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A better understanding of the physicochemical phenomena underlying the direct solubilization of solid chitosan in an aqueous acetic acid medium without the addition of salt is needed. These phenomena have been studied using an inverse approach in which the chitosan is treated as a poly-acid and not as poly-base, and the macrophenomenon observed represents the aggregation of the macromolecules of chitosan instead of their solubilization. The purpose of this study is to present an overview of the physicochemical phenomena underlying this direct solubilization in an aqueous acetic acid medium without the addition of salt through a mathematical model based on equilibrium equations, mass balances, and correlations between experimental data. This model allowed us to model dilute chitosan/acetic acid/water systems without the addition of salt with an adequate fit (R2 > 0.9951) to the trend of the experimental data, enabling the calculation of the pH, degree of ionization, apparent dissociation constant, and the concentrations of the smaller molecules $$\left( {{\text{CH}}_{3} {\text{COOH}}, {\text{CH}}_{3} {\text{COO}}^{ - } ,{\text{H}}_{3} {\text{O}}^{ + } } \right)$$ , with only a priori knowledge of the initial concentration of acetic acid, initial concentration of amine groups, and the dissociation constant of acetic acid. The main finding of this study was that the diluted systems lacking salt studied here showed a tendency toward an apparent dissociation constant of $$pK_{1/2} \to 6.44$$ as the polymer concentration increased. This value is similar to the values reported in the literature for systems containing salt and a degree of deacetylation $$\left( {f_{\text{D}} \sim 0.7} \right)$$ similar to the chitosan evaluated here.

Synthesis, characterization, and study of the cation adsorption properties of four hydrogels are presented. The hydrogels were synthesized via radical copolymerization of a 1:1 mixture of 2-hydroxyethyl-methacrylate and 2-acrylamido-2-methyl-1-propanesulfonic acid, with different initiators and cross-linking reagents. HM1 hydrogel was obtained by adding only ammonium persulfate; HM2 hydrogel was synthesized using a redox initiator solution containing ammonium persulfate and sodium metabisulfite at room temperature. For HM3 hydrogel the initiator benzoyl peroxide and the cross-linking reagent ethylene glycol dimethacrylate were used. Finally, for HM4 hydrogel the polymerization was carried out using ammonium persulfate as initiator and poly(ethylene glycol) diglycidyl ether as cross-linking reagent. The sorption properties were analyzed by pH, contact time, maximum sorption capacity, and selectivity studies. The HM2 and HM3 hydrogels exhibited good ion sorption properties. These copolymers were capable of interacting and removing Cd(II), Cu(II), Pb(II), Ni(II), and Zn(II) ions from synthetic solutions and with real samples from mining wastewaters. The results obtained from the studies of maximum sorption capacity at different concentrations showed that the HM2 hydrogel was capable of adsorbing 226 mg/g Cd(II), 241 mg/g Pb(II), 166 mg/g Cu(II), 161 mg/g Zn(II), and 110 mg/g Ni(II) and the HM3 hydrogel was capable of adsorbing 184 mg/g Ni(II), 172 mg/g Cd(II), 126 mg/g Zn(II), 90 mg/g Pb(II), and 39 mg/g Cu(II). The experimental data were correlated with the Langmuir and Freundlich isotherm models. Thermodynamic parameters such as enthalpy (ΔH°), Gibbs free energy (ΔG°), and entropy (ΔS°) changes were obtained. The sorption kinetics were analyzed using Lagergren pseudo-second-order equation.

Chitosan–tripolyphosphate beads are a highly stable and biocompatible polymer-network with versatile applications. In this study, we relate the main synthesis parameters of these particles using a design of experiments and a multivariate calibration to understand how some structural characteristics (mass, diameter and water retention capacity) of these spherical hydrogels are achieved from the point of view of the ionotropic association between chitosan chains and tripolyphosphate molecules. The results conduct to a better conceptualization of the crosslinking process, establish the ranges where particles with different structural characteristic can be obtained and a better understanding of how the physicochemical behavior of the chitosan and the tripolyphosphate affect the structural parameters of the chitosan–tripolyphosphate beads. As a novelty, we propose a refined 3D junction zone for the interaction between the raw molecules that allows to conclude that one TPP molecule can associate with up to three amino groups as a maximum.

The present study describes the synthesis of a new material prepared by low-temperature thermocatalytic degradation of polystyrene (PS) by using zeolite clinoptilonite as a degradation template and subsequent functionalization with acrylamide (AAm) for the removal of lead (Pb(II)) metal ions from aqueous solutions. Infrared spectroscopy (FTIR), field emission scanning electron microscopy, thermogravimetric analysis and differential scanning calorimeter techniques confirm the successful functionalization of PS oligomers, before applying this material as an alternative adsorbent. A preliminar absorption study using functionalized PS oligomers as an adsorbent indicates that material has a good potential to absorb heavy metal of Pb(II) from the aqueous solutions. Equilibrium data show a maximum adsorption capacity of 33.85 mg g−1 with a percentage removal of 90.94%, which fitted well with Freundlich model and kinetic data were best described by pseudo-second-order model. Desorption studies revealed that PS oligomers functionalized with acrylamide as monomer source can be recovered using 0.5 M EDTA as regenerating agent, with a maximum recovery of Pb(II) metal ions of 97.28%. These results reveal that PS oligomers functionalized with acrylamide could be recommended as a promising adsorbent for Pb(II) metal ions contained in aqueous systems.

This research is focused on molybdate and vanadate removal from aqueous solutions by the liquid-phase polymer-based retention (LPR) technique. In this technique, a cationic water-soluble polymer based on the ammonium quaternary group poly(diallyldimethylammonium chloride), PDDA, was used as a polymeric sorbent, and a regenerated cellulose ultrafiltration membrane was used as a filter. The removal of molybdenum and vanadium using the LPR technique was analyzed by both the washing and enrichment methods. The removal experiments using the washing method were conducted by varying the pH, polymer/metal molar ratio, concentration of metal ions, pressure and presence of interfering ions. In addition, the enrichment method was used to determine the maximum retention capacity of PDDA. The obtained results showed the highest retention capacity of molybdate (100%, using 30 mg/L in the feed) for PDDA at pH 3 and 9. The optimum molar ratio was 20:1 polymer/Mo(VI). The efficient vanadate retention (approximately 90%) was obtained at pH 6 with 10:1 polymer/V(V) molar ratio. The effect of metal concentration on the retention showed a higher retention of Mo(VI) independent of its concentrations. In the case of V(V), the maximum retention was reached when 60 mg/L of vanadium was used in the feed. The enrichment method showed the maximum retention capacities of 370 mg Mo(VI)/g PDDA and 520 mg V(V)/g PDDA. The presence of interfering ions did not affect the retention capacity of PDDA. These results showed that the combination of PDDA with ultrafiltration membranes could represent an alternative method for the removal of molybdate and vanadate from water.

The poly([(2-methacryloyloxy)ethyl]trimethylammonium chloride) [P(MOTA)] based chelating resin was synthesized by radical polymerization and employed for Cr(VI) removal. The sorption capacity of this resin was very high with a fast sorption rate for Cr(VI) obeying a pseudo-second order kinetic model. In agreement to diffusion model equations, the rate determining step was film diffusion according to the infinite solution volume (ISV) model and reacted layer in accordance with the unreacted core (UC) model. In a column-mode sorption study, the breakthrough capacity obtained was 24.3 mg Cr/mL-resin. The elution of Cr(VI) from the resin was achieved using a mixture of 1.0 mol/L NaOH and 1.0 mol/L NaCl with an elution efficiency of about 100 %. Based on FT-IR measurements, it was clearly understood that Cr(VI) was sorbed by the resin through the quaternary amine functional groups.

Poly([(2-methacryloyloxy)ethyl]trimethylammonium chloride) resin, P(MOTA) was successfully synthesized by radical polymerization. The resin was characterized by FTIR and SEM. Parameters including the water absorption capacity, effect of the pH, maximum retention capacity of the metal ions, elution, regeneration, adsorption rate, and adsorption isotherms were studied. All the studies were carried out by batch equilibrium procedure. The changes of thermodynamic parameters such as enthalpy, entropy, and free energy were calculated. The P(MOTA) resin showed higher capacity to remove As(V) from water solution than that Amberlite IRA-400(Cl) commercial resin. The higher capacity displayed by P(MOTA) resin was attributed to the higher degree of swelling and different structure than Amberlite IRA-400(Cl).

Arsenic is a very toxic element that must be removed efficiently from aqueous streams. Among the most promising techniques used for the removal of arsenic are separation methods using membranes. In this study, a regenerated cellulose ultrafiltration (UF) membrane and a poly(diallyl dimethyl ammonium chloride) P(DADMAC) were coupled and used in combination to remove As(V) from an aqueous solution. The influences of pH, the polymer:As(V) molar ratio, and the presence of interfering ions such as chloride and sulfate were investigated in arsenic removal via the washing method. The efficient retention of arsenic was observed at pH 7 with a 5:1 polymer:As molar ratio and with an efficiency of approximately 85 % at Z = 10 for P(DADMAC). The maximum retention capacity of As(V) was determined by the enrichment method, and the results indicated that 194 mg of As(V) was removed per gram of polymer. Finally, using enrichment and washing methods sequentially, the sorption–desorption process and regeneration of P(DADMAC) were performed successfully.

A sample of N,N,N-trimethylchitosan chloride (TMC) was prepared and its ability to remove arsenate and chromate from an aqueous solution was evaluated. The removal capacity was quantified by a liquid-phase polymer-based retention system. A washing method was used to determine the effect of pH, molar ratio, contact time, and interfering ions on the removal of the anions. The results showed that TMC exhibits a high affinity for the divalent species HAsO42− and CrO42− because the majority of the retention capacity occurred at pH values between 6 and 10. A removal maximum was found for experiments with a 10:1 molar ratio and pH 8.0, achieving a 73.0 % removal of As(V) and a 94.0 % removal of Cr(VI). The evaluation of the effect of the contact time of the polymer–SR (species to remove) solution prior to diafiltration revealed that the interaction between TMC and the anions is produced rapidly. Furthermore, TMC selectivity in the presence of interfering ions, such as chloride and sulphate, and maximum retention capacity were evaluated. Finally, permeate flux behaviour was briefly discussed under different conditions of removal.