Cross-linked Magnetic Chitosan Research Articles

Co-immobilization of electron mediator and laccase onto dialdehyde starch cross-linked magnetic chitosan nanomaterials for organic pollutants' removal.

In this study, an amino-functionalized ionic liquid-modified magnetic chitosan (MACS-NIL) containing 2,2-diamine-di-3-ethylbenzothiazolin-6-sulfonic acid (ABTS) was used as a carrier, and dialdehyde starch (DAS) was used as a cross-linking agent to covalently immobilize laccase (MACS-NIL-DAS-lac), which realized the co-immobilization of laccase and ABTS. The carrier was characterized by Fourier infrared transform spectroscopy, scanning electron microscopy, thermogravimetric analysis, X-ray diffraction analysis, electron paramagnetic resonance, etc. The immobilization efficiency and activity retention of MACS-NIL-DAS-lac could reach 76.7% and 69.8%, respectively. At the same time, its pH stability, thermal stability, and storage stability had been significantly improved. In the organic pollutant removal performance test, the removal rate of 2,4-dichlorophenol (10mg/L) by MACS-NIL-DAS-lac (1 U) could reach 100% within 6h, and the removal efficiency could still reach 88.6% after six catalytic runs. In addition, MACS-NIL-DAS-lac also showed excellent degradation ability for other conventional phenolic pollutants and polycyclic aromatic hydrocarbons. The research results showed that MACS-NIL-DAS fabricated by the combination inorganic material, organic biomacromolecules, ionic liquid, and electron mediator could be used as a novel carrier for laccase immobilization and the immobilized laccase showed excellent removal efficiency for organic pollutants.

Synthesis of cross-linked magnetic chitosan beads immobilised with bacteria for aerobic biodegrading benzophenone-type UV filter

Bacterial immobilisation is a technique by which bacteria are embedded into or adsorbed onto a carrier material thereby increasing bacterial tolerance to harsh environments. This technique can be used to enhance bacterial activity and to degrade pollutants. Immobilised bacterial beads that contain nanomagnetic particles allow bead recycling and reuse. In this study, our objective was to produce cross-linked nanomagnetic chitosan beads (MCBs) for the biodegradation of benzophenone-type UV filter chemicals such as 2,4-dihydroxybenzophenone (BP-1) and oxybenzone (BP-3). We found that the optimal concentration for creating these MCBs to be 1.2% by weight chitosan and 10% by weight nano-magnetite. We selected and isolated six benzophenone-n (BPs)-biodegrading bacteria identified to be various Pseudomonas spp., a Gordonia sp., and Rhodococcus zopfii; these were used to create MCBs that were able to effectively biodegrade BP-1 or BP-3 as a sole carbon source. Both BPs were effectively biodegraded and mineralised over 8 days in the presence of the selected MCB-immobilised bacterial strains. The highest pseudo-first-order constant rates for BP biodegradation were 8.7 × 10−3 h−1 for BP-1 (strain BP1-D) and 1.02 × 10−3 h−1 for BP-3 (strain BP3-1). The mechanical strength of the MCBs was measured to be above 90% based on recovered weight. The MCBs released their bacteria at rates in the range of 104–105 CFU/day. We also determined the pathway through which the BPs were being aerobically biodegraded based on the GC/MS profiles of the intermediates. Our findings provide a novel strategy for treating BPs via the use of reusable and recyclable MCBs that are cheap, easy and fast to synthesise.

Using chitosan-based heterogeneous catalyst for degradation of Acid Blue 25 in the effective electro-Fenton process with rotating cathodes

Herein, the capability of glutaraldehyde cross-linked magnetic chitosan nanoparticles (Fe3O4/CS/GA NPs) was investigated as a heterogeneous electro-Fenton catalyst for the degradation of Acid Blue 25. A cylindrical reactor with rotating cathodes was used for performing the electro-Fenton process. Fe3O4/CS/GA NPs were characterized by Fourier-Transform Infrared Spectroscopy (FT-IR), X-ray Powder Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray (EDX), and Vibrating Sample Magnetometer (VSM). According to the results, the dye removal efficiency reached 94.83% after 90 min under the optimal conditions of Fe3O4/CS/GA NPs with the iron content of 15 mmol Fe/g chitosan and concentration of 0.3 g/L, natural pH of dye (6.8), initial dye concentration of 150 mg/L, the current intensity of 0.7 A, and rotational speed of 100 rpm. Also, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removal reached 74.19% and 61.53% after 120 min, respectively. Average oxidation state (AOS) and carbon oxidation state (COS) values were increased after treatment, indicating that wastewater's biodegradability was improved. Moreover, the heterogeneous electro-Fenton process using optimal Fe3O4/CS/GA NPs resulted in about 16% improvement in the removal efficiency compared to the homogeneous process. The catalyst showed good reusability up to 5 cycles. The amounts of leached iron into the solution were much less than allowable amounts of the Iranian wastewater discharge standard, thus no need for secondary treatment. Furthermore, scavengers studies under the optimum conditions showed the dye degradation occurred mainly by surface-bonded hydroxyl radicals. In short, this study proved, Fe3O4/CS/GA NPs are a promising heterogeneous electro-Fenton catalyst due to their low cost, excellent stability and reusability, negligible iron leaching, environmental compatibility, and superior catalytic activity in a wide range of pH.

Degradation-Dependent Controlled Delivery of Doxorubicin by Glyoxal Cross-Linked Magnetic and Porous Chitosan Microspheres.

Glyoxal cross-linked porous magnetic chitosan microspheres, GMS (∼170 μm size), with a tunable degradation profile were synthesized by a water-in-oil emulsion technique to accomplish controlled delivery of doxorubicin (DOX), a chemotherapeutic drug, to ensure prolonged chemotherapeutic effects. The GMS exhibit superparamagnetism with saturation magnetization, Ms = 7.2 emu g–1. The in vitro swelling and degradation results demonstrate that a swelling plateau of GMS is reached at 24 h, while degradation can be modulated to begin at 96–120 h by formulating the cross-linked network using glyoxal. MTT assay, live/dead staining, and F-actin staining (actin/DAPI) validated the cytocompatibility of GMS, which further assured good drug loading capacity (35.8%). The release mechanism has two stages, initiated by diffusion-inspired release of DOX through the swollen polymer network (72 h), which is followed by a disintegration-tuned release profile (>96 h) conferring GMS a potential candidate for DOX delivery.

Magnetic nanobiosorbent (MG-Chi/Fe3 O4 ) for dispersive solid-phase extraction of Cu(II), Pb(II), and Cd(II) followed by flame atomic absorption spectrometry determination.

Trace amounts of Cu (II), Pb (II), and Cd (II) in a wastewater sample were preconcentrated with a novel cross‐linked magnetic chitosan modified with a new synthesised methionine‐glutaraldehyde Schiff's base (MG‐Chi/Fe3O4) as a dispersive solid‐phase extraction (DSPE) adsorbent. The adsorbed metal ions were then eluted with a specific volume of suitable solution and determined by flame atomic absorption spectrometry (FAAS). Various parameters affecting the extraction efficiency of the metal ions were investigated and optimised, including pH, amount of adsorbent, extraction time, type and volume rate of eluent, elution time, sample volume, and effect of interfering ions. The adsorption kinetics are more consistent with the pseudo‐second order model. The results were statistically interpreted and the analytical performance of the proposed method was found to have preconcentration factors of 55, 60, and 50 μg L−1 for Cu(II), Pb(II), and Cd(II), respectively, limits of detection were 0.22, 0.24, and 0.10 μg L−1 for Cu(II), Pb(II), and Cd(II), respectively, with a relative standard deviation (1.5%‐2.8 %), and the liner range was 5–1000 for Cu(II) and Pb(II) and 2.5–1000 for Cd(II). It was concluded that this method was suitable for successful simultaneous determination of Cu(II), Pb(II), and Cd(II) in industrial wastewater samples.

Adsorption of nickel (II) ions from wastewater using glutaraldehyde cross-linked magnetic chitosan beads: isotherm, kinetics and thermodynamics.

Magnetic chitosan beads (MCSB), prepared from solution by using an external magnet, and the adsorption of Ni(II) ions from wastewater by MCSB and its cross-linked derivative with glutaraldehyde (GLU-MCSB) was investigated in an adsorption system. The GLU-MCSB sorbents are insoluble in aqueous acidic solution and improve adsorption capacity. The adsorption process was carried out by considering various parameters, viz. adsorbent dose, contact time, pH and temperature. Thermogravimetric analysis of beads shows that degradation takes place in two stages. Fourier transform infra-red spectra of magnetic beads exhibit an absorption band at 606 cm-1 for Fe-O. The elemental analysis (energy dispersive X-ray analysis) and scanning electron microscopy were used to analyze the structure and characteristics of MCSB and GLU-MCSB. The Ni(II) removal efficiency attains a highest value of 95.12% with cross-linked GLU-MCSB in comparison to 79.5% with MCSB. Adsorption processes follow the pseudo-second-order rate kinetics model, which suggested that the rate-limiting step may be the chemical adsorption rather than the mass transport. The experimental data of adsorption fitted well with the Langmuir and Freundlich isotherms with a high correlation coefficient (R2 > 0.9), showing that monolayer adsorption took place on the surface of GLU-MCSB absorbents. The negative values of entropy change, -175.64 and -163.30 J/(mol·K), and enthalpy change, -54.75 and -49.58 kJ/mol, for MCSB and GLU-MCSB suggest that the process is spontaneous and exothermic in nature.

Preparation of cross-linked magnetic chitosan with methionine-glutaraldehyde for removal of heavy metals from aqueous solutions

ABSTRACTA new nanobiosorbent based on cross-linked chitosan magnetic beads modified with methionine-glutaraldehyde schiff’s base (MG-Chi/Fe3O4) was synthesised for removing Cu(II), Pb(II) and Cd(II) from wastewater samples. Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) analysis, and scanning electron microscope (SEM) have been applied to characterise nanobiosorbent. A variety of parameters influencing uptake behaviours of the metal ions, including pH, adsorbent dose, contact time, initial concentration of the metal ions and desorption conditions were examined and optimised. The pH ZPC of MG-Chi/Fe3O4 was found to be 4.0. Freundlich and Langmuir isotherm models were applied to estimate adsorption mode. The equilibrium data were well fitted with the Langmuir isotherm model. The maximum adsorption capacities for Cu(II), Pb(II), and Cd(II) were 172.4, 175.4 and 163.9 mg g−1, respectively. The adsorption kinetics fitted better with the pseudo-second-order model indicating that chemical adsorption is the rate-limiting step in the adsorption process. The adsorbent (MG-Chi/Fe3O4 nanobiosorbent) performance is maintained for at least 4 adsorption-desorption cycles. Finally, MG-Chi/Fe3O4 nanobiosorbent exhibited high potential to remove the metal ions from Iran Khodro’s wastewater.

Efficiency of magnetic chitosan supported on graphene for removal of perchlorate ions from wastewater

ABSTRACT In this study, we used a synthesized cross-linked magnetic chitosan with graphene oxide beads to study the removal of perchlorate from wastewater. The prepared complex was characterized using transmission electron microscopy (TEM), Fourier Transformation Infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM) and Thermal gravimetric analysis (TGA). Several parameters were studied including the effect of pH, contact time and the co-existing anions. The study showed that the adsorption could be studied in a wide range of pH. The study showed that the adsorption follows a pseudo-second-order model and Langmuir adsorption isotherm. The enthalpy and negative Gibbs standard free energy showed that the adsorption process was exothermic and spontaneous. The perchlorate adsorbent can be regenerated well by 0.1% NaCl solution.

Adsorptive performance of magnetic nano-biosorbent for binary dyes and investigation of comparative biosorption

The individual and competitive biosorption capacities of Metanil Yellow (MY) and Reactive Black 5 (RB5) by glutaraldehyde cross-linked magnetic chitosan nanoparticles (GMCNs) were studied. Competitive biosorption of the MY and RB5 dyes by the GMCNs has never been reported previously. Fourier transform infrared technique has been used to show the biosorbed MY and RB5 dyes onto GMCNs. During the studies, various essential factors influencing the biosorption, like adsorbate concentration, pH of the solution and contact time have been monitored. The equilibrium was achieved within 17 h for single dyes and 3 h for binary mixture at pH 3. The biosorption capacities were 620 mg/g for dye MY and 2549 mg/g for dye RB5 at pH 3, 30 °C. The second-order kinetic model has good compatibility with the dynamical biosorption behavior of a single dye and binary mixture. In order to study the competition biosorption of the RB5 and MY dyes in mixture solutions, the intraparticle diffusion model was used. Competition biosorption through analysis of the intraparticle diffusion model apparently favored the RB5 dye more than the MY dye on the GMCNs in mixture solutions. The biosorbent was regenerated efficiently through the alkaline solution and was then reused ten times for biosorption–desorption cycles.

2,2’-(butane-1,4-diylbis(oxy))dibenzaldehyde cross-linked magnetic chitosan nanoparticles as a new adsorbent for the removal of reactive red 239 from aqueous solutions

In the current work, 2,2’-(butane-1,4-diylbis(oxy))dibenzaldehyde cross-linked magnetic chitosan nanoparticles (Fe3O4@CS-BAL) were successfully synthesized as the new magnetic adsorbent through crosslinking modification of magnetic chitosan nanoparticles (Fe3O4@CS) using 2,2’-(butane-1,4-diylbis (oxy))dibenzaldehyde (BAL) as a crosslinker at room temperature. The chemical structure, surface properties and morphology of the synthesized nanoparticles were characterized by Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD) and Scanning electronic microscope (SEM), Thermogravimetric analysis (TGA) and N2 adsorption-desorption isotherms. The 2,2’-(butane-1,4-diylbis(oxy))dibenzaldehyde-modified magnetic chitosan nanoparticles (Fe3O4@CS-BAL) were used as an effective adsorbent for removal of an anionic reactive dye, Reactive red 239 (RR239) from aqueous solutions by batch adsorption procedure. The effects of various experimental parameters such as adsorbent dosage, pH, contact time and initial dye concentration on the RR239 adsorption onto the Fe3O4@CS-BAL were investigated and optimized. The Langmuir and Freundlich adsorption models were used to describe adsorption isotherms and constants. The equilibrium results revealed that the adsorption behavior of the RR239 dye on the Fe3O4@CS-BAL nanoparticles fitted well with the Langmuir model. On the basis of the Langmuir analysis, the maximum adsorption capacity (qm) of the Fe3O4@CS-BAL for RR239 was found to be 200 mg/g. The experimental results showed that the Fe3O4@CS-BAL could be remove more than 99% of investigated dye within the first 2 min of contact time. Therefore, the Fe3O4@CS-BAL adsorbent can be successfully applied as an efficient and low-cost adsorbent for removal of anionic reactive dyes from aqueous solutions.

Rapid Determination of Trace Palladium in Active Pharmaceutical Ingredients by Magnetic Solid-Phase Extraction and Flame Atomic Absorption Spectrometry

Clutaraldehyde cross-linked magnetic chitosan nanoparticles were synthesized and used as an adsorbent for the dispersive solid-phase extraction of palladium in active pharmaceutical ingredients (APIs) prior to analysis by a flame atomic absorption spectrophotometer. FT-IR, X-ray diffraction, and TEM were used to characterize the adsorbent. Various parameters of experimental performance, such as adsorbent amount, pH, adsorption time, desorption solutions, coexisting ions, and adsorbent reusability, were investigated and optimized. Under the optimized conditions, good linearity was achieved in the 5.0–500 μg/L concentration range, with correlation coefficients of 0.9989. The limit of detection is 2.8 μg/L and the recoveries of spiked samples ranged from 91.7 to 97.6%. It was confirmed that the GMCNs nanocomposite was a promising adsorbing material for extraction and preconcentration of Pd in APIs.

Preparation of cross-linked magnetic chitosan particles from steel slag and shrimp shells for removal of heavy metals

ABSTRACTIn this study, a new method for preparation of cross-linked magnetic chitosan particles (MCPs) from steel slag and shrimp shells using green tea extract as crosslinking reagent has been presented. The MCPs obtained were characterized by means of X-ray diffraction analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy and magnetic properties, and then were used to investigate the adsorption properties of Cu(II) and Ni(II) ions in aqueous solutions. The influence of experimental conditions such as contact time, pH value, adsorbent dose and initial metal concentration, and the possibility of regeneration were studied systematically. The Cu(II) and Ni(II) adsorption isotherms, kinetics and thermodynamics have been measured and discussed. The results show that the synthesized MCPs have high adsorption capacity for both metal ions (126.58 mg/g for Cu(II) and 66.23 mg/g for Ni(II)), and have excellent regeneration stability with efficiency of greater than 83% after five cycles of the adsorption–regeneration process. The adsorption process of Ni(II) and Cu(II) on MCPs was feasible, spontaneous and exothermic, and better described by the Langmuir model and pseudo-second-order kinetic equation. The MCPs can be applied as a low cost and highly efficient adsorbent for removal of heavy metals from wastewater due to its high adsorption capacity, easy recovery and good reusability.

Glutaraldehyde cross-linked magnetic chitosan nanocomposites: Reduction precipitation synthesis, characterization, and application for removal of hazardous textile dyes

Magnetic chitosan nanocomposites (MCNCs) were synthesized by an inexpensive reduction precipitation technique using a glutaraldehyde cross-linking agent at room temperature. Successful chitosan coating of iron oxide nanoparticles was confirmed by X-ray photoemission spectroscopy. X-ray diffraction data revealed crystalline particle sizes for the iron oxide and MCNCs to be around 6–7 and 8–9nm, respectively. In addition, the MCNCs exhibited supermagnetic properties having magnetic saturation of 17.5emu/g. The synthesized MCNCs showed 91.60% absorption of Acid Red 2, while iron oxide 16.40% absorption; enhanced performance in MCNCs was resulted from presence of free amino and hydroxyl groups. Furthermore, the optimum pH and adsorbent concentration were 3 and 1.0g/L, respectively. The Redlich–Peterson isotherm fit experimental data better than Langmuir and Freundlich models, based on non-linear regression. Finally, MCNCs showed 96% American Dye Manufacturing Institute (ADMI) value removal and gave recovery efficiency of 100%, making them attractive for further practical applications.

Adsorption of uranium(VI) from aqueous solutions using cross-linked magnetic chitosan beads

The performance of a cross-linked magnetic chitosan has been investigated for the adsorption of U(VI) from aqueous solutions. The influences of the pH of solution, the initial concentration of U(VI) ions and the contact time on the adsorption amounts have been discussed, and the appropriate process conditions for the adsorption of U(VI) have been obtained. The adsorption experimental equilibrium data was found to fit the Langmuir model well, and the uptake of U(VI) was 161.3 mg g−1. Two simplified models including pseudo-first order and pseudo-second order equations are selected to follow the adsorption process.

Removal of hazardous azo dye Metanil Yellow from aqueous solution by cross-linked magnetic biosorbent; equilibrium and kinetic studies

In this study, glutaraldehyde cross-linked magnetic chitosan nanoparticles (GMCNs) were prepared through cross-linking modification of magnetic chitosan nanoparticles using glutaraldehyde as a cross-linker that exhibited excellent Metanil Yellow (MY) adsorption performance. The characterization of the GMCNs was performed by Fourier transform infrared spectroscopy, transmission electronmicroscopy, scanning electron microscopy, dynamic light scattering, and vibrating sample magnetometry analyses. Adsorption characteristics of MY from aqueous solution onto GMCNs have been studied. During the studies, various essential factors influencing the adsorption, like adsorbate concentration, amount of adsorbent, pH of the solution, and contact time have been monitored. The equilibrium was achieved within 17 h at pH 4, and the adsorption data obeyed the Langmuir equation with a maximum adsorption capacity of 625 mg/g and a Langmuir adsorption equilibrium constant of 5.2 × 10−4 dm3/mg at 25°C. The adsorption kinetics of MY at different initial dye concentrations was evaluated by the first-order and second-order models. The kinetic studies of MY adsorption showed that the adsorption process followed a second-order kinetic model. Furthermore, the GMCNs can be regenerated and reused through dye desorption in alkaline solution at pH 10. Adsorption results for reusability were 100, 93, and 65%, respectively, for three repeats.

Electrospinning of Cross-Linked Magnetic Chitosan Nanofibers for Protein Release.

A poly(vinylalcohol) (PVA) electrospun/magnetic/chitosan nanocomposite fibrous cross-linked network was fabricated using in situ cross-linking electrospinning technique and used for bovine serum albumin (BSA) loading and release applications. Sodium tripolyphosphate (TPP) and glutaraldehyde (GA) were used as cross-linkers which modified magnetic-Fe3O4 chitosan as Fe3O4/CS/TPP and Fe3O4/CS/GA, respectively. BSA was used as a model protein drugs which was encapsulated to form Fe3O4/CS/TPP/BSA and Fe3O4/CS/GA/BSA nanoparticles. The composites were electrospun with PVA to form nanofibers. Nanofibers were characterized by field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). The characterization results suggest that Fe3O4 nanoparticles with average size of 45 nm were successfully bound on the surface of chitosan. The cross-linked nanofibers were found to contain uniformly dispersed Fe3O4 nanoparticles. The size and morphology of the nanofibers network was controlled by varying the cross-linker type. FTIR data show that these two polymers have intermolecular interactions. The sample with TPP cross-linker showed an enhancement of the controlled release properties of BSA during 30-h experimental investigation. Graphical Abstract ᅟ.

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 pseudosecond-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) (2.783mmol/g) was found to be higher than that of Cr(VI) (2.323mmol/g), resulting from the size of the H2PO4− ions being smaller than that of the HCrO4− 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.

Adsorption of food dyes from aqueous solution by glutaraldehyde cross-linked magnetic chitosan nanoparticles

Glutaraldehyde cross-linked magnetic chitosan nanoparticles (GMCNs) were prepared through cross-linking modification of magnetic chitosan nanoparticles (MCNs) using glutaraldehyde as crosslinker, that not only exhibited excellent food dyes adsorption performance, but also showed low cytotoxicity. Adsorption characteristics of GMCNs in FD&C Blue 1 and D&C Yellow 5 aqueous solutions have been studied and results indicated that the adsorption capacities were affected by initial pH values, initial dye concentrations and temperatures. Food dyes adsorption followed with thepseudo-second-orderreaction, and equilibrium experiments were well fitted the Langmuir isotherm model. Maximum adsorption capacities of GMCNs displayed at pH 3.0 and at 25°C, being up to 475.61 and 292.07mg/g, for FD&C Blue 1 and D&C Yellow 5 respectively. Thermodynamic results demonstrated that the adsorption processes were spontaneous and exothermic. Furthermore, it was found that the GMCNs can be regenerated and reused through dye desorption in alkaline solution.

Adsorption of Cr (VI) by Cross-Linked Magnetic Hydroxamated Chitosan

This paper aims to investigate the adsorption of Cr (VI) by cross-linked magnetic hydroxamated chitosan (MHCTS). The adsorption experiments were carried out in batch systems. To determine the optimum condition of the adsorption, factors such as pH, reaction time, initial Cr (VI) concentration and adsorbent dosage were considered. The experimental results showed that MHCTS can adsorb Cr (VI) with high efficiency. Optimum adsorption was observed at pH 4.0, and the highest adsorption removal reached 99.2%. The equilibrium was established within 90 min. The process could be described by pseudo-first-order and pseudo-second-order kinetic model.

Preparation of Genipin Cross-linked Magnetic Chitosan Microsphere and Its Immobilization on Lipase

Inverse suspension combined with the sol-gel method was deployed to prepare a magnetic chitosan microspheres.The lipase was immobilized on magnetic chitosan microspheres with genipin as the cross-linking reagent.The optimum conditions and properties of immobilization enzyme were investigated.The maximal specific activity of 4.31 U/g was achieved when the crosslinking reaction was carried out at 55 ℃ for 8 h using 0.6 g/L genipin.The optimum pH,temperature and Km of the immobilized enzyme were 8,25～35℃ and 0.26 mol/L,respectively.The immobilized lipase showed improved thermal stability and remained active in a broader pH range,compared with those of free lipase.Such immobilized lipase can be recycled via the magnetic separation for a certain extent.