Nanosilver/hyperbranched polyester (HBPE): synthesis, characterization, and antibacterial activity

HBPE of different generations were synthesized using 4-hydroxybenzoic acid and 2,2′,2″-nitrilotriethanol via the A₂ + B₃ method. The reaction was carried out in a dry nitrogen atmosphere using p-toluene sulfonic acid (p-TSA) as an acid catalyst. The chosen molar ratios of 2,2′,2″-nitrilotriethanol to 4-hydroxybenzoic acid were 1:3, 1:6, and 1:21 for the G₁, G₂, and G₅ generations, respectively. The G₅ stage of HBPE was further coupled with acrylic acid to modify the terminal hydroxyl groups. The resulting products were analyzed using ¹H NMR, ¹³C NMR, FTIR spectroscopy, and GPC. Silver nanoparticles were prepared by a reductive technique using HBPEs of the G₅ generation as the matrix. XRD and TEM analysis indicated the formation of highly spherical and stable nanosilver in the HBPE. The antibacterial activity of the nanosilver/HBPE was evaluated against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria.     

Contribution a l'etude des complexes du cation cadmium (II) avec l'acide laćtique et l'acide malonique en milieu Na+(ClO−4)3M A 25°C

The potentiometric study of neutralisation at 25°C, in Na⁺ (ClO^?₄)3M medium, with NaOH as titrant, of solutions: Cd²⁺ cation-lactic acid (between neutralisation rate values 0 to 1); and of Cd²⁺ cation-malonic acid (between neutralisation rate values 1–2), allows consideration of the formation of mononuclear complexes with lactic acid, and mononuclear and polynuclear complexes with malonic acid.The interpretation of experimental data ph = f(x)_R induces one to suppose the existence of the following species: lactic acid: Cd(Lact)⁺, Cd(Lact)₂; malonic acid; Cd(Mal); Cd(Mal)^2?₂; Cd(Mal)^4?₃; Cd₂(Mal)₂; Cd₂(Mal)^2?₃.The constants of formation of those complexes have been determined by non-linear regression.     

Electrooxidation of acetaldehyde on platinum-modified Ti/Ru0.3Ti0.7O2 electrodes

In this study, the electrochemical oxidation of acetaldehyde was investigated at activated massive DSA^® electrodes in acid medium, using differential electrochemical mass spectrometry (DEMS) and high-performance liquid chromatography (HPLC). The electrodes were prepared either by platinum electrodeposition or by depositing a highly nanodispersive-supported catalyst (Pt and Pt-Ni) over electrode surfaces with a Ti/Ru_0.3Ti_0.7O₂ nominal composition. Bulk electrolysis shows evidence of CO₂ and acetic acid formation. The electrocatalytic efficiency of the electrode material was also investigated as a function of the amount of catalyst added over the DSA^® electrode surface. The presence of RuO₂-active sites on the DSA^® substrate plays an important role in the reaction overall efficiency. The addition of platinum to DSA^® enhances the oxidation of acetaldehyde to CO₂. The role of the substrate on the direct activation of acetaldehyde oxidation is discussed on the basis of the direct application of the metal nanoparticle catalyst over conductive oxide surface based on Magneli phase (mixture of Ti_nO_2n−1 and other phases) from Ebonex^®.     

Potential of the Pb,PbSO4/H2SO4 electrode at temperatures up to 240°C

Standard lead—lead sulphate electrode potential was determined over the temperature range 20–240°C from emf measurements of the Pb, PbSO₄H₂SO₄ (0.05M)K₂SO₄KClHCl(0.1M)/AgCl, Ag and Pb, PbSO₄H₂SO₄(m)K₂SO₄H₂SO₄(0.05M)PbSO₄, Pb cells where m = 0.005, 0.01, 0.1 and 0.5 M. To this effect lead—lead sulphate electrode potential was calculated using the temperature relationship of the standard silver—silver chloride electrode potential and activity coefficients of hydrochloric acid determined by Greeley et al. at temperatures up to 260°C. Diffusion potentials occurring at the phase boundaries in the cells under investigation were calculated using the Henderson's equation. Values of the standard lead—lead sulphate electrode potential were determined by extrapolation of the E°′ function to the zero ionic strength which was calculated using the second sulphuric acid dissociation constant determined by Lietzke et al. at temperatures up to 300°C. The standard electrode potential was described in the temperature range 20–240°C by the following relationship: E°_{Pb, PbSO4/SO^2?4}(V) = 0.040-0.00126T. A change in entropy ΔS° of the electrode reaction Pb + SO^2?₄ = PbSO₄ + 2e^? is constant in this temperature range and is ?243 JK^?1 mol^?1 (?1018 cal K^?1 mol^?1).     

A Cd/triazolate/carboxylate metal–organic framework with unprecedented (3,10)-connected topology based on tetranuclear clusters

Using 1,2,4-triazole and adipic acid as coligands, a novel three-dimensional metal–organic framework, namely {[Cd₄Cl(trz)₅(adi)]·H₂O}_n (1) (trz = 1,2,4-triazole, adi = adipic acid) was hydrothermally synthesized and characterized. The crystal structure reveals that three independent Cd(II) centers are linked via one μ₃-Cl and two μ₃-COO^? groups to form a unique [Cd₄Cl(CO₂)₂] tetranuclear cluster, which acts as a 10-connected node joining adjacent four tetranuclear subunits and six 3-connected trz nodes to give a novel (3,10)-connected topological net with the Schläfli symbol (4³)(4¹⁸6²⁵6²).     

Synthesis and characterization of LiNi1/3Mn1/3Co1/3O2 by wet-chemical method

A series of LiNi_1/3Mn_1/3Co_1/3O₂ samples with α-NaFeO₂ structure belonging to the D_3d⁵ space group were synthesized using tartaric acid as a chelating agent by wet-chemical method. Different acid to metal-ion ratios R have been used to investigate the effect of this parameter on the physical and electrochemical properties. We have characterized the reaction mechanism, the structure, and morphology of the powders by TGA, XRD, SEM and TEM imaging, completed by magnetic measurements, Raman scattering spectroscopy, and complex impedance experiments. We find that the LiNi_1/3Mn_1/3Co_1/3O₂ sintered at 900 °C for 15 h with an acid to metal-ion ratio R = 2 was the optimum condition for this synthesis. For this optimized sample, only 1.3% of nickel-ions occupied the 3b Wyckoff site of the lithium-ions sublattice. The electrochemical performance has been investigated using a coin-type cell containing Li metal as the anode. The electronic performance is correlated to the concentration of the Ni(3b) defects that increase the charge transfer resistance and reduce the lithium diffusion coefficient. The optimized cell delivered an initial discharge capacity of 172 mAh g⁻¹ in the cut-off voltage of 2.8-4.4 V, with a coulombic efficiency of 93.4%.     

Solvent-assisted molten salt process: A new route to synthesise α-Fe2O3/C nanocomposite and its electrochemical performance in lithium-ion batteries

Nanostructured α-Fe₂O₃ was synthesised by a simple molten salt process using FeCl₂·4H₂O as a starting material and LiNO₃-LiOH·H₂O-H₂O₂ as a eutectic mixture at 300 °C. To synthesise α-Fe₂O₃/C composite, both α-Fe₂O₃ and malic acid were dispersed together in toluene, where malic acid was used as a carbon source. The morphology and microstructure of both compounds were confirmed by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. Electrochemical testing, including constant current charge-discharge and cyclic voltammetry (CV), was carried out. The α-Fe₂O₃/C composite anode exhibited much better electrochemical performance than the bare α-Fe₂O₃. The discharge capacities of the composite were measured to be 2112 mAh g⁻¹ at C/2 after 100 cycles and 584 mAh g⁻¹ at 20 C after 10 cycles. The superior electrochemical performance of α-Fe₂O₃/C composite can be mainly attributed to the combined effects of the nanostructure, the carbon layering on the α-Fe₂O₃ nanoparticles, and the porous ultra-fine carbon matrix, where the three factors would contribute to provide high electronic conductivity, reduce the traverse time of electrons and lithium-ions, and could also prevent high volume expansion of the anode film during cycling. Our results indicate that the prepared α-Fe₂O₃/C nanocomposite is a very promising anode material for Li-ion power batteries.     

Synthesis of a novel polymeric surfactant by reductive N-alkylation of chitosan with 3-O-dodecyl-d-glucose

A novel chitosan-based polymeric surfactant, DG-chitosan, was prepared via reductive N-alkylation of chitosan with 3-O-dodecyl-d-glucose in acetate buffer (pH 4.3, 0.1 M)-methanol in the presence of sodium cyanoborohydride (NaBH₃CN). DG-chitosan was swelling in water, partly dissolvable in pyridine and DMF, and completely soluble in 0.1% aqueous acetic acid. ¹H and ¹³C NMR spectroscopic analyses in 2% acetic acid-d₄-methanol-d₄ together with elemental analysis showed the degree of substitution was 27%. Formation of polymeric micelles was observed by use of pyrene as a fluorescent probe, and the critical aggregation concentration (CAC) of DG-chitosan was marked equal to 28.1 mg/L.     

Homo- and copolymerization of 5-ethylidene-2-norbornene with ethylene by [2-C5Me4-4,6-Bu2C6H2O]TiCl2/AlBu3/Ph3CB(C6F5)4 catalyst system and epoxidation of the resulting copolymer

5-Ethylidene-2-norbornene (ENB) polymerization and copolymerization with ethylene (E) catalyzed by constrained geometry catalyst 2-tetramethylcyclopentadienyl-4,6-di-tert-butylphenoxytitanium dichloride (1) were studied in the presence of AlⁱBu₃ and Ph₃CB(C₆F₅)₄ (TIBA/B). The catalyst system shows moderate activity on the homopolymerization of ENB, and higher activity on the copolymerization of E/ENB under atmospheric pressure of ethylene. ¹H NMR analysis indicates that ENB was regioselectively incorporated into the copolymer backbone through the endocyclic double bond, leaving the ethylidene double bond unreacted. The ethylidene group contained in the poly(E-co-ENB) was quantitatively converted to the epoxy group with m-chloroperbenzoic acid, producing functionalized poly(E-co-ENB)s. The parent and functionalized copolymers have been characterized using IR, NMR, DSC, and GPC techniques.     

Improvement of the luminescence properties of CaTiO3:Pr obtained by modified solid-state reaction

Using tetra-n-butyl titanate and nitrates as starting materials, the red persistent phosphor CaTiO₃:Pr has been successfully synthesized by modified solid-state reaction. In order to improve the luminescent properties of the phosphor, boric acid as flux regent and aluminum ion as charge compensator were added in, and the influences of partially replacing Ca²⁺ in CaTiO₃ with Zn²⁺ or Mg²⁺ on the long persistent properties were studied. The results of luminescence spectrometer (PL), X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that a certain quantity of boric acid, Al³⁺, Mg²⁺ or Zn²⁺ was effective in improving the photoluminescence intensity of CaTiO₃:Pr phosphor particles, and the optimum molar ratios of Al³⁺ and boric acid to Ca²⁺ were about 0.1% and 30%, respectively. The photoluminescence brightness and decay curves showed that the sample of Ca_0.8Zn_0.2TiO₃:Pr with 0.l% Al³⁺ and 30% H₃BO₃ obtained at the sintering temperature of 900 °C exhibited the optimal luminescent properties.     

Electropolishing of NiTi shape memory alloys in methanolic H2SO4

The electropolishing of NiTi shape memory alloys was surveyed electrochemically. Anodic polarization of NiTi up to 8 V was performed in various aqueous and methanolic H₂SO₄ solutions. The passivity could be overcome in methanolic solutions with 0.1 mol dm−3≤CH₂SO₄≤7 mol dm−3. The dissolution kinetics was studied in dependence of the polarization potential, the H₂SO₄-concentration, the water concentration and the temperature. For lower concentrations of sulfuric acids (CH₂SO₄≤0.3 mol dm−3) electropolishing conditions were not observed for potentials up to 8 V. The dissolution remained under Ohmic control. In the concentration range from 1 to 7 mol dm⁻³ a potential independent limiting current was registered depending linearly on the logarithm of concentration. The best results were obtained with a 3 mol dm⁻³ methanolic sulfuric acid at 263 K which yielded an electropolishing current of 500 A m⁻² at a potential of 8 V. Surface roughness as well as current efficiency showed an optimum under these conditions.     

n-Dodecane Hydroconversion over Ni/AlMCM-41 Catalysts

Mesoporous aluminosilicate (AlMCM-41) samples were synthesized using various aluminum sources: Al(NO₃)₃, aluminum isoproxide (Al(OPr ⁱ )₃) and NaAlO₂. It was found that the AlMCM-41 prepared using NaAlO₂ contained more framework Al(IV) species and stronger acidity compared with those from Al(NO₃)₃ and Al(OPr ⁱ )₃, respectively. Supported with 2.0 wt% nickel metal, the Lewis acid sites of the AlMCM-41 samples increased due to the compensating effect of the coordinately unsaturated nickel cations, while the Bronsted acid sites slightly decreased because of the coverage of the nickel species. In the n-dodecane hydroconversion, the Ni-containing AlMCM-41 sample prepared by using NaAlO₂ gave the symmetrical carbon number distribution and the largest amount of C₄–C₉ hydrocarbons in the cracked products due to its proper balance between metal and acid functions.     

Electrochemical determination of acidity level and dissociation of formic acid/water mixtures as solvent

The autoprotolysis constant K_HS of formic acid/water mixtures as solvent has been calculated from acid-base potentiometric titration curves. A correlation of the acidity scale pK_HS of each medium versus pure water has been implemented owing to the Strehlow R⁰(H⁺) electrochemical redox function. The results show that formic acid/water mixtures are much more dissociated than pure water; such media are sufficiently dissociated to allow electrochemical measures without addition of an electrolyte. It has also been shown that for a same H⁺ concentration the activity of protons increases with formic acid concentration. For more than 80 wt.% of formic acid the acidity is sufficiently increased to locate the whole acidity scale pK_HS in the super acid medium of the generalized acidity scale pHH₂O.     

Microwave enhanced synthesis of chitosan-graft-polyacrylamide

Chitosan-graft-polyacrylamide (Ch-g-PAM) was synthesized without any radical initiator or catalyst using microwave (MW) irradiation. Under optimal grafting conditions, 169% grafting was observed at 80% MW power in 1.16 min. Conventionally under similar conditions a maximum grafting of 82% could be achieved in 1 h using K₂S₂O₈/ascorbic acid as redox initiator coupled with Ag⁺ ions as catalyst and atmospheric oxygen as co-catalyst on a thermostatic water bath at 35±0.2 °C. The representative microwave synthesized graft copolymer was characterized by Fourier transform-infrared spectroscopy, thermo gravimetric analysis and X-ray diffraction measurement, taking chitosan as a reference. The effects of reaction variables as monomer/chitosan concentration, MW power and exposure time on the graft co-polymerization were studied. A probable free radical mechanism for grafting under microwaves has been proposed. The solubility pH for the grafted samples with different extent of grafting was monitored. The adsorption capacity of chitosan was much enhanced after grafting. The microwave synthesized Ch-g-PAM in comparison to that prepared conventionally was found to have much more adsorption ability for Ca²⁺ and Zn²⁺ ions in aqueous solution.     

Partitioning of drug model compounds between poly(lactic acid)s and supercritical CO2 using quartz crystal microbalance as an in situ detector

Quartz crystal microbalance (QCM) was used as an in situ detector to investigate the potential application in the phase equilibrium determination of supercritical CO₂-drug-polymer systems. CO₂ solubility in two biodegradable polymers, poly(d,l-lactic acid) (d,l-PLA) and poly(l-lactic acid) (l-PLA) was primarily measured at 313.15 K and pressures up to 10.0 MPa. d,l-PLA showed a better CO₂ absorption ability due to its amorphous structure. Four drug model compounds of poor solubility in water, ibuprofen, aspirin, salicylic acid and naphthalene were selected as representatives for the examination of drug uptake in PLA matrices, as well as partition coefficient during supercritical impregnation. It was found that partition coefficients of drugs can reach as high as 10³-10⁴ orders of magnitude and greatly affected by the intermolecular interactions between drugs and PLA. Aspirin exhibited the best partitioning during the supercritical impregnation at pressures of 8.0-10.0 MPa due to the existence of carboxylic acid and acetyl groups. Drug partitioning is additionally related to the drug concentration in ScCO₂, i.e. salicylic acid showed little absorption in PLA according to its poor solubility in ScCO₂ at 7.5-8.0 MPa, whereas the well CO₂-soluble compound, naphthalene, exhibited a moderate partition coefficient although its polarity was different from l-PLA.     

The synthesis and characterization of functional poly(citraconic anhydride-co-styrene-co-vinylphosphonic acid)s

New functional terpolymers of citraconic anhydride (CA), styrene (S) and vinylphosphonic acid (VPA) were synthesized at different compositions by complex-radical ternary polymerization. Studied ternary acceptor-donor-acceptor system was described as a binary copolymerization of two monomer complexes of CA…S (1) and VPA…S (2). The monomer reactivity ratios of these complexes were determined by ¹H NMR analysis for monomer mixtures before and after reactions by modified Jaacks equations: r_I = r₁(K_c1/K_c2) = 1.99, r_II = r₂(K_c2/K_c1) = 0.16; r₁ = 18.59, r₂ = 0.018 (taking into account K_c for the corresponding monomer complexes). Copolymerization constants verify the fact that complexed monomer pairs have a tendency towards random copolymerization. Monomer unit compositions and characterizations of a series of poly(CA-co-S-co-VPA)s were investigated by FTIR, Raman, ¹H NMR, ¹³C NMR, DEPT-135, ³¹P NMR, GPC and thermal properties were investigated by TGA and DSC methods. Molecular weight and thermal stability increased with increasing VPA content in terpolymer. Dynamic mechanical properties were investigated by DMA and all terpolymers show typical viscoelastic behavior of an amorphous polymer. Solution properties were also studied by viscometry and titration.     

Structural, electrochemical and thermal properties of LiNi0.8−yTiyCo0.2O2 as cathode materials for lithium ion battery

Multiple substitution compounds with the formula LiNi_0.8−yTi_yCo_0.2O₂ (0≤y≤0.1) were synthesized by sol-gel method using citric acid as a chelating agent. The effects of titanium substitution on the structural, electrochemical and thermal properties of the cathode materials are investigated. A solid solution phase (R-3m) is observed in the range of 0≤y≤0.1 for the titanium-doped materials. X-ray photoelectron spectroscopy (XPS) shows that there are Ni³⁺, Ni²⁺, Co³⁺, Co²⁺ and Ti⁴⁺ five transition metal ions in titanium-doped materials. Rietveld refinement of X-ray diffraction (XRD) patterns indicates that titanium substitution changes the materials’ structure with different cationic distribution. An increase of the Ni/Co amount in the 3a Li site is found with the addition of titanium amount. An improved cycling performance is observed for titanium-doped cathode materials, which is interpreted to a significant suppression of phase transitions and lattice changes during cycling. The thermal stability of titanium-doped materials is also improved, which can be attributed to its lower oxidation ability and enhanced structural stability at delithiated state.     

Electrochemical oscillations of the system Hg,HSO−4, BrO−3 and phenol

The electrochemical oscillations of the system Hg, HSO^?₄, BrO^?₃ and phenol are described. These oscillations arise at the dme in the range of potentials from +0.06 V to +0.01 V against a potential of a 1.5 mol dm^?3 Hg/Hg₂SO₄ electrode in a solution of sulphuric acid, sodium bromate and phenol. The temporal change of the limiting current and that of surface-tension of mercury oscillate in an anodic, anodic—cathodic or cathodic range depending on the concentration of phenol and on the value of the dme potential. The probable mechanism is also discussed. This is based on the simultaneous electroreduction of bromate ions and the electro-oxidation of mercury as the surface-tension changes, produced by the film of Hg₂SO₄ and Hg₂Br₂ formation and by the adsorption of phenol and/or its oxidation products.     

Kinetics and PEMFC performance of RuxMoySez nanoparticles as a cathode catalyst

Kinetics of Ru_xMo_ySe_z nanoparticles dispersed on carbon powder was studied in 0.5 M H₂SO₄ electrolyte towards the oxygen reduction reaction (ORR) and as cathode catalysts for a proton exchange membrane fuel cell (PEMFC). Ru_xMo_ySe_z catalyst was synthesized by decarbonylation of transition-metal carbonyl compounds for 3 h in organic solvent. The powder was characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. Catalyst is composed of uniform agglomerates of nanocrystalline particles with an estimated composition of Ru₆Mo₁Se₃, embedded in an amorphous phase. The electrochemical activity was studied by rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. Tafel slopes for the ORR remain invariant with temperature at −0.116 V dec⁻¹ with an increase of the charge transfer coefficient in dα/dT = 1.6 × 10⁻³, attributed to an entropy turnover contribution to the electrocatalytic reaction. The effect of temperature on the ORR kinetics was analyzed resulting in an apparent activation energy of 45.6 ± 0.5 kJ mol⁻¹. The catalyst generates less than 2.5% hydrogen peroxide during oxygen reduction. The Ru_xMo_ySe_z nanoparticles dispersed on a carbon powder were tested as cathode electrocatalyst in a single fuel cell. The membrane-electrode assembly (MEA), included Nafion^® 112 as polymer electrolyte membrane and commercial carbon supported Pt (10 wt%Pt/C-Etek) as anode catalyst. It was found that the maximum performance achieved for the electro-reduction of oxygen was with a loading of 1.0 mg cm⁻² Ru_xMo_ySe_z 20 wt%/C, arriving to a power density of 240 mW cm⁻² at 0.3 V and 80 °C.     

Phase evolution,microstructure and chemical stability of Ca1-xZr1-xGd2xTi2O7 (0.0 ≤ x ≤ 1.0) system for immobilizing nuclear waste

In order to ascertain the structural relationship of zirconolite and pyrochlore for their potential application in HLW immobilization, the Gd-doped zirconolite-pyrochlore composite ceramics (Ca_1-xZr_1-xGd_2xTi₂O₇) were systematically synthesized with x?=?0.0–1.0 by traditional solid-phase reaction method. The phase evolution and microstructure of the as-prepared samples have been elucidated by XRD and Rietveld refinement, Raman spectroscopy, BSE-EDS and HRTEM analysis. The results showed that zirconolite-2M, zirconolite-4M, perovskite and pyrochlore, four phases were identified in Ca_1-xZr_1-xGd_2xTi₂O₇ system and could be coexisted at x?=?0.4 composition. With the increase of Gd³⁺ substitution, the phase evolution was followed by zirconolite-2M→zirconolite-4M→pyrochlore. It is illustrated that the phase transformation from zirconolite-2M to zirconolite-4M was promoted by the preferential substitution of Gd³⁺ for Ca²⁺. And the solubility of Gd³⁺ in zirconolite-2M, zirconolite-4M and pyrochlore increased in sequence. The chemical stability test was also measured by the PCT leaching method. The normalized elemental release rates of Ca, Zr, Ti and Gd in Ca_1-xZr_1-xGd_2xTi₂O₇ system were fairly low and in the range of 10^?6?10^?8 g?m^?2 d^?1, which indicated a potential ceramics composite ensemble of CaZrTi₂O₇-Gd₂Ti₂O₇ system for nuclear HLW immobilization.