Ion-Imprinted Polymeric Materials for Selective Adsorption of Heavy Metal Ions from Aqueous Solution

Abstract

The introduction of selective recognition sites toward certain heavy metal ions (HMIs) is a great challenge, which has a major role when the separation of species with similar physicochemical features is considered. In this context, ion-imprinted polymers (IIPs) developed based on the principle of molecular imprinting methodology, have emerged as an innovative solution. Recent advances in IIPs have shown that they exhibit higher selectivity coefficients than non-imprinted ones, which could support a large range of environmental applications starting from extraction and monitoring of HMIs to their detection and quantification. This review will emphasize the application of IIPs for selective removal of transition metal ions (including HMIs, precious metal ions, radionuclides, and rare earth metal ions) from aqueous solution by critically analyzing the most relevant literature studies from the last decade. In the first part of this review, the chemical components of IIPs, the main ion-imprinting technologies as well as the characterization methods used to evaluate the binding properties are briefly presented. In the second part, synthesis parameters, adsorption performance, and a descriptive analysis of solid phase extraction of heavy metal ions by various IIPs are provided.

Keywords: adsorption; heavy metal ions; ion-imprinted polymers; selectivity; wastewater treatment.

Figure 1

A timeline showing the number of publications on IIPs and composite IIPs in the last 16 years indexed by the Web of Science™ database.

Figure 2

A schematic representation of the steps employed within the IIPs synthesis. The imprinting process is presented using functional monomers as ligand.

Figure 3

Periodic table of elements. The target metal ions discussed in this work are highlighted in blue.

Figure 4

Strategies applied to prepare IIPs materials (IIT is the abbreviation for ion imprinting technology).

Figure 5

SEM micrographs of Cu(II)-imprinted P(MAA-co-4-VP) microparticles (A); internal morphology of Cu(II)-imprinted P(MAA-co-4-VP) microparticles (B) (reproduced with permission from Ref. [52]. Copyright 2010 Elsevier); SEM micrographs of Cu(II)-imprinted P(MMA-co-PA) beads (C); internal morphology of Cu(II)-imprinted P(MMA-co-PA) beads (D) (reproduced with permission from Ref. [56]. Copyright 2020 Elsevier).

Figure 6

Preparation of Cu(II)-imprinted PAAm/CS/zeolite composite cryogels (A) and the removal of template Cu(II) ions and partial hydrolysis of amide groups in PAAm (B) (reproduced with permission from Ref. [42]. Copyright 2018 Elsevier). SEM micrographs of Cu(II)-imprinted PAAm/CS/zeolite composite cryogels after the elution of Cu(II) ions recorded perpendicular (C) and parallel (D) to the direction of freezing (reproduced with permission from Ref. [42]. Copyright 2018 Elsevier). The kinetics performance of Cu(II)-imprinted PAAm/CS/zeolite composite cryogels in successive sorption and desorption of Cu(II) ions (E) (reproduced with permission of Romanian Academy Publishing House, the owner of the publishing rights, Ref. [23]). Optical images of Cu(II)-imprinted (denoted as II-CC15.H) and non-imprinted (denoted as NI-CC15.H) PAAm/CS/zeolite cryogels before and after HMIs sorption in multicomponent solutions (F) (reproduced with permission from Ref. [42]. Copyright 2018 Elsevier).

Figure 7

Representation with the preparation, and HMIs adsorption and desorption by thermosensitive Cu(II)-imprinted PNIPAAm-CS composites (A). Effect of interfering HMIs on the equilibrium adsorption capacity (q_e, mg/g) (B) and desorption percentage (D, %) (C) of Cu(II)-imprinted PNIPAAm-CS composites. (Adapted with permission from Ref. [64]. Copyright 2020 Elsevier).

Figure 8

Schematic illustration of imprinting process for the preparation of Zn(II)-IP by bulk polymerization. (Adapted with permission from. Ref. [89]. Copyright 2014 Elsevier).

Figure 9

SEM micrographs of (A) exterior and (B) interior of Zn(II)-IP particles composed of 2,2′-bipyridyl and 4-VP monomers cross-linked with EGDMA (reproduced with permission from Ref. [90]. Copyright 2013 Elsevier).

Figure 10

(A) The preparation strategy of Co(II)-imprinted CS/zeolite cryo-composites and removal of template ions with ethylenediaminetetraacetic acid disodium salt dihydrate (Na₂EDTA). (B) Selectivity mechanism of Co(II)-imprinted CS/zeolite cryo-composites at pH 4 and pH 6 (ion-imprinted composites = IIPZH and IIPZNa, non-imprinted composites = NIPZ and NIPNa; zeolites (Z1, Z2) converted into the H⁺ or Na⁺ form; Z1 = 60–70 wt% clinoptilolite, Z2 = 82–86 wt% clinoptilolite). (C) Optical images of IIPZH1 and IIPZNa1 composites loaded with Co(II) ions at pH 4 and pH 6. (D) SEM micrographs of IIPZH1 and IIPZNa1 sorbents loaded with Co(II) ions. (E) Selective sorption of Co(II) ions from their five-component mixtures onto the composite cryo-beads. (F) The reusability performance of IIPZH1 and IIPZNa1 sorbents after five consecutive sorption–desorption cycles. (Reproduced with permission from Ref. [100]. Copyright 2020 Elsevier).

Figure 11

(A) Adsorbed template and competitive ions onto PHEMAC and PHEMAC-Fe(III) monoliths for Fe(III)/competitive ion pairs (reproduced with permission from Ref. [114]. Copyright 2010 John Wiley and Sons). (B) Adsorption of Fe(III) at two temperatures (reproduced with permission from [115]). SEM images of NIP (C) and Fe(II)-IIP (D) particles; Mag 10000x (reproduced with permission from Ref. [119]. Copyright 2017 Elsevier). Effect of the mole ratio between AA and Fe(III) on the selectivity factor (E) and relative Selectivity factor (F) (reproduced with permission from Ref. [120]. Copyright 2019 Elsevier).

Figure 12

(A) Schematic illustration of Hg(II)-IP preparation; (B) Adsorption isotherm curves of IIPs and NIPs for Hg(II) in aqueous solutions; (C) Adsorption capacities for Hg(II) in the presence of 4 mg/L Hg(II) and 40 mg/L of other metal ions (experimental conditions: IIPs, 20 mg; V, 10 mL; pH, 7.0). (Reproduced with permission from Ref. [128]. Copyright 2011 Royal Society of Chemistry).

Figure 13

Schematic illustration of the imprinting process for preparation of the Cr(III)-phen-ST-IP (reproduced with permission from Ref. [140]).

Figure 14

Schematic illustration of the action of PP-IIP in the removal of Cr(VI). Green circle represents Cr₂O₇²⁻ anions (reproduced with permission from Ref. [144]. Copyright 2021 Elsevier).

Figure 15

Preparation scheme of CMC/EDA imprinted polymer (reproduced with permission from Ref. [154]. Copyright 2017 Elsevier).

Figure 16

Schematic illustration of the preparation of the Ru–BnTSn (reproduced with permission from Ref. [165]. Copyright 2009 RSC Publishing).

Figure 17

(A) Ag(I) sorption capacity of CS hydrogels with different imprinting ratios (Nonim = non-imprinted hydrogels; Agim3 to Agim100 = hydrogels with different Ag(I) imprinting mass ratios). (Reproduced with permission from Ref. [170]. Copyright 2012 American Chemical Society) (B) Competitive adsorption of Ag(I) and Cu(II) by Ag(I)-imprinted CS hydrogels with different imprinting ratios. (Reproduced with permission from Ref. [170]. Copyright 2012 American Chemical Society) (C) The effect of pH on Ag(I) and Cu(II) ions sorption by Ag(I)-imprinted CS gel beads. (Reproduced with permission from Ref. [171]. Copyright 2015 Elsevier) (D) Ag(I) sorption isotherms (with Langmuir and Freundlich models fitting profiles) by Ag(I)-imprinted and non-imprinted CS-P(DVB-glycidyl methacrylate (GMA)-ST) particles. (Reproduced with permission from Ref. [172]. Copyright 2015 American Chemical Society) (E) Selectivity of Ag(I) sorption by Ag(I)-imprinted and non-imprinted CS-P(DVB-GMA-ST) particles. (Reproduced with permission from Ref. [172]. Copyright 2015 American Chemical Society) (F) The effect of morphology on Ag(I) sorption by Ag(I)-imprinted CS-P(DVB-GMA-ST) particles. (Reproduced with permission from Ref. [172]. Copyright 2015 American Chemical Society).

Figure 18

(A) Illustration with the Pd(II)-imprinted CS fibers by double ECH cross-linking. (Reproduced with permission from Ref. [178]). (B) The effect of equilibrium pH on the sorption of metal ions by non-imprinted (NIF) and Pd(II)-imprinted (IIF) CS fibers. (Reproduced with permission from Ref. [179]. Copyright 2015 Elsevier) Column adsorption (C) and desorption (D) of Pd(II), Co(II), Ni(II), Cu(II), and Pt(IV) from hydrometallurgy wastewater onto the Pd(II)-imprinted CS fibers. (Reproduced with permission from Ref. [180]. Copyright 2020 Elsevier).

Figure 19

(A) Coordination of uranyl ions in active sites on the CS surface (adapted from Ref. [188]. Copyright 2020 Elsevier). (B) Chelation of lanthanides in cavities of IIP (adapted from Ref. [202]. Copyright 2015 American Chemical Society).

Figure 20

(A) Preparation of P(MAA-EGDMA)-g-CS IPN hydrogels in presence of Pb(II) ions as template. (B) SEM micrograph of the Pb(II)-imprinted P(MAA-EGDMA)-g-CS IPN hydrogels. Sorption of Pb(II) ions in presence of competitive HMIs from printed circuit board recycling unit wastewaters (C) and sorption of Pb(II) and W(VI) in five consecutive cycles (D) in column setup (pH 6, flow rate 2 mL/min, column: height 7 cm, diameter 8 mm). (Adapted with permission from Ref. [207]. Copyright 2016 American Chemical Society).