Characterization of metal ion interactions with chitosan by X-ray photoelectron spectroscopy

Flame retardancy and smoke suppression properties of bio-based chitosan polyelectrolyte flame retardant containing P and N in epoxy resin

This study reports the successful synthesis of flame-retardant and smoke-suppressing epoxy resin (EP) via bio-based polyelectrolyte flame retardants. Herein, a novel polyelectrolyte flame retardant was prepared from chitosan (CS) and hexa-(4-carboxyl-phenoxy)-cyclotriphosphazene (HCPCP) by acid-base neutralization reaction, which the HCPCP was synthesized with hexachlorocyclotriphosphazene (HCCP) and methyl p-hydroxybenzoate (MP) by nucleophilic substitution reaction. The combined effect of the addition on the flame retardant, smoke suppression and mechanical properties of EP samples were systematically investigated. The presence of this bio-based polyelectrolyte provided excellent smoke suppression and flame-retardant properties of the prepared EP. Among them, the peak heat release rate (PHRR), peak smoke production rate (PSPR) and total smoke production (TSP) of EP/9wt%3CS-HCPCP composite (the ratio of CS to HCPCP was 3: 7, and the dosage was 9 wt%) were reduced by 45.42 %, 41.66 % and 22.56 %, respectively. In addition, the EP/CS-HCPCP composites showed a 207.80 % enhancement in char residue compared to pure EP. These results suggest a green and cost-effective strategy for the production of flame-retardant, drip-proof and smoke-suppressed EP composites.

Removal of acetyl-rich impurities from chitosan using liquefied dimethyl ether

Chitosan, recognized for its excellent biodegradability, biocompatibility, and antibacterial properties, has several potential applications, particularly in the biomedical field. However, its widespread use is hindered by inherent limitations such as low mechanical strength and safety concerns arising from a low degree of deacetylation and the presence of impurities. This study aimed to introduce an innovative purification method for chitosan via liquefied dimethyl ether (DME) extraction. The proposed technique effectively addresses the challenges associated with chitosan by facilitating deacetylation and impurity removal. Liquefied DME is emerging as the extraction solvent of choice owing to its advantages, such as low boiling point, safety, and environmental sustainability. The degree of deacetylation of chitosan was extensively evaluated using thermogravimetric-differential thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, intrinsic viscosity measurements, solid-state nuclear magnetic resonance spectroscopy and X-ray photoelectron spectroscopy, and elemental analysis. The solubility of chitosan in liquefied DME was investigated using Hansen solubility parameters. This study contributes to the improvement of the safety profile of chitosan, thereby expanding its potential applications in various fields. The use of liquefied DME as an extraction solvent proved to be efficient in addressing the existing challenges and is consistent with the principles of safety and environmental sustainability.

Synthesis and synergistic antibacterial efficiency of chitosan-copper oxide nanocomposites

Copper and chitosan are used for biomedical applications due to their antimicrobial properties. In this study, a facile method for the synthesis of chitosan-copper oxide nanocomposites (nCuO-CSs) was modified, yielding stable colloidal nCuO-CSs suspensions. Using this method, nCuO-CSs with different copper-to-chitosan (50-190 kDa) weight ratios (1:0.3, 1:1, 1:3) were synthesized, their physicochemical properties characterized, and antibacterial efficacy assessed against Gram-negative Escherichia coli and Pseudomonas aeruginosa, and Gram-positive Staphylococcus aureus. The nCuO-CSs with a primary size of ∼10 nm and a ζ-potential of >+40 mV proved efficient antibacterials, acting at concentrations around 1 mg Cu/L. Notably, against Gram-negative bacteria, this inhibitory effect was already evident after a 1-h exposure and surpassed that of copper ions, implying to a synergistic effect of chitosan and nano-CuO. Indeed, using flow cytometry and confocal laser scanning microscopy, we showed that chitosan promoted interaction between the nCuO-CSs and bacterial cells, facilitating the shedding of copper ions in the close vicinity of the cell surface. The synergy between copper and chitosan makes these nanomaterials promising for biomedical applications (e.g., wound dressings).

Carbon nitride reinforced chitosan/sodium alginate hydrogel as high-performance adsorbents for free hemoglobin removal in vitro and in vivo

Removing free hemoglobin generated during extracorporeal circulation remains a challenge. Currently, there is no adsorbent with specificity and good biosafety for removing hemoglobin. In this study, a new chitosan/sodium alginate/carbon nitride (CS/SA/C3N4) hydrogel adsorbent was prepared by blending SA with C3N4 to drop into CS/CaCl2 solution. The physicochemical properties of CS/SA/C3N4 hydrogel were evaluated using some techniques, including scanning electron microscope, Zeta potential measurement, and thermogravimetric analysis. Hemoglobin adsorption in vitro, stability, hemocompatibility, cell compatibility, inflammatory reaction and blood extracorporeal circulation in vivo were also evaluated. The findings revealed that the CS/SA/C3N4-0.4 % hydrogel exhibited an impressive adsorption capacity of 142.35 mg/g for hemoglobin. The kinetic data of hemoglobin adsorption were well-described by pseudo second-order model, while the isothermal model data conformed to the Langmuir model. The hardness and modulus of CS/SA/C3N4-0.4 % was 11.7 KPa and 94.66 KPa respectively, which indicated robust resistance to breakage. CS/SA/C3N4 demonstrated excellent hemocompatibility, biocompatibility and anti-inflammatory properties. In addition, the results of in vivo rabbit extracorporeal blood circulation experiment demonstrated that CS/SA/C3N4 could adsorb free hemoglobin from blood while maintaining high biosafety standard. Consequently, CS/SA/C3N4 hydrogel emerges as a promising candidate for use as a hemoglobin adsorbent in extracorporeal blood circulation system.

Selective biosorption of Li+ in aqueous solution by lithium ion-imprinted material on the surface of chitosan/attapulgite

The extraction of Li+ from liquid lithium resources is a pivotal focus of current research endeavors. Attapulgite (ATP), characterized by its distinctive layered structure and inherent ion exchange properties, emerges as an exceptional material for fabricating lithium-ion sieve. Ion-imprinted chitosan/ATP composite materials are successfully synthesized, demonstrating efficacy in selectively absorbing Li+. The results emphasize the rich functional groups present in H-CTP-2, enhancing its absorbability and selectivity, with an adsorption capacity of 37.56 mg•g-1. The adsorption conforms to the Langmuir and pseudo-second-order kinetic model. Li+ coordination involves amino and hydroxyl group, indicating a chemisorption process. Furthermore, the substantial pore structure and significant specific surface area of ATP significantly promote Li+ adsorption, suggesting its participation not only in chemisorption but also in physical adsorption. The fabricated ion-imprinted materials boast substantial adsorption capacity, exceptional selectivity, and rapid kinetics, highlighting their potential for effectively separating Li+ from aqueous solution.

Electric-field-sensitive hydrogel based on pineapple peel oxidized hydroxyethyl cellulose/gelatin/Hericium erinaceus residues chitosan and its study in curcumin delivery

This study focused on synthesis of innovative hydrogels with electric field response from modified pineapple peel cellulose and hericium erinaceus chitosan and gelatin based on Schiff base reaction. A series of hydrogels were prepared by oxidized hydroxyethyl cellulose, gelatin and chitosan at different deacetylation degree via mild Schiff base reaction. Subsequently experiments towards the characterization of oxidized hydroxyethyl cellulose/gelatin/chitosan (OHGCS) hydrogel polymers were carried out by FTIR/XRD/XPS, swelling performances and electric response properties. The prepared hydrogels exhibited stable and reversible bending behaviors under repeated on-off switching of electric fields, affected by ionic strength, electric voltage and pH changes. The swelling ratio of OHGCS hydrogels was found reduced as deacetylation degree increasing and reached the maximum ratio ∼ 2250 % for OHGCS-1. In vitro drug releasing study showed the both curcumin loading capacity and release amount of Cur-OHGCS hydrogels arrived about 90 % during 6 h. Antioxidation assessments showed that the curcumin-loaded hydrogels had good antioxidation activities, in which, 10 mg Cur-OHGCS-1 hydrogel could reach to the maximum of about 90 % DPPH scavenging ratio. These results indicate the OHGCS hydrogels have potentials in sensor and drug delivery system.

Flame retardant, high mechanical strength, transparent and water-resistant epoxy composites modified with chitosan derivatives

Adding bio-based flame retardants to improve the flame retardancy of polymer materials without sacrificing other properties is a great challenge. Herein, a novel flame-retardant CS-DOPA was prepared from chitosan and 10-hydroxy-9,10-dihydro-9-oza-10-phosphaphenanthrene-10-oxide by acid-base neutralization reaction and fully characterized. The 4 wt% CS-DOPA modified EP showed good flame retardancy in both gaseous and condensed phase. The peak heat release rate, total smoke production, CO production, and smoke production rate of EP composites containing 4 wt% CS-DOPA were reduced by 55 %, 34 %, 45 %, and 46 %, respectively, to pass the UL-94 V-1 rating with a limiting oxygen index of 34.1 %. The CS-DOPA contributes to the formation of the condensed phase of the thermo-oxidation-resistant high-quality char layer with non-flammable other and phosphorus-containing free radicals released in the gas phase. In addition, EP/4CS-DOPA has good water resistance, mechanical properties, and transparency, with tensile and flexural strength improved by 12.7 % and 13.9 %, respectively, and still has high strength even after water treatment. The present work provides a green and facile strategy to use chitosan as a main raw material to manufacture EP materials with high performance.

Chitosan Biocomposites with Variable Cross-Linking and Copper-Doping for Enhanced Phosphate Removal

The fabrication of chitosan (CH) biocomposite beads with variable copper (Cu2+) ion doping was achieved with a glutaraldehyde cross-linker (CL) through three distinct methods: (1) formation of CH beads was followed by imbibition of Cu(II) ions (CH-b-Cu) without CL; (2) cross-linking of the CH beads, followed by imbibition of Cu(II) ions (CH-b-CL-Cu); and (3) cross-linking of pristine CH, followed by bead formation with Cu(II) imbibing onto the beads (CH-CL-b-Cu). The biocomposites (CH-b-Cu, CH-b-CL-Cu, and CH-CL-b-Cu) were characterized via spectroscopy (FTIR, 13C solid NMR, XPS), SEM, TGA, equilibrium solvent swelling methods, and phosphate adsorption isotherms. The results reveal variable cross-linking and Cu(II) doping of the CH beads, in accordance with the step-wise design strategy. CH-CL-b-Cu exhibited the greatest pillaring of chitosan fibrils with greater cross-linking, along with low Cu(II) loading, reduced solvent swelling, and attenuated uptake of phosphate dianions. Equilibrium and kinetic uptake results at pH 8.5 and 295 K reveal that the non-CL Cu-imbibed beads (CH-b-Cu) display the highest affinity for phosphate (Qm = 133 ± 45 mg/g), in agreement with the highest loading of Cu(II) and enhanced water swelling. Regeneration studies demonstrated the sustainability and cost-effectiveness of Cu-imbibed chitosan beads for controlled phosphate removal, whilst maintaining over 80% regenerability across several adsorption-desorption cycles. This study offers a facile synthetic approach for controlled Cu2+ ion doping onto chitosan-based beads, enabling tailored phosphate oxyanion uptake from aqueous media by employing a sustainable polysaccharide biocomposite adsorbent for water remediation by mitigation of eutrophication.

Thermally-activated gelatin-chitosan-MOF hybrid aerogels for efficient removal of ibuprofen and naproxen

Nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most frequently used drugs and have been frequently detected in aquatic environments. This paper demonstrates a thermally-activated gelatin-chitosan and amine-functionalized metal-organic framework (UiO-66-NH2) aerogel (CGC-MOF), which was successfully synthesized for the efficient removal of ibuprofen (IBP) and naproxen (NPX). Various characterization tools were used to systematically analyze the microstructure and physicochemical properties of the synthesized aerogel. In addition, the effect of key reaction parameters as well as batch and continuous-flow fixed-bed column experiments were carried out to elucidate the adsorption process. Several functional groups in the biopolymer network, combined with excellent MOF properties, synergistically couple to form an adsorbent with great performance. The mesoporous aerogel activated at 200 °C (CGC-MOF200) exhibited a high specific surface area (819.6 m2/g) that is valuable in providing abundant adsorption active sites that facilitate the efficient adsorption of IBP and NPX. CGC-MOF200 exhibited an excellent removal of IBP and NPX, accounting to 99.28 % and 96.39 %, respectively. The adsorption process followed the pseudo-second-order kinetics and the Freundlich isotherm models, suggesting heterogeneous and chemisorption adsorption processes. Overall, this work provides new and valuable insights into the development of a promising biopolymer-MOF composite aerogel for environmental remediation.

Flexible quasi-solid-state supercapacitors for anti-freezing power sources based on polypyrrole@cation-grafted bacterial cellulose

Polypyrrole (PPy)/cellulose nanofiber (CNF) composites have been widely used in flexible energy storage devices because of their lightweight, inherent mechanical flexibility and large specific surface area. However, it is still a challenge to obtain PPy/CNF composite electrodes with high cycling stability. Herein, an electrostatic self-assembly strategy was adopted to deposit anion-doped PPy onto cationic poly(methacryloxyethyltrimethyl ammonium chloride)-grafted bacterial cellulose (BCD) nanofibers. The optimized PPy@BCD electrode demonstrated a high areal capacitance of 6208 mF cm-2 at a current density of 0.5 mA cm-2 and superior cycling stability (a capacitance retention of 100 % after 10,000 charge-discharge cycles at 10 mA cm-2). A quasi-solid-state anti-freezing flexible supercapacitor (AF-FSC) was designed by employing polyacrylamide organohydrogel electrolyte, yielding an areal capacitance of 2930.6 mF cm-2 at 1 mA cm-2 and a capacitance retention of 92.2 % after 1000 cycles at -20 °C. The present AF-FSC is expected to serve as a power source in real-life low-temperature applications.

Effects of different modifying agents on the preparation and properties of coagulants derived from excess sludge

The contents and kinds of oxygen-containing functional groups are very significant when preparing cationic hydrochar coagulants via graft copolymerization. Herein, the hydrothermal conditions to produce sludge-based hydrochar (SBC) precursors were optimized by introducing different kinds and amounts of modifying agents (i.e., HCOOH, citric acid (CA), H2SO4, and H2O2), then the surface properties and flocculation performance of derived cationic coagulants (SBC-g-DMC) were studied. Results showed that the utilization of four modifiers raised the acidic groups on the SBC surface; thereinto, the presence of CA could evidently increase the content of phenolic hydroxyl groups. After DMC monomer grafting, the formed coagulants possess positive zeta potentials over a wide pH range (i.e., 3.0 ~ 11.0), showing a typical cationic property. The grafting ratio and efficiency, as well as the cationic degree of coagulants prepared with different SBC precursors follow a descending order of SBCCA-g-DMC > [Formula: see text]-g-DMC > SBCHCOOH-g-DMC > [Formula: see text]-g-DMC; thus, SBCCA-g-DMC coagulant with the best grafting result shows a superior flocculation performance. When a dosage of 4 mg/L was adopted, the average turbidity removal rate of SBCCA-g-DMC could reach up to 94.44%. Meanwhile, due to the possible and robust oxidation with the initiator, H2O2 seems not a perfect modifier for SBC preparation. This study could provide an essential reference for the optimal synthesis of SBC and its based coagulants for organic matter recovery and pollutant removal.

Thermoreversible and tunable supramolecular hydrogels based on chitosan and metal cations

A new thermoreversible and tunable hydrogel CS-M with high water content prepared by metal cation (M = Cu²⁺, Zn²⁺, Cd²⁺ and Ni²⁺) and chitosan (CS) was reported. The influence of metal cations on the thermosensitive gelation of CS-M systems were studied. All prepared CS-M systems were in the transparent and stable sol state and could become the gel state at gelation temperature (T_g). These systems after gelation could recover to its original sol state at low temperature. CS-Cu hydrogel was mainly investigated and characterized due to its large T_g scale (32-80 °C), appropriate pH range (4.0-4.6) and low Cu²⁺ concentration. The result showed that the T_g range was influenced and could be tuned by adjusting Cu²⁺ concentration and system pH within an appropriate range. The influence of anions (Cl^-, NO3^- and Ac^-) in cupric salts in the CS-Cu system was also investigated. Scale application as heat insulation window was investigated outdoors. The different supramolecular interactions of the -NH₂ group in chitosan at different temperatures were proposed to dominate the thermoreversible process of CS-Cu hydrogel.

Preparation of cationic aggregates derived from sewage sludge for efficient capture of organic matter

Capturing the abundant organic matter residing in wastewater can not only reduce the emission of CO₂ from the source, but the enriched organics can also be used for anaerobic fermentation to generate and offset energy consumption in wastewater treatment processes. The key is to find or develop low-cost materials that can capture organic matter. Herein, sewage sludge-derived cationic aggregates (SBC-g-DMC) were successfully prepared via a hydrothermal carbonization process coupled with a graft copolymerization reaction for recovering organic matter from wastewater. Based upon preliminary screening of synthesized SBC-g-DMC aggregates regarding grafting rate, cationic degree, and flocculation performance, SBC-g-DMC_2.5 aggregate prepared with 60 mg of initiator, DMC-to-SBC mass ratio of 2.5:1, 70 °C, and 2 h of reaction time was selected for further characterization and evaluation. Results showed that SBC-g-DMC_2.5 aggregate has a positively-charged surface over a wide pH range of 3-11 and a hierarchical micro-/nano-structure, endowing it with an excellent organic matter capture efficiency (97.2% of pCOD, 68.8% of cCOD, and 71.2% of tCOD). Meanwhile, SBC-g-DMC_2.5 exhibits inappreciable trapping ability for the dissolved COD, NH₃-N, and PO₄^3-, guaranteeing the regular running of subsequent biological treatment units. Electronic neutralization, adsorption bridging, and sweep coagulation between cationic aggregates surface and organic matter were identified as the primary mechanisms for SBC-g-DMC_2.5 to capture organics. This development is expected to provide a theoretical reference for sewage sludge disposal, carbon reduction, and energy recovery during municipal wastewater treatment.

Hybrid biomaterials to preconcentrate and determine toxic metals and metalloids: a review

Toxic elements represent a serious threat to the environment and cause harmful effects on different environmental components, even at trace levels. These toxic elements are often difficult to detect through the typical instrumentation of an analytical laboratory because they are found at very low concentrations in matrices such as food and water. Therefore, preconcentration plays a fundamental role since it allows the effects of the matrix to be minimized, thus reaching lower detection limits and greater sensitivity of detection techniques. In recent years, solid-phase extraction has been successfully used for the preconcentration of metals as an environmentally friendly technique due to the fact that it eliminates or minimizes the use of reagents and solvents and offers reduced analysis times and low generation of waste in the laboratory. Hybrid biomaterials are low-cost, eco-friendly, and useful as efficient solid phases for the preconcentration of elements. In this review, recent investigations based on the use of hybrid biomaterials for the preconcentration and determination of toxic metals are presented and discussed, given special attention to bionanomaterials. A brief description of hybrid biomaterials often used for analytical purposes, as well as analytical techniques mostly used to characterize the hybrid biomaterials, is explained. Finally, the future prospects that encourage the search for new hybrid biomaterials are commented upon.

Engineering chitosan into fully bio-sourced, water-soluble and enhanced antibacterial poly(aprotic/protic ionic liquid)s packaging membrane

The design and facile preparation of water-soluble and eco-friendly polymer packaging membrane materials is a fascinating research topic, particularly in terms of the increasing concerns on potential microplastics pollution in ecosystem. In this study, taking advantages of the structural features of chitosan (CS) and betaine hydrochloride (BHC), fully bio-sourced and water-soluble poly(aprotic/protic ionic liquid)s (PAPILs) were successfully designed and prepared through the reaction of the amino groups in CS and carboxyl groups in BHC. The structure and thermo-properties of the PAPILs were elucidated by a series of characteristic methods. The rheological properties of the PAPILs aqueous solutions were also investigated. Moreover, water-soluble PAPILs membrane with a smooth surface morphology and a tensile strength of 62.9 MPa was successfully prepared. The PAPILs membrane also exhibited satisfactory biocompatibility, excellent antibacterial activities and high oxygen barrier property. Together with these outstanding material performance and functionality, as a "proof of concept", the potential use of the PAPILs membrane as water-soluble packaging material for laundry detergent capsule and pesticide was preliminarily demonstrated. These findings provide significant insights for the design of sustainable and functional packaging materials by using natural resources.

A bio-inspired versatile free-standing membrane for oral cavity microenvironmental monitoring and remineralization to prevent dental caries

The fast monitoring of oral bacterial infection, bacterial clearance and repairing of enamel damage caused by dental caries relies on an effective way of monitoring, killing and repairing in situ, but presents a major challenge in oral healthcare. Herein, we developed a bio-inspired versatile free-standing membrane by filling TiO₂ nanotube arrays with β-sheet-rich silk fibroin and cleaving them from Ti foil, as inspired by nacre or enamel-like structures. The robust transparent membrane exhibited good mechanical properties, and could indicate acid-base microenvironment variation and the infection of S. mutans in a 5 min test by loading cyanidin cations in the membrane. Meanwhile, it can be used for photocatalysis and nanoreservoirs ascribed to TiO₂ nanotubes, to kill and remove 99% of S. mutans bacteria under interval UV irradiation with low-power density, and load functional peptide to induce the remineralization on the etched-enamel for long-term treatment, tested in vitro and in vivo. The mechanical property of repaired enamel is improved in comparison. This bio-inspired constructed membrane would be applied in the prevention and treatment of oral cavity related diseases, such as enamel demineralization and dental caries, etc.

Tetracycline adsorption trajectories on aged polystyrene in a simulated aquatic environment: A mechanistic investigation

Microplastics (MPs) have attracted widespread attention as an organic class of pollutants as well as pollutant carriers in recipient aquatic ecosystems. In this study, tetracycline (TC) adsorption by polystyrene (PS), with multiple aging-based temporal changes in the adsorption mechanism, was observed. The results revealed that the pseudo-second-order model accurately predicted the TC adsorption kinetics for different types of PS. In addition, the isothermal adsorption processes fit the Freundlich model; however, their interactions were drastically weakened at lower temperatures or increasing salinities. Corresponding to the electrostatic interactions, adsorption TC was largely pH-dependent, with the maximum adsorbed TC content on the PS surface at a pH of 5 in an aqueous environment. More importantly, mechanistic studies have revealed that, compared to virgin PS, TC complexes with aged PS are principally controlled by hydrogen bonding and ionic interactions, followed by π-π, polar-polar, and van der Waals interactions. These findings will aid in understanding the insights of TC and aged PS interactions and the underlying interactive molecular forces, which will be advantageous for comprehending the real case scenario of inter-pollutant interactions and related environmental pollution.

Fabrication of poly(maleic acid)-grafted cross-linked chitosan/montmorillonite nanospheres for ultra-high adsorption of anionic acid yellow-17 and cationic brilliant green dyes in single and binary systems

In this contribution, poly(maleic acid)-grafted cross-linked chitosan/montmorillonite composite nanospheres (PMAL-CTS/MMT) were synthesized via a facile approach for adsorption of organic dyes. The adsorption capacity of PMAL-CTS/MMT towards anionic acid yellow-17 (AY17) and cationic brilliant green (BG) was compared to PMAL-CTS, CTS/MMT, and MMT to emphasize the role of surface functional groups introduced by poly(maleic acid) and montmorillonite. Interestingly, the adsorption efficiency of PMAL-CTS/MMT nanocomposite towards both dyes in the single and binary systems was extremely high due to plenty of functional groups. The affinity of PMAL-CTS/MMT towards cationic and anionic dyes resulted from the feasible modulation of the surface charges as a function of the solution pH. The PMAL-CTS/MMT nanocomposite exhibited a maximum adsorption capacity of 518 and 1910 mg g^-1 for AY17 and BG, respectively, which is higher than most of the adsorbents reported in recent literature studies. The proposed mechanism based on the characterization of PMAL-CTS/MMT after the adsorption highlighted that the adsorption is mainly controlled by electrostatic interaction, π - π interactions, and hydrogen bonding. More importantly, the PMAL-CTS/MMT nanocomposite was successfully applied to separate the AY17 and BG dyes from real-life aquatic environments. Collectively, the simple fabrication and superior adsorption performance reveal that PMAL-CTS/MMT has the potential to treat concomitant organic dyes effectively.

Recirculation of activated sludge for coagulant synthesis under hydrothermal conditions

A hypothesis was proposed that the activated sludge was converted into hydrochar full of phenolic hydroxyl and then was made into coagulant by graft copolymerization. The results show that under the addition of HCl, the content of phenolic hydroxyl on the surface of hydrochar (SBC) under hydrothermal conditions increased sharply, up to 1.586 mmol/g, showing that HCl dosage of 0.10 g/g _{dry sludge} and holding time of 4 h was recommended. Under graft copolymerization with the addition of DMC, the coagulant was synthesized. Based on the analysis by FTIR, XPS, zeta potential, etc., the possible synthesis route of coagulant from SBC was that phenolic hydroxyl on SBC was activated by the initiator and then the polymerization between SBC and DMC was triggered. The optimal grafting conditions are gotten. It was named as SBC_{HCl0.10 g, 4 h}-g-DMC_0.7. The removal by SBC_{HCl0.10 g, 4 h}-g-DMC_0.7 on COD and turbidity in domestic wastewater is up to 69% and 93%, respectively. The component of COD indicated that almost all particulate COD and most of colloidal COD are removed. On the contrary, the removal on dissolved COD can be neglected. Most of NH₃-N and P is kept in the wastewater. This is in favor of subsequent reuse and biological treatment.

Design of Environmentally Friendly Ca-Alginate Beads for Self-Healing Cement-Based Materials

Ca-alginate beads have strong hygroscopicity, which have been used for the self-healing and internal curing of cement-based materials. However, ca-alginate beads in cement will chelate with calcium ions, which decreases the swelling rate of ca-alginate beads in the healing environment and is detrimental to the self-healing of cement-based materials. In this paper, the mechanism and steps for preparing ca-alginate beads with a lower ability to chelate with calcium ions were proposed based on protonation theory. In addition, the molecular structure and the swelling rates in cement filtrate and healing environment of ca-alginate beads prepared by the proposed method were characterized. The results showed that the ca-alginate beads prepared by the proposed method had higher molecular density and a lower ability to chelate with calcium ions. The swelling rate in the healing environment is not decreased. Furthermore, the equilibrium swelling rate in cement filtrate can satisfy the need for internal curing of cement-based materials.

Resource utilization of hazardous Cr/Fe-rich sludge: synthesis of erdite flocculant to treat real electroplating wastewater

Cr/Fe-bearing sludge is a hazardous solid waste, produced at mass production in smelting, plating and surface finishing industries. Such waste is commonly treated by chemical detoxification and safety landfill, whereas only a few Cr-rich sludge is recycled as a tanning reagent. In this study, a novel route was developed to recycle Cr/Fe-bearing sludge as erdite-bearing flocculant for wastewater treatment. Results showed that two sludges were irregular aggregates, one of which contained 1.6 wt.% Cr (short for LS) and the other contained 4.2 wt.% Cr (HS). After hydrothermal treatment, stable Cr(III)/S-bearing product was formed from the Cr(VI) reduction in the sludges. Conversely, erdite was generated in nanorod form with diameter and length of 200 nm and 0.5-1 μm from LS, respectively, whereas grew radially to 1.5-2.5 μm for HS. The two erdite-bearing products were spontaneously hydrolysed to Fe/S-bearing flocs and showed similar performance in the treatment of real electroplating effluent with 91.55, 1.94 and 0.25 mg/L of Zn, Ni and Cr, respectively. For instance, by adding 1 g/L product of LS, the release of Cr from the products did not occur, and the residual Zn, Ni and Cr in the effluent was 0.25, 0.65 and 0.17 mg/L, respectively, which met the discharge standard of the electroplating industry. With the two converted products, the residual Zn/Ni/Cr concentrations were apparently lower than those of the raw sludges and other common reagents (e.g. polymeric ferric sulphate, activated carbon and diatomite). Thus, such erdite-bearing products could serve as a flocculant and then be applied in electroplating wastewater treatment.

Recycling urine for bioelectrochemical hydrogen production using a MoS2 nano carbon coated electrode in a microbial electrolysis cell

In this study, a novel molybdenum disulfide (MoS₂) nano-carbon (NC) coated cathode was developed for hydrogen production in a microbial electrolysis cell (MEC), while treating simulated urine with 2-6 times dilution (conductivity <20 mS cm^-1). MoS₂ nanoparticles were electrodeposited on the NC coated cathodes at -100, -150 and -200 μA cm^-2 and their performances were evaluated in the MEC. The chronopotentiometry (CP) tests showed the improved catalytic activity of MoS₂-NC cathodes with much lower cathode overpotential than non-MoS₂ coated electrodes. The MoS₂-NC200 cathode, electrodeposited at -200 μA cm^-2, showed the maximum hydrogen production rate of 0.152 ± 0.002 m³ H₂ m^-2 d^-1 at 0.9V of E_ap, which is comparable to the previously reported Pt electrodes. It was found that high solution conductivity over 20 mS cm^-1 (>600 mg L^-1 NH₃-N) can adversely affect the biofilm architecture and the bacterial activity at the anode of the MEC. Exoelectrogenic bacteria for this system at the anode were identified as Tissierella (Clostridia) and Bacteroidetes taxa. Maximum ammonia-nitrogen (NH₃-N) and phosphorus (PO₄ ^3--P) removal were 68.7 and 98.6%, respectively. This study showed that the newly fabricated MoS₂-NC cathode can be a cost-effective alternative to the Pt cathode for renewable bioelectrochemical hydrogen production from urine.

Magnetic chitosan microspheres: An efficient and recyclable adsorbent for the removal of iodide from simulated nuclear wastewater

The efficient and recyclable magnetic chitosan microspheres (MCMs) were successfully synthesized to remove iodide from nuclear wastewater and characterized through XRD, FTIR, SEM, EDS, VSM, TGA and XPS. The characterization results indicated that the MCMs exhibited smooth spherical morphology and good magnetic properties. The removal potential of MCMs was investigated for iodide (I^-) anions at different conditions. From pH 3 to pH 9, MCMs performed the high I^- removal efficiency (>90%). The maximum I^- removal capacity of MCMs was up to 0.8087 mmol g^-1 at 298 K, well-fitting with the pseudo-second-order and Sips models. Furthermore, the I^- removal efficiency of MCMs still maintained more than 91% after five adsorption-desorption cycles, performing good regeneration and reusability. This study is expected to prompt the MCMs to become an efficient and recyclable biosorbent for iodide removal from nuclear wastewater.

Magnetic graphene oxide-containing chitosan‑sodium alginate hydrogel beads for highly efficient and sustainable removal of cationic dyes

Developing recyclable and efficient adsorbents for cationic dyes removal from wastewater is crucial for ensuring green ecology and drinking water safety. Herein, we demonstrated a novel magnetic gel bead adsorbent that was synthesized by employing graphene oxide (GO) modified Fe₃O₄ as magnetic nanoparticles doped sodium alginate (SA)/chitosan (CS) gel (SA/GO@Fe₃O₄/CS). The GO@Fe₃O₄ sample was prepared based on GO by the chemical co-precipitation method, which not only reduced the aggregation of Fe₃O₄ but also increases the specific surface area of the composite gel beads. The prepared gel beads were used to adsorb methylene blue (MB), neutral red (NR), and safranine T (ST). The experimental results showed that the adsorption capacity of SA/GO@Fe₃O₄/CS gel beads for MB, NR, and ST reached 21.325 mg/g, 44.654 mg/g and 44.313 mg/g. After five recycles, the removal rates could still reach more than 90% of the original, exhibiting a high recovery rate. Therefore, this paper provides a strategy for the preparation of high efficiency and recyclable cationic dye adsorbents with a large specific surface area.

Facile one pot preparation of magnetic chitosan-palygorskite nanocomposite for efficient removal of lead from water

Development of polymeric magnetic adsorbents is a promising approach to obtain efficient treatment of contaminated water. However, the synthesis of magnetic composites involving multiple components frequently involves tedious preparation steps. In the present study, a magnetic chitosan-palygorskite (MCP) nanocomposite was prepared through a straight-forward one pot synthesis approach to evaluate its lead (Pb²⁺) removal capacity from aqueous solution. The nano-architectural and physicochemical properties of the newly-developed MCP composite were described via micro- and nano-morphological analyses, and crystallinity, surface porosity and magnetic susceptibility measurements. The MCP nanocomposite was capable to remove up to 58.5 mg Pb²⁺ g^-1 of MCP from water with a good agreement of experimental data to the Langmuir isotherm model (R² = 0.98). The Pb²⁺ adsorption process on MCP was a multistep diffusion-controlled phenomenon evidenced by the well-fitting of kinetic adsorption data to the intra-particle diffusion model (R² = 0.96). Thermodynamic analysis suggested that the adsorption process at low Pb²⁺ concentration was controlled by chemisorption, whereas that at high Pb²⁺ concentration was dominated by physical adsorption. X-ray photoelectron and Fourier transform infrared spectroscopy results suggested that the Pb adsorption on MCP was governed by surface complexation and chemical reduction mechanisms. During regeneration, the MCP retained 82% Pb²⁺ adsorption capacity following four adsorption-desorption cycles with ease to recover the adsorbent using its strong magnetic property. These findings highlight the enhanced structural properties of the easily-prepared nanocomposite which holds outstanding potential to be used as an inexpensive and green adsorbent for remediating Pb²⁺ contaminated water.

Development and evaluation of a multi-functional organic-inorganic nanotheranostic hybrid for pancreatic cancer therapy

Pancreatic cancer is a highly invasive disease with low survival rates. The high death rates associated with pancreatic cancer are due to multiple factors including late stage diagnosis, multi-drug resistance, invasive nature and restricted access of the therapeutic moiety to the cancer cells due to the stroma. Smart multifunctional nanocarriers that deliver the therapeutic agent in to the cancer tissue as well as enable imaging of the tissue represent an emerging paradigm in cancer therapy. Accurate and reliable detection of cancerous lesions in pancreas is essential for designing appropriate therapeutic strategy to annihilate the highly aggressive pancreatic cancer. A combination of imaging modalities can enhance the reliability of cancer detection. In this context, we report here a hybrid iron oxide-gold nanoparticle with dual contrast enhancing ability for both magnetic resonance imaging (MRI) and micro-computed tomography (micro-CT) that is co-encapsulated with the nucleotide analogue gemcitabine in a chitosan matrix. The theranostic system displayed enhanced cytotoxicity against PanC-1 pancreatic cancer cells when compared to normal cells over 48 h due to differences in cell internalization. The iron oxide-gold hybrid enabled visualization of the theranostic nanoparticle by MRI as well as micro-CT. Further, the magnetocaloric effect of the iron oxide enabled faster release of the chemotherapeutic agent as well as augmented the cytotoxicity by inducing hyperthermia. This system holds promise for further exploration as an integrated diagnostic and therapeutic platform for pancreatic cancer.

Solid-State Double-Network Hydrogel Redox Electrolytes for High-Performance Flexible Supercapacitors

Flexible supercapacitors have great potential applications in wearable and portable electronics, but their practical applications were limited due to the low energy density and mechanical flexibility of solid-state electrolytes used for the construction of flexible supercapacitors. In this study, we first report the solid-state double-network (DN) hydrogel electrolytes (HEs) incorporated with Na₂MoO₄ redox additives. It is found that the solid-state DN HEs with Na₂MoO₄ redox additives exhibit high electrochemical performance, excellent mechanical properties, and fast self-recovery features. We then demonstrate novel symmetric supercapacitors (SSCs) incorporated with the solid-state Na₂MoO₄ DN HEs and the active carbon cloths as the electrodes. The SSCs exhibit a specific capacitance of 84 mF/cm² at a current density of 1 mA/cm² and an energy density of 70 μWh/cm² at a power density of 3800 μWh/cm². Moreover, the SSCs retain approximately 80% capacitance retention after 7000 charge/discharge cycles, which indicates that the SSCs possess excellent flexibility and stability. All of these results demonstrate that the SSCs incorporated with the solid-state Na₂MoO₄ DN HEs as energy-storage devices have great practical applications in wearable and portable electronics.

Biopolymer-Based Nanohydroxyapatite Composites for the Removal of Fluoride, Lead, Cadmium, and Arsenic from Water

In this study, hydroxyapatite (HAP) nanocomposites were prepared with chitosan (HAP-CTS), carboxymethyl cellulose (HAP-CMC), alginate (HAP-ALG), and gelatin (HAP-GEL) using a simple wet chemical in situ precipitation method. The synthesized materials were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area analysis, and thermogravimetric analysis. This revealed the successful synthesis of composites with varied morphologies. The adsorption abilities of the materials toward Pb(II), Cd(II), F-, and As(V) were explored, and HAP-CTS was found to have versatile adsorption properties for all of the ions, across a wide range of concentrations and pH values, and in the presence of common ions found in groundwater. Additionally, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy confirmed the affinity of HAP-CTS toward multi-ion mixture containing all four ions. HAP-CTS was hence engineered into a more user-friendly form, which can be used to form filters through its combination with cotton and granular activated carbon. A gravity filtration study indicates that the powder form of HAP-CTS is the best sorbent, with the highest breakthrough capacity of 3000, 3000, 2600, and 2000 mL/g for Pb(II), Cd(II), As(V), and F-, respectively. Hence, we propose that HAP-CTS could be a versatile sorbent material for use in water purification.

Effective removal of lead (II) using chitosan and microbial adsorbents: Response surface methodology (RSM)

The ability of chitosan (1% w/v), Bifidobacterium longum (10⁸ CFU mL-¹) and Saccharomyces cerevisiae (10⁸ CFU mL-¹) separately or in combination (chitosan/B. longum, chitosan/S. cerevisiae, B. longum/S. cerevisiae) was assessed for lead (II) removal from aqueous solutions. The results showed chitosan/B. longum adsorbent had higher adsorption percentage in comparison with other adsorbents (p < 0.05). It was selected as the most efficient adsorbent and the effect of process variables including initial metal concentration (0.01-5 mg L^-1), contact time (5-180 min), temperature (4-37 °C) and pH (3-6) on the its removal efficiency was evaluated with a Box-Behnken design. Twenty-seven test runs were performed and the optimal conditions for metal adsorption was observed at metal concentration of 2.5 mg L^-1, contact time of 180 min, temperature of 37 °C and pH 4.5. The maximum lead (II) adsorption yield under optimal conditions was 97.6%. The foreign ions didn't diminish lead (II) adsorption by chitosan/B. longum and it had high selectivity toward the lead (II). Adsorption behavior was analyzed using the Freundlich and the Langmuir isotherms. The correlation coefficients (R²) demonstrated the Langmuir model had a better description on metal adsorption process. Overall, isotherms revealed chemisorption and physisorption were probably involved in metal adsorption on adsorbent.

Self-coagulating polyelectrolyte complexes for target-tunable adsorption and separation of metal ions

Metal-containing wastes in aquatic environments lead to public health hazards and valuable resource lose. Metal-bearing wastewater must be treated to remove heavy metals or recover precious metals. To achieve these, target-tunable adsorbents that bind cationic and anionic metal species were developed through facile polyelectrolyte complexation using polyethylenimine (PEI) and polyacrylic acid (PAA). Utilizing the properties of the two polyelectrolytes and pK_a variabilities, stable tunable adsorbents were fabricated in water without additional solvents. The homogenous complex adsorbents were strategically synthesized via dissolution in 0.1 M NaOH and drop-wise addition of 1 M HCl, followed by crosslinking with glutaraldehyde. Consequently, the adsorbents in alternating weight ratios of 4:1 and 1:4 (PEI:PAA) exhibited good tunability and adsorption properties. The maximum single metal adsorption capacities were 1609.7 ± 49.6 and 558.6 ± 9.67 mg/g for gold and cadmium, respectively. The pseudo-second-order model fitted the kinetics data more appropriately and was recognized as the rate controlling step. In a binary mixture, gold selectivity was observed to be influenced by adsorption-reduction mechanism, which was elucidated by XRD and XPS. Moreover, the adsorbents demonstrated NO₃- sequestration properties, a feat deemed important for environmental remediation of nitrate ions. Finally, sequential separation was achieved with ethylenediaminetetraacetic acid (EDTA) and acidified thiourea.

Acetone Vapor-Sensing Properties of Chitosan-Polyethylene Glycol Using Surface Plasmon Resonance Technique

To non-invasively monitor and screen for diabetes in patients, there is need to detect low concentration of acetone vapor in the range from 1.8 ppm to 5 ppm, which is the concentration range of acetone vapor in diabetic patients. This work presents an investigation for the utilization of chitosan-polyethylene glycol (PEG)-based surface plasmon resonance (SPR) sensor in the detection of trace concentration acetone vapor in the range of breath acetone in diabetic subjects. The structure, morphology, and elemental composition of the chitosan-PEG sensing layer were characterized using FTIR, UV-VIS, FESEM, EDX, AFM, and XPS methods. Response testing was conducted using low concentration of acetone vapor in the range of 0.5 ppm to 5 ppm using SPR technique. All the measurements were conducted at room temperature and 50 mL/min gas flow rate. The sensor showed good sensitivity, linearity, repeatability, reversibility, stability, and high affinity toward acetone vapor. The sensor also showed better selectivity to acetone compared to methanol, ethanol, and propanol vapors. More importantly, the lowest detection limit (LOD) of about 0.96 ppb confirmed the applicability of the sensor for the non-invasive monitoring and screening of diabetes.

Probing synergistic interplay between bio-inspired peptidomimetic chitosan-copper complexes and doxorubicin

The current investigation reports a novel and facile method for modification of low molecular weight chitosan (Cs) with guanidine moieties, aimed at enhancing its cellular interaction and thus augmenting its cellular internalization. Guadinylated chitosan-copper (Cs-Gn-Cu) chelates, based on copper-nitrogen co-ordination, were established. Characterization of chelates was conducted using ¹H NMR, ¹³C NMR, XPS, XRD, TGA-DTA, and GPC techniques. Anticancer activity of formed chelates was confirmed against A549 cells using MTT assay. Experimental outcomes, for the first time, have provided an empirical evidence for synergistic interaction between the chelated polymer (Cs-Gn-Cu) and the established anti-cancer agent, Doxorubicin (Dox), based on analysis by the Chou Talalay method and estimation of their combination indices. ROS induction was demonstrated as the mechanism of action of the chelated polymer, which supplemented rapid destruction of cancerous cells by Dox. These findings strongly advocate the need for harnessing unexplored potential of these innovative metal polymer chelates in cases of Dox resistant lung cancer, wherein the polymeric system itself would serve as an anti-cancer agent.

Green Graphene-Chitosan Sorbent Materials for Mercury Water Remediation

The development of new graphene-based nanocomposites able to provide synergistic effects for the adsorption of toxic heavy metals in realistic conditions (environment) is of higher demand for future applications. This work explores the preparation of a green nanocomposite based on the self-assembly of graphene oxide (GO) with chitosan (CH) for the remediation of Hg(II) in different water matrices, including ultrapure and natural waters (tap water, river water, and seawater). Starting at a concentration of 50 μg L^-1, the results showed that GO-CH nanocomposite has an excellent adsorption capacity of Hg (II) using very small doses (10 mg L^-1) in ultrapure water with a removal percentage (% R) of 97 % R after only two hours of contact time. In the case of tap water, the % R was 81.4% after four hours of contact time. In the case of river and seawater, the GO-CH nanocomposite showed a limited performance due the high complexity of the water matrices, leading to a residual removal of Hg(II). The obtained removal of Hg(II) at equilibrium in river and seawater for GO-CH was 13% R and 7% R, respectively. Our studies conducted with different mimicked sea waters revealed that the removal of mercury is not affected by the presence of NO₃^- and Na⁺ (>90% R of Hg(II)); however, in the presence of Cl^-, the mercury removal was virtually nonexistent (1% R of Hg(II)), most likely because of the formation of very stable chloro-complexes of Hg(II) with less affinity towards GO-CH.

Recovery of gold via adsorption-incineration techniques using banana peel and its derivatives: Selectivity and mechanisms

In this study, banana peel (BP) and its derivatives after sequential extraction of biochemical components were evaluated for selective recovery of gold. In-depth instrumental characterizations including XPS, FTIR, XRD and HR-TEM were performed to understand the adsorption mechanisms. The biomass after lipid extraction, BP-L, demonstrated very good affinity and selectivity towards gold. In multi-metal systems containing 100 mg/L of Pt(IV), Au(III), Pd(II), Zn(II), Co(II), Ni(II) and Li(I), the selectivity coefficient increased from 978.45 in BP to 2034.70 in BP-L. Moreover, the equilibrium gold uptake was improved and reached 475.48 ± 3.08 mg/g owing to reduction-coupled adsorption mechanisms. The BP-L also showed improved gold nanoparticle formation properties that were pH-dependent. In a strategic adsorption-combined incineration process, metallic gold reaching 99.96% in purity was obtained. The BP and its derivative, BP-L have thus shown potentials for multiple applications in the areas of precious metal recovery and nanoscience.

Removal of Ciprofloxacin with Aluminum-Pillared Kaolin Sodium Alginate Beads (CA-Al-KABs): Kinetics, Isotherms, and BBD Model

In recent years, the problem of water pollution caused by antibiotics has attracted wide attention. The common use of antibiotics represents a threat to both human health and environmental safety. The modification of kaolin clay is promising due to its high efficiency, easy operation, and low cost. In this study, a novel material, aluminum-pillared kaolin sodium alginate beads (CA-Al-KABs), was synthesized by gelling and solidification processes. The structure and chemical properties were characterized by various analytical methods. The influencing factors (such as adsorbent dosage, contacting time, pH, ion strength, temperature, and initial concentration) and adsorption mechanism of ciprofloxacin (CIP) were studied. Furthermore, adsorption kinetics, adsorption isotherms, and a Box–Behnken design (BBD) model were conducted. Moreover, CA-Al-KABs’ adsorption efficiency towards other antibiotics were also evaluated. The adsorption experiments showed that the acidic environment (pH = 4) was more favorable for the adsorption of ciprofloxacin. The adsorption kinetics of ciprofloxacin by CA-Al-KABs microspheres were confirmed to be more suitable with the pseudo-first-order kinetics model. The Langmuir isotherm model showed that the maximum adsorption capacity of CA-Al-KABs microspheres to ciprofloxacin was 68.36 mg/g at 308.15 K. The adsorption driving force of CIP near CA-Al-KABs may be the electrostatic attraction. Further, CIP could also form complexes with Ca2+ and Al—Al—OH on CA-Al-KABs, and thus CIP was attracted to the adsorbent. Adsorption thermodynamics showed that the adsorption process was exothermic, feasible, and spontaneous. In addition, the adsorption performance on other antibiotics indicated CA-Al-KABs’ broad application in the treatment of antibiotic wastewater.

Evaluation of orange peel-derived activated carbons for treatment of dye-contaminated wastewater tailings

Dyes are colored compounds which are visible even at trace concentrations. Due to their recalcitrance and esthetic persistence, certain methods are unable to effectively eliminate them. So far, adsorptive treatment using activated carbons (ACs) is one of the most successful methods. In this study, we have employed orange peel (OP) as a cost-effective alternative to the expensive coal- and coir-based precursors to synthesize ACs for cationic methylene blue (MB) and anionic methyl orange (MO) dye adsorption. The pre-carbonized OP was activated via H₂SO₄, NaOH, KOH, ZnCl₂, and H₃PO₄ to study the effects of activation reagents on dye removal efficiencies and mechanisms. Among several isotherm models employed to fit the adsorption data, the Langmuir and Sips models sufficiently estimated the maximum equilibrium uptakes close to the experimental values of 1012.10 ± 29.13, 339.82 ± 6.98, and 382.15 ± 8.62 mg/g, for ZnCl₂-AC (MO), ZnCl₂-AC (MB), and KOH-AC (MB), respectively. The adsorption mechanisms were suggested to involve electrostatic binding, pi-pi interactions, hydrogen bonding, and electron donor-acceptor reactions. Consequently, more than 99% removal efficiency was achieved from a laboratory organic wastewater sample bearing ~ 35 mg/L of MB. The results thus suggest that the synthesized ACs from agricultural waste have the tendencies to be applied to real dye wastewater treatment.

Biofunctional catheter coatings based on chitosan-fatty acids derivatives

Multifunctional and biofunctional coatings for medical devices are an attractive strategy towards tailoring the interactions of the device with the body, thereby influencing the host response, and the susceptibility to microbial colonization. Here we describe the development of a coating process to yield amphiphilic, lubricious coatings, resistant to bacterial colonization, based on chitosan. Chitosan-fatty acid derivatives were obtained by simultaneous N,O-acylation of chitosan with either linoleic, α-linolenic, or dilinoleic acid. Chemical characterization of new materials was carried out using ¹H NMR, FTIR, and XPS. Surface properties of coated polyester samples were studied using SEM and contact angle measurements, which indicated that the incorporation of hydrophobic constituents into chitosan macromolecules led to a decrease of both surface roughness and water contact angle. Importantly, tribological testing demonstrated that these new coatings decrease the coefficient of friction due to the self-organization of fatty acid (from 0.53 for the neat chitosan to 0.35 for chitosan-fatty acid derivative). Meanwhile, preliminary bacterial colonization tests indicated significant-over 80%-reduction in E. coli colonization following coating with chitosan-linoleic and chitosan-α-linolenic derivatives. Finally, cytotoxicity and hemocompatibility studies confirmed that all amphiphilic chitosan-fatty acid derivatives were non-toxic and non-hemolytic. Collectively, our results demonstrate the potential of the developed coating strategy, particularly the chitosan-linoleic and chitosan-α-linolenic acid derivatives, for applications as biofunctional catheter coatings.

Adsorptive decontamination of Cu2+-contaminated water and soil by carboxylated graphene oxide/chitosan/cellulose composite beads

Graphene adsorbents have been applied to remove diverse pollutants from aqueous systems. However, the mechanical strength of most graphene adsorbents is low and the fragile graphene sheets are released into the environment. In this study, we prepared carboxylated graphene oxide/chitosan/cellulose (GCCSC) composite beads with good mechanical strength for the immobilization of Cu²⁺ from both water and soil. The proportional limit of GCCSC beads was 3.2 N, a much larger value than graphene oxide beads (0.2 N). The largest pressure for GCCSC beads recorded before brittle failure was 26 N. The Cu²⁺ adsorption capacity of GCCSC beads was 22.4 mg/g in aqueous systems at initial Cu²⁺ concentration of 40 μg/mL, which is competitive with many efficient adsorbents. The partition coefficient (PC) for the Cu²⁺ adsorption onto GCCSC beads was 1.12 mg/g/μM at C_e of 0.83 mg/L and q_e of 14.3 mg/g. The PC decreased to 0.055 mg/g/μM at C_e of 26.0 mg/L and q_e of 22.4 mg/g. The adsorption kinetics of Cu²⁺ on GCCSC beads were moderately fast and required approximately 3 h to reach equilibrium with a k₂ of 0.0021 g/(mg·min). A lower temperature and higher pH slightly increased the adsorption capacity of GCCSC beads. The ionic strength did not influence the adsorption. The porous structure of GCCSC beads blocked the direct contact between soil and the graphene surface; thus, a high Cu²⁺ immobilization efficiency was achieved by GCCSC beads applied to soil. The implications for the design of high-performance graphene adsorbents for water and soil remediation are discussed.

Chitosan-boehmite desiccant composite as a promising adsorbent towards heavy metal removal

Owing to the widespread occurrence and potential health effects, many treatment strategies have been developed across the world to remove the heavy metal contaminants in water. Developing affordable and sustainable nanoscale materials are the prime factors for the success of such treatment systems in the field. The present study explores the use of desiccant waste, exhausted after several cycles of dehumidification processes. The granulated composite desiccant is composed of boehmite nanoparticles reinforced with chitosan fibrils. The composite was synthesized via a simple and scalable one-pot sol-gel route at atmospheric pressure and room temperature. The desiccant was employed for dehumidification/regeneration cycles. The reuse potential of exhausted desiccant towards enhanced removal of metal ions was analyzed and demonstrated. After adsorption the nanocomposite was characterized to establish its chemical composition and structure. Batch and fixed-bed column adsorption experiments were performed to evaluate the removal efficiency of the nanocomposite and to assess the parameters that influence the adsorption process. The experimental evidences confirm the fast kinetics of adsorption/desorption and effective regeneration of the composite. The enhanced removal capacity, excellent reuse potential, high stable granules, eco-friendly synthesis approach makes the adsorbent an excellent candidate for the removal of wide range of heavy metals in water.