Luminescent cellulose fibers activated by Eu3+-doped nanoparticles

UV- active cellulose fibers were obtained by dry-wet method spinning an 8?% by weight α-cellulose solution in N-methylomorpholine-N-oxide (NMMO) modified by europium-doped gadolinium oxyfluoride Gd₄O₃F₆:Eu³⁺ containing 5?mol (%) of the dopant. Photoluminescent nanoparticles were introduced in the in powder form into a polymer matrix during the process of cellulose dissolution in NMMO. The dependencies of emission intensity on excitation energy and the concentration of Gd₄O₃F₆:Eu³⁺ nanoparticles in the final cellulosic products were examined by photoluminescence spectroscopy (excitation and emission). The fiber structure was studied by X-ray powder diffraction analysis. The size and dispersity of the nanoparticles in the polymer matrix were evaluated using scanning electron microscopy and X-ray microanalysis. The influence of different concentration particles (in the range from 0.5 to 5?% by weight) on the mechanical properties of the fibers, such as tenacity and elongation at break, were determined.     

Preparation,characterization and catalytic activity of biomaterial-supported copper nanoparticles

Synthesis of copper nanoparticles was carried out with nanocrystalline cellulose (NCC) as a support by reducing CuSO₄·5H₂O ions using hydrazine. Ascorbic acid and aqueous NaOH were also used as an antioxidant and pH controller, respectively. The synthesized copper nanoparticles supported on NCC (CuNPs@NCC) were characterized by UV–vis, XRD, TEM, XRF, TGA, DSC, N₂ adsorption-desorption method at 77 K and FTIR. The UV–vis confirmed the formation and stability of the CuNPs, which indicated that the maximum absorbance of CuNPs@NCC was at 590 nm due to the surface plasmon absorption of CuNPs. Morphological characterization clearly showed the formation of a spherical structure of the CuNPs with the mean diameter and standard deviation of 2.71 ± 1.12 nm. Similarly, XRD showed that the synthesized CuNPs@NCC was of high purity. The thermal analysis showed that the CuNPs@NCC exhibited better thermal behaviors than NCC. BET surface area revealed that the N₂ adsorption–desorption isotherms of CuNPs@NCC featured a type IV isotherm with an H3 hysterisis loop. This chemical method is simple, cost effective, and environmentally friendly. Compared to NCC-supported CuNPs and unsupported CuNPs, the as-prepared CuNPs@NCC exhibit a superior catalytic activity and high sustainability for the reduction of methylene blue with NaBH₄ in aqueous solution at room temperature. The CuNPs@NCC achieved complete reduction of MB with completion time, rate constant and correlation coefficient (R ²) of 12 min, 0.7421 min^?1 and 0.9922, respectively.     

Cellulose fibers modified by Eu3+-doped yttria-stabilized zirconia nanoparticles

This paper describes a method for manufacturing luminescent cellulose fibers. Good optical properties of cellulose fibers under UV-C illumination were achieved by incorporating ZrO₂ (0.5?mol% of Eu³⁺) stabilized by Y₂O₃ (7?mol%) into the fiber structure’s particles. Fibers were obtained from 8?wt% cellulose solution in N-methylmorpholine N-oxide (NMMO) with the addition of a luminescent modifier in the range between 0.5 and 10?wt%. The physico-chemical and mechanical parameters and the structure of these fibers were examined.     

Rheological properties of mixed solutions of cellulose and layered aluminosilicates in N-methylmorpholine-N-oxide

The structure and rheological behavior of cellulose solutions in the high-polarity donor solvent N-methylmorpholine-N-oxide containing particles of layered aluminosilicates of various natures, namely, natural hydrophilic montmorillonite (Cloisite Na⁺) and hydrophobized montmorillonite (Cloisite 20A), are studied. The rheological properties of the mixed systems cellulose-N-methylmorpholine-N-oxide-Cloisite Na⁺ and cellulose-N-methylmorpholine-N-oxide-Cloisite 20A are similar, although their structures are different. This similarity may be explained by the fact that the highly developed structure of the cellulose matrix phase resulting from strong interactions between polar components of the system exerts the decisive effect on the character of flow of mixed solutions. Therefore, the filler assumes the minor role. The concentration dependences of solution viscosity turn out to be atypical when the content of moisture in Cloisite 20A is increased above the equilibrium value and when M₂Cloisite Na⁺ nanoparticles modified in a certain manner are introduced into cellulose solutions.     

Sonochemical Synthesis of Spherical Silica Nanoparticles and Polymeric Nanocomposites

In this work spherical SiO₂ nanoparticles were synthesized by sonochemical method using a new Schiff-base as a capping agent. The silica nanoparticles were obtained by hydrolysis of tetraethyl orthosilicate in aqueous alcohol solution. The effect of different parameters such as molar concentration of Schiff-base ligands and ultrasonic irradiation on the morphology and size of the products was examined. The results demonstrated that applying the appropriate amount of Schiff-base could be effective in control of particle size. The influence of SiO₂ nanostructures on the flame retardancy of the poly styrene, poly vinyl alcohol, cellulose acetate and ethyl cellulose was studied. In-situ and ex situ nanocomposites were investigated and results confirm that flame retardancy of in situ nanocomposites were better than ex situ samples. HO···Si–O–Si···OH barrier prevents reaching of flame, heat and oxygen to the polymeric nanocomposites.     

Rapid dissolution of spruce cellulose in H<Subscript>2</Subscript>SO<Subscript>4</Subscript> aqueous solution at low temperature

Dissolution of cellulose is the key challenge in its applications. It has been discovered that spruce cellulose with high molecular weight (4.10 × 10⁵ g mol^?1) can be dissolved in 64 wt% H₂SO₄ aqueous solution at low temperature within 2 min, and the cellulose concentration in solution can reach as high as 5 % (w/v). FT-IR spectra and XRD spectra proved that it is a direct solvent for cellulose rather than a derivative aqueous solution system. The cold H₂SO₄ aqueous solution broke the hydrogen bonds among cellulose molecules and the low temperature dramatically slowed down the hydrolysis, which led to the dissolution of cellulose. The resultant cellulose solution was relatively stable, and the molecular weight of cellulose only slightly decreased after storage at ?20 °C for 1 h. Due to the high molecular weight of cellulose, cellulose solution could form regenerated films with good mechanical properties and transparency at low concentration (2 % w/v). This work has not only provided the new evidence of cellulose dissolution which facilitated the development of cellulose solvent, but also suggested a convenient way to directly transfer cellulose with high molecular weight into materials without structure modifications.     

Novel Approaches to Metallization of Cellulose by Reduction of Cellulose-Incorporated Copper and Nickel Ions

Summary: Copper and nickel nanoparticles were synthesized in the insoluble microcrystalline cellulose support by reduction of metal ions with several reducers in various media resulting in cellulose-metal nanocomposites. Wide-angle X-ray scattering results showed that supramolecular structure of cellulose did not change. Crystalline Cu₂O and Cu⁰ nanoparticles were prepared with reducers NaBH₄ and N₂H₄ · H₂SO₄, CuO nanoparticles – with cellulose itself as a reducer. Crystalline Ni⁰ nanoparticles were synthesized with N₂H₄ · 2HCl and NaBH₄; Ni⁰ nanoparticles in amorphous form were prepared with KH₂PO₂ · H₂O. SEM revealed large agglomerates of metal particles on the fibre surface. ASAXS and TEM have shown the nanoparticles to be in the range 5–55 nm.     

Acid-catalysed hydrolysis of N-sulphonyl sulphilimines—II

The basicity and the acid-catalysed hydrolysis of ph(R)SNTs and o-HC₆H₄(Me)SNTs sulphilimines have been studied by UV spectrophotometric and kinetic methods, respectively, in aqueous HClO₄ (1–10 M) and 1:1 (v/v) EtOH/H₂O-HClO₄ (0.5–6 M). Depending on the constitution of the substrates, sulphilimine hydrolysis can follow three different courses, according to rate-acidity profiles, Bunnett-Olsen's treatment, activation parameters and product analysis. Most typical for sulphilimines is S_N2 hydrolysis with S^IV-N bond cleavage. In this case the reaction starts with the nucleophilic addition of water and is promoted by acid-base catalysis. If a relatively stable carbenium ion can be formed from R group, an S_N1 reaction with S^IVC bond cleavage takes place. Sulphilimine with X = o-CO₂H due to neighbouring-group participation hydrolyses very rapidly via acyloxy-sulphurane and acyloxy-sulphonium ion intermediates with five-memembered ring (S_Ni reaction involving S^IVN bond cleavage).     

NMR spectroscopic studies on dissolution of softwood pulp with enhanced reactivity

N-methylmorpholine N-oxide (NMMO) is a known cellulose solvent used in industrial scale (LyoCel process). We have studied interactions between pretreated softwood pulp fibers and aqueous NMMO using nuclear magnetic resonance (NMR) spectroscopic methods, including solid state cross polarisation magic angle spinning (CP-MAS) ¹³C and ¹⁵N spectroscopies, and ¹H high resolution MAS NMR spectroscopy. Changes in both cellulose morphology and in accessibility of solvents were observed after the pulp samples that were exposed to solvent species were treated at elevated temperature. Evidence about interactions between cellulose and solvent components was observed already after a heat treatment of 15 min. The crystalline structure of cellulose was seen to remain intact for the first 30 min of heat treatment, at the same time there was a re-distribution of solvent species taking place. After a 90 min heat treatment the crystalline structure of cellulose had experienced major changes, and potential signs of regeneration into cellulose II were observed.     

Dissolution and regeneration of cellulose in NaOH/thiourea aqueous solution

A novel cellulose solvent, 1.5 M NaOH/0.65 M thiourea aqueous solution, was used to dissolve cotton linters having a molecular weight of 10.1 × 10⁴ to prepare cellulose solution. Regenerated cellulose (RC) films were obtained from the cellulose solution by coagulating with sulfuric acid (H₂SO₄) aqueous solution with a concentration from 2 to 30 wt %. Solubility of cellulose, structure, and mechanical properties of the RC films were examined by infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, ¹³C NMR, and tensile tests. ¹³C NMR analysis indicated that the novel solvent of cellulose is a nonderivative aqueous solution system. The presence of thiourea enhanced significantly the solubility of cellulose in NaOH aqueous solution and reduced the formation of cellulose gel; as a result, thiourea prevented the association between cellulose molecules, leading to the solvation of cellulose. The RC film obtained by coagulating with 5 wt % H₂SO₄ aqueous solution for 5 min exhibited higher mechanical properties than that with other H₂SO₄ concentrations and a homogenous porous structure with a mean pore size of 186 nm for free surface in the wet state. The RC film plasticized with 10% glycerin for 5 min had a tensile strength of 107 MPa and breaking elongation of 10%, and about 1% glycerin in the RC film plays an important role in the enhancement of the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1521–1529, 2002     

Transparent and flame retardant cellulose/aluminum hydroxide nanocomposite aerogels

Cellulose-based nanocomposite aerogels were prepared by incorporation of aluminum hydroxide (AH) nanoparticles into cellulose gels via in-situ sol-gel synthesis and following supercritical CO₂ drying. The structure and properties of cellulose/AH nanocomposite aerogels were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, ultraviolet-visible spectrometry, N₂ adsorption, thermogravimetric analysis, and micro-scale combustion calorimetry. The results indicated that the AH nanoparticles were homogeneously distributed within matrix, and the presence of AH nanoparticles did not affect the homogeneous nanoporous structure and morphology of regenerated cellulose aerogels prepared from 1-allyl-3-methylimidazolium chloride solution. The resultant nanocomposite aerogels exhibited good transparency and excellent mechanical properties. Moreover, the incorporation of AH was found to significantly decrease the flammability of cellulose aerogels. Therefore, this work provides a facile method to prepare transparent and flame retardant cellulose-based nanocomposite aerogels, which may have great potential in the application of building materials.     

Synthesis and acid catalysis of cellulose-derived carbon-based solid acid

SO₃H-bearing amorphous carbon, prepared by partial carbonization of cellulose followed by sulfonation in fuming H₂SO₄, was applied as a solid catalyst for the acid-catalyzed hydrolysis of β-1,4 glucan, including cellobiose and crystalline cellulose. Structural analyses revealed that the resulting carbon material consists of graphene sheets with 1.5 mmol g^?1 of SO₃H groups, 0.4 mmol g^?1 of COOH, and 5.6 mmol g^?1 of phenolic OH groups. The carbon catalyst showed high catalytic activity for the hydrolysis of β-1,4 glycosidic bonds in both cellobiose and crystalline cellulose. Pure crystalline cellulose was not hydrolyzed by conventional strong solid Brønsted acid catalysts such as niobic acid, Nafion^® NR-50, and Amberlyst-15, whereas the carbon catalyst efficiently hydrolyzes cellulose into water-soluble saccharides. The catalytic performance of the carbon catalyst is due to the large adsorption capacity for hydrophilic reactants and the adsorption ability of β-1,4 glucan, which is not adsorbed to other solid acids.     

Blend membranes from cellulose/konjac glucomannan cuprammonium solution

The blend membranes were prepared from cellulose/konjac glucomannan (KGM) cuprammonium solution by coagulating with aqueous 10 wt% NaOH solution, 20°C and 40°C water, respectively. Miscibility, pore morphology, structure, water permeability and mechanical properties of the blend membranes were investigated. The complex forms of cellulose/KGM in the mixed solutions, the effect of various coagulants and the percent content of KGM (w_KGM) on the structure and properties of the blend membrane are discussed. SEM and mechanical relaxation analysis indicate that the blend membranes are miscible in the range of 0–30 wt% of w_KGM. When w_KGM was smaller than 20 wt%, the tensil strength of the blend membrane coagulated by alkali aqueous solution was enhanced, corresponding to homogeneous structure and small pore size. However, blend membranes having a larger pore size (366 nm by SEM) and water permeability (560 ml/m² h mmHg) were obtained by coagulating the cellulose/KGM (70:30) cuprammonium solution with 40°C water, where ca. 20% of KGM as pore former were removed from the membrane.     

Microwave hydrothermal synthesis,characterisation, and catalytic performance of Zn1−x Mn x O in cellulose conversion

Wurtzite-type Zn_1?x Mn _x O (x = 0, 0.03, 0.05, 0.07) nanostructures were successfully synthesised using a simple microwave-assisted hydrothermal route and their catalytic properties were investigated in the cellulose conversion. The morphology of the nanocatalysts is dopant-dependent. Pure ZnO presented multi-plate morphology with a flower-like shape of nanometric sizes, while the Zn_0.97Mn_0.03O sample is formed by nanoplates with the presence of spherical nanoparticles; the Zn_0.95Mn_0.05O and Zn_0.93Mn_0.07O samples are mainly formed by nanorods with the presence of a small quantity of spherical nanoparticles. The catalyst without Mn did not show any catalytic activity in the cellulose conversion. The Mn doping promoted an increase in the density of weak acid sites which, according to the catalytic results, favoured promotion of the reaction.     

Synthesis of Ordered Porous Graphitic‐C3N4 and Regularly Arranged Ta3N5 Nanoparticles by Using Self‐Assembled Silica Nanospheres as a Primary Template

Uniform‐sized silica nanospheres (SNSs) assembled into close‐packed structures were used as a primary template for ordered porous graphitic carbon nitride (g‐C₃N₄), which was subsequently used as a hard template to generate regularly arranged Ta₃N₅ nanoparticles of well‐controlled size. Inverse opal g‐C₃N₄ structures with the uniform pore size of 20–80 nm were synthesized by polymerization of cyanamide and subsequent dissolution of the SNSs with an aqueous HF solution. Back‐filling of the C₃N₄ pores with tantalum precursors, followed by nitridation in an NH₃ flow gave regularly arranged, crystalline Ta₃N₅ nanoparticles that are connected with each other. The surface areas of the Ta₃N₅ samples were as high as 60 m² g⁻¹, and their particle size was tunable from 20 to 80 nm, which reflects the pore size of g‐C₃N₄. Polycrystalline hollow nanoparticles of Ta₃N₅ were also obtained by infiltration of a reduced amount of the tantalum source into the g‐C₃N₄ template. An improved photocatalytic activity for H₂ evolution on the assembly of the Ta₃N₅ nanoparticles under visible‐light irradiation was attained as compared with that on a conventional Ta₃N₅ bulk material with low surface area.     

Drying of a cellulose II gel: effect of physical modification and redispersibility in water

The agglomeration of cellulosic materials upon drying, often called hornification, causes a reduction of water retention, among other undesired effects. It is one of the main issues in industrial cellulose processing, especially with regard to nanocelluloses. As a consequence, high transportation and storage costs arise since nanocelluloses need to remain in aqueous suspensions unless trade-offs in reactivity, redispersibility and surface properties are accepted. In this study, different drying strategies for TENCEL^® gel, a nanostructured gel derived from the Lyocell process consisting of spherical particles, are compared and evaluated. First, freeze-drying with consideration of the influence of freezing temperature and the use of tert-butanol as cryo-protectant, and second, simple oven-drying at 60 °C. Surprisingly, oven-dried xerogels showed higher water retention values and also better colloidal stability than the cryogels. This is in stark contrast to cellulose nanofibrils for which freeze-drying has been shown to be significantly superior to oven drying in terms of redispersibility. For the TENCEL^® gel, oven-drying was thus selected and the influence of additives on the redispersibility of the cellulose II gel was studied by means of the common water retention value, particle size, colloidal stability, appearance of the redispersed gel and viscosity. The addition of the polysaccharides carboxymethyl cellulose or xanthan showed the most promising results with regard to redispersibility. Also sucrose and ammonium bicarbonate provided higher colloidal stabilities than that of the untreated TENCEL^® gel. The redispersibility of the cellulose II xerogels could thus be significantly improved by simple and cost-efficient mixing with additives prior to drying.     

Amadori ketoses with calcium hydroxide and the Kiliani reaction on 1-deoxy ketoses: two approaches to the synthesis of saccharinic acids

Saccharinic acids (2-C-methyl aldonic acids) may be formed by treatment of Amadori ketoses with calcium hydroxide or by the Kiliani reaction of 1-deoxy ketoses with cyanide. Thus (i) N,N-dibenzyl or N,N-dimethyl-1-amino-1-deoxy-d-fructose with aqueous calcium hydroxide afforded 2-C-methyl-d-ribono-1,4-lactone under green conditions and (ii) reaction of methyl magnesium bromide with 2,3-O-isopropylidene-d-erythronolactone gave 1-deoxy-3,4-O-isopropylidene-d-ribulose, which on subsequent treatment with aqueous sodium cyanide and hydrolysis, formed 2-C-methyl-d-arabinono-1,4-lactone. Such branched sugar lactones are likely to be of value as chirons containing branched carbon chains.     

Antiinflammatory polymer-bound steroids for topical applications II. Controlled release of the steroids

The release of hydrocortisone and dexamethasone due to hydrolysis of the carbonate linkage from the polymeric supports of poly(oxyethyleneglycol), hydroxypropyl cellulose, and N-vinylpyrrolidone/hydrocortisone–²¹CH₂–vinylcarbonate copolymer was observed in a living system, by induction of αGPDH activity in rat C6 glial cells, and in vitro by a kinetic study of release in aqueous sodium phosphate buffer medium. The glucocorticoid release is pH and temperature dependent and highly sensitive to steric hindrance. In vivo testing on antiinflammatory activity in rats with poly(oxyethyleneglycol) and hydroxypropyl cellulose bound dexamethasone was performed. However, it produced negative results probably due to difficulty in splitting the carbonate linkage in the inflammatory region of acidic pH values.     

Bis(N-benzyl-N-furfuryldithiocarbamato-S,S′)mercury(II) as a precursor for the preparation of mercury sulfide nanoparticles

Bis(N-benzyl-N-furfuryldithiocarbamato-S,S′)mercury(II), [Hg(bzfdtc)₂] (1) and bis(N,N-difurfuryldithiocarbamato-S,S′)mercury(II), [Hg(dfdtc)₂] (2) were synthesized and characterized by IR, NMR and single-crystal X-ray crystallography. Single-crystal X-ray structures of 1 and 2 indicate that both complexes are dimeric, with each mercury in a distorted [HgS₅] square pyramidal geometry. The thioureide (N¹³CS₂) carbon signals were observed at 206.8 and 206.7 ppm for 1 and 2, respectively, with very weak intensity, characteristic of the quaternary carbon signal. Complex 1 has been used as a precursor for the preparation of HgS nanoparticles. The as-prepared HgS nanoparticles have been characterized by powder XRD, FESEM, EDAX, UV–visible and IR spectroscopies. FESEM images of HgS nanoparticles show that the particles are spherical in shape. The blue shift in the absorption maxima in the UV–visible spectra of HgS1 and HgS2 is a consequence of the quantum confinement effect.     

Fluorous dimethylthiocarbamate (DMTC) protecting groups for alcohols

N,N-Bis(perfluoroalkyl)thiocarbamoyl chlorides (^FDMTC-Cls) were synthesized as reagent for the protection of alcohols. Using the crystalline ^FDMTC-Cls, the ^FDMTC groups were introduced into the alcohol molecules in excellent yields in the presence of sodium hydride in THF at room temperature. The products were separated from the excess alcohols by solid-phase extraction with a fluorous reverse-phase silica gel column (Fluorous Solid Phase Extraction; FSPE). The ^FDMTC groups were readily removed by oxidation with m-chloroperbenzoic acid (m-CPBA) and subsequent hydrolysis with KHCO₃.