A New and Rapid HPLC Method to Determine the Degree of Deacetylation of Glutaraldehyde-Cross-Linked Chitosan.

Chitosan is a linear biopolymer composed of D-glucosamine and N-acetylglucosamine units. The percentage of D-glucosamine in the polymeric chain can vary from one sample to another and is expressed as the degree of deacetylation (DDA). Since this parameter has an impact on many properties, its determination is often critical, and potentiometric titration is a common analytical technique to measure the DDA. Cross-linking with glutaraldehyde is one of the most explored modifications of chitosan; however, the determination of the DDA for the resulting reticulated chitosan resins can be challenging. In this paper, we report a new, rapid, and efficient method to determine the DDA of glutaraldehyde-cross-linked chitosan resins via HPLC. This method relies on the use of 2,4-dinitrophenylhydrazine (DNPH) as a derivatizing agent to measure the level of reticulation of the polymer (LR) after the reticulation step. In this study, we prepare three calibration curves (with an R2 value over 0.92) for three series of reticulated polymers covering a large range of reticulation levels to demonstrate that a correlation can be established between the LR established via HPLC and the DDA obtained via titration. The polymers are derived from three different chitosan starting materials. These standard calibration curves are now used on a routine basis in our lab, and the HPLC method has allowed us to change our DDA analysis time from 20 h to 5 min.

Simultaneous removal of aqueous same ionic type heavy metals and dyes by a magnetic chitosan/polyethyleneimine embedded hydrophobic sodium alginate composite: Performance, interaction and mechanism.

Heavy metals and azo dyes caused huge harm to the aqueous system and human health. A magnetic chitosan/polyethyleneimine embedded hydrophobic sodium alginate composite (MCPS) was designed and prepared to simultaneously remove aqueous same ionic type heavy metals and azo dyes. In mono-polluted system, the optimal pH for Cr(VI), MO (methyl orange), Cu(Ⅱ) and MB (methylene blue) were 3, 2, 6 and 12 with a saturated adsorption capacity of 87.53, 66.41, 351.03 and 286.54 mg/g, respectively. Pseudo-second-order was suitable to describe the adsorption kinetics of them and the adsorption isotherms were more consistent with the Langmuir isotherm model being a spontaneous, endothermic, and entropy-increasing process. In binary-polluted system, MCPS possessed simultaneous adsorption for Cr (Ⅵ)-MO and Cu(Ⅱ)-MB pollutants at their optimal pH, in addition, whether in anionic or cationic solution, the removal of heavy metals were promoted with the add of azo dyes but the removal of azo dyes were suppressed with the add of heavy metals. Both Cr (Ⅵ)-MO and Cu(Ⅱ)-MB pollutants could be effectively adsorbed and desorbed from MCPS by changing the pH of the aqueous solution to realize recyclability. Lastly, removal mechanism was revealed in detail by FT-IR, EDS and XPS.

An effective uranium removal using diversified synthesized cross-linked chitosan bis-aldehyde Schiff base derivatives from aqueous solutions.

Three new cross-linked chitosan derivatives were yielded through intensification of chitosan with diverse types of bis-aldehydes. The prepared cross-linked chitosan was characterized by FTIR, 1H NMR, XRD, and TGA techniques. TGA indicated an improvement in thermal stability of the cross-linked chitosan compared with pure chitosan. Batch adsorption experiments showed that the three novel cross-linked chitosan bis-aldehyde derivatives possessed good adsorption capacity against U(VI) in the order of BFPA > BFB > BODB (adsorption capacity of the three adsorbents for U(VI) reaches 142, 124, and 114 mg/g respectively) and the adsorption isotherm and kinetic were well described by the Langmuir and the pseudo-second-order kinetic model, respectively. In addition, the prepared cross-linked chitosan bis-aldehyde derivatives were examined as U(VI) catcher from waste solutions.

Chitosan Schiff bases-based polyelectrolyte complexes with graphene quantum dots and their prospective biomedical applications.

Chitosan (Cs) bis-aldehyde Schiff base derivatives were synthesized by condensation of Cs with three bis-aldehydes namely; butane-1,4-diyl bis(4-formylbenzoate), N,N'-(butane-1,4-diyl)bis(2-(4-formylphenoxy)acetamide) and 4,4'-(butane-1,4-diylbis(oxy))dibenzaldehyde. The prepared Cs derivatives were blended with carboxymethyl chitosan(CMC) and graphene quantum dots (GQDs) to produce semi-IPNs polyelectrolyte complexes (PECs). and characterized with respect to their molecular structure and physio-chemical properties. The antibacterial activity against H. pylori (and in vitro Inosine 5'-monophosphate dehydrogenase IMPDH inhibitory assay) was evaluated. Additionally, a preliminary in vitro assessment for wound healing was performed against PECs in which wound closure percentages, and rates were investigated indicating an accelerated wound healing compared with untreated cells. The PEC based on Schiff base PEC containing amide linkage showed the highest wound healing ability. A minimal inhibitory concentration (MIC) was obtained for the PEC sample containing Cs Schiff base derived from 4,4'-(butane-1, 4-diylbis(oxy))dibenzaldehyde at a dose of 0.98 µg/ml inhibiting H. pylori growth by 100%. Additionally, the selected above-mentioned compound was selected to test its inhibitory activity against the HpIMPDH enzyme in addition to its selectivity towards the hIMPDH2 enzyme and was found to have promising activity against the HpIMPDH enzyme with IC50 value of 0.65 µM, and to be safer and less active against the hIMPDH2 enzyme with IC50 > 10 µM, reflecting its selectivity.

Phyto-Assisted Assembly of Metal Nanoparticles in Chitosan Matrix Using S. argel Leaf Extract and Its Application for Catalytic Oxidation of Benzyl Alcohol.

The design and synthesis of eco-friendly solid-supported metal nanoparticles with remarkable stability and catalytic performance have gained much attention for both industrial and environmental applications. This study provides a novel, low-cost, simple, and eco-friendly approach for decorating cross-linked chitosan with gold nanoparticles (AuNPs), greenly prepared with Solenostemma argel (S. argel) leaf extract under mild conditions. Glutaraldehyde-modified chitosan beads were used to coordinate with Au(III) ions and act as stabilizing agents, and S. argel leaf extract was used as a cost-effective phyto-reducing agent to reduce gold ions to elemental Au nanoparticles. The successful cross-linking of chitosan with glutaraldehyde, the coordination of Au(III) ions into the chitosan matrix, and the phytochemical reduction of Au(III) to Au nanoparticles were investigated via FT-IR spectroscopy. The obtained Au nanoparticles have a uniform spherical shape and size <10 nm, as confirmed by both X-ray diffraction (XRD) (~8.8 nm) and TEM (6.0 ± 3 nm). The uniformity of the AuNPs' size was confirmed by Scanning Electron Microscopy (SEM) and Transition Electron Microscopy (TEM). The powder X-ray diffraction technique showed crystalline AuNPs with a face-centered cubic structure. The elemental analysis and the Energy Dispersive Spectroscopy (EDS) analysis both confirmed the successful integration of Au nanoparticles with the chitosan network. The catalytic activity of this highly stable nanocomposite was systematically investigated via the selective oxidation of benzyl alcohol to benzaldehyde. Results showed a remarkable conversion (97%) and excellent selectivity (99%) in the formation of benzaldehyde over other side products.

Inhibitory Effect of Chitosan and Phosphate Cross-linked Chitosan against Cucumber Mosaic Virus and Pepper Mild Mottle Virus.

Cucumber mosaic virus (CMV) and Pepper mild mottle virus (PMMoV) causes severe economic loss in crop productivity of both agriculture and horticulture crops in Korea. The previous surveys showed that naturally available biopolymer material - chitosan (CS), which is from shrimp cells, reduced CMV accumulation on pepper. To improve the antiviral activity of CS, it was synthesized to form phosphate cross-linked chitosan (PCS) and compared with the original CS. Initially, the activity of CS and PCS (0.01%, 0.05%, and 0.1% concentration) compound against PMMoV infection and replication was tested using a half-leaf assay on Nicotiana glutinosa leaves. The total number of local lesions represented on a leaf of N. glutinosa were counted and analyzed with phosphate buffer treated leaves as a negative control. The leaves treated with a 0.1% concentration of CS or PCS compounds exhibited an inhibition effect by 40-75% compared with the control leaves. The same treatment significantly reduced about 40% CMV accumulation measured by double antibody sandwich enzyme-linked immunosorbent assay and increased the relative expression levels of the NPR1, PR-1, cysteine protease inhibitor gene, LOX, PAL, SRC2, CRF3 and ERF4 genes analyzed by quantitative reverse transcriptase-polymerase chain reaction, in chili pepper plants.

Performance of oxalic acid-chitosan/alumina ceramic biocomposite for the adsorption of a reactive anionic azo dye.

A biocomposite system was developed and tested for the removal of the azo dye Reactive Red (RR195) from wastewater. The biocomposite was synthesized using ceramic particles containing 75% alumina which were coated using chitosan cross-linked with oxalic acid. The biocomposite showed high performance at low pH (maximum adsorption capacity = 345.3mg.g-1 at pH=2.0). The physicochemical and structure characteristics of the matrix were evaluated by Z-potential, FTIR-ATR, SEM-EDS, XRD, and porosity. Langmuir sorption isotherm and pseudosecond-order model gave the best fit. The electrostatic interaction between RR195 (due to the sulfonate groups) and the free amino groups of chitosan, enabled successive desorption/regeneration cycles. The maximum removal percentage (>80%) occurred at pH=2.0 due to the cross-linking effect. Experiments at different temperatures allowed the calculation of thermodynamic parameters (ΔG, ΔS, ΔH); adsorption was spontaneous, exothermic, and enthalpy controlled. The presence of inorganic ions ([Formula: see text] ) was analyzed during the adsorption process. This novel biocomposite can be applied as a cost-effective and environmentally friendly adsorbent for anionic azo dye removal from wastewater. The application of chitosan cross-linked with oxalic acid as a coating of the ceramic support enhanced the adsorption capacity and enabled its use under acidic conditions without solubilization.

Cross-Linked Chitosan/Multi-Walled Carbon Nanotubes Composite as Ecofriendly Biocatalyst for Synthesis of Some Novel Benzil Bis-Thiazoles.

Aminohydrazide cross-linked chitosan (CLCS) and its MWCNTs (CLCS/MWCNTs) were formulated and utilized as a potent ecofriendly basic heterogeneous biocatalyst under ultrasonic irradiation for synthesis of two novel series of benzil bis-aryldiazenylthiazoles and benzil bis-arylhydrazonothiazolones from the reaction of benzil bis-thiosemicarbazone with 2-oxo-N'-arylpropanehydrazonoyl chlorides and ethyl 2-chloro-2-(2-phenylhydrazono) acetates, respectively. The chemical structures of the newly synthesized derivatives were elucidated by spectral data and alternative methods, where available. Additionally, their yield % was estimated using a traditional catalyst as TEA and green recyclable catalysts as CLCS and CLCS/MWCNTs composite in a comparative study. We observed that, under the same reaction conditions, the yield % of the desired products increased by changing TEA to CLCS then to CLCS/MWCNT from 72-78% to 79-83% to 84-87%, respectively. The thermal stability of the investigated samples could be arranged as CLCS/MWCNTs composite > CLCS > chitosan, where the weight losses of chitosan, CLCS and CLCS/MWCNTs composite at 500 °C were 65.46%, 57.95% and 53.29%, respectively.

One pot synthesis of new cross-linked chitosan-Schiff' base: Characterization, and anti-proliferative activities.

Four novel chitosan hydrogels were successfully synthesized through the cross-linking reaction of chitosan with different concentrations of ethyl 5-(3,5-dihydroxy-1,4-dioxan-2-yl)-2-methylfuran-3-carboxylate. Their structures were confirmed by Fourier transform infrared spectroscopy (FT-IR), 13C Cross polarization magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS 13C NMR), ultraviolet-visible spectroscopy, thermogravimetric analysis (TGA, DTA), and X-ray diffraction (XRD). Cytotoxicity on hepatocellular carcinoma (HepG-2) cell line and a normal African green monkey kidney (Vero) cell line were studied using the MTT assay. The resultant hydrogels showed a good inhibitory effect comparing to the un-modified parent; the hydrogels with the lowest degree cross-linking (0.125 and 0.25 mol cross-linker per one chitosan residue) showed potent anticancer activity in the HepG2 cells with IC50 of 57.9 and 80.9 µg/ml, respectively. These results show that the newly synthesized cross-linked chitosan derivatives demonstrated more selectivity to the HepG2 than the Vero cells, indicating its potential for Investigation in the cure of hepatocellular carcinoma.

Batch adsorption studies on surface tailored chitosan/orange peel hydrogel composite for the removal of Cr(VI) and Cu(II) ions from synthetic wastewater.

Elimination of heavy metals from wastewater has been a significant process to improve the aquatic source's quality. Various materials act as very effective adsorbents to remove heavy metals, which cause toxicity to plants and all other living organisms. Thus, the present work focuses on removing heavy metals chromium (Cr) and copper (Cu) ions containing wastewater using biodegradable and cost-effective chitosan-based hydrogel composite. The composite was prepared via chemical cross-linking of radical chitosan with polyacrylamide and N,N'-Methylene bisacrylamide and blended with orange peel. The synthesis of the adsorbent has been confirmed by using Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscopy - Energy dispersive X-ray analysis (SEM-EDAX) and X-ray diffraction (XRD) studies. The adsorption power of the composite of metal ions at different time, pH, adsorbent dosages, different metal ion concentrations were analyzed by using Atomic Absorption Spectroscopy (AAS). The results concluded that the optimum pH for Cr(VI) and Cu (II) were 4 and 5, contact time: 360 min, adsorbent dosage: 4 g, and initial metal ion concentration: 100 mg/L for each metal ions. The adsorption isotherm models follow the Freundlich model and pseudo-second-order kinetics. From the results, the adsorption capacity was observed to be 80.43% for Cr(VI) and 82.47% for Cu(II) ions, respectively.

Synthesis and characterization of γ-MnO2/chitosan/Fe3O4 cross-linked with EDTA and the study of its efficiency for the elimination of zinc(II) and lead(II) from wastewater.

In this research, a novel γ-MnO2/chitosan/Fe3O4 nanocomposite was synthesized and modified by ethylenediaminetetraacetic acid (EDTA) for the separation and simultaneous elimination of Zn(II) and Pb(II) ions from aqueous solutions in a batch system. The magnetic nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and elemental analysis (EDAX). The results demonstrated that the magnetic nanocomposite was successfully synthesized and cross-linked. The predominant influential experimental parameters including pH, contact time, initial concentration, and temperature were analyzed in relation to the adsorption capacity. The experimental data were well converged with the double exponential kinetic model. Also, the results were well matched with the Langmuir isotherm, where the maximum adsorption values were 310.4 and 136 mg g-1 for Pb(II) and Zn(II), respectively. On the other hand, in the binary-component system, the Langmuir-Freundlich model dominated the experimental data. The thermodynamic results (ΔG° < 0, ΔH° > 0, and ΔS° > 0) within the temperature range of 25-40 °C showed that the nature of adsorption by the nanocomposite for both ions was spontaneous and endothermic and was favored at higher temperatures. The simultaneous removal of two ions, the excellent magnetic separation, and the high efficiency in reuse (five effective recovery cycles) indicated the high capability of the EDTA-modified γ-MnO2/chitosan/Fe3O4 nanocomposite in the treatment of industrial effluents from Pb(II) and Zn(II).

Controlled enzymatic hydrolysis and synthesis of lignin cross-linked chitosan functional hydrogels.

This study presents a novel fully enzymatic process for the controlled depolymerisation of fungal and shrimp chitosan, and their subsequent use in the synthesis of lignin cross-linked chitosan (CTS) hydrogels. Cellobiosehydrolase (CBH) was used to depolymerize CTS resulting in decrease in average molecular weight (Mw) of shrimp CTS from 140 kDa and degree of deacetylation (DD %) from 91.3% to an average MW of 15 kDa and 16% DD. Similarly, fungal chitosan average molecular weight decreased from 92 kDa and the degree of deacetylation (DD) of 48.3% to 12 kDa and a DD of 13%. The depolymerized CTS were completely soluble in water and miscible with lignosulfonates without encountering the usual problem of formation of flocs. Introduction of laccase into a lignosulfonate-chitosan mixture resulted in the oxidation and generation of lignin reactive phenoxyl radicals that cross-linked with CTS-NH2 reactive groups resulting in the increase of Mw from 20 kDa to >500 kDa and viscosity from 20 mPa to >500 mPa. This resulted in the formation of stable lignin-cross-linked hydrogels with elongation at break of 111% and tensile strength of 7 mPa. The produced functional hydrogels have potential application in food and biomedical industries as e.g. as oxygen barriers in packaging or as functional wound dressing or tissue engineering platforms.

Pd Nanocatalyst Adorned on Magnetic Chitosan@N-Heterocyclic Carbene: Eco-Compatible Suzuki Cross-Coupling Reaction.

A novel magnetic-functionalized-multi-walled carbon nanotubes@chitosan N-heterocyclic carbene-palladium (M-f-MWCNTs@chitosan-NHC-Pd) nanocatalyst is developed in two steps. The first step entails the fabrication of a three-component cross-linking of chitosan utilizing the Debus-Radziszewski imidazole approach. The second step comprised the covalent grafting of prepared cross-linked chitosan to the outer walls of magnetically functionalized MWCNTs (M-f-MWCNTs) followed by introducing PdCl2 to generate the m-f-MWCNTs@cross-linked chitosan with a novel NHC ligand. The repeated units of the amino group in the chitosan polymer chain provide the synthesis of several imidazole units which also increase the number of Pd linkers thus leading to higher catalyst efficiency. The evaluation of catalytic activity was examined in the expeditious synthesis of biaryl compounds using the Suzuki cross-coupling reaction of various aryl halides and aryl boronic acids; ensuing results show the general applicability of nanocatalyst with superior conversion reaction yields, high turnover frequencies (TOFs) and turnover numbers (TON). Meanwhile, nanocatalyst showed admirable potential in reusability tests, being recycled for five runs without losing significant activities under optimum reaction conditions. The successfully synthesis of catalyst and its characterization was confirmed using the Fourier transform infrared spectrometer (FT-IR), spectrometer transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photo-electron spectroscopy (XPS) and thermogravimetric analysis (TGA).

A novel biocompatible core-shell magnetic nanocomposite based on cross-linked chitosan hydrogels for in vitro hyperthermia of cancer therapy.

In this work, the chemical cross-linked interaction between chitosan polymeric chains and synthetic terephthaloyl diisothiocyanate as a cross-linker was accomplished in order to fabricate three dimensional cross-linked chitosan hydrogel. This cross-linked hydrogel with considerable characteristics including high stability and homogeneity in aqueous solution (water) and high porosity was applied as new substrate for generation of new magnetic terephthaloyl thiourea cross-linked chitosan nanocomposite. The features of this new magnetic nanocomposite were characterized by FT-IR, EDX, FE-SEM, TEM and VSM analysis. The Size distribution of nanoparticles according to the size histogram of FE-SEM images was estimated between 30 and 40 nm. The performance of designed magnetic nanocomposite was evaluated by magnetic fluid hyperthermia procedure. Under the alternating magnetic field (AMF), the specific absorption rate (66.92 w·g-1) was determined and as well, its saturation magnetization value was reported 78.43 emu·g-1.

Synthesis and characterization of novel trimellitic anhydride isothiocyanate-cross linked chitosan hydrogels modified with multi-walled carbon nanotubes for enhancement of antimicrobial activity.

Novel trimellitic anhydride isothiocyanate was successfully synthesized and utilized in various concentrations to obtain four novel cross linked chitosan hydrogels H1-H4. Three multi-walled carbon nanotube (MWCNT) biocomposites based on H1 were also prepared. Their structures were proven by elemental analysis, FTIR, XRD, SEM and TEM. They were found to be pH- and temperature-responsive materials. Their swell abilities appreciably depend on their cross linking moiety contents and MWCNTs concentration. They are more potent against Bacillis subtilis, Streptococcus pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Geotrichum candidum, Candida albicans, Aspergillus fumigatus, and Syncephalastrum racemosum than chitosan as judged by their greater inhibition zone diameters and their lower minimum inhibitory concentration (MIC) values. Their antimicrobial activities increased with increasing their cross linking moiety contents. They showed a better potency against Gram-positive than Gram-negative bacteria. The hydrogel H4 and H1/MWCNT composites have comparable or even higher activities than the reference bactericides or fungicides against some of tested microbes. Thus, combination between chitosan and the functionalized groups of the incorporated cross linker as well as MWCNTs in one system has efficiently improved the chitosan features. It is a good way for attaining adequate systems as antimicrobial agents that can be taken as promising candidates in biomedical fields.

3-Aminopropyltriethoxysilane-aided cross-linked chitosan membranes for gas separation: grand canonical Monte Carlo and molecular dynamics simulations.

Molecular simulations were performed to consider the structural and transport properties of chitosan/3-aminopropyltriethoxysilane (APTEOS) mixed matrix membranes (MMMs). In order to consider the presence of APTEOS content on the performances of membrane, various amounts of APTEOS were added to the polymeric matrix as a cross-linker. Structural characterizations such as radial distribution function (RDF), fractional free volume (FFV) and X-ray diffraction (XRD) were carried out on the simulated cells. Self-diffusivity and solubility of membranes were calculated using mean square displacement (MSD) and adsorption isotherms, respectively. Additionally, permeability and permselectivity of CO2 and N2 gases were calculated by grand canonical Monte Carlo and molecular dynamics methods. The system temperature was set to 298 K using a Nose-Hoover thermostat. According to the results, upon increasing APTEOS loading, CO2 permeability increases until 10 wt.% loading. Then, by adding 20 wt.% of APTEOS, CO2 permeability decreases, which could be related to higher crystallinity. XRD graphs indicated that the crystallinity decreased when adding 10 wt.% APTEOS, while higher APTEOS content (up to 20 wt.%) led to higher crystallinity percentage, consistent with permeability results. Compared to literature reports, the present simulation indicated higher accuracy for defining the structural and transport properties of APTEOS cross-linked chitosan MMMs. Graphical abstract 3-Aminopropyltriethoxysilane-aided cross-linked chitosan membranes for gasseparation.

Functionalized cross-linked chitosan with ionic liquid and highly efficient removal of azo dyes from aqueous solution.

In this study, a new ionic liquid functionalized cross-linked chitosan (IL-CCS) was prepared and utilized as an adsorbent for removing sunset yellow FCF (SY) from aqueous solutions. The physicochemical properties of the adsorbent were characterized using infrared spectroscopy (IR), scanning electron microscope (SEM), nitrogen adsorption-desorption isotherms and thermogravimetric analysis (TG). The effects of the experimental parameters such as initial pH, the adsorbent dose and contact time on the absorption process of SY on IL-CCS were investigated in detail. The results showed that the adsorption capacity of IL-CCS for SY had no significant differences when pH of the solution changed from 2.0 to 10.0, and the maximum adsorption capacity of IL-CCS was 300.28 mg/g, obviously higher than that of CCS (36.08 mg/g). In addition, the results of adsorption isotherm, kinetic and thermodynamics showed that the adsorption process could fit with Langmuir model, pseudo-second order model, separately. The exothermic nature of the reaction was revealed through thermodynamic parameters. From the above, IL-CCS has a good prospect for treatment of wastewater containing anionic dyes due to high efficiency adsorption during a broad pH range.

Enhanced Antibacterial Activity of Silver Doped Titanium Dioxide-Chitosan Composites under Visible Light.

Nano titanium dioxide (TiO2) with photocatalytic activity was firstly modified by diethanolamine, and it was then doped with broad spectrum antibacterial silver (Ag) by in situ method. Further, both Ag doped TiO2-chitosan (STC) and TiO2-chitosan (TC) composites were prepared by the inverse emulsion cross-linking reaction. The antibacterial activities of STC composites were studied and their antibacterial mechanisms under visible light were investigated. The results show that in situ doping and inverse emulsion method led to good dispersion of Ag and TiO2 nanoparticles on the cross-linked chitosan microsphere. The STC with regular particle size of 1⁻10 µm exhibited excellent antibacterial activity against E. coli, P. aeruginosa and S. aureus under visible light. It is believed that STC with particle size of 1⁻10 µm has large specific surface area to contact with bacterial cell wall. The increased antibacterial activity was attributed to the enhancement of both electron-hole separations at the surface of nano-TiO2 by the silver ions under the visible light, and the synergetic and sustained release of strong oxidizing hydroxyl radicals of nano-TiO2, together with silver ions against bacteria. Thus, STC composites have great potential applications as antibacterial agents in the water treatment field.

Synthesis and characterization of Zr(IV) doped immobilized cross-linked chitosan/perlite composite for acid orange II adsorption.

To enhance the adsorption capacity of chitosan for acid orange II (AOII) adsorption, a novel adsorbent, zirconium(IV) doped immobilized cross-linked chitosan/perlite (Zr(IV)-CS-PT) composite was synthesized and characterized. Batch studies were conducted to analyze the effect of different parameters on AOII adsorption, such as Zr (IV) loading amount, pH, adsorbent dosage and temperature. Also, kinetic data revealed that AOII adsorption was well described by pseudo-second order kinetic model. Langmuir adsorption isotherm model was best described the isotherm data and maximum adsorption capacity was found 476.2 mg/g at natural pH. The thermodynamic data showed that the AOII adsorption occurred spontaneously and endothermic nature. Desorption and recycle experiments showed that after six cycle the adsorption efficiency was decreased from 95.6% to 90.1%, which shows the Zr(IV)-CS-PT is a reusable, cost-effective and high adsorption capacity adsorbent.

Successive grafting of poly(hydroxyethyl methacrylate) brushes and melamine onto chitosan microspheres for effective Cu(II) uptake.

Cross-linked chitosan (CCS) microspheres tethered with melamine-conjugated poly(hydroxyethyl methacrylate) (PHEMA) brushes were synthesized by combination of surface-initiated atom transfer radical polymerization (ATRP) of HEMA and subsequent covalent immobilization of melamine onto the chain ends of PHEMA brushes. The as-synthesized CCS microsphere was used as a novel adsorbent for effective uptake of Cu(II) ions from aqueous solution. Success in each functionalization step was ascertained by SEM, ATR-FTIR and XPS characterization. Batch adsorption experimental results demonstrated that the adsorption equilibrium of Cu(II) ions on the melamine-grafted CCS microsphere was rapidly established within 20 min, and the adsorption process was found to be governed by intra-particle diffusion and chemisorption processes. The Langmuir-fitted maximum adsorption capacity of Cu(II) ions on the as-synthesized CCS microspheres was as high as circa 4.67 mmol L-1 (299 mg g-1). The calculated thermodynamic parameters revealed an endothermic and spontaneous adsorption process of Cu(II) ions on the melamine-grafted CCS microspheres. XPS spectra revealed that the adsorption mechanism was attributed to coordination (or chelation) interactions between amino (or hydroxyl) groups with cationic Cu(II) ions.