Integration of wood-based components - Cellulose nanofibrils and tannic acid - into a poly(vinyl alcohol) matrix to improve functional properties.

Poly(vinyl alcohol) (PVA) biocomposite films reinforced with cellulose nanofibrils (CNF) and biologically active tannic acid (TA) were prepared. The influence of different concentrations of CNF and TA in the PVA polymer matrix was investigated in terms of mechanical properties, thermal properties and hydrophobicity improvement of the prepared films. The results showed that in all cases the addition of CNF and TA improved the values of tensile strength and elastic modulus. The PVA film with 10 % CNF exhibited a 30 % higher tensile strength, and the three-component PVA film with 2 % CNF and 10 % TA (P2C10T) exhibited a 40 % higher tensile strength compared to the neat PVA film. The thermal properties (Tg, Tonset) of the PVA biocomposite films were greatly improved, with a significant effect observed for the three-component PVA films. The Tg of the PVA film with 10 % CNF and 10 % TA was 87 °C, 12 °C higher than that of the neat PVA film. For three-component PVA biocomposites with 4 % and 6 % CNF and with all weight percentages of TA, the Tonset shifted to a higher temperature range by about 30 °C compared to the neat PVA film. The PVA film with 2 % CNF and 10 % TA exhibited about a 20° higher contact angle than the neat PVA film. Moreover, the addition of both fillers to the PVA matrix resulted in PVA biocomposites with lower water absorption. PVA film with 10 % TA absorbed about 90 % less water and PVA film with 10 % CNF and 10 % TA absorbed about 80 % less water than the neat PVA film after the films were soaked in water for one hour. The better properties of the composite films produced are due to hydrogen and ester bonds between the components of the composite, which was confirmed by FT-IR spectroscopy. Antioxidant effective films were also obtained due to the biologically active TA to the PVA and PVA/CNF systems.

The Role of Cerium Valence in the Conversion Temperature of H2Ti3O7 Nanoribbons to TiO2-B and Anatase Nanoribbons, and Further to Rutile.

CeO2-TiO2 is an important mixed oxide due to its catalytic properties, particularly in heterogeneous photocatalysis. This study presents a straightforward method to obtain 1D TiO2 nanostructures decorated with CeO2 nanoparticles at the surface. As the precursor, we used H2Ti3O7 nanoribbons prepared from sodium titanate nanoribbons by ion exchange. Two cerium sources with an oxidation state of +3 and +4 were used to obtain mixed oxides. HAADF-STEM mapping of the Ce4+-modified nanoribbons revealed a thin continuous layer at the surface of the H2Ti3O7 nanoribbons, while Ce3+ cerium ions intercalated partially between the titanate layers. The phase composition and morphology changes were monitored during calcination between 620 °C and 960 °C. Thermal treatment led to the formation of CeO2 nanoparticles on the surface of the TiO2 nanoribbons, whose size increased with the calcination temperature. The use of Ce4+ raised the temperature required for converting H2Ti3O7 to TiO2-B by approximately 200 °C, and the temperature for the formation of anatase. For the Ce3+ batch, the presence of cerium inhibited the conversion to rutile. Analysis of cerium oxidation states revealed the existence of both +4 and +3 in all calcined samples, regardless of the initial cerium oxidation state.

Pyrithione metal (Cu, Ni, Ru) complexes as photo-catalysts for styrene oxide production.

Selective photochemical oxidation of styrene was performed in an active acetonitrile medium, using H2O2 with or without ultraviolet (UV) light radiation. Pyrithione metal complexes (M-Pth: M = Cu(II), Ni(II), Ru(II); Pth = 2-mercaptopyridine-N-oxide) were used as catalysts. Catalytic testing measurements were done by varying the time, chemical reaction temperature and H2O2 concentration with or without UV energy. Epoxide styrene oxide (SO), benzaldehyde and acetophenone were the major synthesized products. A high batch rate, conversion and selectivity towards SO was shown in the presence of UV. A minor constant formation of CO2 was observed in the stream. Coordinated Ru-based compounds demonstrated the highest process productivity of SO at 60 °C. The effect of the functional alkyl substituent on the ligand Pth, attached to the specific ruthenium(II) centre, decreased the activity of the substance. Ni-Pth selectively yielded benzaldehyde. The stability of the catalysts was examined by applying nuclear magnetic resonance (NMR) spectroscopy and thermogravimetric analysis coupled with mass spectrometry. Tested metal complexes with pyrithione (M-Pth) exhibited excellent reuse recyclability up to 3 cycles.

Highly active and efficient Cu-based hydrotalcite-like structured materials as reusable heterogeneous catalysts used for transcarbonation reaction.

A series of robust and efficient Cu-Al hydrotalcite-like compounds (HTLc) as catalysts were prepared by the simple precipitation method with different Cu/Al molar ratios and investigated for the transcarbonation of glycerol with dimethyl carbonate (DMC) for glycerol carbonate (GC) synthesis in a batch reactor. The structural and textural properties of the Cu-Al (HTLc) catalysts were analyzed by several methods like N2-sorption, SEM-EDX/TEM, XRD, FTIR, CO2-TPD, TGA/DTA and ICP-OES. It was found that the transcarbonation of glycerol is directly dependent on the strong basic sites of the catalysts. The Cu/Al molar ratio has easily tuned the glycerol conversion and the GC yield. Among all synthesized catalysts, the Copper-Aluminum (3Cu-Al@500) catalyst showed excellent catalytic activity for a glycerol conversion (96%) and a GC yield (86%) with reaction rate (irrespective to glycerol) of approximately 0.106 mol L-1 h-1. Furthermore, the optimization of the reaction conditions (i.e. molar ratio of the reactants, catalyst mass, reaction time and temperature) and the reusability of the 3Cu-Al@500 catalyst for glycerol conversion and GC yield with TOF value were studied. In addition, the effect of stirring speed and particle size on the minimization of external and internal mass transfer resistance, respectively, was investigated.

Acrylate-Based Hybrid Sol-Gel Coating for Corrosion Protection of AA7075-T6 in Aircraft Applications: The Effect of Copolymerization Time.

Pre-hydrolysed/condensed tetraethyl orthosilicate (TEOS) was added to a solution of methyl methacrylate (MMA) and 3-methacryloxypropyltrimethoxysilane (MAPTMS), and then copolymerised for various times to study the influence of the latter on the structure of hybrid sol-gel coatings as corrosion protection of aluminium alloy 7075-T6. The reactions taking place during preparation were characterised using real-time Fourier transform infrared spectroscopy, dynamic light scattering and gel permeation chromatography. The solution characteristics were evaluated, using viscosimetry, followed by measurements of thermal stability determined by thermogravimetric analysis. The optimal temperature for the condensation reaction was determined with the help of high-pressure differential scanning calorimetry. Once deposited on 7075-T6 substrates, the coatings were evaluated using a field emission scanning electron microscope coupled to an energy dispersive spectrometer to determine surface morphology, topography, composition and coating thickness. Corrosion properties were tested in dilute Harrison's solution (3.5 g/L (NH4)2SO4 and 0.5 g/L NaCl) using electrochemical impedance spectroscopy. The copolymerization of MMA and MAPTMS over 4 h was optimal for obtaining 1.4 µm thick coating with superior barrier protection against corrosion attack (Z10 mHz 1 GΩ cm2) during three months of exposure to the corrosive medium.

Molecular dynamics of 1-ethyl-3-methylimidazolium triflate ionic liquid studied by 1H and 19F nuclear magnetic resonances.

The molecular dynamics of an ionic liquid (IL) composed of a 1-ethyl-3-methylimidazolium cation and a triflate (trifluoromethanesulfonate) anion, abbreviated as [Emim][TfO], were studied by NMR spectroscopy. By measuring the temperature-dependent high-field 1H and 19F spin-lattice relaxation (SLR) rates, the frequency-dependent 1H and 19F SLR dispersion curves using fast-field-cycling relaxometry, and the temperature-dependent 1H and 19F diffusion constants, and by utilizing the fact that the primary NMR-active nucleus on the Emim cation is 1H, whereas on the TfO anion it is 19F, the cationic and anionic dynamics were studied separately. A single theoretical relaxation model successfully reproduced all the experimental data of both types of resonant nuclei by fitting all the data simultaneously with the same set of fit parameters. Upon cooling, [Emim][TfO] exhibited a supercooled liquid phase between TSL = 256 K and the crystallization temperature TCr ≈ 227-222 K, as confirmed by differential scanning calorimetry (DSC) experiments. Theoretical analysis revealed that within the liquid and the supercooled liquid states of [Emim][TfO], the 1H and 19F relaxation rates are affected by both the rotational and translational diffusional processes with no discontinuous change at TSL. While the rotational diffusion is well described as an Arrhenius thermally activated process, the translational diffusion undergoes strong freezing dynamics that are well described by the Vogel-Fulcher model assuming a freezing temperature of T0 = 157 K. The existence of the supercooled liquid region in the [Emim][TfO] IL should be taken into account when using this IL for a specific application.

Hydroxyl radical scavenging-based method for evaluation of TiO2 photocatalytic activity.

A novel hydroxyl radical scavenging method was developed to establish the photocatalytic activity of TiO2 thin films. Transparent TiO2 thin films were prepared on soda-lime glass substrates using the sol-gel method and characterized using X-ray diffraction. During photoirradiation in aqueous buffered solutions, activity of the films was followed using the substituted nitrobenzene N,N'-(5-nitro-1,3-phenylene)bisglutaramide as a hydroxyl radical scavenger and its hydroxylated products were quantified using HPLC. The yield of hydroxyl radicals was evaluated at various pH of the reaction media, and reflected the dependence of the rate of the hydroxylation reaction on the experimental conditions and on the different qualities of the TiO2 thin films. The proposed method allows for direct assessment of hydroxyl radical production, it is straightforward and is proposed for routine use.

The influence of the reaction temperature on the morphology of sodium titanate 1D nanostructures and their thermal stability.

We have synthesized large quantities of sodium-titanate-based nanotubes and nanoribbons with high yields under hydrothermal conditions from anatase powder in an aqueous NaOH solution. The reaction temperatures were from 95 to 195 degrees C, in steps of 20 degrees C. We observed that the morphology of the nanomaterials, which is reflected in their specific surface areas, depends strongly on the reaction temperature. For the materials synthesized in the range 95-135 degrees C and above 155 degrees C only a single morphology type was observed for the nanostructures, i.e., nanotubes and nanoribbons, respectively. In contrast, when the reaction was carried out at 155 degreesC, both nanotubes and nanoribbons were found in the product. SEM, TEM, and XRD techniques were used to determine the materials' morphological and structural properties, and the thermal stability of the materials was investigated with TGA and DSC. The largest weight loss, of approximately 25%, was observed in a temperature range from 25 up to 600 degrees C for the product obtained at 95 degrees C, probably due to the presence of unrolled titanate sheets.