Aminopolycarboxylic Acids-Functionalized Chitosan-Based Composite Cryogels as Valuable Heavy Metal Ions Sorbents: Fixed-Bed Column Studies and Theoretical Analysis

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.

Innovative Green Alginate-Cellulose Composite for Light Lanthanides: Experimental Design and Comprehensive Studies on Kinetics, Equilibrium, Thermodynamics, and Reusability

Nowadays, there is a great interest in efficient adsorbent development due to the recent demand for lanthanides, which are widely used in high-tech technology. Alginates, owing to their natural occurrence, gel formation capability, and safety, could be promising feasible adsorbents for lanthanide removal. This study proposes the alginate-cellulose composite as an ecological, sustainable adsorbent for light lanthanide sorption. The structure, morphology, qualitative and quantitative compositions, average diameter, and pHpzc of the composite were discussed in great detail. Using the batch approach, sorption trials were performed to evaluate the metal sorption performance. The maximum lanthanide accumulation was attained at pH 5.0 and a dosage of 0.05 g. The uptake kinetics are successfully explained by the Ho and McKay model, whereas the equilibrium data is best represented by the Langmuir equation. The presence of Cl-, NO3 -, SO4 2-, Ni(II), and Co(II) did not have any impact on the adsorption capacity. In turn, the presence of Fe(III) ions led to a 15 % reduction in the adsorption. The lanthanide ions were eluted from the adsorbent following the treatment with 0.1 M HNO3. The adsorbent retained over 95 % of its initial adsorption capacity after 6 series of sorption/desorption studies.

Aminopoly(carboxylic acid)-Functionalized PolyHIPE Beads toward Eliminating Trace Heavy Metal Ions from Water

Many advanced materials are designed for the removal of heavy metal ions from water. However, materials for eliminating trace heavy metal ions from wastewater to meet drinking water standards remain a major challenge. Herein, epoxy group-functionalized open-cellular beads are synthesized by UV polymerization of a water-in-oil-in-water system. The epoxy groups are further transformed into diethylenetriaminepentaacetic acid (DTPA) with hexamethylene diamine as a bridging agent. The resulting material (DTPA@polyHIPE beads) can eliminate trace Cu(II), Cr(III), Pb(II), Fe(III), or Cd(II) from water. When 0.15 g of DTPA@polyHIPE beads are used to adsorb metal ions of 20 mg in 100 mL of water, the residue concentrations of Cu(II), Cr(III), Pb(II), Fe(III), and Cd(II) are reduced to 0.08, 0.06, 0.02, 0.09, and 0.07 mg/L, respectively. The adsorption efficiencies of the beads for these ions are all higher than 99.55%. The adsorbent is durable and exhibits good recyclability by retaining an adsorption capacity of ≥91% after 5 cycles. The negative values of ΔG in the adsorption process indicate that the adsorption is feasible and spontaneous. The chemical adsorption follows the Freundlich adsorption model, indicating a multilayer heterogeneous adsorption. The DTPA@polyHIPE beads have a great potential application in dealing with trace heavy metal ion polluted water.

Retention of Ciprofloxacin and Carbamazepine from Aqueous Solutions Using Chitosan-Based Cryostructured Composites

Water pollution is becoming a great concern at the global level due to highly polluted effluents, which are charged year by year with increasing amounts of organic residues, dyes, pharmaceuticals and heavy metals. For some of these pollutants, the industrial treatment of wastewater is still relevant. Yet, in some cases, such as pharmaceuticals, specific treatment schemes are urgently required. Therefore, the present study describes the synthesis and evaluation of promising cryostructured composite adsorbents based on chitosan containing native minerals and two types of reinforcement materials (functionalized kaolin and synthetic silicate microparticles). The targeted pharmaceuticals refer to the ciprofloxacin (CIP) antibiotic and the carbamazepine (CBZ) drug, for which the current water treatment process seem to be less efficient, making them appear in exceedingly high concentrations, even in tap water. The study reveals first the progress made for improving the mechanical stability and resilience to water disintegration, as a function of pH, of chitosan-based cryostructures. Further on, a retention study shows that both pharmaceuticals are retained with high efficiency (up to 85.94% CIP and 86.38% CBZ) from diluted aqueous solutions.

Feather-weight cryostructured thiourea-chitosan aerogels for highly efficient removal of heavy metal ions and bacterial pathogens

Designing of economically feasible and recyclable polysaccharide-based materials with thiourea functional groups for removal of specific metal ions such as Ag(I), Au(I), Pb(II) or Hg(II) remains a major challenge for environmental applications. Here, we introduce ultra-lightweight thiourea-chitosan (CSTU) aerogels engineered by combining successive freeze-thawing cycles with covalent formaldehyde-mediated cross-linking and lyophilization. All aerogels exhibited outstanding low densities (0.0021-0.0103 g/cm³) and remarkable high specific surface areas (416.64-447.26 m²/g), outperforming the common polysaccharide-based aerogels. Benefitting from their superior structural features (honeycomb interconnected pores and high porosity), CSTU aerogels demonstrate fast sorption rates and excellent performance in sorption of heavy metal ions from highly-concentrated single or binary-component mixtures (1.11 mmol Ag (I)/g and 0.48 mmol Pb(II)/g). A remarkable recycling stability was observed after five sorption-desorption-regeneration cycles when the removal efficiency was up to 80 %. These results support the high potential of CSTU aerogels in the treatment of metal-containing wastewater. Moreover, the Ag(I)-loaded CSTU aerogels exhibited excellent antimicrobial properties against Escherichia coli and Staphylococcus aureus bacterial strains, the killing rate being around 100 %. This data points towards the potential application of developed aerogels in circular economy, by employing the spent Ag(I)-loaded aerogels in the biological decontamination of waters.

Organic-soluble chitosan-g-PHMA (PEMA/PBMA)-bodipy fluorescent probes and film by RAFT method for selective detection of Hg2+/Hg+ ions

Chitosan as the plentiful and easily available natural polymer, its solubility in organic solvents is still a challenge. In this article, three different chitosan-based fluorescent co-polymers were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. They could not only dissolve in several organic solvents, but also could selectively recognize Hg²⁺/Hg⁺ ions. Firstly, allyl boron-dipyrrolemethene (bodipy) was prepared, and used as one of the monomers in the subsequent RAFT polymerization. Secondly, chitosan-based chain transfer agent (CS-RAFT) was synthesized through classical reactions for dithioester preparation. Finally, three methacrylic ester monomers and bodipy bearing monomers were polymerized and grafted as branched-chains onto chitosan respectively. By RAFT polymerization, three chitosan-based macromolecular fluorescent probes were prepared. These probes could be readily dissolved in DMF, THF, DCM, and acetone. All of them exhibited the 'turn-on' fluorescence with selective and sensitive detection for Hg²⁺/Hg⁺. Among them, chitosan-g-polyhexyl methacrylate-bodipy (CS-g-PHMA-BDP) had the best performance, its fluorescence intensity could be increased to 2.7 folds. In addition, CS-g-PHMA-BDP could be processed into films and coatings. When loading on the filter paper, fluorescent test paper was prepared and it could realize the portable detection of Hg²⁺/Hg⁺ ions. These organic-soluble chitosan-based fluorescent probes could enlarge the applications of chitosan.

Phosphonation of Alginate-Polyethyleneimine Beads for the Enhanced Removal of Cs(I) and Sr(II) from Aqueous Solutions

Although Cs(I) and Sr(II) are not strategic and hazardous metal ions, their recovery from aqueous solutions is of great concern for the nuclear industry. The objective of this work consists of designing a new sorbent for the simultaneous recovery of these metals with selectivity against other metals. The strategy is based on the functionalization of algal/polyethyleneimine hydrogel beads by phosphonation. The materials are characterized by textural, thermo-degradation, FTIR, elemental, titration, and SEM-EDX analyses to confirm the chemical modification. To evaluate the validity of this modification, the sorption of Cs(I) and Sr(II) is compared with pristine support under different operating conditions: the pH effect, kinetics, and isotherms are investigated in mono-component and binary solutions, before investigating the selectivity (against competitor metals) and the possibility to reuse the sorbent. The functionalized sorbent shows a preference for Sr(II), enhanced sorption capacities, a higher stability at recycling, and greater selectivity against alkali, alkaline-earth, and heavy metal ions. Finally, the sorption properties are compared for Cs(I) and Sr(II) removal in a complex solution (seawater sample). The combination of these results confirms the superiority of phosphonated sorbent over pristine support with promising performances to be further evaluated with effluents containing radionuclides.

Polysaccharide-Based Composite Hydrogels as Sustainable Materials for Removal of Pollutants from Wastewater

Nowadays, pollution has become the main bottleneck towards sustainable technological development due to its detrimental implications in human and ecosystem health. Removal of pollutants from the surrounding environment is a hot research area worldwide; diverse technologies and materials are being continuously developed. To this end, bio-based composite hydrogels as sorbents have received extensive attention in recent years because of advantages such as high adsorptive capacity, controllable mechanical properties, cost effectiveness, and potential for upscaling in continuous flow installations. In this review, we aim to provide an up-to-date analysis of the literature on recent accomplishments in the design of polysaccharide-based composite hydrogels for removal of heavy metal ions, dyes, and oxyanions from wastewater. The correlation between the constituent polysaccharides (chitosan, cellulose, alginate, starch, pectin, pullulan, xanthan, salecan, etc.), engineered composition (presence of other organic and/or inorganic components), and sorption conditions on the removal performance of addressed pollutants will be carefully scrutinized. Particular attention will be paid to the sustainability aspects in the selected studies, particularly to composite selectivity and reusability, as well as to their use in fixed-bed columns and real wastewater applications.

TEGylated Phenothiazine-Imine-Chitosan Materials as a Promising Framework for Mercury Recovery

This paper reports new solid materials based on TEGylated phenothiazine and chitosan, with a high capacity to recover mercury ions from aqueous solutions. They were prepared by hydrogelation of chitosan with a formyl derivative of TEGylated phenothiazine, followed by lyophilization. Their structural and supramolecular characterization was carried out by 1H-NMR and FTIR spectroscopy, as well as X-ray diffraction and polarized light microscopy. Their morphology was investigated by scanning electron microscopy and their photophysical behaviour was examined by UV/Vis and emission spectroscopy. Swelling evaluation in different aqueous media indicated the key role played by the supramolecular organization for their hydrolytic stability. Mercury recovery experiments and the analysis of the resulting materials by X-ray diffraction and FTIR spectroscopy showed a high ability of the studied materials to bind mercury ions by coordination with the sulfur atom of phenothiazine, imine linkage, and amine units of chitosan.