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.     

Mesoporous structures in never-dried softwood cellulose fibers investigated by nitrogen adsorption

Nitrogen adsorption was used to characterize mesoporous structures in never-dried softwood cellulose fibers. Distinct inflections in desorption isotherms were observed over the relative vapor pressure (P/P₀) range of 0.5–0.42 for never-dried cellulose fibers and partially delignified softwood powders. The reduction in N₂ adsorption volume was attributed to cavitation of condensed N₂ present in mesopores formed via lignin removal from wood cell walls during delignification. The specific surface areas of significantly delignified softwood powders were ~150 m² g^?1, indicating that in wood cell walls 16 individual cellulose microfibrils, each 3–4 nm in width, form one cellulose fibril bundle surrounded with a thin layer of lignin and hemicelluloses. Analysis of N₂ adsorption isotherms indicates that mesopores in the softwood cellulose fibers and partially delignified softwood powders had peaks ranging from 4 to 20 nm in diameter.     

Influence of finishing oil on structure and properties of multi-filament fibers from cellulose dope in NaOH/urea aqueous solution

Cellulose multi-filament fibers have been spun successfully on a pilot plant scale, from a cellulose dope in 7 wt% NaOH/12 wt% urea aqueous solution pre-cooled to −12 °C. Coagulation was accomplished in a bath with 10 wt% H₂SO₄/12 wt% Na₂SO₄ and then 5 wt% H₂SO₄ aqueous solution. By using different finishing oil, including H₂O, 4% glycerol aqueous solution, 2% polyvinyl alcohol (PVA) aqueous solution, 2% polyethylene glycol octyl phenylether (OP) aqueous solution, mobol and 2%glycerol/1%PVA/1%OP aqueous solution (PGO), we prepared six kinds of the cellulose multi-filaments, with tensile strength of 1.7–2.1 cN/dtex. Their structure and properties were investigated with scanning electron microscope (SEM), ¹³C NMR solid state, wide-angle X-ray diffraction (WAXD) and tensile testing. The cellulose fibers treated with PGO possessed higher mechanical properties and better surface structure than others. Interestingly, although the orientation of the cellulose multi-filaments is relatively low, the tensile strength of the single-fiber was similar to that of Lyocell. It was worth noting that the dyeability of the multi-filament fibers was superior to viscose rayon.     

Effect of alkali metal salts on decomposition of ionic liquid like organic salt

N ¹,N ¹,N ²,N ²-tetramethylethane-1,2-diamine-based ionic salts (TMEDA), N ¹,N ¹,N ¹,N ²,N ²,N ²-hexamethylethane-1,2-diaminium dicyanamide (HMEDA-(DCA)₂) were prepared following the quaternization and subsequent ion exchange. The chemical structure of the HMEDA-(DCA)₂ was confirmed using ¹³C NMR spectrum and elemental analysis. The corresponding viscosity of its 60 wt% solution was found to be lower than 5 cP at room temperature, which was critical for propellant application. The ignition delay of 40 wt% HMEDA-(DCA)₂ solution was decreased to 20–30 ms dramatically using alkali metal salts, Li(CH₃COO), Mg(CH₃COO)₂, and Ca(CH₃COO)₂ as a co-catalyst when white fume nitric acid was utilized as an oxidizer.     

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.     

Proton-conducting membranes: poly (N-vinyl pyrrolidone) complexes with various ammonium salts

The present study focuses on the proton-conducting polymer electrolytes; poly (N-vinyl pyrrolidone)–ammonium thiocyanate and poly (N-vinyl pyrrolidone)–ammonium acetate prepared by solution casting technique. The XRD analysis indicates the amorphous nature of the polymer electrolytes. The Raman spectra of the C=O vibration of pure polymer PVP at 1,663 cm^?1 has been appeared as doublet in the polymer electrolytes. The introduction of this new peak in the salt-doped polymer electrolytes may be due to interaction of the cation with the polymer. The room temperature ionic conductivity σ _303κ has been found to be high, 1.7?×?10^?4 S cm^?1 for 80 mol% PVP–20 mol% NH₄SCN and 1.5?×?10^?6 S cm^?1 for 75 mol% PVP–25 mol% CH₃COONH₄. The polymer electrolytes have been tested for their application in Zn–air battery.     

Kinetics and mechanism of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) by N-bromosuccinimide in aqueous acidic medium

The kinetics of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) complex by N-bromosuccinimide (NBS) in aqueous acid and H₂O–MeOH solvent mixtures were studied spectrophotometrically over the 20–40 °C range, 0.1–0.5 mol dm^?3 ionic strength, 2.2–2.8 pH range and 0–40 wt% MeOH–H₂O solvent mixtures for a range of NBS and complex concentrations. The rate shows first-order dependence on both [NBS] and [complex] and decreases with pH over the range studied. The protonated form of N-bromosuccinimide was identified as the main reactive species. An inner-sphere mechanism involving free radicals is proposed.     

Kinetics of vapor nitration of cellulose

The kinetics of vapor nitration of cellulose with nitric anhydride at various pressures was studied under conditions of natural convection in the absence of air, using the nonisothermal kinetic method. The process rate was found to be proportional to the N₂O₅ pressure. The nitration is described by a law of the dη/dt =k ₁/(1+βν) type, wherek ₁ = 10^3.82±0.5 exp[-(36000±(RT)]p _{N 2}O₅ s^?1. β = 10^?7.33±1.4exp[(41300±8000)/(RT)] s^?1, s^?1, within the extents of conversion from 0.04 to 0.4. At high levels of conversion, the nitration occurs with autoacceleration caused by the accumulation of the HNO₃ formed. The diffusion mechanism of vapor nitration of cellulose was suggested and discussed. The values of the effective diffusion constant for N₂O₅ in cellulose and the corresponding activation energy (38.4±2.8 kJ mol^?1) have been estimated.     

Assembly of novel Tb3+/Eu3+ sensitized cellulose gels and their emission behaviors

In this paper, a novel luminescent hydrogel was successfully prepared by incorporating Tb-HSA (HSA = Human Serum Albumin) complex into cellulose host. The green luminescence intensities of Tb(III) exhibited on–off changes in terms of pH variation. At the same time, europium activated phosphor (GdVO₄:Eu³⁺) was immobilized into the cellulose hydrogels through two approaches. The photophysical properties of luminescent gels with the temperature variation were investigated by fluorescence. The new group of soft materials will display task-specific usages in sensing fields.     

Synthesis, characterization and degradability of the novel aliphatic polyester bearing pendant N-isopropylamide functional groups

The synthesis, characterization, and degradability of the novel aliphatic polyester bearing pendant N-isopropylamide functional group are reported for the first time. 2-(N-Isopropyl-2-carbamoylethyl)cyclohexanone (CCH) was first synthesized by the Michael reaction of N-isopropylacrylamide with cyclohexanone and was subsequently converted into 6-(N-isopropyl-2-carbamoylethyl)-?-caprolactone (CCL) by the Baeyer-Villiger oxidation reaction using 3-chloroperoxybenzoic acid (mCPBA) as the oxidant. Finally, the novel functionalized poly(?-caprolactone) bearing the pendant N-isopropylamide functional groups, poly(6-(N-isopropyl-2-carbamoylethyl)-?-caprolactone-co-?-caprolactone)s (poly(CCL-co-CL)), were carried out successfully by bulk ring-opening polymerization of CCL and ?-CL initiated by Sn(Oct)₂. Poly(CCL-co-CL) were characterized by ¹H NMR, ¹³C NMR, SEC and DSC. The copolymer containing 9.1 mol% CCL formed flexible films and was used to study its degradability. A phosphate buffer (pH = 7.4) with temperature 37 °C was adopted to proceed the degrading study all through. Compared with poly(?-caprolactone), the hydrolytic degradation of poly(CCL-co-CL) was much faster, which is confirmed by the weight loss and change of intrinsic viscosity.     

Preparation and characterization of luminescent cellulose–Y<Subscript>4</Subscript>Si<Subscript>2</Subscript>O<Subscript>7</Subscript>N<Subscript>2</Subscript>:Ce<Superscript>4+</Superscript> hybrid hydrogels

Novel luminescent bio-based hydrogels comprising cellulose and Y₄Si₂O₇N₂:Ce⁴⁺ (YC) were prepared in an alkali/urea aqueous system using epichlorohydrin as a cross-linker. The structure, characteristics and properties of the hydrogels were investigated by various techniques, including FTIR spectroscopy, wideangle X-ray diffraction, scanning electron microscopy, etc. The results showed that when the content of YC was less than 0.05 g, the YC particles were tightly embedded in the macro porous of cellulose matrix, which not only supplied cavities for YC immobilization, but also supplied the pore wall to protect the structure and character of YC. Hence, the cellulose–YC hybrid hydrogels exhibited strong cyan fluorescence under a UV lamp. However, excess of YC particles were enshrouded in the cellulose matrix resulted in smaller pores, weaker fluorescence intensity, lower swelling ratio and higher mechanical properties.     

Synthesis of antibacterial cellulose materials using a “clickable” quaternary ammonium compound

Development of advanced functional materials from naturally abundant polymers such as cellulose are of significant importance. Of particular interest is embedding antibacterial functionality to cellulose materials to make permanent antibacterial materials and devices. In the present research, a “clickable” quaternary ammonium compound, N-(2-ethoxy-2-oxoethyl)-N,N-dimethylprop-2yn-1-aminium bromide (EdMPABr) was synthesized via a simple reaction with nearly stoichiometric yield and well characterized with 1D (¹H, ¹³C) and 2D (COSY, HSQC) NMR and ATR-FTIR. EdMPABr can be covalently bonded to many molecules containing an azido group to form non-leaching antibacterial materials via the simple Cu(I)-catalyzed alkyne-azide [2 + 3] cycloaddition reaction. As an example, EdMPABr was attached to our previously reported 3-O-azidopropoxypoly(ethylene glycol)-2,6-di-O-thexyldimethylsilyl cellulose (3-N₃PEG-2,6-TDMS cellulose, DS = 0.54 at C3 determined by ¹H NMR). Significant antibacterial activity of the synthesized 3-O-quaternary ammonium-2,6-di-O-thexyldimethylsilyl cellulose (3-QA-2,6-TDMS cellulose, DS = 0.30 at C3 determined by using N content from elemental analysis) was confirmed by testing against the representative bacteria Escherichia coli. By linking the EdMPABr to the honeycomb film of 3-N₃PEG-2,6-TDMS cellulose, the formed honeycomb film exhibited both antibacterial and antifouling properties. This research provides a simple and robust route towards the development of permanent antibacterial materials and biomedical devices.     

Electrical, electrochemical, and thermomechanical properties of perovskite-type (La1?x Sr x )1?y Mn0.5Ti0.5O3?δ (x?=?0.15–0.75, y?=?0–0.05)

Strontium additions in (La_1?x Sr _x )_1?y Mn_0.5Ti_0.5O_3?δ (x?=?0.15–0.75, y?=?0–0.05) having a rhombohedrally distorted perovskite structure under oxidizing conditions lead to the unit cell volume contraction, whilst the total conductivity, thermal and chemical expansion, and steady-state oxygen permeation limited by surface exchange increase with increasing x. The oxygen partial pressure dependencies of the conductivity and Seebeck coefficient studied at 973–1223?K in the p(O₂) range from 10^?19 to 0.5?atm suggest a dominant role of electron hole hopping and relatively stable Mn³⁺ and Ti⁴⁺ states. Due to low oxygen nonstoichiometry essentially constant in oxidizing and moderately reducing environments and to strong coulombic interaction between Ti⁴⁺ cations and oxygen anions, the tracer diffusion coefficients measured by the ¹⁸O/¹⁶O isotopic exchange depth profile method with time-of-flight secondary-ion mass spectrometric analysis are lower compared to lanthanum–strontium manganites. The average thermal expansion coefficients determined by controlled-atmosphere dilatometry vary in the range 9.8–15.0?×?10^?6?K^?1 at 300–1370?K and oxygen pressures from 10^?21 to 0.21?atm. The anodic overpotentials of porous La_0.5Sr_0.5Mn_0.5Ti_0.5O_3?δ electrodes with Ce_0.8Gd_0.2O_2-δ interlayers, applied onto LaGaO₃-based solid electrolyte, are lower compared to (La_0.75Sr_0.25)_0.95Cr_0.5Mn_0.5O_3?δ when no metallic current-collecting layers are introduced. However, the polarization resistance is still high, ~2 Ω?×?cm² in humidified 10?% H₂–90?% N₂ atmosphere at 1073?K, in correlation with relatively low electronic conduction and isotopic exchange rates. The presence of H₂S traces in H₂-containing gas mixtures did not result in detectable decomposition of the perovskite phases.     

Homogeneous alkalization of cellulose in <Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide/water solution

Alkali cellulose is an important intermediate in the production of cellulose derivatives. N-methylmorpholine-N-oxide (NMMO)/H₂O was used as a homogeneous reaction medium for the cellulose alkalization process to intensify the alkalization degree and improve the substitution uniformity. The morphology, specific surface area and crystalline structure of pristine cellulose, the as-synthesized alkali cellulose and dissolved-regenerated cellulose were characterized by SEM, BET, XRD and FT-IR, respectively. The results showed that the homogeneous reaction medium not only offered a low mass transfer resistance, but also facilitated a disruption of the hydrogen bond in cellulose, thus resulting in the transformation of the cellulose structure from complicated stacking chains to simple glucose chains. The interior hydroxyl groups in the cellulose became accessible to the alkaline reagent NaOH to enhance the alkalization process for the increase in bonding alkali content and the improvement in substitution uniformity. The bonding alkali content was calculated by the difference between total added alkali and free alkali and was achieved as 0.61 g/g cellulose at the optimized operation conditions: reaction temperature of 95 °C, reaction time of 90 min, NMMO dosage of 90.00 g, cellulose 1.0 g and NaOH concentration of 1.40 wt%. Meanwhile, in the conventional alkalization process, the bonding alkali content was just 0.41 g/g cellulose. The alkali cellulose prepared in NMMO/H₂O medium has a large specific surface area of 125 m² g^?1 and an extremely low crystallinity degree. The NMMO/H₂O system represents a potential homogeneous solvent for the cellulose alkalization process.     

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.     

Crystal growth kinetics of Sb2S3 in Ge–Sb–S amorphous thin films

Sb₂S₃ crystal growth kinetics in (GeS₂) _x (Sb₂S₃)_1?Cx thin films (x?=?0.4 and 0.5) have been investigated through this study by optical microscopy in the temperature range of 575?C623?K. Relative complex crystalline structures composed of submicrometer-thin Sb₂S₃ crystal fibers develop linearly with time. The data on temperature dependence of crystal growth rate exhibit an exponential behavior. Corresponding activation energies were found to be E _G?=?279?±?7?kJ?mol^?1 for x?=?0.4 and E _G?=?255?±?5?kJ?mol^?1 for x?=?0.5. These values are similar to activation energies of crystal growth in bulk glasses of the same compositions. The crystal growth is controlled by liquid?Ccrystal interface kinetics. It seems that the 2D surface-nucleated growth is operative in this particular case. The calculated crystal growth rate for this model is in good agreement with experimental data. The crystal growth kinetic characteristic is similar for both the bulk glass and thin film for x?=?0.4 composition. However, it differs considerably for x?=?0.5 composition. Thermodynamic and kinetic aspects of crystal growth are discussed in terms of Jackson??s theory of liquid?Ccrystal interface.     

Hybrid materials of SBA-16 functionalized by rare earth (Eu, Tb) complexes of modified β-diketone (TTA and DBM): Covalently bonding assembly and photophysical properties

Novel mesoporous SBA-16 type of hybrids TTA-S16 and DBM-S16 were synthesized by co-condensation of modified β-diketone (TTA-Si and DBM-Si, DBM=1,3-diphenyl-1,3- propanepione, TTA=2-thenoyltrifluoroacetone) and tetraethoxysilane (TEOS) in the presence of Pluronic F127 as template, which were confirmed by FTIR, XRD, ²⁹Si CP-MAS NMR, and N₂ adsorption measurements. Novel organic-inorganic mesoporous luminescent hybrid containing RE³⁺ (Eu³⁺, Tb³⁺) complexes covalently attached to the functionalized ordered mesoporous SBA-16 (TTA-S16 and DBM-S16), which were designated as bpy-RE-TTA-S16 and bpy-RE-DBM-S16, were obtained by sol-gel process. The luminescence properties of these resulting materials were characterized in detail, and the results reveal that mesoporous hybrid material bpy-Eu-TTA-S16 present stronger luminescent intensities, longer lifetimes, and higher luminescent quantum efficiencies than the corresponding DBM-containing materials bpy-Eu-DBM-S16, while bpy-Tb-DBM-S16 exhibit the stronger characteristic emission of Tb³⁺ and longer lifetime than the corresponding TTA-containing materials bpy-Tb-TTA-S16.     

Determination of the optimum Eu3+-concentration in LaAlO3:Euphosphors by X-ray diffraction and fluorescence measurements

Combining X-ray powder diffraction with fluorescence measurements is an efficient way to determine the optimum activator concentration of inorganic phosphors. La_1?xEu_xAlO₃ samples (perowskite structure), prepared by solid state reactions with 0.5<x<5.0 at 1480 K, were investigated by both analytical methods. The luminescence emission spectra show strong ⁵D₀-⁷F₁ and ⁵D₀-⁷D₂ transitions and fluorescence intensity reaches a maximum at 1 mol% Eu³⁺. X-ray diffraction shows the formation of an EuAlO₃ phase at Eu³⁺ concentration above 1 mol%. Below 1 mol%, Eu³⁺ substitutes for La³⁺, as can be seen from the change in the lattice constant c.     

Synthesis and magnetic properties of Cu0.5Fe0.5 ? x In x Cr2S4 (x = 0?0.4) solid solutions

Multistep synthesis with X-ray diffraction monitoring of the phase composition has been carried out, optimal synthesis parameters have been determined, and the magnetic properties of solid solutions between thiospinels with ordered tetrahedral A lattices (ferrimagnet Cu_0.5Fe_0.5Cr₂S₄ (T _C = 347 K) and anti-ferromagnet Cu_0.5In_0.5Cr₂S₄ (T _N = 35 K) have been studied. Both compounds crystallize in F $\bar 4$ 3m (T _d ² ) structure. Measurements over wide ranges of fields (0.05?C40 kOe) and temperatures (5?C300 K) highlighted the nature of magnetism in the samples; new magnetic species have been discovered.     

Preparation, morphology, and luminescent properties of europium-doped nanodispersed scandium sesquioxide

Scandium sesquioxide-based solid solutions of composition Sc_{2 ? 2x} Eu_2x O₃ (0.005 ?? x ?? 0.05) were prepared by thermolysis of Sc_{1 ? x} Eu _x (CH₃COO)₃ and by reacting mixtures of scandium and europium nitrates with ethylene glycol. Thermal decomposition of Sc_{1 ? x} Eu _x (CH₃COO)₃ was found to yield Sc_{2 ? 2x} Eu_2x O₃ with the shapes of aggregates atypical of the cubic structure of this oxide, and the reaction products of scandium and europium nitrates were found to have a loose spongelike structure. A spectroscopic study showed that Sc_{2 ? 2x} Eu_2x O₃ and Sc_{1 ? x} Eu _x (CH₃COO)₃ are potential luminescent materials active in the visible spectral region. The tervalent europium in the Sc_{2 ? 2x} Eu_2x O₃ structure is the source of strong red emission (⁵ D ₀ ?? ⁷ F ₂) and can be used in fluorescent lamps, colored lightning, and optoelectronic devices.