Preparation and sorption studies of glutaraldehyde cross-linked chitosan copolymers

Preparation of cylindrical Chitosan/β-Cyclodextrin/MIL-68(Al) foam column for solid-phase extraction of sulfonamides in water, urine, and milk

This study describes the preparation of a cylindrical polymer foam column termed Chitosan/β-Cyclodextrin/MIL-68(Al) (CS/β-CD/MIL-68(Al)). An ice template-freeze drying technique was employed to prepare the CS/β-CD/MIL-68(Al) foam column by embedding MIL-68(Al) in a polymer matrix comprising cross-linked chitosan (CS) and β-cyclodextrin (β-CD). The cylindrical CS/β-CD/MIL-68(Al) foam was subsequently inserted into a syringe to develop a solid phase extraction (SPE) device. Without the requirement for an external force, the sample solution passed easily through the SPE column thanks to the porous structure of the CS/β-CD/MIL-68(Al) foam column. Moreover, the CS/β-CD/MIL-68(Al) foam column was thought to be a superior absorbent for SPE since it included the adsorptive benefits of CS, β-CD, and MIL-68(Al). The SPE was utilized in conjunction with high-performance liquid chromatography to analyze six sulfonamides found in milk, urine, and water. With matrix effects ranging from 80.49 % to 104.9 % with RSD values of 0.4-14.0 %, the method showed high recoveries ranging from 80.6 to 107.4 % for water samples, 93.4-105.2 % for urine, and 87.4-100.9 % for milk. It also demonstrated good linearity in the range of 10-258 ng·mL-1 with the limits of detection ranging from 1.88 to 2.58 ng·mL-1. The cylindrical CS/β-CD/MIL-68(Al) foam column prepared in this work offered several advantages, including its simple fabrication, excellent water stability, absence of pollutants, biodegradability, and reusability. It is particularly well-suited for SPE. Furthermore, the developed SPE method, employing CS/β-CD/MIL-68(Al) foam column, is straightforward and precise, and its benefits, including affordability, ease of preparation, lack of specialized equipment, and solvent economy, underline its broad applicability for the pretreatment of aqueous samples.

Removal of Cr(VI) by glutaraldehyde-crosslinked chitosan encapsulating microscale zero-valent iron: Synthesis, mechanism, and longevity

Microscale zero-valent iron (mZVI) has shown great potential for groundwater Cr(VI) remediation. However, low Cr(VI) removal capacity caused by passivation restricted the wide use of mZVI. We prepared mZVI/GCS by encapsulating mZVI in a porous glutaraldehyde-crosslinked chitosan matrix, and the formation of the passivation layer was alleviated by reducing the contact between zero-valent iron particles. The average pore diameter of mZVI/GCS was 8.775 nm, which confirmed the mesoporous characteristic of this material. Results of batch experiments demonstrated that mZVI/GCS exhibited high Cr(VI) removal efficiency in a wide range of pH (2-10) and temperature (5-35°C). Common groundwater coexisting ions slightly affected mZVI/GCS. The material showed great reusability, and the average Cr(VI) removal efficiency was 90.41% during eight cycles. In this study, we also conducted kinetics and isotherms analysis. Pseudo-second-order model was the most matched kinetics model. The Cr(VI) adsorption process was fitted by both Langmuir and Freundlich isotherms models, and the maximum Langmuir adsorption capacity of mZVI/GCS reached 243.63 mg/g, which is higher than the adsorption capacities of materials reported in most of the previous studies. Notably, the column capacity for Cr(VI) removal of a mZVI/GCS-packed column was 6.4 times higher than that of a mZVI-packed column in a 50-day experiment. Therefore, mZVI/GCS with a porous structure effectively relieved passivation problems of mZVI and showed practical application prospects as groundwater Cr(VI) remediation material with practical application prospects.

Controlled delivery of 5-fluorouracil from monodisperse chitosan microspheres prepared by emulsion crosslinking

This work aims to determine the optimal conditions for emulsion cross-linking of chitosan (CHS) with various molecular weights using glutaraldehyde as a cross-linking agent to produce 5-fluorouracil-loaded CHS microspheres (5-FU/CHS). Their drug loading and encapsulation efficiencies are found to be in the range of 3.87-12.35% and 20.13-70.45%, respectively. The dynamic light scattering results show that 5-FU/CHS microspheres are micron-sized with a uniform size distribution, and the scanning electron microscopy results show that they are spherical. The results of thermogravimetric analysis, X-ray diffraction, and Fourier transform infrared spectroscopy demonstrate that 5-FU is successfully incorporated into the microspheres. The in vitro release tests show that 5-FU/CHS have a prolonged, pH-responsive release pattern of 5-FU, and the cumulative release rate under acidic condition is much larger than that under neutral conditions. The drug release kinetic analysis further demonstrates that the release of 5-FU can be well described by the Fickian diffusion model.

Static and dynamic adsorption of arsenate from water by Fe3+ complexed with 3-aminopropyltriethoxysilane-modified carboxymethyl chitosan

Fe3+ complexed with 3-aminopropyltriethoxysilane (APTES)-modified carboxymethyl chitosan (CMC) named Fe-ACMC was synthesized by a one-step method at room temperature and pressure. The surface morphology and chemical structure of Fe-ACMC were characterized by SEM-EDS, XRD, BET, FT-IR, XPS, and ζ-potential. In batch adsorption, the optimum pH for arsenate [As(V)] adsorption onto Fe-ACMC was 3-9 with removal efficiency > 99%. The adsorption of As(V) could reach equilibrium within 25 min and the maximum adsorption capacity was 84.18 mg g-1. The pseudo-second-order model fitted well the kinetic data (R2 = 0.995), while the Freundlich model well described the adsorption isotherm of As(V) on Fe-ACMC (R2 = 0.979). The co-existing anions (NO3-, CO32-, and SO42-) exhibited a slight impact on the As(V) adsorption efficiency, whereas PO43- inhibited As(V) adsorption on Fe-ACMC. The real applicability of Fe-ACMC was achieved to remove ca. 10.0 mg L-1 of As(V) from natural waters to below 0.05 mg L-1. The regeneration and reuse of Fe-ACMC for As(V) adsorption were achieved by adding 0.2 mol L-1 HCl. The main adsorption mechanism of As(V) on Fe-ACMC was attributed to electrostatic attraction and inner-sphere complexation between -NH2···Fe3+ and As(V). In fixed-bed column adsorption, the Thomas model was the most suitable model to elucidate the dynamic adsorption behavior of As(V). The loading capacity of the Fe-ACMC packed column for As(V) was 47.04 mg g-1 at pH 7 with an initial concentration of 60 mg L-1, flow rate of 3 mL min-1, and bed height of 0.6 cm.

Development of a membrane and a bilayer of chitosan, gelatin, and polyhydroxybutyrate to be used as wound dressing for the regeneration of rat excisional wounds

The skin is the largest organ in the human body that acts as a protective barrier from the outside environment. Certain dermatological pathologies or significant skin lesions can result in serious complications. Several studies have focused on the development of tissue-engineered skin substitutes. In this study, a new bilayer scaffold composed of a chitosan-gelatin membrane and a chitosan-polyhydroxybutyrate (PHB) porous matrix was synthesized and populated with human adipose-derived mesenchymal stem cells (hASCs) to be potentially used for wound dressing applications. By combining this membrane and porous matrix with the stem cells, we aimed to provide immunomodulation and differentiation capabilities for the wound environment, as well as mechanical strength and biocompatibility for the underlying tissue. The membrane was prepared from the mixture of chitosan and gelatin in a 2:1 ratio and the porous matrix was prepared from the mixture of chitosan and PHB, in equal proportions to form a final solution at 2.5% (m/v). Fourier transform infrared spectroscopy analysis showed the formation of blends, and micro-computed tomography, scanning electron microscopy and atomic force microscopy images demonstrated membrane roughness and matrix porosity. The MTT assay showed that the scaffolds were biocompatible with hASC. The membrane and the bilayer were used as dressing and support for cell migration in the dorsal excisional wound model in Wistar rats. Histological and gene transcriptional analyses showed that the animals that received the scaffolds regenerated the hair follicles in the deep dermis in the central region of the wound. Our results demonstrate the potential of these new biomaterials as dressings in wound healing studies, favoring tissue regeneration.

Aerogels based on cationically modified chitosan and poly(vinyl alcohol) for efficient capturing of viruses

In this study, we developed a new filtering bioaerogel based on linear polyvinyl alcohol (PVA) and the cationic derivative of chitosan (N-[(2-hydroxy-3-trimethylamine) propyl] chitosan chloride, HTCC) with a potential antiviral application. A strong intermolecular network architecture was formed thanks to the introduction of linear PVA chains, which can efficiently interpenetrate the glutaraldehyde(GA)-crosslinked HTCC chains. The morphology of the obtained structures was examined using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The aerogels and modified polymers' elemental composition (including the chemical environment) was determined using X-ray photoelectron spectroscopy (XPS). New aerogels with more than twice as much developed micro- and mesopore space and BET-specific surface area were obtained concerning the starting sample chitosan aerogel crosslinked by glutaraldehyde (Chit/GA). The results obtained from the XPS analysis showed the presence of cationic 3-trimethylammonium groups on the surface of the aerogel, which can interact with viral capsid proteins. No cytotoxic effect of HTCC/GA/PVA aerogel was also observed on fibroblast cells of the NIH3T3 line. Furthermore, the HTCC/GA/PVA aerogel has been shown that efficiently traps mouse hepatitis virus (MHV) from suspension. The presented concept of aerogel filters for virus capture based on modified chitosan and polyvinyl alcohol has a high application potential.

Synthesis of glutaraldehyde-modified silica/chitosan composites for the removal of water-soluble diclofenac sodium

Composite materials are effective adsorbents for the removal of various types of contaminants, such as pharmaceutical products. However, they require improvement to achieve a good adsorption capacity. This study presents the development of a promising adsorbent: silica/chitosan modified with different proportions of glutaraldehyde, which involves the D-glucosamine units from chitosan. The developed materials were evaluated for their ability to remove diclofenac sodium. The adsorption data showed that the diclofenac adsorption efficiency increased with increasing degree of glutaraldehyde crosslinking. The equilibrium and kinetic data were well fit by the Liu and Elovich models, respectively, and the maximum adsorption capacity was 237.8 mg/g. Therefore, it can be assumed that the process is predominantly chemical and exothermic, with a high affinity between the adsorbents and diclofenac sodium. The adsorption mechanisms were investigated to better understand the interactions, and the predominance of covalent bonds with the self-polymerized glutaraldehyde was verified.

Arsenic removal approaches: A focus on chitosan biosorption to conserve the water sources

Globally, millions of people have no access to clean drinking water and are either striving for that or oppressed to intake polluted water. Arsenic is considered one of the most hazardous contaminants in water bodies that reaches there due to various natural and anthropogenic activities. Modified chitosan has gained much attention from researchers due to its potential for arsenic removal. This review focuses on the need and potential of chitosan-based biosorbents for arsenic removal from water systems. Chitosan is a low-cost, abundant, biodegradable biopolymer that possesses unique structural aspects and functional sites for the adsorption of contaminants like arsenic species from contaminated water. The chitosan-based biosorbents had also been modified using various techniques to enhance their arsenic removal efficiencies. This article reviews various forms of chitosan and parameters involved in chitosan modification which eventually affect the arsenic removal efficiency of the resultant sorbents. The literature revealed that the modified chitosan-based sorbents could express higher adsorption efficiency compared to those prepared from native chitosan. The sustainability of the chitosan-based sorbents has also been considered in terms of reusability. Finally, some recommendations have been underlined for further improvements in this domain.

Pharmacokinetic variables of medium molecular weight cross linked chitosan nanoparticles to enhance the bioavailability of 5-fluorouracil and reduce the acute oral toxicity

To prepare glutaraldehyde-based cross-linked medium molecular weight chitosan nanoparticles encapsulated with 5-Fluorouracil (5-FU), to overcome dosing frequency as well as reducing acute oral toxicity and poor bioavailability of the drug. Medium molecular weight chitosan nanoparticles (MMWCH-NPs) were prepared by reverse micelles method based on glutaraldehyde (GA) cross-linking and optimized by the process as well as formulation variables like a various drug to polymer ratio, cross-linker volumes, varying stirring speeds (rpm), different time of rotation/stirring, respectively and their effects on the mean particles size distribution and entrapment efficiency %EE and %LC of NPs. Characterization of formulations was done by FTIR studies, TEM, PXRD, TGA, Stability, and dissolution drug release studies were performed by dialysis bag technique at both pH (1.2 & 7.4) and acute oral toxicity studies in albino rabbits. The formulated nanoparticles showed a smooth morphology with smaller particle size distribution (230–550 nm), zeta potential (−15 to −18 mV) required to achieve enhanced permeation and retention effect (EPR), entrapment efficiency (%EE 12–59%). These NPs exhibited a controlled drug release profile with 84.36% of the drug over a period of 24 h. Drug release data were fitted to different kinetic models which predominantly followed Fickian diffusion mechanism (R² = 0.972–0.976, N = 0.326–0.256). The optimized formulation (5-FU6) was observed under DSC/TGA, TEM. PXRD curves, FTIR, which confirmed thermal stability, structural integrity, amorphous state, compatibility between drug and polymer of optimized (5-FU6) as well as reduced acute oral toxicity in albino rabbits. Cross-linked medium molecular weight chitosan nanoparticles are nontoxic, well-tolerated therefore could be the future candidate for therapeutic effects as novel drug delivery carrier for anticancer drug(s).

Gold(III) recovery from aqueous solutions by raw and modified chitosan: A review

Chitosan, a prestigious versatile biopolymer, has recently received considerable attention as a promising biosorbent for recovering gold ions, mainly Au(III), from aqueous solutions, particularly in modified forms. Confirming the assertion, this paper provides an up-to-date overview of Au(III) recovery from aqueous solutions by raw (unmodified) and modified chitosan. A particular emphasis is placed on the raw chitosan and its synthesis from chitin, characteristics of raw chitosan and their effects on metal sorption, modifications of raw chitosan for Au(III) sorption, and characterization of raw chitosan before and after modifications for Au(III) sorption. Comparisons of the sorption (conditions, percentage, capacity, selectivity, isotherms, thermodynamics, kinetics, and mechanisms), desorption (agents and percentage), and reusable properties between raw and modified chitosan in Au(III) recovery from aqueous solutions are also outlined and discussed. The major challenges and future prospects towards the large-scale applications of modified chitosan in Au(III) recovery from aqueous solutions are also addressed.

pH-Sensitive magnetite mesoporous silica nanocomposites for controlled drug delivery and hyperthermia

In clinical applications, chemotherapy and hyperthermia are commonly used together. To achieve this, we synthesized multifunctional magnetite mesoporous silica nanoparticles (MMSNs) coated with a chitosan hydrogel. pH-Responsive chitosan hydrogels (cross-linked glutaraldehyde) were used to cover mesoporous silica pores. The infrared spectroscopy (FT-IR) and electron microscopy images (SEM and TEM) confirm that a hydrogel layer and a silica shell were formed. By applying alternating magnetic fields (AMF) to nanogels, heat generation (43 °C) occurred within a short time. The drug release (tamoxifen) of nanogels was studied for 72 h at different pH and temperatures. Drug release at pH 7.4/T = 37 °C (simulating physiological condition) and pH 5/T = 43 °C (pH simulating endosomes/hyperthermia) were 15 and 70%, respectively, so, drug release was increased with hyperthermia. To determine the biocompatibility of the nanogels, an MTT assay of L929 cells was performed for 24, 48 and 72 h. The results show high biocompatibility of nanogels even at high concentrations (over 80% cell viability after 72 h for all concentrations).

Magnetite mesoporous silica nanoparticles coated with chitosan for simulanious hypertherima and chemotherapy.

Viscoelastic Properties of Crosslinked Chitosan Films

Chitosan films containing citric acid were prepared using a multi-step process called heterogeneous crosslinking. These films were neutralized first, followed by citric acid addition, and then heat treated at 150 °C/0.5 h in order to potentially induce covalent crosslinking. The viscoelastic storage modulus, E′, and tanδ were studied using dynamic mechanical analysis, and compared with neat and neutralized films to elucidate possible crosslinking with citric acid. Films were also prepared with various concentrations of a model crosslinker, glutaraldehyde, both homogeneously and heterogeneously. Based on comparisons of neutralized films with films containing citric acid, and between citric acid films either heat treated or not heat treated, it appeared that the interaction between chitosan and citric acid remained ionic without covalent bond formation. No strong evidence of a glass transition from the tanδ plots was observable, with the possible exception of heterogeneously crosslinked glutaraldehyde films at temperatures above 200 °C.

Fabricating MOF/Polymer Composites via Freeze Casting for Water Remediation

Various porous materials have been used as adsorbents for water remediation. Among them, metal-organic framework (MOF) particles have been explored intensively, due to their size-controlled micropores and high surface areas. MOF nanoparticles are often used because of high external surface area and easy access to the micropores. However, recovering MOF nanoparticles, usually by filtration or centrifugation, is time-consuming and is difficult to scale up. We report here the preparation of porous MOF/polymer monoliths by freeze casting for water remediation. Chitosan and UiO-66 (Universitetet i Oslo) nanoparticles (including different surface functional groups) are used to prepare such monoliths. In order to improve the mechanical stability and the tendency of disintegrating in water, the freeze-dried UiO-66/chitosan monoliths are further treated by heating, washing with aqueous NaOH solution, or chemical crosslinking with glutaraldehyde. All these treated monoliths are used for adsorption of a herbicide methylchlorophenoxypropionic acid (MCPP) from aqueous solution. Particularly, the crosslinked chitosan/UiO-66 monolith achieves an adsorption capacity of 47.67 mg g−1, with a 60 ppm MCPP solution. It is superior to that presented by the sole UiO-66 nanoparticles, exhibiting over a 30% increase in the adsorption capacity. The monoliths can be easily removed using tweezers, providing facile recyclability, which is advantageous for upscaling. The recycled monolith upheld approximately 75% of the adsorption capacity compared to the original monolith after three reuse cycles.

“Pillaring Effects” in Cross-Linked Cellulose Biopolymers: A Study of Structure and Properties

Modified cellulose materials (CLE-4, CLE-1, and CLE-0.5) were prepared by cross-linking with epichlorohydrin (EP), where the products display variable structure, morphology, and thermal stability. Adsorptive probes such as nitrogen gas and phenolic dyes in aqueous solution reveal that cross-linked cellulose has greater accessible surface area (SA) than native cellulose. The results also reveal that the SA of cross-linked cellulose increased with greater EP content, except for CLE-0.5. The attenuation of SA for CLE-0.5 may relate to surface grafting onto cellulose beyond the stoichiometric cellulose and EP ratio since ca. 30% of the hydroxyl groups of cellulose are accessible for cross-linking reaction due to its tertiary fibril nature. Scanning electron microscopy (SEM) results reveal the variable surface roughness and fibre domains of cellulose due to cross-linking. X-ray diffraction (XRD) and 13C NMR spectroscopy indicate that cellulose adopts a one-chain triclinic unit cell structure (P1 space group) with gauche-trans (gt) and trans-gauche (tg) conformations of the glucosyl linkages and hydroxymethyl groups. The structural characterization results reveal that cross-linking of cellulose occurs at the amorphous domains. By contrast, the crystalline domains are preserved according to similar features in the XRD, FTIR, and 13C NMR spectra of cellulose and its cross-linked forms. This study contributes to an improved understanding of the role of cross-linking of native cellulose in its structure and functional properties. Cross-linked cellulose has variable surface functionality, structure, and textural properties that contribute significantly to their unique physicochemical properties over its native form.

Preparation and properties of chitosan-metal complex: Some factors influencing the adsorption capacity for dyes in aqueous solution

Chitosan-metal complexes have been widely studied in wastewater treatment, but there are still various factors in complex preparation which are collectively responsible for improving the adsorption capacity need to be further studied. Thus, this study investigates the factors affecting the adsorption ability of chitosan-metal complex adsorbents, including various kinds of metal centers, different metal salts and crosslinking degree. The results show that the chitosan-Fe(III) complex prepared by sulfate salts exhibited the best adsorption efficiency (100%) for various dyes in very short time duration (10min), and its maximum adsorption capacity achieved 349.22mg/g. The anion of the metal salt which was used in preparation played an important role to enhance the adsorption ability of chitosan-metal complex. SO₄^2- ions not only had the effect of crosslinking through electrostatic interaction with amine group of chitosan polymer, but also could facilitate the chelation of metal ions with chitosan polymer during the synthesis process. Additionally, the pH sensitivity and the sensitivity of ionic environment for chitosan-metal complex were analyzed. We hope that these factors affecting the adsorption of the chitosan-metal complex can help not only in optimizing its use but also in designing new chitosan-metal based complexes.

Preparation and platelet adhesion of chitosan/PVA nanofibrous membrane

In this study, chitosan (CTS) dissolved in acetic acid was electrospun together with aqueous poly(vinyl alcohol) solution (PVA) to prepare membranes (CTS/PVA) with nanofibers. The morphology of the membranes varied with the electrospinning conditions. High polymer concentration, high distance or high voltage was facilitative in obtaining a membrane with nanofibers. A CTS/PVA membrane with evenly distributed nanofibers (50 nm dia.) was obtained under the following conditions: 4·5 g CTS in 55 ml 27% acetic acid, 0·4 g PVA in 5 ml water (H2O), 0·1 g sodium chloride (NaCl), electrospinning voltage of 40 kV and distance of 25 cm from the injector to the collector. The water contact angle of CTS/PVA membranes increased after cross-linking with glutaraldehyde steam. Platelet adhesion measurement expressed that CTS/PVA with only nanofibers had no platelet adhesion, indicating good blood compatibility. Cross-linked CTS/PVA mats were stable while in contact with phosphate-buffered saline solution.

Magnetite/Polymer Brush Nanocomposites with Switchable Uptake Behavior Toward Methylene Blue

The grafting from approach was used to prepare pH-responsive polyacid brushes using poly(itaconic acid) (PIA) and poly(acrylic acid) (PAA) at the amine functional groups of chitosan. Hybrid materials consisting of polymer brushes and magnetite nanoparticles (MNPs) were also prepared. The products were structurally characterized and displayed reversible pH-responsive behavior and controlled adsorption/desorption of methylene blue (MB). Switchable binding of MB involves cooperative effects due to conformational changes of brushes and swelling phenomena in solution which arise from response to changes in pH. Above the pKa, magnetic nanocomposites (MNCs) are deprotonated and display enhanced electrostatic interactions with high MB removal efficiency (>99%). Below the pKa, MNCs undergo self-assembly and release the cationic dye. The switchable binding of MB and the structure of the polymer brush between collapsed and extended forms relate to changes in osmotic pressure due to reversible ionization of acid groups at variable pH. Reversible adsorption-desorption with variable binding affinity and regeneration ability was demonstrated after five cycles.

Removal of direct dyes from aqueous solution by oxidized starch cross-linked chitosan/silica hybrid membrane

In this research, chitosan/oxidized starch/silica (CS/OSR/Silica) hybrid membrane was prepared by using oxidized starch and 3-aminopropyltriethoxysilane (APTES) as cross-linking agents. The characterizations of the hybrid membrane were investigated by using attenuated total reflection (ATR) spectroscopy, scanning electron microscopy (SEM), thermogravimetry (TG) analysis and swelling measurement. The CS/OSR/Silica hybrid membrane exhibited the improved thermal stability and low degree of swelling in water. The adsorption properties of the CS/OSR/Silica hybrid membrane were studied by using two direct dyes (Blue 71 and Red 31). The results indicated the adsorption capacity of the CS/OSR/Silica hybrid membrane was found optimal at pH 9.82 and temperature 60°C for Blue 71 and Red 31. The adsorption kinetic data followed pseudo-second order kinetic model and the adsorption behavior of the two dyes on the hybrid membrane fitted well with the Freundlich model. The CS/OSR/Silica hybrid membrane can be used as an appropriate biosorbent for removal of direct dyes from colored wastewater.

Fractionation of carboxylate anions from aqueous solution using chitosan cross-linked sorbent materials

The sorptive uptake properties are reported for chitosan and cross-linked chitosan–glutaraldehyde (CG) polymers with single component and mixtures of carboxylic acids (surrogates; Si, i = 1–4).

Preparation and characterization of the linked lanthanum carboxymethylcellulose microsphere adsorbent for removal of fluoride from aqueous solutions

Linked carboxymethyl cellulose microspheres loaded with lanthanum(iii) (linked-CMC–La) were fabricated with glutaraldehyde. The linked-CMC–La had good adsorption properties compared with CMC–La, and also showed better physical properties.

Preparation of cross-linked magnetic chitosan with quaternary ammonium and its application for Cr(VI) and P(V) removal

Pollutants that exist in anionic species are issues of concern in water treatment. Compared to cationic pollutants, the removal of anionic pollutants by adsorption is more difficult because most adsorbents carry predominantly negative charges in neutral and alkaline environments. In this study, a cross-linked chitosan derivative with quaternary ammonium and magnetic properties (QM-chitosan) was prepared and employed to remove chromium (VI) and phosphorus (V) (Cr(VI) and P(V)) from aqueous environments. The QM-chitosan was characterized by Fourier transform infrared spectrometry (FT-IR), thermogravimetric analysis (TGA), energy dispersive X-ray (SEM-EDX) and zeta potential. Batch experiments show that QM-chitosan can effectively remove Cr(VI) and P(V), and the main mechanism was believed to be electrostatic interaction. A pseudo second-order model was fitted to describe the kinetic processes of Cr(VI) and P(V) removal. The adsorption isotherms of both Cr(VI) and P(V) on the QM-chitosan were well fitted by the Langmuir isotherm equation. The saturated adsorption capacity of P(V) (2.783 mmol/g) was found to be higher than that of Cr(VI) (2.323 mmol/g), resulting from the size of the H(2)PO(4)(-) ions being smaller than that of the HCrO(4)(-) ions. However, the theoretical calculation and experimental results showed that QM-chitosan had a stronger affinity for Cr(VI) than P(V). The adsorption-desorption of the QM-chitosan was evaluated, and high regeneration rates were demonstrated.

Sorptive Uptake Studies of an Aryl-Arsenical with Iron Oxide Composites on an Activated Carbon Support

Sorption uptake kinetics and equilibrium studies for 4-hydroxy-3-nitrobenzene arsonic acid (roxarsone) was evaluated with synthetic magnetite (Mag-P), commercial magnetite (Mag-C), magnetite 10%, 19%, and 32% composite material (CM-10, -19, -32) that contains granular activated carbon (GAC), and synthetic goethite at pH 7.00 in water at 21 °C for 24 h. GAC showed the highest sorptive removal of roxarsone and the relative uptake for each sorbent material with roxarsone are listed in descending order as follows: GAC (471 mg/g) > goethite (418 mg/g) > CM-10 (377 mg/g) CM-19 (254 mg/g) > CM-32 (227 mg/g) > Mag-P (132 mg/g) > Mag-C (29.5 mg/g). The As (V) moiety of roxarsone is adsorbed onto the surface of the iron oxide/oxyhydrate and is inferred as inner-sphere surface complexes; monodentate-mononuclear, bidentate-mononuclear, and bidentate-binuclear depending on the protolytic speciation of roxarsone. The phenyl ring of roxarsone provides the primary driving force for the sorptive interaction with the graphene surface of GAC and its composites. Thus, magnetite composites are proposed as multi-purpose adsorbents for the co-removal of inorganic and organic arsenicals due to the presence of graphenic and iron oxide active adsorption sites.