Alternative processes to produce chitin, chitosan, and their oligomers.

Sustainable recovery of chitin and its derivatives from shellfish waste will be achieved when the industrial production of these polymers is achieved with a high control of their molecular structure, low costs, and acceptable levels of pollution. Therefore, the conventional chemical method for obtaining these biopolymers needs to be replaced or optimized. The goal of the present review is to ascertain what alternative methods are viable for the industrial-scale production of chitin, chitosan, and their oligomers. Therefore, a detailed review of recent literature was undertaken, focusing on the advantages and disadvantages of each method. The analysis of the existing data allows suggesting that combining conventional, biological, and alternative methods is the most efficient strategy to achieve sustainable production, preventing negative impacts and allowing for the recovery of high added-value compounds from shellfish waste. In conclusion, a new process for obtaining chitinous materials is suggested, with the potential of reducing the consumption of reagents, energy, and water by at least 1/10, 1/4, and 1/3 part with respect to the conventional process, respectively.

Study of the Efficiency of a Polycation Using the Diafiltration Technique in the Removal of the Antibiotic Oxytetracycline Used in Aquaculture.

The presence of antibiotics in aquatic systems in recent years has become a global environmental and public health concern due to the appearance of strains resistant to these antibiotics. Oxytetracycline (OXT) is a high-impact antibiotic used for both human and veterinary consumption, and it is the second most used antibiotic in aquaculture in Chile. Based on the above, this problem is addressed using a linear polymer whose structure is composed of aromatic rings and quaternary ammonium groups, which will help enhance the removal capacity of this antibiotic. To obtain the polycation, a radical polymerization synthesis was carried out using (4-vinylbenzyl)-trimethylammonium chloride as the monomer. The polycation was characterized via Fourier Transform Infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR). The removal studies were conducted under different experimental conditions such as pH levels (3.0, 5.0, 7.0, 8.0, and 11.0), ionic strength (0.0-0.50 mg L-1 of NaCl), polymer dose (0.25-25.5 mg), variation of the antibiotic concentration (1-100 mg L-1), and evaluation of the maximum retention capacity, as well as load and discharge studies. The antibiotic retention removal was higher than 80.0%. The antibiotic removal performance is greatly affected by the effect of pH, ionic strength, molar ratio, and/or OXT concentration, as these parameters directly affect the electrostatic interactions between the polymer and the antibiotics. The diafiltration technique was shown to be highly efficient for the removal of OXT, with maximum removal capacities of 1273, 966, and 778 mg OXT g-1 polycation. In conclusion, it can be said that coupling water-soluble polymers to the diafiltration technique is an excellent low-cost way to address the problem of antibiotics in aquatic systems.

Comparative Study of the Removal Efficiency of Nalidixic Acid by Poly[(4-vinylbenzyl)trimethylammonium Chloride] and N-Alkylated Chitosan through the Ultrafiltration Technique and Its Approximation through Theoretical Calculations.

Emerging antibiotic contaminants in water is a global problem because bacterial strains resistant to these antibiotics arise, risking human health. This study describes the use of poly[(4-vinylbenzyl) trimethylammonium chloride] and N-alkylated chitosan, two cationic polymers with different natures and structures to remove nalidixic acid. Both contain ammonium salt as a functional group. One of them is a synthetic polymer, and the other is a modified artificial polymer. The removal of the antibiotic was investigated under various experimental conditions (pH, ionic strength, and antibiotic concentration) using the technique of liquid-phase polymer-based retention (LPR). In addition, a stochastic algorithm provided by Fukui's functions is used. It was shown that alkylated N-chitosan presents 65.0% removal at pH 7, while poly[(4-vinylbenzyl)trimethylammonium chloride] removes 75.0% at pH 9. The interaction mechanisms that predominate the removal processes are electrostatic interactions, π-π interactions, and hydrogen bonding. The polymers reached maximum retention capacities of 1605 mg g-1 for poly[(4-vinylbenzyl) trimethylammonium chloride] and 561 mg g-1 of antibiotic per gram for alkylated poly(N-chitosan). In conclusion, the presence of aromatic groups improves the capacity and polymer-antibiotic interactions.

In-Situ Modification of Nanofiltration Membranes Using Carbon Nanotubes for Water Treatment.

Modification of thin-film composite (TFC) nanofiltration (NF) membranes to increase permeability and improve separation performance remains a significant challenge for water scarcity. This study aimed to enhance the permeability and selectivity of two commercial polyamide (PA) NF membranes, NF90 and NF270, by modifying them with carbon nanotubes (CNTs) using microwave (MW)-assisted in-situ growth. The conducting polymer, polypyrrole (Ppy), and a ferrocene catalyst were used to facilitate the growth process. Chemical and morphological analyses confirmed that the surface of both membranes was modified. The NF270-Ppy-CNT membrane was selected for ion rejection testing due to its superior permeability compared to the NF90-Ppy-CNT. The modified NF270 membrane showed a 14% increase in ion rejection while maintaining constant water permeability. The results demonstrated that it is feasible to attach CNTs to a polymeric surface without compromising its functional properties. The Spliegler-Kedem model was employed to model the rejection and permeate flux of NF270-Ppy-CNT and NF270 membranes, which indicated that diffusive transport contributes to the modification to increase NaCl rejection. The present study provides a promising approach for modifying membranes by in-situ CNT growth to improve their performance in water treatment applications, such as desalination.

Bio-Based Polymeric Membranes: Development and Environmental Applications.

Nowadays, membrane technology is an efficient process for separating compounds with minimal structural abrasion; however, the manufacture of membranes still has several drawbacks to being profitable and competitive commercially under an environmentally friendly approach. In this sense, this review focuses on bio-based polymeric membranes as an alternative to solve the environmental concern caused by the use of polymeric materials of fossil origin. The fabrication of bio-based polymeric membranes is explained through a general description of elements such as the selection of bio-based polymers, the preparation methods, the usefulness of additives, the search for green solvents, and the characterization of the membranes. The advantages and disadvantages of bio-based polymeric membranes are discussed, and the application of bio-based membranes to recover organic and inorganic contaminants is also discussed.

Removal of Dyes by Polymer-Enhanced Ultrafiltration: An Overview.

The current problem of contamination caused by colored industrial effluents has led to the development of different techniques to remove these species from water. One of them, polymer-enhanced ultrafiltration (PEUF), has been systematically studied in this mini review, in which research works from 1971 to date were found and analyzed. Dye retention rates of up to 99% were obtained in several cases. In addition, a brief discussion of different parameters, such as pH, interfering salts, type of polymer, dye concentration, and membrane type, and their influence in dye removal is presented. It was concluded from the above that these factors can be adapted depending on the pollutant to be remediated, in order to optimize the process. Finally, theoretical approaches have been used to understand the intermolecular interactions, and development of the studied technique. In this revision, it is possible to observe that molecular docking, molecular dynamics simulations, density functional theory calculations, and hybrid neural-genetic algorithms based on an evolutionary approach are the most usual approximations used for this purpose. Herein, there is a detailed discussion about what was carried out in order to contribute to the research development of this important science field.

Hydrogels derived from galactoglucomannan hemicellulose with inorganic contaminant removal properties.

The adsorption of Cu(ii), Cd(ii), and Pb(ii) ions onto hydrogels derived from modified galactoglucomannan (GGM) hemicellulose was studied. GGM hemicellulose was modified with methacrylate groups (GGM-MA) to incorporate vinyl groups into the polymeric structure, which reacted later with synthetic monomers such as 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). The results show that all the synthesized hydrogels were capable of adsorbing contaminating ions with high adsorption efficiency during short periods of time. Furthermore, an increase in the content of GGM-MA generated a hydrogel (H3) with a similar ion adsorption property to the other hydrogels but with a lesser degree of swelling. The H3 hydrogel had an adsorption capacity of 60.0 mg g-1 Cd(ii), 78.9 mg g-1 Cu(ii), and 174.9 mg g-1 Pb(ii) at 25 °C. This result shows that modified GGM hemicelluloses can be employed as renewable adsorbents to remove Cu(ii), Cd(ii), and Pb(ii) ions from aqueous solutions.

Antibiotics removal using a chitosan-based polyelectrolyte in conjunction with ultrafiltration membranes.

The emergence of antibiotics as pollutants in the environment is one of the worldwide concerns because the bacterial strains generate a threat to the aquatic ecosystem and human health. In this study, an alkylated chitosan polyelectrolyte (ChA-PE) was used in conjunction with ultrafiltration membranes to remove three commonly used antibiotics, including amoxicillin (AMX), tetracycline (TET), and ciprofloxacin (CIP), in aqueous systems. The removal study considered diverse experimental variables through two methods: washing (pH, ionic strength, polymer ratio, and antibiotic concentration) and enrichment (maximum retention capacity). The retention percentage reached 80% at a pH of 11.0 at different polymer/antibiotic molar ratios. The ChA-PE presented irreversibly bound antibiotic interaction values of 0.51, 0.74, and 0.92 for CIP, AMX, and TET, respectively, at a pH of 11, showing that the polymer presents stronger permanent interactions with AMX and TET. On the other hand, the ChA-PE presented maximum retention capacity values of 185.6, 420.2, and 632.8 mg g-1 for CIP, AMX, and TET, respectively, in accordance with the association efficiency percentage values of 73.54, 87.08, and 93.83% for CIP, AMX, and TET, respectively.

N-Alkylated chitosan coupled to the liquid-phase polymer-based retention (LPR) technique to remove arsenic (V) from aqueous systems.

Water-soluble polymer based on alkylated chitosan with a quaternary ammonium group (Ch-QAG) was prepared, characterized, and applied to remove arsenate ions from aqueous solution by LPR technique. The arsenic removal was performed by the washing method (WM) and enrichment method (EM). Through the WM, studies of the pH and variation in the concentrations of interferents and arsenate ions were carried out. The effect of the removal of arsenate ions in simulated water was determined from the Camarones River in northern Chile. Ch-QAG showed high affinity for binding arsenate species (99% of removal) at pH 11.0 at a molar ratio of 20:1 polymer: As(V). High selectivity was also observed in the presence of interfering ions such as Cl-, SO42-, and PO43-, resulting in a removal rate over 80% at percentages over 95% for a concentration of 100 mg L-1 of As (V). The maximum retention capacity obtained was 112, 105, and 98 mg g-1 for three load cycles. The retention percentage for simulated water was 46.3% at a concentration of 1300 µ g L-1. In conclusion, the results presented in this study show that using Ch-QAG with ultrafiltration membranes is a great alternative to remove As (V) at high removal rates.

Polyelectrolyte nanocomposite hydrogels filled with cationic and anionic clays.

Polyelectrolyte nanocomposite hydrogels (NHGs) were synthesized. NHGs were formed from a polymer matrix composed of a cationic, anionic, and alkylated chitosan polymer modified with vinyl groups (ChAV) to achieve greater crosslinking. Cationic and anionic clays montmorillonite and hydrotalcite, respectively, were used as nanofillers to introduce electrostatic interaction with the matrix. NHGs were obtained via in situ polymerization. The ChAV and NHGs were then characterized. Based on X-ray diffraction and transmission electron microscopy results, the morphology of the nanocomposite was generally intercalated with some nanocomposites showing exfoliation. Rheological studies revealed improvements in shear modulus of NHGs with respect to hydrogel without clay. Lower relaxation times were noted as the clay content increased and it was attributed to the interactions between the clay sheets and the polymer. In conclusion the rheological properties of the material are improved with the addition of clay and the interactions present with the polymer matrix.

Magnetic methacrylated gelatin-g-polyelectrolyte for methylene blue sorption.

The presence of organic dyes in wastewater is a problem of growing interest due to its effect on the environment and human health. The aim of this work was to obtain magnetic hydrogels of methacrylated gelatin-g-polyelectrolyte to be used for the removal of methylene blue (MB) used as a model contaminant dye. Grafted gelatins with two degrees of functionalization (48% and 76%) were obtained and subsequently crosslinked using 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) and sodium 4-vinylbenzenesulfonate (SSNa) monomers. Magnetic nanoparticles were formed by an in situ precipitation method to easily remove the hydrogel from the adsorption medium. Our data show that the hydrogel with a low degree of methacrylation displayed a high degree of swelling and decreased stiffness due to its less connected polymer network. MB adsorption experiments showed that neither the low degree of methacrylation nor the presence of the aromatic group in the PSSNa polyelectrolyte generated an increase in the adsorption capacity of the hydrogel. However, a significant increase in the adsorption capacity was observed when dry hydrogels were combined compared to that of previously swollen hydrogel. The experimental data were non-linearly fitted to the pseudo-first and pseudo-second order models and in both cases, the highest q e values were obtained for the GelMA-HF/PAMPS and GelMA-LF/PAMPS hydrogels. The Freundlich isotherm model was the one with the best correlation with the data (r 2 > 0.9700). Higher k f values were obtained for the GelMA-HF/PAMPS and GelMA-LF/PAMPS hydrogels at 20 °C. The results obtained from this study demonstrated that magnetic polyelectrolyte-grafted gelatins are an efficient option for the removal of contaminant dyes from aqueous solutions.

Tetracycline removal by polyelectrolyte copolymers in conjunction with ultrafiltration membranes through liquid-phase polymer-based retention.

In this study, we used a liquid-phase polymer-based retention technique assisted by polyelectrolyte copolymers containing quaternary ammonium and sulfonate groups that are capable of removing the antibiotic tetracycline (TC) through electrostatic interactions. The polymers were synthesized using zwitterionic, anionic, and cationic monomers with the aim of obtaining copolymers with different charge balances at the ratios of 1:1, 2:1, and 1:2 (negative: positive). The parameters investigated for each copolymer included the pH, ionic strength, concentration of polymer, maximum retention capacity, and sorption-elution process at pH 11.0 and 3.0. The copolymers with a charge ratio of 1:2 achieved the highest retention (80.0%) at alkaline pH, while the copolymers with charge ratios of 2:1 and 1:1 exhibited the maximum retention (72.0%) at acidic pH. Based on these results, the pH and charge of the polyelectrolyte copolymers play important roles in the TC removal processes. Additionally, the maximum retention capacity (MRC) recorded was 731.2, 176.8, and 214.8 mg TC/g of copolymer in the first charge for the three copolymer polyelectrolytes, and the second charge of the MRC process did not improve compared with the first load.

Molecularly Imprinted Nanoparticles Assay (MINA) in Pseudo ELISA: An Alternative to Detect and Quantify Octopamine in Water and Human Urine Samples.

In 2004, octopamine was added to the list of drugs banned by the world anti-doping agency (WADA) and prohibited in any sport competition. This work aims to develop a new analytical method to detect octopamine in water and human urine samples. We proposed a pseudo-enzyme-linked immunosorbent assay (pseudo-ELISA) by replacing traditional monoclonal antibodies with molecularly imprinted polymer nanoparticles (nanoMIPs). NanoMIPs were synthesised by a solid-phase approach using a persulfate initiated polymerisation in water. Their performance was analysed in pseudo competitive ELISA based on the competition between free octopamine and octopamine-HRP conjugated. The final assay was able to detect octopamine in water within the range 1 nmol·L-1-0.1 mol·L-1 with a detection limit of 0.047 ± 0.00231 µg·mL-1 and in human urine samples within the range 1 nmol·L-1-0.0001 mol·L-1 with a detection limit of 0.059 ± 0.00281 µg·mL-1. In all experiments, nanoMIPs presented high affinity to the target molecules and almost no cross-reactivity with analogues of octopamine such as pseudophedrine or l-Tyrosine. Only slight interference was observed from the human urine matrix. The high affinity and specificity of nanoMIPs and no need to maintain a cold chain logistics makes the nanoMIPs a competitive alternative to antibodies. Furthermore, this work is the first attempt to use nanoMIPs in pseudo-ELISA assays to detect octopamine.

Copolymer-hydrous zirconium oxide hybrid microspheres for arsenic sorption.

In this work, a hybrid organic-inorganic adsorbent based on polyelectrolyte copolymers of poly(4-vinylbenzyl trimethylammonium chloride-co-2-hydroxyethyl methacrylate) microspheres mixed with a hydrous zirconium oxide phase were applied to remove arsenic species from aqueous solutions. The hybrid adsorbent was synthesized in a two-step procedure: first, the polymeric microspheres were obtained through emulsion radical copolymerization, and then, the microspheres were impregnated with a zirconium oxide precursor followed by the subsequent sol-gel reaction. The purpose of this hybrid material was to combine properties of each component in the interaction with arsenic oxoanions and compare its performance with commercial adsorbents. The polymer hybrid microspheres were shown to remove arsenate, and the presence of the inorganic phase also allowed for the removal of arsenite. The hybrid adsorbent exhibited arsenic sorption independent of pH, is able to regenerate, displays fast kinetics and has the ability to reduce arsenic concentration in treated water below 10 µg L-1 even in real samples with an initial concentration as high as 380 µg L-1.

Polymer films containing chemically anchored diazonium salts with long-term stability as colorimetric sensors.

We have prepared polymeric films as easy-to-handle sensory materials for the colorimetric detection and quantification of phenol derivatives (phenols) in water. Phenols in water resources result from their presence in pesticides and fungicides, among other goods, and are harmful ecotoxins. Colorless polymeric films with pendant diazonium groups attached to the acrylic polymer structure were designed and prepared for use as sensory matrices to detect phenol-derived species in water. Upon dipping the sensory films into aqueous media, the material swells, and if phenols are present, they react with the diazonium groups of the polymer to render a highly colored azo group, giving rise to the recognition phenomenon. The color development can be visually followed for a qualitative determination of phenols. Additionally, quantitative analysis can be performed by two different techniques: a) by using a UV-vis spectrophotometer (limit of detection of 0.12 ppm for 2-phenylphenol) and/or b) by using a smartphone with subsequent RGB analysis (limit of detection of 30 ppb for 2-phenylphenol).

Heavy metal removal from aqueous systems using hydroxyapatite nanocrystals derived from clam shells.

Hydroxyapatite (HA) was synthesized by wet chemical precipitation, using clam shell (CS) waste as feedstock. SEM and TEM observation of the produced hydroxyapatite revealed the presence of rod-shaped nanocrystals, while XRD and EDS analyses confirmed the characteristic patterns of hydroxyapatite molecules. This material was subsequently employed as a sorbent for heavy metal removal from aqueous solutions, both in batch and column equilibrium procedures. In batch studies, higher sorption efficiencies were obtained at pH 5, with the highest adsorption capacities of 265, 64, and 55 mg g-1 for Pb(ii), Cd(ii), and Cu(ii), respectively. In addition, an adsorption capacity of 42.5 mg g-1 was determined using a CS-HA packed bed column fed with a solution of Pb(ii). Finally, the breakthrough curve was fitted with Thomas model in order to predict column behavior and scaling up.

Water-Soluble and Insoluble Polymers, Nanoparticles, Nanocomposites and Hybrids With Ability to Remove Hazardous Inorganic Pollutants in Water.

The polymeric materials have presented a great development in adsorption processes for the treatment of polluted waters. The aim of the current review is to present the recent developments in this field of study by examining research of systems like functional water-soluble polymers and water-soluble polymer-metal complexes coupled to ultrafiltration membranes for decontamination processes in liquid-liquid phase. Noticing that a water-soluble polymer can be turned into insoluble compounds by setting a crosslinking point, connecting the polymer chains leading to polymer resins suitable for solid-liquid extraction processes. Moreover, these crosslinked polymers can be used to develop more complex systems such as (nano)composite and hybrid adsorbents, combining the polymers with inorganic moieties such as metal oxides. This combination results in novel materials that overcome some drawbacks of each separated components and enhance the sorption performance. In addition, new trends in hybrid methods combining of water-soluble polymers, membranes, and electrocatalysis/photocatalysis to remove inorganic pollutants have been discussed in this review.

Molecularly Imprinted Polymers for the Selective Extraction of Bisphenol A and Progesterone from Aqueous Media.

This paper describes the development of a novel sorbent for selective extraction of endocrine disruptors (EDs) from aqueous media. The main goal was to obtain sufficient molecularly imprinted polymers (MIPs) for selective detection, preconcentration, and extraction of EDs such as bisphenol A (BPA) and progesterone (PG). Series of MIPs and their analogues, non-molecularly imprinted polymers (NIPs), were synthesised following a non-covalent imprinting strategy based on radical polymerisation. Sets of synthesis were performed in order to optimise variables of the polymerisation including solvent, cross-linker, and template ratio. The retention capacity of MIPs was determined using HPLC in the range of 33.3% to 96.6% and 32.5% to 96% for BPA and PG, respectively. The adsorption mechanism was studied by isothermal and kinetic assays. The kinetic analysis showed a high retention capacity within 15 min of contact. The polymer yield was obtained in the range of 30% to 100%. Additionally, there was no significant cross-reactivity observed upon testing MIPs with structural analogues and other endocrine disruptors instead of target molecules. The results also revealed the high importance of different concentrations of cross-linker and solvent during the polymerisation. Firstly, the pre-organisation of complementary functional groups, which were present in the polymerisation mixture, and secondly, selective cavity formation for target molecules.

Metal-ion retention properties of water-soluble amphiphilic block copolymer in double emulsion systems (w/o/w) stabilized by non-ionic surfactants.

Metal-ion retention properties of water-soluble amphiphilic polymers in presence of double emulsion were studied by diafiltration. Double emulsion systems, water-in-oil-in-water, with a pH gradient between external and internal aqueous phases were prepared. A poly(styrene-co-maleic anhydride) (PSAM) solution at pH 6.0 was added to the external aqueous phase of double emulsion and by application of pressure a divalent metal-ion stream was continuously added. Metal-ions used were Cu(2+) and Cd(2+) at the same pH of polymer solution. According to our results, metal-ion retention is mainly the result of polymer-metal interaction. Interaction between PSMA and reverse emulsion globules is strongly controlled by amount of metal-ions added in the external aqueous phase. In addition, as metal-ion concentration was increased, a negative effect on polymer retention capacity and promotion of flocculation phenomena were produced.

Removal of As(III) and As(V) by Tin(II) compounds.

The retention capacity for arsenic species of new nanomaterials based on tin(II) inorganic oxides or hybrid (inorganic and organic) materials was studied. The synthesis of a polymer-metal complex was performed with poly(acrylic acid) and tin(II) chloride. Poly(AA)-Sn(II) with 10 and 20 wt% of tin and a structure with a mol ratio tin:carboxylate group of 1:1, were characterized. These compounds with 10 and 20 wt% of tin content were used to compare the arsenic removal capability through the liquid-phase polymer-based retention, (LPR), technique. Also, tin oxide was prepared by adding alkaline solution to tin(II) chloride salt. The intermediate tin compound was studied by UV-Vis spectroscopy at different pH values and quantified by potentiometric titration. The solid structure is characterized by Fourier transformed infrared spectroscopy, X-ray diffraction, and specific area BET (N(2)). Removal of arsenite and arsenate species from solution by hydrolysated tin was carried out by LPR technique with ultrafiltration membranes and a fixed-bed column unsupported or supported on SiO(2). In all these cases, a washing method at constant pH was applied. The arsenic retention ability depended on the class of tin compounds prepared, with a higher efficiency for arsenic being observed at basic pH for soluble complex poly(AA)-Sn(II) than that for tin hydroxide or hydrolysate of Sn(+2).