17 18 19 20 21 22 3.2 Characterization 3.2.1 SEM The surface topographies of Nylon-6, Co(II)-PMMA-IICM16, and PMMA-NICM16 were obtained using SEM (Fig 8), and indicate that the surface morphology and pore structures of Co(II)-PMMA-IICM16 and PMMA-NICM16 were different than the Nylon-6 membrane The surface of the Nylon-6 base membrane (Fig 8a) exhibited a symmetrical and flat network structure compared with Co(II)-PMMA-IICM16 (Fig 8b) The corresponding surface of PMMA-NICM16 (Fig 8c) appears rough, indi­ cating that the surfaces of the base membranes of Co(II)-PMMA-IICM16 and PMMA-NICM16 were coated with a thin polymer layer L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 Fig The adsorption capacity as a function of membrane soaking time (mCo(II)-PMMA-IICM = 20 mg; CCo(II) = 25 mg mL− 1; t = 12 h; pH = 7; T = 25 ◦ C) Fig SEM images of the surfaces of Nylon-6(a), Co(II)-PMMA-IICM16 (b), and PMMA-NICM16 (c) It was also clearly shown that Co(II)-PMMA-IICM16 (Fig 8b) had a greater pore diameter than PMMA-NICM16 (Fig 8c), which can be attributed to the influence in the membrane surface area and pore structure during imprinting Ion-imprinted cavities were located at the surface and inside Co(II)-PMMA-IICM16, and these cavities can match the size and function of imprinted molecules Furthermore, these results are consistent with those obtained in adsorption experiments NICM16 were obviously different As summarized in Table 2, all related parameters of Co(II)-PMMAIICM16 and PMMA-NICM16 were displayed, including the specific sur­ face area and average pore diameter which values are distributed at 9.019, 9.660 m2 g− and 11.768, 10.518 nm, respectively It can be inferred that both Co(II)-PMMA-IICM16 and PMMA-NICM16 belong to mesoporous material according to pore diameter, the Co(II)-PMMAIICM16 is higher than PMMA-NICM16 between two kinds of value Large surface area can provide more recognition sites to facilitate cobalt adsorption, and the pore sizes of the materials further demonstrate that there is a “template effect” in Co(II)-PMMA-IICM16 3.2.2 BET To determine the effect of the template (Co(II) ions) during prepa­ ration and Co(II) adsorption ability, Co(II)-PMMA-IICM16 and PMMANICM16 were subjected to BET analysis, which is depicted in Fig 9a and b, respectively Both the pore diameter distributions and surface areas were tested The results shown in Fig 9, according to the IUPAC clas­ sification method, show that Co(II)-PMMA-IICM16 and PMMA-NICM16 were a type IV isotherms and typical mesoporous materials In addition, the slopes of the adsorption-desorption isotherms of Co(II)-PMMAIICM16 and PMMA-NICM16 were significantly different, indicating that the membrane pore structure of Co(II)-PMMA-IICM16 and PMMA- 3.3 Adsorption isotherms The Co(II) adsorption capacity using Co(II)-PMMA-IICM16 and PMMA-NICM16 with an initial concentration range of 5–30 mg mL− was studied at a pH of The results are shown in Fig 10 The adsorption capacities of Co(II)-PMMA-IICM16 and PMMA-NICM16 gradually increased as the initial concentration of Co(II) ions increased As the L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 Fig The N2 adsorption-desorption isotherms of Co(II)-PMMA-IICM16 (a) and PMMA-NICM16 (b) (insets are the pore diameter distributions) relatively higher than PMMA-NICM16 because PMMA-NICM16 may not have had any cavities which matched the Co(II) ions The PMMANICM16 could adsorb Co(II) ions to some extent, but not selectively Co (II)-PMMA-IICM16 contains many cavities which match the shape and size of Co(II) ions, and these cavities could specifically recognize and memorize Co(II) ions Thus, the adsorption capacity of PMMA-NICM16 was lower than Co(II)-PMMA-IICM16 The data was fitted as 1/Ce versus 1/Qe and lnCe versus lnQe to study the Langmuir and Freundlich models, respectively, the results are shown in Fig 11a and b KL, qm, n, and KF were calculated using the slope and intercept of the correlation lines, and the results are summarized in Fig 11 The linear correlation coefficient (R2) of the plot of the Freundlich model was relatively better than the Langmuir model, which indicates that the adsorption process was closer to a Freundlich model Table The corresponding parameters of Co(II)-PMMA-IICM16 and PMMA-NICM16 Material Surface area (m2.g− 1) Pore volume (cm3.g− 1) Average pore diameter (nm) Co(II)-PMMAIICM16 PMMA-PMMANICM16 9.660 0.032 11.768 9.019 0.031 10.518 initial concentration of Co(II) increased, the mass transfer driving force between the solution and the membrane increased, which increased the adsorption capacity Additionally, the adsorption ability of Co(II)-PMMA-IICM16 was Fig 10 Effect of initial Co(II) concentration on the adsorption capacity of Co(II)-PMMA-IICM16 L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 Fig 11 The Langmuir model (a) and Freundlich model (b) for the adsorption of the Co(II) ions on the Co(II)-PMMA-IICM16 This suggests that adsorption may have occurred through a multilayer adsorption process NICM16 This may be due to the fact that the initial adsorption included adsorption by surface imprinted pores As the adsorption time increased, the surface imprinted pores became saturated When the imprinted ions were transferred into the membrane interior, the resistance increased, which decreased the adsorption rate Finally, the adsorption amount slowly increased and finally reached equilibrium, but there were no pores which corresponded to the template ion structure in PMMANICM16 The adsorption was mainly affected by the non-specific adsorption of the surface non-imprinted composite membrane, and so adsorption equilibrium was quickly reached Plots of t versus log (Qe-Qt) for the Co(II) ions adsorption kinetics behavior are shown in Fig 13a, and the constants of Co(II)-PMMAIICM16 and PMMA-NICM16 were calculated from the correlation line 3.4 Adsorption kinetics The residence times of the adsorbate at the solid-solution interface and solute adsorption rate were determined using kinetics models using data obtained from experiments performed between and 180 Fig 12 shows that the adsorption rate of Co(II)-PMMA-IICM16 and the corresponding PMMA-NICM16 rapidly increased within 30 min, and the adsorption amount of Co(II)-PMMA-IICM16 increased much more rapidly than PMMA-NICM16 Finally, the adsorption amount tended to reach equilibrium at 45 using Co(II)-PMMA-IICM16 and PMMA- Fig 12 Kinetic adsorption curves of Co(II)-PMMA-IICM16 and PMMA-NICM16 L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 Fig 13 The pseudo-first-order (a) and pseudo-second-order (b) kinetic models of Co(II)-PMMA-IICM16 and PMMA-NICM16 The linear correlation coefficients (R2) of these plots were relatively worse Plots of t versus t/Qt for the Co(II) ions adsorption kinetic behavior are shown in Fig 13b Compared with the plots in Fig 13a, the linear correlation (R2) demonstrated that a pseudo-first-order kinetics model was not as good as the pseudo-second-order kinetics model The rate constant K2 for Co(II)-PMMA-IICM16 and PMMA-NICM16 were 0.0024 and 0.0027 g mg⋅min− 1, respectively, which may be due to diffusion resistance of the Co(II) ions to functional monomers [36] The above data indicate that the entire adsorption process of Co(II) ions on Co(II)-PMMA-IICM16 and PMMA-NICM16 was mainly controlled by chemical adsorption In other words, the adsorption capacity of ad­ sorbents was proportional to the number of active sites on their surface, and chemisorption may be the rate-limiting step in the overall adsorp­ tion process 3.6 Effects of pH during Co(II) adsorption The adsorption process was significantly affected by the pH of aqueous solution, which can affect the protonation of the amino group and the degree of ionization of the adsorbate The effects of the pH value of Co(II) ion solution on Co(II)-PMMA-IICM16 adsorption were studied and discussed in this section, and the results are shown in Fig 14 When the pH increased from to 7, the amount of adsorbed Co(II) increased from 312.56 mg g− to 359.47 mg g− 1, and reached a maximum value (359.47 mg g− 1) when the pH was Further increasing the pH caused the adsorption amount to decrease to 348.49 mg g− The reason for the initial increase followed by the decrease may be that the amino group was protonated [38], which affected the surface morphology of Co(II)-PMMA-IICM16 3.7 Permeation selectivity of membranes 3.5 Adsorption thermodynamics Permeation selectivity experiments provided a key understanding of the relationship between the template imprinting sites and arrangement of functional groups According to the various ways of transferring imprinting ions in the membrane, the mass transfer mechanisms of the imprinted membrane can be classified as either “promoting” or “delaying” permeation [39] Due to the presence of a concentration gradient, imprinted ions and other ions spread in the same direction during the promoting permeation process In this process, the imprinted ions are preferentially adsorbed onto the holes with specific recognition abilities, which can slow down other ion penetration rates and promote the mass transfer of target ions Moreover, during delayed permeation, the specific recognition holes interact with target ions to reach satura­ tion, but other ions which not interact with the recognition sites can diffuse to the other side of the membrane The permeation selectivity of the Co(II)-PMMA-IICM16, which pos­ sesses the optimal adsorption capacity and imprinting factor, was studied and discussed in this part Co(II), Cd(II), and Cu(II) ions were add to the feeding solution at identical concentrations, and the results are shown in Table The permeation flux J of Co(II), Cd(II) and Cu(II) ions on Co(II)-PMMA-IICM16 reached 4.09 × 10− 5, 8.39 × 10− and 66.25 × 10− mg cm− s− 1, respectively Additionally, the permeability coefficient P of Co(II), Cd(II), and Cu(II) ions reached 7.57 × 10− 10, 1.60 × 10− and 1.17 × 10− cm2 s− 1, respectively The transmittance of Co (II) ions was significantly lower than Cu(II) and Cd(II) ions, possibly because the holes on the Co(II)-PMMA-IICM16 interacted with the Co(II) To study the effects of temperature on the adsorption amounts of the Co(II)-PMMA-IICM16, experiments were carried out between 15 and 55 ◦ C The adsorption thermodynamics were studied by calculating several parameters From Table 3, it can be seen that the value of ΔGθ was negative, indicating that the adsorption of Co(II) on the Co(II)PMMA-IICM16 was a spontaneous process The values of ΔHθ and ΔSθ were − 5288 J mol− and 3.574 J mol− K− 1, respectively The negative value of ΔHθ indicates that the adsorption reaction was exothermic Therefore, a higher temperature hindered the adsorption of Co(II) ions on Co(II)-PMMA-IICM16 The positive values of ΔSθ indicate that the randomness of the solid/dissolved interface increased during adsorption [37] Table The thermodynamics model parameters T (K) ΔGθ (J⋅mol− 1) 263 273 283 293 303 − − − − − 6228 6264 6299 6335 6371 ΔHθ (J⋅mol− 1) ΔSθ (J⋅mol− 1⋅K− 1) − 5288 3.574 10 L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 Fig 14 Effect of pH on the adsorption capacity of Co(II)-PMMA-IICM16 Table The permeation selectivity of Co(II), Cd(II), and Cu(II) ions through Co(II)PMMA-IICM16 Membranes Co(II)-PMMAIICM16 Substrates Co(II) ions J (mg cm− s− 1) 4.09 × 10− − Cd(II) ions 8.39 × 10 Cu(II) ions 6.25 × 10− P (cm2 s− 1) 7.57 × 10− 10 1.60 × 10− 1.17 × 10− β Co/ β Cd Cu 2.11 1.55 Co/ ions until adsorption reached saturation In contrast, Cd(II) and Cu(II) ions did not interact with the recognition sites and diffused to the other side of Co(II)-PMMA-IICM16 Therefore, the penetration of Co(II) ions through Co(II)-PMMA-IICM16 follows a “delayed” permeation mass transfer mechanism, and demonstrates that there is indeed a hole in Co (II)-PMMA-IICM16 that selectively binds to the template ions, giving rise to selective permeability Fig 15 Regeneration testing of Co(II)-PMMA-IICM16 3.8 Regeneration testing imprinted composite membranes (Co(II)-PMMA-IICMs) to selectively adsorb Co(II) ions Co(II)-PMMA-IICM16 was prepared which showed a high Co(II) adsorption capacity (428.24 mg g− 1) and imprinting factor (2.36) The material was prepared in a pre-polymerized solution of DMF: H2O (v/v) 1:1 for 180 s via thermal initiation with AIBN, Nylon-6 as the supporting membrane, and a molar ratio of template (Co(II) ions), functional monomer (N-(pyrrolidin-2-ylmethyl) methacrylamide), and cross-linker (EDGMA) of 1:4:50 The batch adsorption experiments indicated that the initial adsorp­ tion of Co(II) ions was relatively fast, and the absorption process reached equilibrium within only 45 The adsorption kinetics were fit to a pseudo-second-order reaction kinetics model, and the adsorption iso­ therms for Co(II) were closer to a Freundlich model, suggesting that the adsorption may proceed via monolayer adsorption The permeation selectivity experiments indicated that Co(II)-PMMAIICM16 could selectively recognize imprinted Co(II) ions The Recycling properties is extremely vital for adsorbed materials, especially in the treatment of actual samples, excellent performance can not only save production costs but also maximize profits to a certain extent For investigating the regeneration ability of Co(II)-PMMAIICM16, a set of testing were conducted As Fig 15 displayed, after four cycles of using, it still has good adsorption performance, and the adsorption rate only decreases by 16.6%, in addition, it can also be seen that the membrane of loading Co(II) is easier to elute target ion In summary, Co(II)-PMMA-IICM16 exhibit high adsorption rate and regeneration for Co(II) which expected to be used for the treatment of cobalt in actual sewage Conclusions In this study, a novel functional monomer, N-(pyrrolidin-2-ylmethyl) methacrylamide, was synthesized and used to fabricate Co(II) ion11 L Zhao et al Microporous and Mesoporous Materials 334 (2022) 111707 permeation selectivity factors (β) of Co(II)-PMMA-IICM16 for Co(II) ions was 2.11 and 1.55 for Cd(II) ions and Cu(II) ions, respectively, showing that Co(II)-PMMA-IICM could be used to selectively recognize and adsorb Co(II) ions The effective adsorption ability of Co(II)-PMMA-IICM verified that Co(II)-PMMA-IICM is a promising material for the selective adsorption of Co(II) ions from aqueous solutions [15] [16] [17] CRediT authorship contribution statement Li Zhao: Methodology, Project administration, Data curation, Writing – original draft Deqiong Hu: Writing – original draft, Writing – review & editing, Software Huiling Cheng: Supervision [18] [19] Declaration of competing interest [20] The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper [21] Acknowledgements [22] This work was financially supported by the Natural Science Foun­ dation of China (no 21764008 and 51674128) [23] References [24] [1] F.S.K.A.H Esmaeili, Synthesis of 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Synthesis, characterization and application of a novel ion-imprinted polymer based voltammetric sensor for selective extraction and trace determination of cobalt (II) ions [J], Sensor Actuator B