Adsorption of chromium from aqueous solution using chitosan beads

A basic investigation on the removal of Cr(III) and Cr(VI) ions from aqueous solution by chitosan beads was conducted in a batch adsorption system. The chitosan beads were prepared by casting an acidic chitosan solution into an alkaline solution. The influence of different experimental parameters; pH, agitation period and different concentration of Cr(III) and Cr(VI) ions was evaluated. A pH 5.0 was found to be an optimum pH for Cr(III) adsorption, and meanwhile pH 3.0 was the optimum pH for the adsorption of Cr(VI) onto chitosan beads. The Langmuir and Freundlich adsorption isotherm models were applied to describe the isotherms and isotherm constants for the adsorption of Cr(III) and Cr(VI) onto chitosan beads. Results indicated that Cr(III) and Cr(VI) uptake could be described by the Langmuir adsorption model. The maximum adsorption capacities of Cr(III) and Cr(VI) ions onto chitosan beads were 30.03 and 76.92 mg g⁻¹, respectively. Results showed that chitosan beads are favourable adsorbents. The Cr(III) and Cr(VI) ions can be removed from the chitosan beads by treatment with an aqueous EDTA solution.     

Physical properties of ion beam treated electrospun poly(vinyl alcohol) nanofibers

We show that the mechanical properties of nano-sized electrospun poly(vinyl alcohol) fibers can be modified using broad-energy ion beam implantation. The elastic moduli were determined using atomic force microscopy multi-point mechanical bending tests on individual fibers before and after treatment. With a dose of 8.0 × 10¹⁵ ions/cm² of nitrogen ion we observed 30% increases in fiber elastic modulus with a simultaneous fiber diameter reduction. Two additional doses of nitrogen ion as well as a 8.0 × 10¹⁵ ions/cm² of helium ion treatment showed that this stiffness improvement effect was dependent on ion dosage and ion species. The surface morphological features of the fiber mat were shown to be unaltered due to the ion beam treatment. Key chemical modifications via nitrogen ion treatment were the introduction of the functional groups amine and amide. These groups are important in promoting cell compatibility on polymer surfaces.     

Adsorption of acid yellow dye on flakes of chitosan prepared from fishery wastes

Chitosan flakes, extracted from prawns and labeo rohita scales, with high adsorption capacity were prepared after chemical treatment and were used to remove acid yellow dye from water. The results showed that adsorption capacity is dependent on pH, initial concentration of dye, BET, Langmuir surface area and pore volume of the adsorbent. In acidic conditions, the polymer amino groups were protonated (positively charged polymer chain), which showed attraction with negative ions of anionic dye. Chitosan from prawns scales showed higher dye adsorption under the same experimental conditions. Adsorption isotherms were developed and equilibrium data fitted well to Langmuir and Freundlich isotherm models.     

Controlled release of doxorubicin from electrospun MWCNTs/PLGA hybrid nanofibers

In this study, multiwalled carbon nanotubes (MWCNTs) were used to encapsulate a model anticancer drug, doxorubicin (Dox). Then, the drug-loaded MWCNTs (Dox/MWCNTs) with an optimized drug encapsulation percentage were mixed with poly(lactide-co-glycolide) (PLGA) polymer solution for subsequent electrospinning to form drug-loaded composite nanofibrous mats. The structure, morphology, and mechanical properties of the formed electrospun Dox/PLGA, MWCNTs/PLGA, and Dox/MWCNTs/PLGA composite nanofibrous mats were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and tensile testing. In vitro viability assay and SEM morphology observation of mouse fibroblast cells cultured onto the MWCNTs/PLGA fibrous scaffolds demonstrate that the developed MWCNTs/PLGA composite nanofibers are cytocompatible. The incorporation of Dox-loaded MWCNTs within the PLGA nanofibers is able to improve the mechanical durability and maintain the three-dimensional structure of the nanofibrous mats. More importantly, our results indicate that this double-container drug delivery system (both PLGA polymer and MWCNTs are drug carriers) is beneficial to avoid the burst release of the drug and able to release the antitumor drug Dox in a sustained manner for 42 days. The developed composite electrospun nanofibrous drug delivery system may be used as therapeutic scaffold materials for post-operative local chemotherapy.     

Preparation and characterization of crosslinked chitosan-based nanofibers

Crosslinked chitosan-based nanofibers were successfully prepared via electrospinning technique with heat mediated chemical crosslinking followed.The structure,morphology and mechanical property of nanofibers were characterized by attenuated total reflection-Fourier transform infrared spectroscopy(ATR-FTIR),scanning electron microscopy(SEM),Instron machine,respec- tively.The results showed that,nanofibers exhibited a smooth surface and regular morphology,and tensile strength of nanofibers improved with increasing of triethylene glycol dimethacrylate(TEGDMA)content.     

Adsorption of graphene oxide/chitosan porous materials for metal ions

Porous graphene oxide/chitosan（PGOC） materials were prepared by a unidirectional freeze-drying method.Their porous structure,mechanical property and adsorption for metal ions were investigated.The results show that the incorporation of graphene oxide（GO） significantly increased the compressive strength of the PGOC materials.The saturated adsorption capacity of Pb²⁺ increased about 31%,up to 99 mg/g when 5 wt%GO was incorporated These biodegradable,nontoxic,efficient PGOC materials will be a potential adsorbent for metal ions in aqueous solution.     

Adsorption of reactive dye on chitosan in air-lift reactor

This study was undertaken to identify factors exerting the strongest influence on the adsorption of dye. The maximum adsorption capacity (at the adopted operating conditions) was the main parameter used to evaluate the process. In addition, the feasible adsorption capacity of chitosan was evaluated. Breakthrough experiments were carried out in a circulating air-lift reactor at a constant concentration of reactive dye Black 8 (100 mg/dm³). The tests studied different chitosan concentrations in the reactor and a range of flow intensities. The results of the breakthrough tests were compared by means of apparent mass transfer coefficients, determined by slopes at C/C ₀=1/2. The adsorption capacity of chitosan was affected to the greatest extent by the flow rate of the medium to the reactor. In turn, the utilization of the maximum adsorption capacity of chitosan, at the assumed efficiency of dye removal, was determined by chitosan concentration in the reactor.     

Adsorption and desorption of binary mixtures of copper and mercury ions on natural and crosslinked chitosan membranes

Copper and mercury ion adsorption on chitosan membranes was investigated in batch systems (with both single and binary solutions). The Langmuir model and its extensions (extended Langmuir, Jain-Snoeyink, and Langmuir-Freundlich models) were tested for the modeling of experimental data. Chitosan membranes presented more affinity for Hg ions than for Cu ions. The decrease of the amount of metal adsorbed on natural chitosan in binary systems (compared to single-metal solutions) showed the competition effects between the two metal ions. For glutaraldehyde-crosslinked chitosan and epichlorohydrin-crosslinked chitosan, the mixture effect was present, producing unexpected result such as higher adsorption capacities, when compared to the monocomponent solution of each metal. The desorption of the metals was also investigated, and copper and mercury ions could be selectively recovered using a combined process by using NaCl and H₂SO₄ as eluant.     

Lignin bio-oil-based electrospun nanofibers with high substitution ratio property for potential carbon nanofibers applications

We reported a new approach for development of lignin bio-oil-based electrospun nanofibers (LENFs) that had high substitution ratio (up to 80 wt%) and good morphology. This approach was particularly unique and translatable as it used small molecule lignin bio-oil with high reactivity and low heterogeneity obtained via lignin depolymerization reaction to produce well-oriented LENFs. Firstly, effects of various blends solutions ratios and electrospinning parameters on the characteristics of the obtained LENFs were analyzed. The results showed that the optimal parameters that resulted in the best electrospun nanofibers were as follows: blend solution ratio, the 20 wt% blend solution containing 80 wt% straw lignin bio-oil (SLB) and 20 wt% polyacrylonitrile (PAN), flow rate, 1 mL/h, voltage, 20 kV, rotational speed, 500 r/min and the distance between needle and collection screen, 20 cm. Secondly, used the best LENFs, we also applied to prepare lignin bio-oil-based carbon nanofibers (LCNFs) and estimated its properties by scanning electron microscope (SEM), X-ray diffraction (XRD) patterns, Raman spectroscopy and tension testing. Our results demonstrated that compared with pure PAN carbon nanofibers (PCNFs), the as-prepared LCNFs had similar smooth surfaces, similar crystallinity and similar mechanical properties. This work can promote the utilization of lignin depolymerization main-products to produce lignin-based materials, while also help to reduce use of high-cost PAN.     

The stabilization of electrospun chitosan nanofibers by reversible acylation

Chitosan nanofibers fabricated by electrospinning are contaminated by acidic anions from the acid spinning solution, leading to instability of the nanofibers in aqueous solutions, and the traditional fiber treatment method will also lead to the deterioration of the nanostructure. Here we demonstrate a novel approach to removing the acidic anions with full preservation of the nanofibrous structure. The as-spun nanofibers are first protected (stabilized) by reversible acylation. Second, contaminants are then eliminated by hydrolysis; finally, acylation is reversed. Chemical analysis showed the removal of the acidic anions and the graft and removal of acyl groups. Morphological analysis showed that the reversibly acylated fibers had diameters <150 nm and nanofiber structure was maintained after immersion in aqueous solution. The membranes also were compatible with bone cells in culture. The resultant pure chitosan nanofibers show excellent stability in aqueous solution and exhibit broad potential in biomedical applications.     

Adsorption of anionic dyes on chitosan beads. 1. The influence of the chemical structures of dyes and temperature on the adsorption kinetics

In this work, chitosan beads were synthesized in acidic medium and cross-linked in 1% glutaraldehyde solution. The characterization of the materials using TG/DTG, XRD, and BET surface areas showed that the beads did not modify their characteristics after the cross-linking reaction. The cross-linked beads were utilized as adsorbents for the removal of the yellow-, blue-, and red-anionic reactive dyes from aqueous solutions at pH 2.0. Adsorption of the yellow-dye increased from 25 to 50 degrees C. However, adsorption of the blue-dye decreased from 25 to 50 degrees C. Interestingly, the adsorption of the red-dye decreased from 25 to 35 degrees C and increased from 45 to 50 degrees C. The kinetic data were evaluated using an Avrami kinetic model, where the parameter n was related to the determination of changes in the adsorption mechanisms. Adsorption data of the dyes in relation to the contact time, the chemical structures of the dyes, and temperature were presented and were discussed.     

The influence of oxidative degradation on the preparation of chitosan nanoparticles

Chitosan nanoparticles were obtained via ionic crosslinking by using the sulfate ion. Chitosan molecular weight was varied by oxidative degradation of the chitosan β-glycoside bond, the molecular weight being indirectly monitored as the chitosan solution reduced viscosity at a fixed polymer concentration. The dependence between some physical properties of the resultant dispersions (turbidity, viscosity, zeta potential, and sedimentation column profile) and reduced viscosity was established. Atomic force microscopy images have shown the resultant particles formed to be clusters of chitosan nanoparticles with a diameter of ca. 70 nm, the interaction between these particles being characterized by FTIR spectroscopy as the result of sulfate bridging. At the end of the paper, the potential of these dispersions for the incorporation of anionic drugs via adsorption was evaluated using a model compound. The resultant dispersions were capable of adsorbing more than 25% of mass of chitosan, being the partition coefficient higher than 3,500.     

交联壳聚糖对氨基酸的吸附性能

本文研究了交联壳聚糖对甘氨酸、谷氨酸和赖氨酸的吸附性能，吸附率依次为甘氨酸＞赖氨酸＞谷氨酸，并决定于上柱液的ＰＨ值及其浓度。用０．０５和０．１ｍｏｌ／ｌＮＨ４ＯＨ可以解吸。     

交联壳聚糖分离富集-火焰原子吸收法测定水样中痕量银

以甲醛、环硫氯丙烷为交联剂,由壳聚糖合成了一种新型的交联壳聚糖微球(FCCIS)分离树脂,研究了不同条件下FCCTS对Ag(Ⅰ)的吸附性能.在pH 3.6时FCCTS对Ag(Ⅰ)定量吸附,吸附在树脂上的Ag(Ⅰ)可用0.5 moL/L的氨水将其洗脱,用火焰原子吸收光谱测定.该法对Ag(Ⅰ)的检出限为61 ng/mL(3σ,n=8),相对标准偏差为2.2%(n=7,ρ=2μg/mL),线性范围为0.05～4μg/mL,加标回收率在98.8%～101.7%之间.该法已用于水样中痕量银测定.     

Folic acid modified electrospun poly(vinyl alcohol)/polyethyleneimine nanofibers for cancer cell capture applications

Capture and detection of metastatic cancer cells are crucial for diagnosis and treatment of malignant neoplasm. Here, we report the use of folic acid (FA) modified electrospun poly(vinyl alcohol) (PVA)/polyethyleneimine (PEI) nanofibers for cancer cell capture applications. Electrospun PVA/PEI nanofibers crosslinked by glutaraldehyde vapor were modified with FA via a poly(ethylene glycol) (PEG) spacer, followed by acetylation of the fiber surface PEI amines. The formed FA-modified nanofibers were well characterized. The morphology of the electrospun PVA/PEI nanofibers is smooth and uniform despite the surface modification. In addition, the FA-modified nanofibers display good hemocompatibility as confirmed by hemolysis assay. Importantly, the developed FA-modified nanofibers are able to specifically capture cancer cells overexpressing FA receptors, which were validated by quantitative cell counting assay and qualitative confocal microscopy analysis. The developed FA-modified PVA/PEI nanofibers may be used for capturing circulating tumor cells for cancer diagnosis applications.     

A review on electrospun polymeric nanofibers: Production parameters and potential applications

This review deals with electrospun nanofibers and their applications in several fields. Nanofibers have mainly been produced via electrospinning technique due to the simple, cost-effective, and versatile setup. Electrospinning is defined as a process, which produces fibers from its polymer solutions under exposure of high electric field voltage. The technique needs optimization of several parameters such solution, processing and ambient parameters to refine nanofiber morphology, diameter and porosity. The basic technique has been modified to produce composite fibers and to increase production capacity. Nanofiber characterization methods are summarized with examples. The relation between electrospinning and electrospraying is discussed. Nanofibers have the ability to form highly porous mesh with large surface to volume ratio enhancing its performance for various applications such as water filtration, tissue engineering scaffold, wounds, fiber composites, drug release and protective clothes. Single nanofibers could potentially be used as soft microrobots for drug delivery. Finally, results from modeling and simulations are illustrated.     

Hydrophobic surface modification of chitosan gels by stearyl for improving the activity of immobilized lipase

The hydrophobic surface modification of chitosan gels was carried out using the amidating reaction of amido groups on a gel surface with stearic acid activated by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride(EDC) and N-hydroxysuccinimide (NHS).Lipases from Candida rugosa were adsorbed on the nascent chitosan gels(CS) and stearyl-modified gels(SCS) with different degrees of amidation.The increased surface hydrophobicity of chitosan gels improved the adsorption capacity and activity of the ...     

Preparation of electrospun chitosan/poly(vinyl alcohol) membranes

Electrospinning of chitosan from its solutions in 2% aqueous acetic acid was studied by adding poly(vinyl alcohol) (PVA) as a “guest” polymer. Properties of the chitosan/PVA solutions including viscosity, conductivity, and surface tension were measured, and effects of the polymer concentration, chitosan/PVA mass ratio and processing parameters (applied voltage, flow rate, capillary-to-collector distance) on the electrospinnability of chitosan/PVA were investigated. Analyses of scanning electron micrographs and transmission electron micrographs suggested that the chitosan/PVA ultrafine fibers were often obtained along with beads, and chitosan was located in the elctrospun fibers as well as in the beads. Uniform chitosan/PVA fibers with an average diameter of 99 ± 21 nm could be prepared from a 7% chitosan/PVA solution in 40:60 mass ratio. Results of Fourier transform infrared spectroscopy and X-ray diffraction demonstrated that there were possible hydrogen bonds between chitosan and PVA molecules, which could weaken the strong interaction in chitosan itself and facilitate chitosan/PVA electrospinnability. The electrospun chitosan/PVA membranes showed higher water uptake and would have potential applications in wound dressings.     

Kinetics and mechanism of chelating reaction between chitosan derivatives with Ca(II)

Chitosan derivatives, such as chitosan alpha-ketoglutaric acid (KCTS) and hydroxamated chitosan alpha-ketoglutaric acid (HKCTS), are prepared and their coordination behavior toward Ca(II) was studied. The adsorption isotherms were correlated by dc/dt?=??kcⁿ at 20°C, 30°C, 40°C, 50°C, and 60°C. By linear correlation, the shapes of the isotherm curves were similar to the kinetic function of 1/c?=?kt and the rate equation was dc/dt?=??kc ²; the activation energies were 13.31 and 14.76?kJ?mol^?1 for KCTS and HKCTS, respectively. The overall rate of Ca(II) adsorption is likely to be controlled by the chemical process. The coordination mechanism of chitosan derivatives with Ca(II) was studied by infrared and X-ray photoelectron spectroscopy. The results indicated that –NH– of KCTS was coordinated. Nitrogen of amino, oxygens of hydroxamic acid, and carbonyl in HKCTS coordinated with Ca(II).