Aspartic acid grafting on cellulose and chitosan for enhanced Nd(III) sorption

Facile synthesis of eco-friendly alginate-chitosan bio-adsorbent for critical raw materials adsorption: A comprehensive study

Sustainable management of critical raw materials is of paramount importance to ensure a steady supply and reduce environmental impact. The application of newly synthesized and environmentally friendly ALG@CS material as a bio-adsorbent for the effective rare earth elements removal from aqueous solution has been presented. The synthesized material underwent FTIR, XPS, EDX, and SEM analysis to determine its suitability for metal uptake. To evaluate the adsorption capacity of ALG@CS for rare earth elements several factors were taken into consideration. These factors included alginate:chitosan ratios, bead size, pH level, composite mass, interaction time, metal ion concentration, and temperature, being all varied during the batch mode evaluation process. Under the optimal conditions, the maximum adsorption capacities were found to be 145.90 mg La(III)/g, 168.44 mg Ce(III)/g, 132.51 mg Pr(III)/g, 128.40 mg Nd(III)/g, 154.36 mg Sm(III)/g, and 165.10 mg Ho(III)/g. The equilibrium data fits well with non-linear three-parameter Sips and Redlich-Peterson isotherm models. The PSO model finds the highest process suitability. The synthesized ALG@CS bio-adsorbent showed excellent regenerative capacity in ten cycles, making it a suitable adsorbent for rare earth elements uptake. The unique bio-adsorbents combination allows for efficient critical raw materials adsorption providing a promising solution for their recovery and recycling.

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.

Recovery of Heavy Metal Ions Using Magnetic Glycine-Modified Chitosan—Application to Aqueous Solutions and Tailing Leachate

The necessity of decontaminating effluents for the dual purpose of environmental beneficiation and valorization of low-grade resources is driving the development of new sorbents. The functionalization of biopolymers is a promising strategy for improving sorption performance. Incorporating magnetic micro-particles offers an opportunity for the facilitated recovery of spent micron-size sorbent. Combining magnetic facilities and biopolymer functionalization represents a winning strategy. Magnetic glycine-grafted chitosan (G@MChs) was synthesized for the sorption of Ni(II), Zn(II), and Hg(II) before being applied to the removal of hazardous and strategic metals from tailing leachates. The sorbent was characterized using Fourier transform infrared spectroscopy and scanning electron microscopy, before and after metal sorption. The acid–base properties of functionalized sorbent were also determined (pHPZC). Uptake kinetics were studied in mono- and multi-component solutions using different equations for kinetic modeling at optimized pH (i.e., pH0: 5.5). Langmuir and Sips equations were applied to model sorption isotherms in single-component solutions. In addition, sorption isotherms in multi-component solutions were used to evaluate the preference for selected metals. Maximum sorption capacities were 0.35 mmol Hg g−1, 0.47 mmol Zn g−1, and 0.50 mmol Ni g−1. Acidified urea solution (pH 2.7) successfully desorbs metal ions from G@MChs (desorption > 90%). The sorbent was tested for the recovery of hazardous and strategic metal ions from acidic leachates of tailings. This study demonstrates the promising performance of G@MChs for the treatment of complex metal-bearing solutions.

Reducing lactose content of milk from livestock and humans via lactose imprinted poly(2-hydroxyethyl methacrylate-N-methacryloyl-i-aspartic acid) cryogels

Lactase, which can cause lactose intolerance in its deficiency, is a vital enzyme concerning digestion. To overcome lactose intolerance for patients with digestion problem depending of this kind of issue, lactose in food should be removed. In this study, lactose imprinted poly(2-hydroxyethyl methacrylate-N-methacryloyl-l-aspartic acid), poly(HEMA-MAsp), cryogels were synthesized to reduce the amount of lactose content of milk samples. Occurrence of desired bounds, structural integrity, and surface characteristics were analyzed via Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), scanning electron microscope (SEM), micro computed tomography (CT), and confocal microscope methods. Water retention characteristic were tested in solution with different electrolytic nature. Adsorption parameters were optimized in an aqueous medium. The adsorption performance of imprinted cryogels was studied in milk samples obtained from cow, sheep, goat, buffalo, and from human volunteers at different intervals after birth. Amount of lactose adsorbed in aqueous media and milk sample from humans were 322 (56.7%) and 179.5 (5.94%) mg lactose/g polymer, respectively. Selectivity studies revealed an approximately 8-fold increase in adsorption rate of molecularly imprinted cryogels as compared to that of nonimprinted cryogels. In addition, competitive adsorption was conducted using lactose-imprinted cryogels in aqueous media containing lactose, glucose, and galactose molecules resulting in adsorption rates of 220.56, 57.87, and 61.65 mg biomolecule/g polymer, respectively.

Direct N-substituted N-thiocarboxyanhydride polymerization towards polypeptoids bearing unprotected carboxyl groups

Synthesis of poly(α-amino acid)s bearing carboxyl groups is a critical pathway to prepare biomaterials to simulate functional proteins. The traditional approaches call for carboxyl-protected monomers to prevent degradation of monomers or wrong linkage. In this contribution, we synthesize N-carboxypentyl glycine N-thiocarboxyanhydride (CPG-NTA) and iminodiacetic acid N-thiocarboxyanhydride (IDA-NTA) without protection. Initiated by amines, CPG-NTA directly polymerizes into polyCPG bearing unprotected carboxyl groups with controlled molecular weight (2.8-9.3 kg mol-1) and low dispersities (1.08-1.12). Block and random copolymerizations of CPG-NTA with N-ethyl glycine N-thiocarboxyanhydride (NEG-NTA) demonstrate its versatile construction of complicated polypeptoids. On the contrary, IDA-NTA transforms amines into cyclic IDA dimer-capped species with carboxyl end group in decent yields (>89%) regio-selectively. Density functional theory calculation elucidates that IDA repeating unit is prone to cyclize to be the six-membered ring product with low ΔG. The polymer is a good adhesive reagent to various materials with adhesive strength of 33-229 kPa.

Adsorption kinetics, thermodynamics, and isotherm studies for functionalized lanthanide-chelating resins

Conventional ion exchange resins are widely utilized to remove metals from aqueous solutions, but their limited selectivity precludes dilute ion extraction. This research investigated the adsorption performance of ligand-functionalized resins towards rare earth elements (REE). Functionalized resin particles were synthesized by grafting different ligands (diethylenetriaminepentaacetic dianhydride (DTPADA), phosphonoacetic acid (PAA), or N,N-bis(phosphonomethyl)glycine (BPG)) onto pre-aminated polymeric adsorbents (diameter ∼ 0.6 mm). Lanthanide uptake trends were evaluated for the functionalized resins using batch adsorption experiments with a mixture of three REEs (Nd, Gd, and Ho at 0.1-1000 mg/L each). Resin physical-chemical properties were determined by measuring their surface area, ligand concentrations, and acidity constants. The aminated supports contained 4.0 mmol/g primary amines, and ligand densities for the functionalized resins were 0.33 mmol/g (PAA), 0.22 mmol/g (BPG), and 0.42 mmol/g (DTPADA). Kinetic studies revealed that the functionalized resins followed pseudo-second order binding kinetics with rates limited by intraparticle diffusion. Capacity estimates for total REE adsorption based on Langmuir q_Max were 0.12 mg/g (amine; ≈ 0.77 µmol/g), 5.0 mg/g (PAA; ≈ 32.16 µmol/g), 3.0 mg/g (BPG; ≈ 19.30 µmol/g), and 2.9 mg/g (DTPADA; ≈ 18.65 µmol/g). Attaching ligands to the aminated resins greatly improved their REE binding strength and adsorption efficiency.