Cellulose/chitosan hybrid nanofibers from electrospinning of their ester derivatives

A facile approach has been established to generate cellulose/chitosan hybrid nanofibers with full range of compositions by electrospinning of their ester derivatives, cellulose acetate (CA) and dibutyryl chitin (DBC), followed by alkaline hydrolysis to cellulose (Cell) and chitosan (CS). DBC was synthesized by acid-catalyzed acylation of chitin (CHI) with butyric anhydride and the newly formed butyl groups on C3 and C6 were confirmed by FT-IR and ¹HNMR. DBC had robust solubility in acetone, DMAc, DMF, ethanol, and acetic acid, all except ethanol were also solvents for CA, allowing mixing of these ester derivatives. Fiber formation by electrospinning of either DBC or CA alone and together in these common solvents and their mixtures were studied. The 1/1 acetone/acetic acid was found to be the optimal solvent system to generate fibers from either DBC or CA as well as their mixtures at all CA/DBC ratios, resulting in hybrid fibers with diameters ranging from 30 to 350 nm. DBC and CA were well mixed and showed no phase separate in the hybrid fibers. Alkaline hydrolysis (NaOH) of the equal mass CA/DBC nanofibers regenerated Cell and CHI readily via O-deacylation, then proceeded to further deacetylate CHI to CS via N-deacetylation at higher alkaline concentrations and/or temperatures. Under conditions studied, hydrolysis with 5N NaOH at 100 °C for 3 h was optimal to regenerate cellulose/chitosan hybrid nanofibers.     

The structure and electric characters of proton‐conducting chitosan membranes with various ammonium salts as complexant

The structural and electric properties of chitosan electrolytes doped by three different ammonium salts [CH₃COONH₄, NH₄Cl, and (NH₄)₂SO₄] were discussed. The chitosan electrolytes were prepared by solution casting technique. The results show that the addition of ammonium salts leads to: The formation of complexation between ammonium salts and chitosan matrix, the destruction of crystal forms, and the enhancement of amorphous nature. With the rise of salt content, both the glass transition temperature and the activation energy show a “V”‐type trend, whereas the conductivity exhibits a reverse trend. For different ammonium salts, the electric properties of the chitosan electrolyte are different due to the Coulomb force between anion of salts and functional groups. The CH₃COONH₄ doped chitosan electrolyte exhibits the optimum electric properties, whereas those of (NH₄)₂SO₄ doped chitosan electrolyte are worst. The chitosan electrolyte doped with 40 wt % CH₃COONH₄ has the lowest glass transition temperature of 369 K, the lowest activation energy of 0.19 eV, and the highest ionic conductivity of 2.87 × 10^?4 S cm^?1 at room temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 880–885, 2010     

Preparation and characterization of conductive chitosan–ionic liquid composite membranes

Anhydrous conductive membranes composing of a composite of chitosan (CS) and ionic liquids with symmetrical carboxyl groups were explored. Scanning electron microscope images revealed that porous composite membranes could be obtained by combining CS with different amounts of 1,4‐bis(3‐carboxymethyl‐imidazolium)‐1‐yl butane chloride ([CBIm]Cl). Fourier transform infrared and proton nuclear magnetic resonance confirmed that the formation of ammonium salts after CS was combined with [CBIm]Cl. The thermal property of CS–ionic liquid composite membranes was studied through thermogravimetric analysis. The anhydrous ionic conductivities of CS–[CBIm]X (X = Cl, Ac, BF₄, and I) composite membranes were measured using ac impedance spectroscopy at room temperature in N₂ atmosphere. The conductivities (0.4–0.7 × 10^?4 Scm^?1), found to be in the same range as semiconductors, were significantly higher than those of pure CS membrane (<10^?8 Scm^?1). In addition, the anhydrous conductivity of composite membrane based on CS–[CBIm]I at room temperature reached a level as high as 0.91 × 10^?2 Scm^?1 when iodine was doped. Copyright © 2011 John Wiley & Sons, Ltd.     

Polyamine chitosan adsorbent for the enhanced adsorption of anionic dyes from water

A simple synthesis route for amine protected-introduced-released chitosan (APIR-CS) was investigated to improve the adsorption of anionic dyes. The C₂ amine groups of the chitosan (CS) were initially protected via a Schiff-base reaction by benzaldehyde. They were then synthesized by the introduction of ethylenediamine into C₆ hydroxyl groups on CS via epichlorohydrin. The final product was obtained after removal of the Schiff base with dilute hydrochloride solution. Amine-introduced chitosan (AI-CS) was directly synthesized at the C₂ amine groups. The adsorbents were characterized by FTIR, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). For Congo red (CR) and methyl orange (MO), most of the amine groups in CS were converted to–N?CH₂ groups after the benzaldehyde treatment. Hydrochloric acid treatment after the cross-linking reaction released protected nitrogen atoms into the form of the primary amine again. APIR-CS had significantly greater adsorption capacities than AI-CS. The increased adsorption performance was attributed to the large number of primary amine groups on the surfaces. The adsorption mechanism was based on electrostatic interaction, while the adsorption process was mainly physisorption.     

Pico- and nano-second laser flash photolysis study on photoinduced charge separation in oligothiophene-C60 dyad molecules

Photoinduced charge separation (CS) and charge recombination (CR) processes of octathiophene-C₆₀ and dodecathiophene-C₆₀ dyad molecules (8T-C₆₀ and 12T-C₆₀, respectively) have been investigated by time-resolved absorption spectroscopy in the visible and near-IR regions. In toluene, ¹8T*-C₆₀ and ¹12T*-C₆₀ showed energy transfer to ¹C*-moiety predominantly, while 60 contribution of CS was small. In various polar solvents, on the other hand, CS states were predominantly formed from both singlet-excited oligothiophene and ¹C6*0-moiety because of lower CS level in polar environments. The CR process generating both the triplet state of oligothiophene and the ground state was confirmed in anisole and anisole/toluene mixture within a few nanoseconds. In more polar solvents (dielectric constant (∈_s) > 7), CS states showed two components decay: Slow decay component showed lifetime in the hundred nanosecond-region, while fast component decayed within a few nanoseconds. For the mechanism of the long-living CS state in polar solvents (∈_s > 7), equilibrium between the CS state and the triplet state was proposed. Furthermore, effects of length of oligothiophene on the CS and CR processes were discussed on the basis of the free energy changes.     

Electrospun cellulose acetate fibers: effect of solvent system on morphology and fiber diameter

This paper reports an investigation of the effects of solvent system, solution concentration, and applied electrostatic field strength (EFS) on the morphological appearance and/or size of as-spun cellulose acetate (CA) products. The single-solvent systems were acetone, chloroform, N,N -dimethylformamide (DMF), dichloromethane (DCM), methanol (MeOH), formic acid, and pyridine. The mixed-solvent systems were acetone–DMAc, chloroform–MeOH, and DCM–MeOH. Chloroform, DMF, DCM, MeOH, formic acid, and pyridine were able to dissolve CA, forming clear solutions (at 5% w/v), but electrospinning of these solutions produced mainly discrete beads. In contrast, electrospinning of the solution of CA in acetone produced short and beaded fibers. At the same solution concentration of 5% (w/v) electrospinning of the CA solutions was improved by addition of MeOH to either chloroform or DCM. For all the solvent systems investigated smooth fibers were obtained from 16% (w/v) CA solutions in 1:1, 2:1, and 3:1 (v/v) acetone–DMAc, 14–20% (w/v) CA solutions in 2:1 (v/v) acetone–DMAc, and 8–12% (w/v) CA solutions in 4:1 (v/v) DCM–MeOH. For the as-spun fibers from CA solutions in acetone–DMAc the average diameter ranged between 0.14 and 0.37 μm whereas for the fibers from solutions in DCM–MeOH it ranged between 0.48 and 1.58 μm. After submersion in distilled water for 24 h the as-spun CA fibers swelled appreciably (i.e. from 620 to 1110%) but the physical integrity of the fibrous structure remained intact.     

Effect of the type of nanoaddition on the thermal properties of polyacrylonitrile fibres

Thermal properties of precursor polyacrylonitrile fibres containing nanoparticles of additives such as SiO₂, hydroxyapatite and montmorillonite have been examined. The thermal curves of the fibres under investigation obtained by the derivatographic method in air and DSC in a neutral gas atmosphere were interpreted from the point of view of physical and chemical changes in the fibre-forming polymer. Based on the thermogravimetric curves, the coefficients of thermal stability of the fibres were found. It has been found that the thermal stability of PAN fibres is affected by the type of nanoadditives and the value of the as-spun draw out ratio used during fibre spinning.     

Preparation of electrically conducting cellulose fibres utilizing polyelectrolyte multilayers of poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) and poly(allyl amine)

The primary goal with this work is to create electrically conductive cellulose fibres, this has been done to explore possible new applications for fibre based material. This research uses various methods to create polyelectrolyte multilayers (PEMs) on bleached softwood fibres and on SiO₂ model surfaces, by sequentially treating these materials with poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) (PEDOT:PSS) and poly(allyl amine) (PAH). Paper sheets were then produced from the PEM-modified pulp and evaluated in terms of tensile strength, adsorbed amount of polymer, and electrical conductivity. To evaluate the influence of fibre charge on the measured paper properties, pulps of two different initial fibre charge densities were prepared via carboxymethylation. Because of the bluish colour of PEDOT:PSS, the build-up of PEM could be easily followed, since the fibres grew increasingly darker blue throughout the modification sequence. The conductivity of the fibre network increased by 2−3 orders of magnitude when the pulp of a higher fibre charge density was used. This suggests that it is more important to create a fibrous network with a high fibre-fibre joint strength and a large total joined area in the sheet rather than to maximize the adsorbed amount of PEDOT:PSS. A difference in conductivity could also be noted depending on the polyelectrolyte adsorbed in the outer layer, PAH lowered the conductivity compared to PEDOT:PSS. Evaluating the mechanical properties revealed that the use of PEDOT:PSS reduces the tensile strength of the paper. When five double layers had been adsorbed onto the carboxymethylated sample in which PEDOT:PSS formed the outer layer, calculations indicated a 25% decrease in tensile strength compared to that of reference material without PEMs. ESEM studies indicate that PEM treatment produces a significantly changed and somewhat smoother fibre surface.     

A Signal‐Amplified Electrochemical Immunosensor Based on Prussian Blue and Pt Hollow Nanospheres as Matrix

Through electrodepositing Prussian blue (PB) and chitosan (CS), then casting Pt hollow nanospheres (HN‐Pt) and assembling CA19‐9 antibody on the electrode surface, an immunosensor was achieved. A new signal amplification strategy based on PB and HN‐Pt toward the electrocatalytic reduction of H₂O₂ was employed when performing the determination. The resulting immunosensor showed a high sensitivity, broad linear response to carbohydrate antigen 19‐9 (CA19‐9) in two ranges from 0.5 to 30 and 30 to 240 U mL^?1 with a low detection limit of 0.13 U mL^?1 (S/N=3). Moreover, it displayed good reproducibility and stability, and would be potentially attractive for clinical immunoassay of CA19‐9.     

Preparation and antibacterial activity of electrospun chitosan/poly(ethylene oxide) membranes containing silver nanoparticles

Fairly uniform chitosan (CS)/poly(ethylene oxide) (PEO) ultrafine fibers containing silver nanoparticles (AgNPs) were successfully prepared by electrospinning of CS/PEO solutions containing Ag/CS colloids by means of in situ chemical reduction of Ag ions. The presence of AgNPs in the electrospun ultrafine fibers was confirmed by X-ray diffraction patterns. The AgNPs were evenly distributed in CS/PEO ultrafine fibers with the size less than 5 nm observed under a transmission electron microscope. X-ray photoelectron spectroscopy suggested that the existence of Ag―O bond in the composite ultrafine fibers led to the tight combination between Ag and CS. Evaluation of antimicrobial activities of the electrospun Ag/CS/PEO fibrous membranes against Escherichia coli showed that the AgNPs in the ultrafine fibers significantly enhanced the inactivation of bacteria.     

Poly(ammonium/ pyridinium)-chitosan Schiff base as a smart biosorbent for scavenging of Cu2+ ions from aqueous effluents

Chitosan Schiff bases (CSBs) decorated with ammonium or pyridinium motifs for recyclable biosorption of Cu²⁺ ions from aqueous effluents were tailored by grafting of salicylaldehyde ionic liquids (Sal-ILs) onto chitosan surface. Biosorption capacity of poly(ionic-salicylidene) CSBs (PISCSB_1,2) was compared with chitosan and poly(neural-salicylidene) CSBs (PSCSB). The ionic salicylidene-functionalized chitosan, poly(pyridinium)-salicylidene chitosan Schiff base (PISCSB₂), exhibited excellent adsorption capacity (99.1%), in comparison to chitosan (85%) and PSCSB (95%). Biosorption of Cu²⁺ ions onto PSCSB followed pseudo-first-order kinetic model while onto chitosan (CS) and PISCSB_1,2 followed pseudo-second-order kinetic model. However, Cu²⁺ ions biosorption onto all biosorbents fitted Langmuir adsorption isotherm model. Negative values of ΔG^o and ΔH^o confirmed the spontaneity and exothermic behavior of adsorption process. The new biosorbents could be successfully regenerated in aqueous 0.01 M EDTA solution with negligible loss in their adsorption capacity. Consequently, our new chitosan-based biosorbents may offer promising green and renewable scavengers for Cu²⁺ ions from wastewater.     

Preparation of spinel ferrite NiFe2O4 fibres by organic gel-thermal decomposition process

Functional spinel ferrite fibers are attractive for high-tech applications. The spinel NiFe₂O₄ fibres have been successfully prepared by the organic gel-thermal decomposition process from raw materials of Ni, Fe nitrate salts and citric acid. The gel spinning performance was a major factor for preparation of uniform gel fibrous precursors. The gel spinnability was related to the citrate-metal complex structure and linear-type structural molecules [(C₆H₆O₇)₄NiFe₂]_n for the gel precursor was possibly formed during the complexation reaction between the citric acid and metal ions at pH 5. The composition, structure of the gel precursors and products derived from thermal decomposition of these precursors were characterized by FTIR, XRD, and SEM. The thermal decomposition process of the gel precursors was investigated by TG-DSC. The prepared spinel NiFe₂O₄ fibres having grain sizes of 60–70 nm were featured with diameters of about 1 μm, and aspect ratios up to 10⁶ (length/diameter).     

壳聚糖纳米粒子荧光探针的制备和表征

通过低分子量的壳聚糖(LCS)聚阳离子与三聚磷酸钠(TPP)的静电作用制备纳米级壳聚糖微球,并利用壳聚糖链上丰富的氨基与荧光素异硫氰酸酯(FITC)反应从而制备纳米壳聚糖微球荧光探针(NFCS)。结果表明,当壳聚糖分子量为60000,LCS与TPP的质量比为6∶1时,可得到粒度均一的球形纳米粒子,平均粒径为40±3 nm。荧光倒置显微镜观察证实FITC结合到壳聚糖微球上。荧光光谱分析显示NFCS的最大激发波长、最大发射波长与游离态FITC无显著差异。光漂白实验证实NFCS的稳定性比游离态FITC有显著提高。     

Fabrication of Chitosan‐Multiwall Carbon Nanotube Nanocomposite Containing Ferri/Ferrocyanide: Application for Simultaneous Detection of D‐Penicillamine and Tryptophan

We report a simple and effective strategy for fabrication of the nanocomposite containing chitosan (CS) and multiwall carbon nanotube (MWNT) coated on a glassy carbon electrode (GCE). The characterization of the modified electrode (CS‐MWNT/GC) was carried out using scanning electron microscopy (SEM) and UV–vis absorption spectroscopy. The electrochemical behavior of CS‐MWNT/GC electrode was investigated and compared with the electrochemical behavior of chitosan modified GC (CS/GC), multiwalled carbon nanotube modified GC (MWNT/GC) and unmodified GC using cyclic voltammetry (CV) and electron impedance spectroscopy (EIS). The chitosan films are electrochemically inactive; similar background charging currents are observed at bare GC. The chitosan films are permeable to anionic Fe(CN)₆^3?/4? (FC) redox couple. Electrochemical parameters, including apparent diffusion coefficient for the Fe(CN)₆^3?/4? redox probe at FC/CS‐MWNT/GC electrode is comparable to values reported for cast chitosan films. This modified electrode also showed electrocatalytic effect for the simultaneous determination of D‐penicillamine (D‐PA) and tryptophan (Trp). The detection limit of 0.9 μM and 4.0 μM for D‐PA and Trp, respectively, makes this nanocomposite very suitable for determination of them with good sensitivity.     

Spectroscopic characterization and preparation of low molecular,water‐soluble chitosan with free‐amine group by novel method

Low molecular, water‐soluble chitosan (LMWSC) with a free amine group was prepared by the novel salts‐removal method described in this study. A weight‐average molecular weight and degree of deacetylation (DDA) of LMWSC were determined by viscometry and Kina titration, resulting in 18,579 Da and 93% DDA, respectively. In the Fourier transform infrared spectroscopic, ¹H NMR, and ¹³C NMR spectra the absorption band by the carboxyl group derived from lactic acid and the impurities formed in the enzymatic process disappeared or were significantly lower than that of the control chitosan. Also, from the ¹H NMR and ¹³C NMR spectra the empirical value for the area ratio of the proton and carbon corresponds nearly to its theoretical values. The matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrum identified the difference in the two adjacent peaks as 161. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3796–3803, 2002     

The effect of fibre diameter on filtration and flux distribution — relevance to submerged hollow fibre modules

This paper examines the effect of fibre diameter on filtration and flux distribution with inter-fibre two-phase flow for conditions relevant to submerged bioreactors (SMBR). Hollow fibres of different diameters fixed in a specially designed holder providing shell-side feed were tested for a model biomass feed with pumping and submerged systems. The experimental results showed that the effect of the fibre diameter on filtration increased with the increase in turbulence around the fibres. For filtration with two-phase flow, the performance was sensitive to changes in fibre diameter and significantly lower flux declines were obtained with smaller fibres. On the other hand, a theoretical analysis of flux distribution along the fibre in a submerged system showed the smaller fibres to be disadvantaged. The theoretical model based on the simplified Navier–Stokes equations and filtration equations revealed that the flux distribution along the fibre depends on fibre inner diameter, length and fibre permeability. The effect of these factors can be related to a dimensionless coefficient ζ=4lR_i^−3/2R_m^−1/2. Sensitivity analysis demonstrated that for ζ>2, the maximum flux along the fibre can be approximately estimated by J_max=ζJ_mi. Although, the effect of high initial local flux on performance of filtration is still to be assessed, the flux distribution model is useful in design and operation of the SMBR system.     

Eco‐friendly synthesis of 3,4‐dihydroquinoxalin‐2‐amine,diazepine‐tetrazole and benzodiazepine‐2‐carboxamide derivatives with the aid of MCM‐48/H5PW10V2O40

A heterogeneous material composed of MCM‐48/H₅PW₁₀V₂O₄₀ was produced and used as an efficient, eco‐friendly and highly recyclable catalyst for the one‐pot and multicomponent synthesis of 3,4‐dihydroquinoxalin‐2‐amine, diazepine‐tetrazole and benzodiazepine‐2‐carboxamide derivatives in aqueous media and at room temperature with high yields in short reaction times (40–60 min). The recoverable catalyst was easily recycled at least five times without any loss of catalytic activity. The structures of obtained products were confirmed using ¹H NMR and ¹³C NMR spectra.     

Superparamagnetic pH‐sensitive multilayer hybrid hollow microspheres for targeted controlled release

The superparamagnetic multilayer hybrid hollow microspheres have been fabricated using the layer‐by‐layer assembly technique by the electrostatic interaction between the polyelectrolyte cation chitosan (CS) and the hybrid anion citrate modified ferroferric oxide nanoparticles (Fe₃O₄‐CA) onto the sacrificial polystyrene sulfonate microspheres templates after etching the templates by dialysis. The saturation magnetization and magnetite contents of the superparamagnetic multilayer hybrid hollow microspheres were 32.46 emu/g and 51.3%, respectively. The hybrid hollow microspheres showed pH‐sensitive characteristics. The adsorption and release of the basic dye (methylene blue) were applied to investigate the interaction between the amino groups of CS and the carboxyl groups of the Fe₃O₄‐CA nanoparticles in different pH media. The superparamagnetic pH‐sensitive multilayer hybrid hollow microspheres are expected to be used for the targeted controlled release of drugs or in diagnostics. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3135–3144, 2010     

Chitosan-Polyoxometalate Nanocomposites: Synthesis,Characterization and Application as Antimicrobial Agents

Polyoxometalates (POMs) were used, together with chitosan (CS), to obtain hybrid nanoaggregates. Three representative POMs were efficiently assembled into nanoparticles of few hundred nm diameter, featuring entangled ribbons substructure. In order to establish suitable preparation and stability conditions, the assemblies were characterized in solution by UV–Vis spectroscopy, dynamic light scattering and ζ-potential. The nanoparticles were tested against E. coli (10⁶ CFU/ml) in aqueous solution, showing a synergic activity of the heteropolyacid H₅PMo₁₀V₂O₄₀ and CS. For such components, a highly porous and antibacterial film was obtained upon lyophilisation of the colloidal mixture.     

PEGylation of chitosan for improved solubility and fiber formation via electrospinning

PEG-N-chitosan and PEG-N,O-chitosan were synthesized via reductive amination and acylation of chitosan, respectively. The structures were confirmed by FTIR and H¹NMR. The extents of PEGylation increased with reducing chain lengths of either chitosan (M _v = 137–400 kDa) or poly(ethyelene glycol) (PEG, M _n = 500–2 kDa). Water solubility were easily achieved at degree of substitution (DS) as low as 0.2 for either derivtive whereas the PEG-N,O-chitosan at DS = 1.5 was soluble in organic solvents, including CHCl₃, DMF, DMSO and THF. None of the aqueous solutions of PEG-N-chitosan or PEG-N,O-chitosan alone could be electrospun into fibers. Electrospinning of PEG550-N,O-chitosan145 at 25% in DMF produced fibrous structure intermixed with beads. The efficiency of fiber formation and the uniformity of fibers were improved by increasing the solution viscosity using a cosolvent or reducing the solution surface tensions with a non-ionic surfactant. Ultra-fine fibers with diameters ranging from 40 nm to 360 nm and an average diameter of 162 nm were efficiently generated from electrospinning of 15% PEG550-N,O-chitosan145 in 75/25 (v/v) THF/DMF cosolvents with 0.5% Triton X-100^TM.