Preparation of a novel magnetic Pd(II) ion-imprinted polymer for the fast and selective adsorption of palladium ions from aqueous solutions

Selective adsorption of arsenic by water treatment residuals cross-linked chitosan in co-existing oxyanions competition system

Selective adsorption of arsenic in co-existing oxyanions competition systems remains a significant challenge in water treatment due to the limitations of adsorbent materials that often overlook competitive adsorption, resulting in an overestimation of their actual purification potential for target contaminants. In this study, a novel hydrogel bead adsorbent, composed of water treatment residuals (WTRs) and chitosan (Chi), was developed to selectively remove arsenic, while minimizing the interference from phosphate, which is the strongest and most representative competitor in multi-oxyanion systems. The WTRs-Chi beads (WCB) adsorbents were optimized by adjusting the ratios of WTRs:Chi, with characterization results indicating that increased WTR doping improved the degree of crosslinking and the formation of bidentate complexes with enhanced electrostatic selectivity. Importantly, the co-existence of phosphate had minimal adverse effects on arsenic removal compared to other reported adsorbents. The maximum adsorption capacity for As (V) in the binary system was 34.12 mg/g, and the adsorption behavior was fitted well by the pseudo-second-order kinetic model and the extended Langmuir isotherm model. The experimental results, supported by X-ray photoelectron spectroscopy analysis (XPS), revealed that both As (V) and P (V) adsorption in the single system were driven by electrostatic attraction and ligand exchange. However, in the binary system, the inhibition of P (V) adsorption was attributed to competitive desorption caused by electrostatic repulsion, which hindered the formation of inner-sphere complexes. This study provides a practical approach for developing selective adsorbents to address arsenic contamination in complex water environments and promotes the recycling of municipal solid waste.

The Multi-Challenges of the Multi-Ion-Imprinted Polymer Synthesis

Multi-ion-imprinted polymers (MIIPs) are materials with a wide range of applications mainly focused on environmental recovery, mining, technology, sensors, etc. MIIPs can incorporate ions such as heavy metals, transition metals, rare earth elements, radionuclides, and other types of ions. The chemical structures of MIIPs can be designed for different purposes and with certain morphologies, such as gels, crystals, or powders, and the surface area and porosity are also considered. All these properties provide the material with several desirable characteristics, like high selectivity, high specificity, adequate efficiency, good stability, the possibility of reusability, and strategy technology adaptation. In this review, we show the multitude of challenges of multi-ion imprinted polymer chemical synthesis based on the different and interesting methods reported previously.

Magnetic Ion-Imprinted Materials for Selective Adsorption of Cr(VI): Adsorption Behavior and Mechanism Study

With the increase of hexavalent Cr(VI) wastewater discharged from industrial production, it seriously pollutes water bodies and poses a risk to human health. Adsorption is used as an effective means to treat Cr(VI), but its effectiveness is affected by pH, and the adsorption performance decreases when acidity is strong. Furthermore, research on the mechanism of Cr(VI) adsorption using DFT calculations needs to be developed. This study focuses on the development of magnetically responsive core-shell nano-ion imprinted materials (Fe3O4@GO@IIP) through magnetic separation and surface imprinting techniques. Characterization techniques including FT-IR, XRD, and EDS confirmed the core-shell nanostructure of Fe3O4@GO@IIP. Batch adsorption experiments and model simulations demonstrated the exceptional adsorption capacity of Fe3O4@GO@IIP for Cr(VI) in strongly acidic solutions (pH = 1), reaching a maximum of 89.18 mg/g. The adsorption mechanism was elucidated through XPS and DFT calculations, revealing that Fe3O4@GO@IIP operates through electrostatic interactions and chemical adsorption, with charge transfer dynamics quantified during the process. This research provides new insights for addressing Cr(VI) treatment in highly acidic environments.

A novel cationic covalent organic framework as adsorbent for simultaneous removal of methyl orange and hexavalent chromium

The simultaneous removal of toxic, carcinogenic organic dyes and metal ions from water by one material offers significant advantages when fast, facile, and robust water purification is required. Ionic covalent organic frameworks (ICOFs) have the combined properties of COFs and ion exchange resins and are expected to achieve simultaneous capture of heavy metal ions and organic dyes from water. Herein, a novel guanidinium-based ICOF was synthesized using a solvothermal method. Benefitting from the cationic character, porosity and nanoscale pore size of ICOFs, the adsorbent exhibited high simultaneous adsorption capacities of 290 mg g-1 and 158 mg g-1 for methyl orange (MO) and Cr(vi), respectively, and retained more than 90% adsorption capacity after six adsorption-desorption cycles. In addition, based on dual control of size-exclusion and charge-selection, precisely selective adsorption is achieved towards diverse mixed anionic and cationic pollutants. This strategy offers a practical solution for COFs to confront environmental pollution issues.

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

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.

Speciation of Hexavalent Chromium in Aqueous Solutions Using a Magnetic Silica-Coated Amino-Modified Glycidyl Methacrylate Polymer Nanocomposite

A new magnetic amino-functionalized polymeric sorbent based on glycidyl methacrylate was synthesized and used in the separation of chromium Cr(VI) oxyanions sorption from aqueous solutions in a static batch system. The kinetic and isothermal parameters of the sorption process were determined. The experimental data were best fitted by a pseudo-second-order model with R² = 0.994 and χ² = 0.004. The sorption process of Cr(VI) removal by amino-functionalized sorbent was controlled by both intraparticle diffusion and liquid film diffusion. The equilibrium results showed that the sorption process is best described by the Freundlich model, followed closely by the Sips isotherm model, with a maximum sorption capacity of 64 mg/g. Quantum chemical modeling revealed that the sorption sites on the sorbent surface are fragments with diethylenetriamine and aminopropyl silane groups that coated the magnetic nanoparticles. The calculations showed that Cr(VI) oxyanions (Cr₂O₇^2-, CrO₄^2- and HCrO₄^-) bind to both sorption sites, with diethylenetriamine centers slightly favored. The X-ray photoelectron spectroscopy (XPS) spectra demonstrate that the chromium bound to the sorbent in the form of Cr(III), indicating that the Cr(VI) can be converted on the surface of the sorbent to a less harmful form Cr(III) due to the sorbent's chemical composition.

Rapid adsorption of some heavy metals using extracted chitosan anchored with new aldehyde to form a schiff base

A new aldehyde 2,2’-[propane-1,3-diylbis(oxy)] dibenzaldehyde was synthesized from refluxing 2-hydroxy acetophenone and 2-hydroxy 1,3-dichloropropanean in an alcoholic medium. The compositions and properties of the new aldehyde compound were characterized by elemental analysis, FTIR, and nuclear magnetic resonance spectroscopy studies. The extracted chitosan was made to react with a new aldehyde to form a Schiff base by a suitable method. The effects of initial concentration of metal ions, exposure time, imine weight, and pH on the adsorption of Cu(II), Cr(III), and Zn(II) metal ions were examined. An adsorption batch experiment was conducted. The adsorption process followed a second-order reaction and Langmuir model with qe 25 mg/g, 121 mg/g, and 26.31 mg/g for Cu(II), Zn(II), and Cr(III) respectively. The Gibbs free energy showed a negative value and the adsorption/desorption tests provided a high value 5 times.

Recognizing adsorption of Cd(Ⅱ) by a novel core-shell mesoporous ion-imprinted polymer: Characterization, binding mechanism and practical application

A novel monodispersed Cd(II) ion-imprinted polymer (IIP) was synthesized inside core-shell mesoporous silica (C-SMS) particles to improve the diffusion kinetics of the polymer. The synthesized IIP@C-SMS was characterized and subsequently used in solid-phase extraction (SPE) for the selective adsorption of Cd(II) in aquatic samples. The results indicated that IIP had been successfully assembled inside the C-SMS particles with a high specific surface area (546.3 m² g^-1) and uniform mesoporous size (2.07 nm). The obtained IIP@C-SMS takes only 15 min to reach the adsorption equilibrium due to the highly developed mesoporous structure. IIP@C-SMS also presented a maximal adsorption capacity (201.9 μmol g^-1) for Cd(II), which was much higher than that of NIP@C-SMS (80.3 μmol g^-1). The relative selectivity coefficient of IIP@C-SMS for Cd(II)/M(II) (M = Cu(II), Pb(II), Cr(II), and Ni(II)) were 7.15, 8.70, 7.18, and 7.36, respectively, further confirming the satisfactory selectivity of IIP@C-SMS. The adsorption isotherms of IIP@C-SMS toward Cd(II) could be described by Langmuir model; whereas the adsorption kinetics could be fitted by the pseudo-second-order model, indicating chemisorption was the rate-limiting step. The FT-IR, ITC and XPS analysis further confirmed that the Cd(II)-induced cavities during the ion-imprinting process and the coordination between Cd(II) and -SH groups were the main adsorption mechanism. Furthermore, in real samples, IIP@C-SMS-SPE adsorbed approximately 93-104% of Cd(II). This work provides new insights for the design of novel macroporous sorbents for Cd(II).

Selective and rapid removal of Mo(VI) from water using functionalized Fe3O4-based Mo(VI) ion-imprinted polymer

Fe₃O₄ nanoparticles-based magnetic Mo(VI) surface ion-imprinted polymer (Mo(VI)-MIIP) was elaborated employing 4-vinyl pyridine as a functional monomer. The adsorbent preparation was confirmed by Fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, vibrating sample magnetometer, thermogravimetric analysis, and surface area analysis. Batch adsorption experiments showed that the maximum adsorption capacity of Mo(VI)-MIIP was 296.40 mg g^-1 at pH 3, while that of the magnetic non-imprinted polymer (MNIP) was only 147.10 mg g^-1. The adsorption isotherm model was well fitted by the Langmuir isotherm model. The adsorption experiments revealed that Mo(VI)-MIIP reached adsorption equilibrium within 30 min, and the kinetics data fitting showed that the pseudo-second-order kinetics model suitably described the adsorption process. Mo(VI)-MIIP exhibited an excellent adsorption selectivity to Mo(VI) in binary mixtures of Mo(VI)/Cr(VI), Mo(VI)/Cu(II), Mo(VI)/H₂PO4₄^-, Mo(VI)/Zn(II), and Mo(VI)/I^-, with relative selectivity coefficients toward MNIP of 13.71, 30.27, 20.01, 23.53, and 15.89, respectively. After six consecutive adsorption-desorption cycles, the adsorption capacity of Mo(VI)-MIIP decreased by 9.5% (from 228.4 mg g^-1 to 206.7 mg g^-1 at initial Mo(VI) concentration of 250 mg L^-1), demonstrating its reusability.

Exploring the Mechanisms of Selectivity for Environmentally Significant Oxo-Anion Removal during Water Treatment: A Review of Common Competing Oxo-Anions and Tools for Quantifying Selective Adsorption

Development of novel adsorbents often neglects the competitive adsorption between co-occurring oxo-anions, overestimating realistic pollutant removal potentials, and overlooking the need to improve selectivity of materials. This critical review focuses on adsorptive competition between commonly co-occurring oxo-anions in water and mechanistic approaches for the design and development of selective adsorbents. Six "target" oxo-anion pollutants (arsenate, arsenite, selenate, selenite, chromate, and perchlorate) were selected for study. Five "competing" co-occurring oxo-anions (phosphate, sulfate, bicarbonate, silicate, and nitrate) were selected due to their potential to compete with target oxo-anions for sorption sites resulting in decreased removal of the target oxo-anions. First, a comprehensive review of competition between target and competitor oxo-anions to sorb on commonly used, nonselective, metal (hydr)oxide materials is presented, and the strength of competition between each target and competitive oxo-anion pair is classified. This is followed by a critical discussion of the different equations and models used to quantify selectivity. Next, four mechanisms that have been successfully utilized in the development of selective adsorbents are reviewed: variation in surface complexation, Lewis acid/base hardness, steric hindrance, and electrostatic interactions. For each mechanism, the oxo-anions, both target and competitors, are ranked in terms of adsorptive attraction and technologies that exploit this mechanism are reviewed. Third, given the significant effort to evaluate these systems empirically, the potential to use computational quantum techniques, such as density functional theory (DFT), for modeling and prediction is explored. Finally, areas within the field of selective adsorption requiring further research are detailed with guidance on priorities for screening and defining selective adsorbents.

Evolution of Environmentally Friendly Strategies for Metal Extraction

The demand for the recovery of valuable metals and the need to understand the impact of heavy metals in the environment on human and aquatic life has led to the development of new methods for the extraction, recovery, and analysis of metal ions. With special emphasis on environmentally friendly approaches, efforts have been made to consider strategies that minimize the use of organic solvents, apply micromethodology, limit waste, reduce costs, are safe, and utilize benign or reusable materials. This review discusses recent developments in liquid- and solid-phase extraction techniques. Liquid-based methods include advances in the application of aqueous two- and three-phase systems, liquid membranes, and cloud point extraction. Recent progress in exploiting new sorbent materials for solid-phase extraction (SPE), solid-phase microextraction (SPME), and bulk extractions will also be discussed.

Fabrication of chromium-imprinted polymer: a real magneto-selective sorbent for the removal of Cr(vi) ions in real water samples

Graphical representation (a and b) show the procedure for the synthesis of Cr(vi) ion-imprinted magnetic polymer.

Ion-Imprinted Polypropylene Fibers Fabricated by the Plasma-Mediated Grafting Strategy for Efficient and Selective Adsorption of Cr(VI)

To improve the adsorption selectivity towards hexavalent chromium anion (Cr(VI)), surface Cr(VI)-imprinted polypropylene (PP) fibers were fabricated by the plasma-mediated grafting strategy. Hence, a non-thermal Rradio frequency discharge plasma irradiation followed by a gaseous phase grafting was used to load acrylic acid (AA) onto PP fibers, which was afterwards amidated with triethylenetetramine and subjected to imprinting with a Cr(VI) template. The plasma irradiation conditions, i.e., gas species, output power, pressure, and time, were optimized and then the influence of grafting time, pressure, and temperature on the grafting degree of AA was investigated. Scanning electron microscopy and Fourier transform infrared spectroscopy were used for the characterization of pristine and modified fibers and to confirm the synthesis success. The hydrophilicity of modified fibers was greatly improved compared with pristine PP fibers. The adsorption thermodynamics and kinetics of Cr(VI) were investigated, as well as the elution efficiency and reusability. The prepared imprinted fibers showed superior adsorption selectivity to Cr(VI) compared with non-imprinted fibers. Finally, the stability of the imprinted fibers against the oxidation ability of Cr(VI) is discussed.