A Novel Cu(II) Ion-Imprinted Alginate–Chitosan Complex Adsorbent for Selective Separation of Cu(II) from Aqueous Solution

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.

A critical review of sodium alginate-based composites in water treatment

The global freshwater crisis is a pressing issue, especially in areas with little rainfall and inner continental regions. The growing attention to water scarcity has induced increased interest in research on advanced water treatment technologies. As an abundant bioactive material in nature, sodium alginate (SA) has been widely used in water management due to its outstanding water absorption and holding ability, reversible swelling property, and pollutant adsorption performance. Building on this, progress made in using various modified forms of SA to access clean water is addressed in this review. Covering studies concern the adsorption and separation of pollutants in wastewater by SA-based absorbents and freshwater harvesting by SA-based collectors. This review explores SA-based composites' composition-structure-construction designs and emphasizes the impact of materials like inorganic materials, functional polymers, and porous matrices and how they can be exploited for water treatment. It also highlights the mechanisms of contaminants adsorption and freshwater desorption of SA-based composites. Finally, the shortcomings and future orientation of SA-based composites are proposed, including performance optimization, structural modification, application expansion, and mechanism in-depth investigation. This review aims to offer a theoretical basis and technical guidance for the use of natural materials to respond to the shortage of freshwater resources.

Effect of biocomposite production factors on the development of an eco-friendly chitosan/alginate-based adsorbent with enhanced copper removal efficiency

Nowadays, wastewater treatment is a critical concern, particularly regarding the removal of heavy metals through adsorption methods. Extensive research has been conducted on obtaining high-yield and environmentally friendly adsorbents. Natural polymer adsorbents especially have shown promise in ion and organic molecule adsorption. To enhance the practical applicability of adsorbents, the combination of biopolymers to form biocomposites is a promising alternative. In this study, adsorbents based on a 1:1 wt./wt. of chitosan (CS) and alginate (SA) were prepared. The influence of the regeneration route and drying conditions on the copper adsorption capacity was investigated, along with reaction parameters such as contact time, adsorbent particle size, and pH. The highest adsorption capacity was observed in the composite material obtained through a one-pot regeneration process and freeze-dried. The CSAR3L sample exhibited a remarkable adsorption capacity of 288 mg Cu(II)/g after 360 min at 25 °C. The synergistic effect between the CS and SA precursors was confirmed by analyzing the individual precursors and their mechanical mixture. The initial adsorption rates at pH 6 followed the order: CSAR3-L > Bk-CSR3L > Bk-SAR3L + Bk-CSR3L > Bk-SAR3L. The physicochemical and morphological properties of the materials were studied by FTIR, XRD, DLS, XPS, optical microscopy, EDS-SEM, elemental chemical analysis, and TGA-DTG. The utilization of different drying methods resulted in the formation of calcium carbonate crystalline phases in the as-prepared materials, thus creating substantial adsorption active sites. After the adsorption process, hydroxylated copper sulfate phases and a significant decrease in calcium concentration were observed, indicating that an ion exchange adsorption mechanism occurred. The analysis of adsorption kinetics and the shape of the adsorption isotherms, in agreement with the characterization results, suggested the presence of multiple active sites and the formation of a chemisorption monolayer.

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.

Optimization of preparation parameters for environmentally friendly attapulgite functionalized by chitosan and its adsorption properties for Cd2

This work focused on using attapulgite and chitosan as raw materials to improve the adsorption capacity of Cd²⁺ from the aqueous phase by optimizing the preparation experimental parameters. The modification parameters (attapulgite-chitosan mass ratio, calcination temperature, and time) were specifically studied and optimized. The results indicated that the mass ratio of attapulgite to chitosan was 1:4, the calcination temperature was 300 °C, and the calcination time was 1 h. Both raw and functionalized attapulgite samples were characterized by nitrogen adsorption-desorption isotherms at 77 K, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and zeta potential analysis. A series of adsorption experiments showed that the pseudo-second-order kinetic model and Langmuir adsorption isotherm better corresponded with the adsorption characteristics of the newly prepared adsorbent, and the maximum adsorption amount of Cd²⁺ was 109.30 mg/g. Moreover, the effects of the pH value and coexisting cations on the Cd²⁺ adsorption in aqueous solution were investigated. Adsorption mechanism of Cd²⁺ on adsorbent might attribute to complexation, ion exchange reaction, and self-polarization.

Preparation of an ion imprinted chitosan-based porous film with an interpenetrating network structure for efficient selective adsorption of Gd(iii)

In this work, a new Gd(III) ion imprinted CS-based porous film with interpenetrating network structure was fabricated by a simple polymerization–evaporation approach for the efficient selective adsorption of Gd(III) from aqueous solution.

Study on Synthesis and Adsorption Properties of ReO4 - Ion-Imprinted Polymer

In this work, an ion imprinted polymer (ReO₄ ^--IIP) of the perrhenate ion based on acrylamide (AM) and acrylic acid (AA) was prepared by solution polymerization using ReO₄ ^- as a template ion, N,N-methylenebisacrylamide (NMBA) as cross-linkers, hydrogen peroxide-vitamin C (H₂O₂-Vc) as an initiator, and a mixed solution of water (H₂O) and methanol (CH₃OH) with volume ratio v(H₂O)/v(CH₃OH) = 3:7 as a solvent. During the process of synthesis condition investigation and optimization, the adsorption capacity (Q) and the separation degree (R) in the equimolar concentration mixture solutions of NH₄ReO₄ and KMnO₄ were adopted as indexes, and the obtained optimal conditions were as follows: the molar ratios of NMBA, NH₄ReO₄, AA, H₂O₂, and Vc to AM were 5.73, 0.052, 1.29, 0.02, and 0.003, and the temperature and time of polymerization were 40 °C and 28 h, respectively. Under optimal conditions, the sample with indexes, Q and R of 0.064 mmol/g and 3.20, were harvested. What is more, a further reusability study found that good adsorption selectivity was maintained after repeating the experiment 9 times. Taking the non-IP prepared under the same conditions as a control, Fourier transform infrared spectroscopy, transmission electron microscopy, and Brunauer Emmett Teller were used to characterize the structure of the ReO₄ ^--IIP prepared under the optimal conditions. Finally, the kinetic study results showed that the zero-order kinetic model could better describe the adsorption process. The thermodynamic study results showed that the Langmuir model was more suitable for describing the isotherm adsorption process of the IIP.

Preparation of ion-imprinted montmorillonite nanosheets/chitosan gel beads for selective recovery of Cu(Ⅱ) from wastewater

The novel ion-imprinted montmorillonite nanosheets/chitosan (IIMNC) gel beads were prepared for selective adsorption of Cu²⁺. The IIMNC gel beads were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results showed that IIMNC was successfully assembled and rich in honeycombed pores, which performed well in the removal of Cu²⁺ through the synergistic effect of montmorillonite nanosheets and chitosan. The elimination of copper was followed by pseudo-second-order model and was enhanced by introduced montmorillonite nanosheets (MMTNS) because MMTNS attracted Cu(Ⅱ) by its negative charge and provided active adsorption sites through its high performance of cation exchange. This composite gel also showed excellent reusability, performing well in the removal of Cu²⁺ after undergoing adsorption-desorption in five cycles, because the adsorption sites of MMTNS can be continually reactivated by NaOH solution. More importantly, its high selectivity for Cu²⁺ provides a feasible way to recover Cu²⁺ from wastewater containing various cations.

Chromium (III) coordination capacity of chitosan

Polycationic chitosan has a strong coordination to heavy metal ions due to its multifunctional hydroxyl and amino groups. However, due to the fast and facile dissolution of chitosan in acidic medium, it is difficult to measure the exact adsorption amount or coordination capacity accurately. In this work, a simple method of lyophilization plus ethanol-washing was employed to separate and purify chitosan/Cr(III) complex for further determining the coordination capacity. Meanwhile, the coordination structure of Bridge-chitosan-N(OH)₃(H₂O) and morphology of regenerated fibrillar sponge of CS/Cr(III) were further certified. The coordination capacity of Cr(III) on chitosan increased with the rising concentration of Cr(III) ions till the maximum coordination capacity was reached up to 355.03 mg/g. The mechanisms and characteristic parameters of the adsorption process were fit using two-parameter isotherm models which revealed the following order (based on the coefficient of determination) of Langmuir > Halsey > Freundlich > Temkin > Dubinin-Radushkevich. A proposed coordination formula of CS/Cr (III) might be a good certificate for the homogeneous chemical combination nature of Cr(III) on the monolayer surface of chitosan in a molecular scale.