Morphological behavior of spherically granulated hydrated zirconium dioxide during its chemical and hydrothermal treatments

Hydrated zirconium dioxide samples were synthesized via original sol–gel route by two-step neutralization of zirconium oxychloride. Spherical granules of zirconia materials were prepared using a well-known “oil-drop” method. By the use of low temperature nitrogen adsorption, it is shown that surface fractal dimension of synthesized xerogels strongly depends on synthesis conditions, chemical and hydrothermal treatments. It is established that the change of synthesis conditions allows to obtain zirconium containing materials with developed porous structure: BET surface area—250–450 m²/g, pore diameter—2.0–4.2 nm, surface fractal dimension—2.28–2.63. It is shown that surface fractal dimension is an important parameter allowing to control the final properties of synthesized material and to determine the reasons of non-reproducibility of adsorptive, catalytic and other physical and chemical properties of zirconium containing oxides from synthesis to synthesis.     

Anion-exchange properties of composite ceramic membranes containing hydrated zirconium dioxide

Composite membranes consisting of an inert ceramic matrix based on aluminum and zirconium oxides and of an ion-exchange component, hydrated zirconium dioxide, were prepared. The selectivity of these membranes to Cl^? ions was studied.     

Sorption recovery of sulfate complexes of iridium on hydrated zirconium dioxide

The sorption on a hydrated zirconium(IV) dioxide from solutions of trinuclear iridium(IV,IV,IV) and iridium(III,III,IV) oxosulfates was studied. The effect of temperature, sorbent grain size, concentration of sulfate complexes of iridium in solution, and acidity of the medium on the sorption recovery was considered.     

Stabilization of isopropanol dispersions of nanosized powders of yttrium oxide-stabilized zirconium dioxide

The properties of dispersions of nanosized powders of yttrium oxide-stabilized cubic zirconium dioxide (YSZ) are studied. The sizes of YSZ aggregates are determined under different conditions. Dispersants for dispersions of YSZ nanosized powders in isopropanol are obtained through partial esterification of poly(acrylic acid) with triethyl orthoformate. The composition and structure of the dispersants are optimized.     

IR spectroscopy study of the radiation-thermal decomposition of water on nanosized zirconium dioxide

Radiation-thermal decomposition of water on nanosized ZrO₂ in the temperature range of 300–673 K has been studied by FTIR spectroscopy. It has been revealed by the X-ray diffraction method that the sample used has the centrsymmetric monoclinic crystal structure. It has been shown that nanosized zirconium dioxide adsorbs water on via the molecular and dissociative mechanisms. Intermediate products of the radiation-induced heterogeneous decomposition of water, namely, the molecular oxygen and hydrogen peroxide radical ions, zirconium hydride, and hydroxyl radicals have been detected. A comparative analysis of changes in the absorption bands of molecular water and surface hydroxyl groups with temperature has been conducted, and the stimulating role of radiation in the radiation-thermal process of water decomposition has been revealed.     

A cataluminescence sensor for propionaldehyde based on the use of nanosized zirconium dioxide

A sensor is described for the detection of propionaldehyde in the gas phase. The sensing scheme is based on the blue cataluminescence (CTL) emission that results from the catalytic oxidation of propionaldehyde on the surface of nanosized zirconium dioxide. The sensor displays high sensitivity to propionaldehyde, a response time of 3 s, and a recovery time of 8 s. Under optimized conditions, the intensity of CTL is linearly related to the concentration of propionaldehyde in the 2.5–1,300 mg·m^?3 concentration range, with a limit of detection of 0.6 mg·m^?3 (at an SNR of 3) and a relative standard deviation (for n?=?6) of 2.2 % at a level of 80 mg·m^?3 of propionaldehyde. Relatively weak interference is observed for ethanol, acetone and acetaldehyde. The method was applied to analyze environmental air samples containing propionaldehyde, and data were compared with those obtained by GC-MS. The results were in good agreement, thereby indicating the utility of the sensor for routine monitoring. A possible mechanism for the catalytic oxidation of propionaldehyde on the ZrO₂ surface is discussed on the basis of the chromatograms of the reaction products.

Preparation and properties of polybenzoxazole-silica nanocomposites via sol-gel process

A novel organic/inorganic hybrid material has been prepared through the sol-gel process. A high temperature polymer, polybenzoxazole (PBO), was chosen as the organic phase due to its inherent low dielectric constant and low water absorption. The inorganic phase was generated via sol-gel reaction from a silica precursor, phenyltriethoxysilane (PTEOS). Due to the hydroxyl groups in the PBO precursor backbone and the water release during the cyclization of the precursor, the sol-gel reaction proceeded without the addition of water and any catalyst. After curing at 350 °C, we obtained the PBO/silica nanocomposites. From TEM and SEM photographs, the silica particles dispersed in the PBO matrix were nano-sized. With an addition of 100 wt% of PTEOS, the T_g of PBO was increased 35 °C. The dielectric constant of the hybrid materials increased with the increasing amount of PTEOS.     

EXAFS study of zirconium alkoxides as precursors in the sol-gel process: II. The influence of the chemical modification

EXAFS studies of primary zirconium alkoxides Zr(OR)₄ with OR = n-propoxide and n-butoxide, dissolved in their corresponding alcohols and chemically modified with acetylacetone (Hacac) and acetic acid (HOAc) in different molal ratios, are presented. The EXAFS-spectroscopic results, supported by FT-IR-studies, indicate a different chemical behavior of the complexing agents. In contrast to acetylacetone, the addition of acetic acid does not change the oligomeric structure of the zirconium alkoxides. Amazingly, the modification with acetic acid leads, in comparison to the pure compounds, to a shortened metal centre distance, whereas in the reaction with acetylacetone the Zr-Zr distance is not changed. With the determined distances and a rough quantitative inclusion of the coordination numbers it was possible to deduce detailed structure models.     

Synthesis of micro- and nanosized manganese oxides from hydrated manganese oxalates and products of their chemical modification with ethylene glycol

The reactions of ethylene glycol with manganese oxalates MnC₂O₄ · 2 H₂O and MnC₂O₄ · 3H₂O on heating in air were studied. At temperature below 100°C, ethylene glycol was found to displace water from oxalates to give a new solvate compound according to the reaction MnC₂O₄ · nH₂O + HOCH₂CH₂OH = MnC₂O₄(HOCH₂CH₂OH) + nH₂O↑. The crystals of the solvates retain the morphology of the initial oxalates, which is then inherited by the products of their thermolysis. Thus, thermolysis of MnC₂O₄ · 3H₂O and MnC₂O₄(HOCH₂CH₂OH) having quasi-unidimensional structure gave Mn₃O₄ and Mn₂O₃ nanowhiskers in air and MnO in an inert gas environment. Heating of MnC₂O₄ · nH₂O in ethylene glycol at temperatures above 100°C results in anhydrous manganese oxalate.     

Enhanced removal of phosphonates from aqueous solution using PMS/UV/hydrated zirconium oxide process

Traditional treatment processes cannot completely remove phosphonates in circulating cooling water by one-step method. Herein, we designed peroxymonosulfate/UV irradiation/hydrated zirconium oxide (PMS/UV/HZO) coupling process to enhance the phosphonates removal. In particular, nitrilotris-methylenephosphonic acid (NTMP) removal efficiency by PMS/UV/HZO process was much higher than that of PMS/UV process, UV/HZO process and other processes in comparison experiments. Specifically, almost 97.2% NTMP in water was degraded, and the total phosphorous (TP) reduced from 9.3 mg/L to 0.26 mg/L at pH 7 within 180 min. TP removal efficiency still reached above 90% after 5 cycles adsorption-desorption of HZO. Moreover, Clˉ, NO₃ˉ and SO₄²ˉ ions all had negligible effect on NTMP removal. During the process, NTMP was first destroyed to form phosphates and other intermediates by the reactive oxygen species (ROS), then phosphates were in situ immobilized via HZO adsorption. Sulfate radical (SO₄^??) has been confirmed to be the major ROS in the reaction system by quenching experiment and electron paramagnetic resonance (EPR) characterization. And the excellent selective adsorption capacity of HZO for phosphate produced was attributed to the strong inner-sphere coordination between H₂PO₄ˉ/HPO₄²ˉ and Zr-OH on the surface of HZO. These results suggest that PMS/UV/HZO process is a promising technique for enhanced phosphonates decontamination.     

Porous nanocomposites of zirconium dioxide and silicate

Highly porous nanocomposites of zirconium dioxide and silicate are synthesised in an aqueous system from an inorganic salt of zirconium; the nanacomposites, with tailorable pore structures, exhibit superior performance as catalyst supports.     

In situ preparation of Al-containing PVDF ultrafiltration membrane via sol-gel process

Recently, inorganic nanoparticles blended within polymeric membranes have shown improved antifouling performance in wastewater treatment. However, agglomeration of nanoparticles remains as one of the major obstacles for generating a uniform surface. In this study, a new method for in situ preparation of Al-containing PVDF ultrafiltration membranes to improve the dispersion of nanoparticles is reported. The strategy of this method is to combine sol-gel process with traditional immersion precipitation process. Al sol was synthesized by the addition of anionic exchange resin in N,N-dimethylformamide (DMF) solvent containing aluminum chloride. Homogeneous Al-containing PVDF casting solution was then obtained by dissolving PVDF polymer in the Al sol. The membrane formation mechanism was investigated by precipitation kinetics and morphology. Results indicate that the addition of Al species can accelerate phase inversion of casting solution. Scanning electron microscopic images show that a typical transition from sponge-like structure to finger-like structure occurred with increasing Al species content. The existence and dispersion states of Al species in the resultant membrane matrix were further examined by transmission electron microscope and X-ray photoelectron spectrometer. The results indicate the Al species nanoparticles were well dispersed throughout PVDF matrix. Dynamic BSA fouling resistance experiments demonstrate the Al-containing PVDF membranes possess improved separation performances over the pure PVDF membranes.     

Physicochemical and photocatalytic properties of nanosized titanium dioxide deposited on silicon dioxide microspheres

The synthesis of SiO₂ core-TiO₂ shell composites from a titanium dioxide sol and a suspension of microspherical silicon dioxide is described. The main factors ensuring the formation of a composite with a preset morphology are the size and charge of the TiO₂ sol particles (10–45 nm) and silicon dioxide core particles (300–700 nm), the pH values of the suspensions of the starting components and the resulting composite, and the proportions and way of mixing of the siliconand titanium-containing components. The SiO₂ core-TiO₂ shell composites show high photocatalytic activity in the degradation of Rhodamine FL-BM dye (rate constant of k = 0.0813 min⁻¹) and are much more active than precipitated TiO₂ powder (k = 0.0022 min⁻¹). The activity of the composite is determined by the calcination temperature (700–800°C), by the proportion and accessibility of the active component (TiO₂), and by the presence of a dopant (P₂O₅).     

Influence of pH on nanosized Mn–Zn ferrite synthesized by sol–gel auto combustion process

Sol–gel auto combustion process was employed to synthesize nanosized Mn–Zn ferrite at different pH values (<1, 5, 6, 7, 8 and 10). Although self propagating combustion behavior of gel was noted at pH 5 but more effective combustion was observed at pH 6. The smoldering effect was observed in gel prepared at pH 7, 8 and 10, whereas pH < 1 showed localized burning. Thermogravimetric (TG) and X-ray diffraction (XRD) analyses were done to investigate the effect of pH on the combustion behavior, particle size and the formation of desired magnetic (spinel) phase. From TG curves of burnt powders, activation energy of ignition reaction at each pH value was calculated. The results showed that fuel to oxidant ratio and the amount of gel residuals decided the value of activation energy required to further purify the burnt powders. Calcination parameters (time and temperature in air) of powders P1 and P6 synthesized at pH < 1 and pH 6 were also determined. B–H loop results showed that calcined powder C6 was more ferromagnetic than C1 due to fully developed spinel phase and larger particle size.     

Preparation and properties of a new composite photocatalyst based on nanosized titanium dioxide

The use of photocatalysts supported on adsorbents is receiving substantial attention. Supporting TiO₂ with zeolites is found to be one of the best solutions to increase the efficiency of TiO₂-based photocatalysts. This work was focused on simple preparation of a TiO₂/Na-ZSM-5 composite catalyst by the solid state dispersion (SSD) method and its modification with an organic photosensitizer — polythiophene (PT). Using the XRD diffractometry, structure of the new composite catalyst was proved. Beside this composite catalyst, mechanical mixtures of TiO₂-based catalysts with Na-ZSM-5 zeolite were prepared. The efficiency of all five available photocatalysts (TiO₂, TiO₂-PT, mechanical mixture of TiO₂ + Na-ZSM-5, mechanical mixture of TiO₂-PT + Na-ZSM-5, and the modified SSD-PT composite) on photodegradation of 4-chlorophenol was compared. By measuring the formation of chloride ions and decreasing the 4-chlorophenol concentration at two different initial concentrations of 4-chlorophenol in the basic aqueous solution, the photoefficiency and adsorption properties of our photocatalysts were determined. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

Preparation and antibacterial activity of hybrid materials containing quaternary ammonium salts via sol-gel process

Organic-inorganic hybrid coatings containing quaternary ammonium salts (QAS) bonded to the organic-inorganic network were prepared from tetraethoxysilane and triethoxysilane terminated poly(ethylene glycol)-block-poly(ethylene) using a sol-gel process. They were applied as a thin layer (0.6-1 μm) to PE films and the antibacterial activity of the coated films was tested against both Gram-negative (Escherichia coli ATCC 25922) and Gram-positive (Staphylococcus aureus ATCC 6538) bacteria. Measurements at different contact times showed a rapid decrease of the viable count for both the tested strains. In particular, after 48 h of contact, a decrease of 96.4% and 99.1% of E. coli and S. aureus, respectively, was observed. The permanence of the antibacterial activity of the coated films was demonstrated through repeated washings and prolonged immersion in physiological saline solutions at 37 °C. Indeed, due to the removal of QAS moieties by the nucleophilic attack of water, the antibacterial activity after 24 h was strongly reduced when measured on samples submitted to several washings. However, a quite good antibacterial activity was observed even on the same samples after 96 h, probably due to a spontaneous partial restoring of the QAS on the surface. Very good transparency, quite good adhesion and high wettability are further features of these hybrid coatings.     

The formation of mesoporous TiO2 spheres via a facile chemical process

The mesoporous TiO(2) solid and hollow spheres have been synthesized via a controllable and simple chemical route. Structural characterization indicates that these TiO(2) mesoporous spheres after calcined at 500 degrees C have an obvious mesoporous structure with the diameters of 200-300 nm for solid spheres and 200-500 nm for hollow spheres. The average pore sizes and BET surface areas of the mesoporous TiO(2) solid and hollow spheres are 6.8, 7.0 nm and 162, 90 m(2)/g, respectively. Optical adsorption investigation shows that TiO(2) solid and hollow spheres possess a direct band gap structure with the optical band gap of 3.68 and 3.75 eV, respectively. A possible formation mechanism for TiO(2) solid and hollow spheres is discussed.     

The hydrated electron: a seemingly familiar chemical and biological transient

Since the discovery of the hydrated electron in bulk water in 1962, the species has been the subject of intense research and speculation. For many decades even the basic features of the simplest of all chemical and biological transients and reactants--such as its structure, binding motifs, lifetimes, and binding energies--remained elusive. Recently, another milestone in the research of the hydrated electron was the determination of its vertical binding energy (VBE). Also a long-lived hydrated electron near the surface of liquid water has been discovered. The present Minireview discusses the implications and consequences of this and other new findings in addition to the emerging complex picture of a solvated electron in water.