Concentration Of OH Groups Research Articles

Dependence of the textural properties and surface species of ZnO photocatalytic materials on the type of precipitating agent used in the hydrothermal synthesis

Three different precipitating agents (NaOH, \(\hbox {NH}_{4}(\hbox {H})\hbox {CO}_{3}\) and \(\hbox {CO}(\hbox {NH}_{2})_{2}\)) have been applied for the hydrothermal synthesis of ZnO powder materials, aiming at obtaining various types of porosity and surface species on ZnO. The synthesis procedures were carried out in the presence and in the absence of tri-block copolymer Pluronic (P123, EO20PO70EO20). These materials were characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM)–energy-dispersive X-ray spectroscopy (EDX), BET method and TG–differential thermal analysis (DTA) method, and their photocatalytic activities were tested in the removal azo dye Reactive Black 5 (RB5). The urea precipitant yields spongy-like surface forms and the greatest share of mesopores. It has the highest specific surface area, highest degree of crystallinity of wurtzite ZnO phase and largest content of surface OH groups in comparison with the other two precipitants. The zinc hydroxycarbonate intermediate phase is missing in the case of NaOH as precipitating agent; therefore, it manifests poorer textural characteristics. The morphology of P123-modified sample is different and consists of needle-shaped particles. The urea-precipitated samples display superior performance in the photocatalytic oxidation reaction, compared with the other precipitated samples. The other two precipitating agents are inferior in regard to their photocatalytic activity due to greater share of micropores (not well-illuminated inner surface) and different surface morphologies.

Monte Carlo simulations of amorphous hydroxylated silica (SiO2) nanoparticles

Monte Carlo simulations were carried out on bulk amorphous silica (SiO2) and amorphous hydroxylated silica nanoparticles with different particle sizes (diameter ≈1–10nm). The potential developed by D. M. Tether, and modified and tested by Cormack, Du et al. was used to model the interatomic interactions of SiO2 in both cases (bulk and nanoparticles). The bulk system was realized using periodic boundary conditions. The SiO2 nanoparticles were generated by cutting out a sphere from the bulk silica melt to the required particle size. Free valences on the nanoparticle surfaces were saturated via additional hydroxyl groups and then quenched to T=300K under free boundary conditions.The effect of particle size on bulk and surface properties of the nanoparticles were calculated at T=300K and P=0GPa and studied via radial distribution functions, bond angle distributions, bond distances, coordination numbers, different types of OH group concentrations (isolated, geminol and vicinal groups) and radial density profiles. In addition, a comparison study was done between amorphous hydroxylated SiO2 nanoparticles and bulk amorphous silica properties in order to study differences between them.The study shows that the bulk properties of amorphous hydroxylated SiO2 nanoparticles are size-dependent and different from those of the bulk silica. However, increasing the particle size leads to an approach of the particle’s bulk properties to the bulk properties of the (quasi) infinite system. In addition, the study also shows that decreasing the particle size (i.e., increase in surface area-to-volume and surface-to-core atom ratios) results in increasing the surface effects and surface OH group concentration. Accordingly, small-sized SiO2 nanoparticles have higher surface OH group concentration and larger surface effects than large-sized SiO2 nanoparticles. The simulation results also show that decreasing the particle size not only results in increasing the surface effects but also results in shifting the bond distances and angles towards higher values. Details of the modeling, simulations results and the study are presented in this paper.

Effect of nitrogen deficiency on the ion-exchange properties of cell wall polymers from wheat roots

The ion-exchange properties of cell wall polymers isolated from the roots of wheat (Triticum aestivum L.) plants grown on either nitrate-free (N-deficient) or nitrate-containing (+N) hydroponic nutrient medium have been investigated. Irrespective of the nitrogen nutrition regimen, the studied cell walls contained four types of ion-exchange groups: primary amino groups of structural proteins (pKa < 3), carboxyl groups of polygalacturonic acid in pectin (pK a ~4.7), carboxyl groups of hydroxycinnamic acids (pK a ~7.3), and phenolic OH-groups of lignin (pKa ~10.2). The quantitative ratio between these types of ion-exchange groups, the mass fraction of cell walls in the dry weight of roots, and the swelling coefficient of cell walls depended on the nitrate presence in the growing medium. Compared to the +N variant, the N-deficient variant was characterized by a 2.4 times higher content of phenolic OH-groups in cell walls and 1.24 times higher mass fraction of cell walls; at the same time, the swelling coefficient for this variant was lower by 10%. The obtained data indicate that nitrogen deficiency results in a formation of thicker root cell walls with a higher degree of polymer cross-linking that may be caused by the increased lignin content.

Yb3+-Activated Phosphate Glass

Phosphate glass with different Yb3+ concentrations was synthesized and studied. The composition of the glass made it possible to obtain optically uniform glass in small-volume crucibles. The basic spectral characteristics of the obtained glasses were determined and it was shown that the proposed matrix gives a high quantum yield of luminescence in a wide range of Yb3+ concentrations. The influence of the content of OH groups on the decay time of the Yb3+ luminescence was investigated. In view of its good cooking and casting properties this glass holds promise for use in the active media for near-IR solid-state and fiber lasers.

Effect of composition on rheological behavior of iron oxides produced by hydrothermal method

The aim of the present work was to investigate the rheological properties of different iron oxides (Fe3O4, NiFe2O4, ZnFe2O4 and Ni0.5Zn0.5Fe2O4) aqueous suspensions. The oxides were produced through mixing the respective metallic sulfates within a closed isothermal reactor at 100°C and at pH ≈12, in an oxidant environment (provided by H2O2 0.63% w/v). The reactor was coupled with an adequate real-time data (RTD) acquisition system enabling measurement of temperature, pH and pressure. Obtained RTD data showed that once the isothermal conditions are reached, the pressure slowly decreases over time, which is a result of O2 consumption through oxidation of Fe2+ to Fe3+. To characterize the suspensions as a function of temperature and shear rate, the steady rheology was used. The results revealed that the effect of temperature on viscosity of all suspensions was insignificant while steady rheology showed pseudoplastic behavior for all ferrites. The magnitude of viscosity and pseudoplasticity turned out to be in agreement with the hydrodynamic diameters of particles complying with the order: NiFe2O4>Fe3O4>Ni0.5Zn0.5Fe2O4>ZnFe2O4. Finally, the rheological behavior of suspensions was attributed to the concentration of OH groups on the surface of particles and this hypothesis was effectively supported by DRX, FTIR and TGA/DTA measurements.

Study on mechanism controlling 5D3/5D4emissions of Tb3+ in glasses

Tb3+ doped SiO2-ZnO-BaO glasses are prepared by melting quenching method and their unique photoluminescent properties for the UV excitation are studied by using emission/excitation spectra and decay curves. Glasses in the composition (mol%) of 60SiO2-xZnO-(40-x)BaO-0.2Tb3+(x=30, 20, 10) show the strongest emission peaking at 436nm which is different from majority of other reported work. Lower content of the free OH groups mainly contribute to this phenomenon due to the decreased probability of the multi-phonon aided non-radiative relaxation process from 5D3 to 5D4 energy levels of Tb3+ ions. The Tb3+ concentration also affects the 5D3/5D4 emissions as a result of the cross-relaxation effect on two nearby Tb3+ ions (5D3-5D4⇒7F6-7F0). Moreover, by adjusting Tb3+ concentration and/or ZnO/BaO concentration ratio of the host glass we obtained the adjustable emission with the required CIE chromaticity from blue to green, suggesting that the present Tb3+-doped SiO2-ZnO-BaO glasses are potential as blue/green dual-color luminescent materials for different applications.

Blade-coated sol-gel indium-gallium-zinc-oxide for inverted polymer solar cell

The inverted organic solar cell was fabricated by using sol-gel indium-gallium-zinc-oxide (IGZO) as the electron-transport layer. The IGZO precursor solution was deposited by blade coating with simultaneous substrate heating at 120 °C from the bottom and hot wind from above. Uniform IGZO film of around 30 nm was formed after annealing at 400 °C. Using the blend of low band-gap polymer poly[(4,8-bis-(2-ethylhexyloxy)-benzo(1,2-b:4,5-b’)dithiophene)-2,6-diyl-alt- (4-(2-ethylhexanoyl)-thieno [3,4-b]thiophene-)-2-6-diyl)] (PBDTTT-C-T) and [6,6]-Phenyl C71 butyric acid methyl ester ([70]PCBM) as the active layer for the inverted organic solar cell, an efficiency of 6.2% was achieved with a blade speed of 180 mm/s for the IGZO. The efficiency of the inverted organic solar cells was found to depend on the coating speed of the IGZO films, which was attributed to the change in the concentration of surface OH groups. Compared to organic solar cells of conventional structure using PBDTTT-C-T: [70]PCBM as active layer, the inverted organic solar cells showed significant improvement in thermal stability. In addition, the chemical composition, as well as the work function of the IGZO film at the surface and inside can be tuned by the blade speed, which may find applications in other areas like thin-film transistors.

Surface Hydroxyl OH Defects of η-Al2O3 and χ-Al2O3 by Solid State NMR, XRD, and DFT Calculations

Abstract For the first time, the detailed structure of χ-Al2O3 and η-Al2O3 surface has been established by implementing the NMR crystallography approach. The surface of η-Al2O3 has been demonstrated to be formed primarily by the (111) facets, while the χ-Al2O3 surface is a combination of (111) and (110) facets. This observation supports the block model of aluminum oxides previously proposed by Tsybulya and Kryukova [S. V. Tsybulya, G. N. Kryukova, Phys. Rev. B 77 (2008) 024112.]. The additional terminal OH groups, observed experimentally and not contributing to (111) and (110) theoretical calculations, are considered to be bonded to the tetrahedral aluminum sites. Their origin is related to the junctions of crystallographic faces of spinel building blocks, being a part of discussed model. Higher content of these terminal OH groups in χ-Al2O3 is a result of more junctions in the case of its more mosaic structure compared to η-Al2O3.

Structural and Electrochemical Properties of Physisorbed and Chemisorbed Water Layers on the Ceramic Oxides Y2O3, YSZ, and ZrO2.

A combination of operando Fourier transform infrared spectroscopy, operando electrochemical-impedance spectroscopy, and moisture-sorption measurements has been exploited to study the adsorption and conduction behavior of H2O and D2O on the technologically important ceramic oxides YSZ (8 mol % Y2O3), ZrO2, and Y2O3. Because the characterization of the chemisorbed and physisorbed water layers is imperative to a full understanding of (electro-)catalytically active doped oxide surfaces and their application in technology, the presented data provide the specific reactivity of these oxides toward water over a pressure-and-temperature parameter range extending up to, e.g., solid-oxide fuel cell (SOFC)-relevant conditions. The characteristic changes of the related infrared bands could directly be linked to the associated conductivity and moisture-sorption data. For YSZ, a sequential dissociative water ("ice-like" layer) and polymeric chained water ("liquid-like") water-adsorption model for isothermal and isobaric conditions over a pressure range of 10(-5) to 24 mbar and a temperature range from room temperature up to 1173 K could be experimentally verified. On pure monoclinic ZrO2, in contrast to highly hydroxylated YSZ and Y2O3, a high surface concentration of OH groups from water chemisorption is absent at any temperature and pressure. Thus, the ice-like and following molecular water layers exhibit no measurable protonic conduction. We show that the water layers, even under these rather extreme experimental conditions, play a key role in understanding the function of these materials. Furthermore, the reported data are supposed to provide an extended basis for the further investigation of close-to-real gas adsorption or catalyzed heterogeneous reactions.

Influence of TiO2 hydrophilicity on the photocatalytic decomposition of gaseous acetaldehyde in a circulated flow reactor

The raw titania pulp was heated from 350 up to 700 °C and the impact of TiO2 properties on the photocatalytic decomposition of acetaldehyde under UV–Vis light was investigated. The physico-chemical parameters such as BET surface area, extent of surface hydroxylation, phase composition and size of TiO2 crystallites, were measured. It appeared that low-hydroxylated TiO2 prepared at 400 °C with relatively high BET surface area (106 m2/g) and the crystallized anatase phase was the most active for the acetaldehyde decomposition. High hydroxylation of TiO2 surface and the presence of amorphous TiO2 slowed down the photocatalytic process in the gas phase. On the other hand, high concentration of OH groups on TiO2 surface favored the generation of a high amount of OH radicals in an aqueous environment under UV irradiation. A sufficient amount of hydroxyl groups adsorbed on TiO2 surface is needed to facilitate electron–hole separation and OH radicals formation. On the other hand, an excessive content of these groups results in the creation of a barrier for adsorption of acetaldehyde and thus deteriorates photocatalytic process. Additionally, the high concentration of hydroxyl groups on TiO2 surface could accelerate recombination of radicals and reduce its photocatalytic efficiency in the gas phase.

Blue and NIR emission from nanostructured Tm3+/ Yb3+ co-doped SiO2–Ta2O5 for photonic applications

This paper reports on the synthesis of Tm3+/Yb3+ co-doped SiO2–Ta2O5 nanocomposites prepared by a sol–gel route. XRD analysis revealed initial crystallization of the L-Ta2O5 structure dispersed in the silica host, which depended on lanthanide concentration. Vibrational spectroscopy showed low OH groups content, SiO2–Ta2O5 nanocomposite formation, and controlled phase separation characterized by the presence of Ta2O5 nanoparticles. Emission in the near infrared was evident and also depended on lanthanide concentration and excitation wavelength. Direct excitation on the host promoted NIR luminescence; higher intensity emerged at 980 nm, attributed to Yb3+ ions. Excitation of the Tm3+ excited levels elicited energy transfer between Tm3+ and Yb3+ ions. Excitation of the Tm3+ levels (visible range) and the host (UV) promoted emission in the S telecom band for all the samples. Excitation at 980 nm gave rise to upconversion emissions at 476 nm (blue) and 793 nm (NIR). At higher lanthanide concentration, the presence of a dominant cross-relaxation process reduced the blue emission with respect to the NIR emission. The color coordinates were similar to the coordinates of standard blue. All these luminescent properties make the synthesized materials potential candidates for photonic applications like energy converting devices, solar concentrators, and blue emitters.

Production of phenol-rich bio-oil during catalytic fixed-bed and microwave pyrolysis of palm kernel shell

Catalytic fixed-bed and microwave pyrolysis of palm kernel shell using activated carbon (AC) and lignite char (LC) as catalysts and microwave receptors are investigated. The effects of process parameters including temperature and biomass:catalyst ratio on the yield and composition of pyrolysis products were studied. The addition of catalyst increased the bio-oil yield, but decreased the selectivity of phenol in fixed-bed. Catalytic microwave pyrolysis of PKS significantly enhanced the selectivity of phenol production. The highest concentration of phenol in bio-oil of 64.58 %(area) and total phenolics concentration of 71.24 %(area) were obtained at 500°C using AC. Fourier transform infrared spectroscopy (FTIR) results indicated that concentration of OH, CH, CO and CO functional groups in char samples decreased after pyrolysis. Scanning electron microscopy (SEM) analysis clearly indicated the development of liquid phase in biomass particles during microwave pyrolysis, and the mechanism is also discussed.

Effects of Al3 + doping on the structure and properties of goethite and its adsorption behavior towards phosphate

Al substitution in goethite is common in soils, and has strong influence on the structure and physicochemical properties of goethite. In this research, a series of Al-doped goethites were synthesized, and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The adsorption behavior of these samples towards PO43− was also investigated. Characterization results demonstrated that increasing Al content in goethite led to a reduction in crystallinity, increase in specific surface area (SSA), and morphology change from needle-like to granular. Rietveld structure refinement revealed that the lattice parameter a remained almost constant and b slightly decreased, but c was significantly reduced, and the calculated crystal density increased. EXAFS analysis demonstrated that the Fe(Al)–O distance in the structure of the doped goethites was almost the same, but the Fe–Fe(Al) distance decreased with increasing Al content. Surface analysis showed that, with increasing Al content, the content of OH groups on the mineral surface increased. The adsorption of phosphate per unit mass of Al-doped goethite increased, while adsorption per unit area decreased owing to the decrease of the relative proportion of (110) facets in the total surface area of the minerals. The results of this research facilitate better understanding of the effect of Al substitution on the structure and properties of goethite and the cycling of phosphate in the environment.

Assesment of technical lignins for uses in biofuels and biomaterials: Structure-related properties, proximate analysis and chemical modification

The potential of organosolv and kraft eucalyptus and spruce lignin as feedstock for polymeric materials and biofuel applications was assessed. Proximate analysis was used to predict the heating values and char formation. Chemical modification, based on the esterification reaction with methacryloyl chloride, was applied to introduce vinyl groups into the lignin macromolecules for enhanced reactivity. Kraft eucalyptus and spruce lignins had a more condensed structure than organosolv lignins, which resulted in greater thermal stability for these lignins. For different species within the same process, the thermal parameters showed a correlation with certain structural and compositional parameters (ash and sugars content, molecular weight and degree of condensation). Organosolv spruce lignin produced the highest heating value of 24MJ/Kg, which is suitable for biofuel applications. The content of phenolic OH groups was higher for kraft lignins and especially higher for softwood lignins, both organosolv and kraft. The degree of methacrylation, estimated from the content of vinyl groups per C9 lignin unit, was significantly greater for organosolv lignins than for kraft lignins despite the higher OH-groups content in the latter.

Water-Soluble Lignins from Different Bioenergy Crops Stimulate the Early Development of Maize (Zea mays, L.).

The molecular composition of water-soluble lignins isolated from four non-food bioenergy crops (cardoon CAR, eucalyptus EUC, and two black poplars RIP and LIM) was characterized in detail, and their potential bioactivity towards maize germination and early growth evaluated. Lignins were found to not affect seed germination rates, but stimulated the maize seedling development, though to a different extent. RIP promoted root elongation, while CAR only stimulated the length of lateral seminal roots and coleoptile, and LIM improved only the coleoptile development. The most significant bioactivity of CAR was related to its large content of aliphatic OH groups, C-O carbons and lowest hydrophobicity, as assessed by 31P-NMR and 13C-CPMAS-NMR spectroscopies. Less bioactive RIP and LIM lignins were similar in composition, but their stimulation of maize seedling was different. This was accounted to their diverse content of aliphatic OH groups and S- and G-type molecules. The poorest bioactivity of the EUC lignin was attributed to its smallest content of aliphatic OH groups and largest hydrophobicity. Both these features may be conducive of a EUC conformational structure tight enough to prevent its alteration by organic acids exuded from vegetal tissues. Conversely the more labile conformational arrangements of the other more hydrophilic lignin extracts promoted their bioactivity by releasing biologically active molecules upon the action of exuded organic acids. Our findings indicate that water-soluble lignins from non-food crops may be effectively used as plant biostimulants, thus contributing to increase the economic and ecological liability of bio-based industries.

Determination of Polyurethane Foam Growth Kinetics by a Simple Column Height Test

In the present work, the height of foam column has been used to monitor the reaction of the isocyanate group. Kinetic modeling describes the conversion versus time curves. The global reaction can be divided into two different paths: the blowing reaction and the polymerization. The kinetics of the reaction of toluene diisocyanate with a polypropylene glycol has been studied with auxiliary blowing agents; the concentration of NCO and OH groups could be considered equivalent during all the experiments as a model for similar polyurethane systems. Despite the complexity of the system in which different kinetic orders are possible, as well a physically controlled diffusion process, data were fitted to a simple kinetic model of an apparent order. The results obtained have enabled us to propose a reaction path and catalyzed second-order kinetic model.

Impact of dual-fuel combustion with n-butanol or hydrous ethanol on the oxidation reactivity and nanostructure of diesel particulate matter

This work evaluated the oxidation reactivity, nanostructure and morphological characteristics of the particulate matter (PM) produced by dual-fuel combustion with n-butanol or hydrous ethanol in an automotive diesel engine operating under two different engine loads (equivalence ratios) at the same engine speed (2410min−1). 10% and 15% of ultra-low sulfur diesel (ULSD) fuel on an energy basis were replaced by alcohol fumigation. Thermogravimetric analysis (TGA) showed that independently of engine load, the soot produced by alcohol fumigation was more reactive to oxidation and exhibited higher active surface area (ASA) than ULSD, following the order hydrous ethanol>n-butanol>ULSD. The same trend was obtained for the volatile organic fraction (VOF) of the particulate matter (PM). All PM samples exhibited higher soot reactivity, ASA and VOF at low load in comparison with high load. FTIR spectra showed significant differences on the content of OH group (3100–3600cm−1 wavelength) and aliphatic groups (2850–2950cm−1 wavelength) among all PM samples. Finally, it was found that soot nanostructure, determined with XRD and Raman spectroscopy, as well as PM morphological characteristics (primary particulate diameter and fractal dimension), determined through digital image analysis of TEM micrographs, were not modified significantly by alcohol fumigation neither by engine load. From this experimental setting and engine configuration, it can be concluded that independently of engine load, the intake fumigation of n-butanol or hydrous ethanol (ethanol to a greater extent) increases soot oxidation reactivity, ASA and VOF without affecting soot nanostructure, or PM morphology in comparison to ULSD fuel.

Composites Based on Polystyrene Microspheres with Nano-Scaled Titanium Dioxide

This study produced for the first time composites based on polystyrene microspheres with nano-sized titania synthesized by sulfate and sol-gel methods, as well as commercial Hombifine N, Hombikat UV100, and Degussa P25. The starting samples and the composites were characterized by X-ray diffraction, scanning electron microscopy, nitrogen adsorption capacity, and IR spectroscopy. The highest content of nano-titanium dioxide both in the bulk and on the surface of microspheres was obtained with the use of Hombikat UV100. This sample has the largest specific surface area and a high content of reactive OH groups. The adsorption properties of composites were investigated.

Preparation and characterization of monodisperse polystyrene-silica nanocomposites

Polystyrene-silica nanocomposites were successfully prepared by UV-induced graft polymerization of styrene onto a silica surface. Composites were prepared by batch and continuous-circulation reactions, and results indicated that polystyrene was successfully grafted onto inorganic silica particles for both reactions. Scanning electron microscopy and thermogravimetry analyses of the composites indicated 45% volume increase and 37% polymer content after an optimal reaction time of 30 minutes, respectively, for the batch reaction. For the continuous-circulation reaction, the corresponding results were 63% volume increase and 42% polymer content after 140 min of reaction time. Fourier Transform-Raman spectroscopy analysis of composites showed the characteristic peaks of both silica and polystyrene thus confirming the successful graft-polymerization for both reactions. Disappearance of C-H and C=C ring stretching bands at 3070 and 1578 cm-1 in composites after their optimal reaction times for both reactions indicated a possible ring opening mechanism due to prolonged exposal to the UV light source. For the batch reaction, composites showed new vibration bands at 1052 and 812 cm-1 for asymmetric and symmetric Si-O-C stretching, respectively, indicating a covalent bond between the grafted polymer and silica surface. X-Ray photoelectron spectroscopy (XPS) analysis showed an increase in the elemental concentration of carbon from 5 to 46% for 30 minute composites in batch reaction. XPS analysis also indicated that the relative OH group content of the surface of the silica particles determines the effectiveness of the graft-polymerization of styrene. Open image in new window

Influence of OH-group concentration on optical properties of silica glass in terahertz frequency region

We evaluated the optical properties of various types of silica glass with different OH-group concentrations by using terahertz (THz) time-domain spectroscopy. The results show that the absorption coefficient in the THz frequency region varied with the OH-group concentration and that the variation depended only on the OH-group concentration, irrespective of the glass-manufacturing process. On the other hand, the refractive index did not depend on the OH-group concentration. Thus, the THz optical properties of silica glass can be predicted based on the OH-group concentration in the glass, and vice versa.