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

Preparation and Performance Research of Pb(II)-Imprinted Acrylonitrile-Co-Acrylic Acid Composite Material with Modified Sand Particles as Carrier

Lead (Pb) is classified as a prevalent metallic pollutant, significantly impacting the ecological environment, especially human health. Consequently, it is crucial to develop adsorbent materials that are environmentally friendly, cost-effective, and which possess high selectivity. This study aims to fabricate a Pb(II)-imprinted acrylonitrile-co-acrylic acid composite material by using modified sand particles as the carrier, and then to investigate its properties. Through pretreatment of sand particles, acrylonitrile and acrylic acid were polymerized on the surface of modified sand particles, and Pb(II) served as a template ion for imprinting. A variety of characterization methods were used to verify the composite material and conduct an analysis of its morphology, chemical composition, and pore characteristics. The adsorption efficiency of this composite material for Pb(II) is comprehensively explored, with the process involving adsorption kinetics, adsorption isotherms, selective adsorption, and reuse experiments. Through static adsorption experiments, multiple elements influencing the adsorption ability of the composite material towards Pb(II) are investigated. It was demonstrated by the results that the composite material prepared possesses a rich pore structure and excellent Pb(II) recognition ability. The investigation on adsorption kinetics is in line with the quasi-first-order and quasi-second-order kinetic models, while the adsorption isotherm, obeys the Langmuir model. The ideal adsorption conditions were pH = 7, with the adsorption reaching equilibrium within 105 min. Even when multiple interfering ions were present, it still had high selectivity for Pb(II). The composite material showed an adsorption saturation capability reaching 41.83 mg·g-1, considerably surpassing the non-imprinted counterpart. After being reused eight times, the composite material can still maintain an adsorption efficiency for Pb(II) that is above 79% and demonstrates high potential in the practical application environment.

Synthesis and Study of Sorption Properties of Zinc-Imprinted Polymer

Zinc-imprinted polymer (ZnIP) and non-imprinted polymer (NIP) were synthesized by radical polymerization, and their properties were studied. The novelty of the work lies in the use of humic acids isolated from coals of the Shubarkol deposit (Karaganda, Kazakhstan) as a basis for the imprinted polymer matrix, with methacrylic acid and ethylene glycol dimethacrylate as a functional monomer and a cross-linking agent, respectively. The composition and structure of ZnIP and NIP were characterized using various physicochemical methods. The specific surface area of ZnIP determined by the BET method was 40.60 ± 0.4 m2/g, which is almost twice as high as the similar indicator for NIP (21.50 ± 0.3 m2/g). In sorption tests of solutions with bimetallic ions, ZnIP demonstrates higher adsorption: 96.15% for Zn2+ and 74.88% for Pb2+, while NIP adsorbs only 81.33% and 60.11%, respectively. Sorption on both polymers is described by a pseudo-first-order equation (r > 0.99). The distribution coefficients for ZnIP are higher than for NIP. ZnIP has a relative selectivity that exceeds NIP by 2.90 times. The research results indicate the promise of using ZnIP for the selective removal of zinc ions from solutions of multicomponent systems, including wastewater, making it a valuable material for solving environmental and technological problems.

Green and Mild Fabrication of Magnetic Poly(trithiocyanuric acid) Polymers for Rapid and Selective Separation of Mercury(II) Ions in Aqueous Samples

The removal and detection of highly toxic mercury(II) ions (Hg2+) in water used daily is essential for human health and monitoring environmental pollution. Efficient porous organic polymers (POPs) can provide a strong adsorption capacity toward heavy metal ions, although the complex synthetic process and inconvenient phase separation steps limit their application. Hence, a combination of POPs and magnetic nanomaterials was proposed and a new magnetic porous organic polymer adsorbent was fabricated by a green and mild redox reaction in the aqueous phase with trithiocyanuric acid (TA) and its sodium salts acting as reductive monomers and iodine acting as an oxidant. In the preparation steps, no additional harmful organic solvent is required and the byproducts of sodium iodine are generally considered to be non-toxic. The resulting magnetic poly(trithiocyanuric acid) polymers (MPTAPs) are highly porous, have large surface areas, are rich in sulfhydryl groups and show easy magnetic separation ability. The experimental results show that MPTAPs exhibit good adsorption affinity toward Hg2+ with high selectivity, rapid adsorption kinetics (10 min), a large adsorption capacity (211 mg g-1) and wide adsorption applicability under various pH environments (pH 2~8). Additionally, MPTAPs can be reused for up to 10 cycles, and the magnetic separation step of MPTAPs is fast and convenient, reducing energy consumption compared to centrifugation and filtration steps required for non-magnetic adsorbents. These results demonstrate the promising capability of MPTAPs as superior adsorbents for effective adsorption and separation of Hg2+. Based on this, the prepared MPTAPs were adopted as magnetic solid-phase extraction (MSPE) materials for isolation of trace Hg2+ from aqueous samples. Under optimized conditions, the extraction and quantification of trace Hg2+ in water samples were accomplished using inductively coupled plasma mass spectrometry (ICP-MS) detection after MSPE procedures. The proposed MPTAPs-based MSPE-ICP-MS method is efficient, rapid, sensitive and selective for the determination of trace Hg2+, and was successfully employed for the accurate analysis of trace Hg2+ in tap water, wastewater, lake water and river water samples.

Preparation and application of a new ion-imprinted polymer for nanomolar detection of mercury(II) in environmental waters

This study introduces a novel ion-imprinted polymer for the ultrasensitive detection of mercury(II) in water. The ion-imprinted polymer was synthesized via a simple bulk polymerization process using methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, morpholine-4-carbodithioic acid phenyl ester as the chelating agent, and ammonium persulfate as the initiator. The electrochemical mercury(II) sensing capability of the ion-imprinted polymer was studied via the modification of a cost-effective carbon paste electrode. A stripping voltammetric technique was utilized to quantify the analyte ions following open-circuit enrichment. Critical experimental parameters, including the nature and concentration of the eluent, solution pH, preconcentration duration, ion-imprinted polymer dosage, sample solution volume and reduction potential, were systematically studied and optimized. Under optimal conditions, the sensor exhibited a linear response in the range of 1.0 to 240.0 nM, with a low detection limit of 0.2 nM. The sensor demonstrated remarkable selectivity against potential interfering ions, including lead(II), cadmium(II), copper(II), zinc(II), manganese(II), iron(II), magnesium(II), calcium(II), sodium(I) and cobalt(II). The practical applicability of the developed method was successfully validated through the analysis of real water samples, suggesting its potential for environmental monitoring applications.

Deep Cleaning of Crystal Violet and Methylene Blue Dyes from Aqueous Solution by Dextran-Based Cryogel Adsorbents

Polysaccharides have recently attracted growing attention as adsorbents for various pollutants, since they can be extracted from a variety of renewable sources at low cost. An interesting hydrophilic and biodegradable polysaccharide is dextran (Dx), which is well-known for its applications in the food industry and in medicine. To extend the application range of this biopolymer, in this study, we investigated the removal of crystal violet (CV) and methylene blue (MB) dyes from an aqueous solution by Dx-based cryogels using the batch technique. The cryogel adsorbents, consisting of cross-linked Dx embedding a polyphenolic (PF) extract of spruce bark, were prepared by the freeze-thawing approach. It was shown that the incorporation of PF into the Dx-based matrix induced a decrease in porosity, pore sizes and swelling ratio values. Moreover, the average pore sizes of the DxPF cryogels loaded with dyes further decreased from 42.30 ± 7.96 μm to 23.68 ± 2.69 μm, indicating a strong interaction between the functional groups of the cryogel matrix and those of the dye molecules. The sorption performances of the DxPF adsorbents were evaluated in comparison to those of the Dx cryogels and of the PF extract. The experimental sorption capacities of the DxPF cryogel adsorbents were higher in comparison to those of the Dx cryogels and the PF extract. The DxPF cryogels, particularly those with the highest PF contents (sample DxPF2), demonstrated sorption capacities of 1.2779 ± 0.0703 mmol·g-1, for CV, and 0.3238 ± 0.0121 mmol·g-1, for MB. The sorption mechanisms were analyzed using mathematical models, including Langmuir, Freundlich, Sips and Dubinin-Radushkevich isotherms, and kinetic models, like pseudo-first-order (PFO), pseudo-second-order (PSO), Elovich and intra-particle diffusion (IPD). The sorption process was best described by the Sips isotherm and PSO kinetic models, indicating chemisorption as the dominant mechanism. This study outlines the importance of developing advanced renewable materials for environmental applications.

Application Prospect of Ion-Imprinted Polymers in Harmless Treatment of Heavy Metal Wastewater

With the rapid development of industry, the discharge of heavy metal-containing wastewater poses a significant threat to aquatic and terrestrial environments as well as human health. This paper provides a brief introduction to the basic principles of ion-imprinted polymer preparation and focuses on the interaction between template ions and functional monomers. We summarized the current research status on typical heavy metal ions, such as Cu(II), Ni(II), Cd(II), Hg(II), Pb(II), and Cr(VI), as well as metalloid metal ions of the As and Sb classes. Furthermore, it discusses recent advances in multi-ion-imprinted polymers. Finally, the paper addresses the challenges faced by ion-imprinted technology and explores its prospects for application.

Advancements in mercury detection using surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs): a review

Mercury (Hg) contamination remains a major environmental concern primarily due to its presence at trace levels, making monitoring the concentration of Hg challenging. Sensitivity and selectivity are significant challenges in the development of mercury sensors. Surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs) are two distinct analytical methods developed and employed for mercury detection. In this review, we provide an overview of the key aspects of SERS and IIP methodologies, focusing on the recent advances in sensitivity and selectivity for mercury detection. By examining the critical parameters and challenges commonly encountered in this area of research, as reported in the literature, we present a set of recommendations. These recommendations cover solid and colloidal SERS substrates, appropriate Raman reporter/probe molecules, and customization of IIPs for mercury sensing and removal. Furthermore, we provide a perspective on the potential integration of SERS with IIPs to achieve enhanced sensitivity and selectivity in mercury detection. Our aim is to foster the establishment of a SERS-IIP hybrid method as a robust analytical tool for mercury detection across diverse fields.

Trends in polysaccharide-based hydrogels and their role in enhancing the bioavailability and bioactivity of phytocompounds

Over the years, polysaccharides such as chitosan, alginate, hyaluronic acid, k-carrageenan, xanthan gum, carboxymethyl cellulose, pectin, and starch, alone or in combination with proteins and/or synthetic polymers, have been used to engineer an extensive portfolio of hydrogels with remarkable features. The application of polysaccharide-based hydrogels has the potential to alleviate challenges related to bioavailability, solubility, stability, and targeted delivery of phytocompounds, contributing to the development of innovative and efficient drug delivery systems and functional food formulations. This review highlights the current knowledge acquired on the preparation, features and applications of polysaccharide/phytocompounds hydrogel-based hybrid systems in wound management, drug delivery, functional foods, and food industry. The structural, functional, and biological requirements of polysaccharides and phytocompounds on the overall performance of such hybrid systems, and their impact on the application domains are also discussed.

"Ion-imprinting" strategy towards metal sulfide scavenger enables the highly selective capture of radiocesium

Highly selective capture of radiocesium is an urgent need for environmental radioactive contamination remediation and spent fuel disposal. Herein, a strategy is proposed for construction of "inorganic ion-imprinted adsorbents" with ion recognition-separation capabilities, and a metal sulfide Cs2.33Ga2.33Sn1.67S8·H2O (FJSM-CGTS) with "imprinting effect" on Cs+ is prepared. We show that the K+ activation product of FJSM-CGTS, Cs0.51K1.82Ga2.33Sn1.67S8·H2O (FJMS-KCGTS), can reach adsorption equilibrium for Cs+ within 5 min, with a maximum adsorption capacity of 246.65 mg·g-1. FJMS-KCGTS overcomes the hindrance of Cs+ adsorption by competing ions and realizes highly selective capture of Cs+ in complex environments. It shows successful cleanup for actual 137Cs-liquid-wastes generated during industrial production with removal rates of over 99%. Ion-exchange column filled with FJMS-KCGTS can efficiently treat 540 mL Cs+-containing solutions (31.995 mg·L-1) and generates only 0.12 mL of solid waste, which enables waste solution volume reduction. Single-crystal structural analysis and density functional theory calculations are used to visualize the "ion-imprinting" process and confirm that the "imprinting effect" originates from the spatially confined effect of the framework. This work clearly reveals radiocesium capture mechanism and structure-function relationships that could inspire the development of efficient inorganic adsorbents for selective recognition and separation of key radionuclides.

Polymeric Materials in Speciation Analysis Based on Solid-Phase Extraction

Speciation analysis is a relevant topic since the (eco)toxicity, bioavailability, bio (geo)chemical cycles, and mobility of a given element depend on its chemical forms (oxidation state, organic ligands, etc.). The reliability of analytical results for chemical species of elements depends mostly on the maintaining of their stability during the sample pretreatment step and on the selectivity of further separation step. Solid-phase extraction (SPE) is a matter of choice as the most suitable and widely used procedure for both enrichment of chemical species of elements and their separation. The features of sorbent material are of great importance to ensure extraction efficiency from one side and selectivity from the other side of the SPE procedure. This review presents an update on the application of polymeric materials in solid-phase extraction used in nonchromatographic methods for speciation analysis.

Design of a New Phthalocyanine-Based Ion-Imprinted Polymer for Selective Lithium Recovery from Desalination Plant Reverse Osmosis Waste

In this study, a novel technique is introduced that involves the combination of an ion-imprinted polymer and solid-phase extraction to selectively adsorb lithium ions from reverse osmosis brine. In the process of synthesizing ion-imprinted polymers, phthalocyanine acrylate acted as the functional monomer responsible for lithium chelation. The structural and morphological characteristics of the molecularly imprinted polymers and non-imprinted polymers were assessed using Fourier transform infrared spectroscopy and scanning electron microscopy. The adsorption data for Li on an ion-imprinted polymer showed an excellent fit to the Langmuir isotherm, with a maximum adsorption capacity (Qm) of 3.2 mg·g-1. Comprehensive chemical analyses revealed a significant Li concentration with a higher value of 45.36 mg/L. Through the implementation of a central composite design approach, the adsorption and desorption procedures were systematically optimized by varying the pH, temperature, sorbent mass, and elution volume. This systematic approach allowed the identification of the most efficient operating conditions for extracting lithium from seawater reverse osmosis brine using ion-imprinted polymer-solid-phase extraction. The optimum operating conditions for the highest efficiency of adsorbing Li+ were determined to be a pH of 8.49 and a temperature of 45.5 °C. The efficiency of ion-imprinted polymer regeneration was evaluated through a cycle of the adsorption-desorption process, which resulted in Li recoveries of up to 80%. The recovery of Li from the spiked brine sample obtained from the desalination plant reverse osmosis waste through the ion-imprinted polymer ranged from 62.8% to 71.53%.

Thorium Removal, Recovery and Recycling: A Membrane Challenge for Urban Mining

Although only a slightly radioactive element, thorium is considered extremely toxic because its various species, which reach the environment, can constitute an important problem for the health of the population. The present paper aims to expand the possibilities of using membrane processes in the removal, recovery and recycling of thorium from industrial residues reaching municipal waste-processing platforms. The paper includes a short introduction on the interest shown in this element, a weak radioactive metal, followed by highlighting some common (domestic) uses. In a distinct but concise section, the bio-medical impact of thorium is presented. The classic technologies for obtaining thorium are concentrated in a single schema, and the speciation of thorium is presented with an emphasis on the formation of hydroxo-complexes and complexes with common organic reagents. The determination of thorium is highlighted on the basis of its radioactivity, but especially through methods that call for extraction followed by an established electrochemical, spectral or chromatographic method. Membrane processes are presented based on the electrochemical potential difference, including barro-membrane processes, electrodialysis, liquid membranes and hybrid processes. A separate sub-chapter is devoted to proposals and recommendations for the use of membranes in order to achieve some progress in urban mining for the valorization of thorium.

Ice-Templated and Cross-Linked Xanthan-Based Hydrogels: Towards Tailor-Made Properties

The use of polysaccharides with good film-forming properties in food packaging systems is a promising area of research. Xanthan gum (XG), an extracellular polysaccharide, has many industrial uses, including as a common food additive (E415). It is an effective thickening agent, emulsifier, and stabilizer that prevents ingredients from separating. Nevertheless, XG-based polymer films have some disadvantages, such as poor mechanical properties and high hydrophilic features, which reduce their stability when exposed to moisture and create difficulties in processing and handling. Thus, the objective of this work was to stabilize a XG matrix by cross-linking it with glycerol diglycidyl ether, 1,4-butanediol diglycidyl ether, or epichlorohydrin below the freezing point of the reaction mixture. Cryogelation is an ecological, friendly, and versatile method of preparing biomaterials with improved physicochemical properties. Using this technique, XG-based cryogels were successfully prepared in the form of microspheres, monoliths, and films. The XG-based cryogels were characterized by FTIR, SEM, AFM, swelling kinetics, and compressive tests. A heterogeneous morphology with interconnected pores, with an average pore size depending on both the nature of the cross-linker and the cross-linking ratio, was found. The use of a larger amount of cross-linker led to both a much more compact structure of the pore walls and to a significant decrease in the average pore size. The uniaxial compression tests indicated that the XG-based cryogels cross-linked with 1,4-butanediol diglycidyl ether exhibited the best elasticity, sustaining maximum deformations of 97.67%, 90.10%, and 81.80%, respectively.