Photooxidation of iodide ion on some semiconductor and non-semiconductor surfaces

In 80% aqueous ethanol, TiO₂ (anatase), ZrO₂, ZnO, V₂O₅, Fe₂O₃ and Al₂O₃ photocatalyze the oxidation of iodide ion but CdO and CdS do not; the wavelength of illumination is 365 nm. However, Fe₂O₃ fails to bring in a sustainable photocatalysis in 60% aqueous ethanol. The photooxidation of iodide ion on TiO₂, ZrO₂, ZnO, V₂O₅ and Al₂O₃ in 60% aqueous ethanol was studied as a function of [I⁻], amount of catalyst suspended, airflow rate, light intensity and solvent composition. The metal oxides examined show sustainable photocatalytic activity. Iodine formation is larger with illumination at 254 nm than at 365 nm. The mechanisms of photocatalysis on semiconductor and non-semiconductor surfaces have been discussed. Photocatalytic generation of iodine has been analyzed using a kinetic model. The photocatalytic efficiencies are of the order V₂O₅ > TiO₂ > ZrO₂ > ZnO > Al₂O₃ and V₂O₅ > TiO₂ > ZrO₂ > ZnO=Fe₂O₃ > Al₂O₃ in 60% and 80% aqueous ethanol.     

Thermal expansion and characteristic points of –Na2O–SiO2 glass with added oxides

A differential method with an optical lever system was used to determine the thermal expansion of the glasses based on Na₂O–SiO₂ and containing the following oxides: Al₂O₃, CaO, TiO₂, ZnO, Al₂O₃–TiO₂, CaO–TiO₂, or ZnO–TiO₂. The determination was carried out on both as-drawn and annealed rods. The influence of the thermal history as well as of the added oxide(s) on the thermal expansion of glasses is dealt with in this paper. The experimental results for the thermal expansion of annealed rods show that the addition of CaO–TiO₂ in the glass has the lowest value while the addition of CaO in the glass has the highest value for the coefficient of linear expansion. At the same time, the characteristic points of the annealed glasses, determined from the expansion-temperature curves, show that the addition of ZnO in the glass has the lowest values while the addition of TiO₂ in the glass has the highest values.     

Evaluation of water treatment sludge as a catalyst for aqueous ozone decomposition

A new, novel, efficient, and stable green catalyst has been successfully used as a catalyst in aqueous ozone decomposition in acidic medium. The catalyst was characterized by using X-ray fluorescence (XRF), transmission electron microscope (TEM), scanning electron microscope (SEM), and X-ray diffraction (XRD) techniques. The sludge mainly consists of various metal and non-metal oxides. The effect of various experimental parameters such as catalyst loading, initial ozone concentrations, and various metal oxide catalysts on the decomposition of ozone was investigated. The decomposition of dissolved ozone was substantially enhanced by increasing the catalyst loading from 125 to 750 mg and by increasing the initial ozone concentration. The ozone decomposition efficiencies of Al₂O₃, SiO₂, TiO₂, Fe₂O₃, ZnO, and sludge have been studied and the efficiencies of these catalysts were found to be in the following order: ZnO ≈ sludge > TiO₂ > SiO₂ > Al₂O₃ ≈ Fe₂O₃. The catalytic stability was also investigated for up to four successive cycles and it was found that the catalyst was stable and ozone did not affect the catalyst morphology and its composition. However, the surface area of the catalyst increased after 1st cycle then it became stable. It was concluded that the sludge powder used in this study was a promising catalyst for aqueous ozone decomposition.     

Preparation of titanium oxide,iron oxide,and aluminium oxide from sludge generated from Ti-salt,Fe-salt and Al-salt flocculation of wastewater

In this study, the settled floc (sludge) produced by aluminum sulfate (Al₂(SO₄)₃), ferric chloride (FeCl₃) and titanium tetrachloride (TiCl₄) flocculation was recycled with a novel flocculation process, which has a significant potential to the lower cost of waste disposal, protect the environment and public health and yield economically useful by-products. Three coagulants removed 70% of organic matter in synthetic wastewater. The settled floc was incinerated in the range from 100 °C to 1000 °C. Alumina (Al₂O₃), hematite (Fe₂O₃), titanium oxide (TiO₂) which are the most widely used metal oxides were produced from the wastewater sludge generated by the flocculation in wastewater with Al₂(SO₄)₃, FeCl₃ and TiCl₄, respectively. TiO₂ particles produced from the sludge consisted of the large amount of nano size particles. Hematite (Fe₂O₃) and grattarolaite (Fe₃ (PO₄)O₃ or Fe₃PO₇) included the majority of micro size (40%) particles. Alumina (Al₂O₃) also consisted of micro size (40%). Due to TiO₂ usefulness of the application, detailed characterisation of TiO₂ after calcination at different temperatures were investigated in terms of X-ray diffraction, energy dispersive X-ray, surface area and photoactivity.     

Effect of Mg-and Fe-ions on formation mechanism of aluminium titanate

The presence of Mg²⁺- and Fe³⁺-ions has an effect on the formation of Al₂TiO₅. Crystalline phases produced under the influence of the heat treatment have been identified in a heated X-ray diffraction chamber in the temperature range of 20–1500 °C. In the presence of Mg²⁺- and Fe³⁺-ions transitional phases are formed in the temperature range of 1000–1350 °C during Al₂TiO₅ formation. The XRD technique was used to identify the crystalline phases formed. On addition of MgO, chemical composition of the transitional phase formed is Mg_0.3Al_1.4Ti_1.3O₅, whereas on addition of Fe₂O₃ we have calculated a Powder Diffraction File card data for the transitional phase. Determination of the lattice parameters of the Al₂TiO₅ ceramics produced enabled verification of incorporation of Mg²⁺- or Fe³⁺-ions into the crystal lattice of Al₂TiO₅, i.e. the formation of Mg²⁺- and Fe³⁺-containing solid solutions.     

RELATION OF ELECTRICAL CONDUCTIVITY TO CHEMICAL COMPOSITION OF GLASS*

The electrical conductivity of some glasses in the soda-lime-silica system was measured at 400 °C. with an apparatus which is described. The specific resistance at this temperature ranged from 0.06 to 5.0 × 10⁵ ohms per cc. Measurements were made on other glasses containing equivalent amounts of various oxides incorporated in a parent soda-lime-silica glass. It was found that an increase in resistance was produced by additions of MnO, ZnO, B₂O₃, Fe₂O₃, BaO, PbO, TiO₂, and K₂O, the resistances increasing in this order. A decreased resistance was produced by Na₂O, CaO, and Al₂O₃. Previously published data on the power factors of these glasses are reviewed.     

Effect of inorganic matter on reactivity and kinetics of coal pyrolysis

Two Chinese coals, Shenfu subbituminous coal and Huolingele lignite, were used to investigate the effect of mineral matter in coal on reactivity and kinetic characteristics of coal pyrolysis. The experiments were carried out by using thermogravimetry to check the pyrolysis behavior of raw coal, HCl/HF demineralized coal and demineralized coal with inorganic matter (CaO, K₂CO₃ and Al₂O₃) added, respectively. The results showed that inherent mineral in coal had no evident effect on the reactivity and kinetics of coal pyrolysis. CaO, K₂CO₃ and Al₂O₃ all had a catalytic effect on the reactivity of coal pyrolysis, their effects were closely related to temperature region and coal types. The pyrolysis process of all the samples studied can be described by three independent first order kinetic model. Addition of inorganic matter the activation energy decreased and the characteristic temperature of coal changed.     

Effect of alkali roasting and sulfatization on the extraction of different metal oxides from waste alum sludge

Water treatment plants (WTP) generate a significant amount of sludge as byproducts with environmentally harmful elements. Thus, this work focused on the recycling of alum sludge through the extraction of different metal oxides, i.e., Al₂O₃, Fe₂O₃ and SiO₂, for use in different applications, such as ceramics, cement, and agriculture. The extraction of Al₂O₃, Fe₂O₃, and SiO₂ from alum sludge was performed using sulfatization and roasting to compare which of the two processes could produce the metal oxides of the highest purity. Precipitated powders were calcined at 700°, 900° and 1100 °C. Moreover, the obtained prepared and calcined powders were characterized by studying their phase compositions, microstructure, particle size, and surface area. Results indicated that roasting achieved the highest yield of alumina. Iron oxide was extracted mostly in maghemite form through roasting after calcination at 1100 °C. Further, silica was obtained in cristobalite and quartz phases after calcination at 1100 °C for the samples prepared through sulfatization. However, these phases of silica were combined with albite and obtained after calcination at 1100 °C for the samples prepared through roasting method.     

Thermoelectric properties of oxide ceramics

Thermoelectric properties of several oxides were investigated. Al₂O₃-, TiO₂- or ZrO₂-doped ZnO showed large power factor over the wide temperature range. Fe₂O₃. showed large power factor by doping of TiO₂. BaO-doped RuO₂, BaRuOi₃ and CaRuO₃ showed large power factor at high temperature. Improvement of electrical conductivity by doping was effective to increase power factor in these oxide materials.     

Thermal stability and deformation of poly(acrylic acid)–metal oxides

In this work, we investigated the thermal stability and deformation of the compound of poly(acrylic acid) (PAA) and metal oxides (ZnO, CaO, CuO, Al₂O₃, and Cr₂O₃). The kinetic parameters of the desorption of water from PAA–metal oxide were calculated. The activation energies of the water desorption of PAA–metal oxide were less than 5 kcal/mol. The order of bonding capability of oxygen (PAA–O–metal) and water was PAA–CaO > PAA–ZnO > PAA–CuO > PAA–Cr₂O ₃ > PAA–Al₂O₃. The reaction types of the composites were clarified. Incorporating metal oxide into PAA increased the thermal stability. The factors which influence the mechanical properties of the composites, e.g., the chemical compositions, curing environment, and curing time, were also studied. The various curing environments (pure water, 0.1N HCl, 0.1N NaOH, and methanol) decreased the compressive strength of PAA—metal oxide. Moreover, the thermal stability and compressive strength of PAA–ZnO and PAA–CuO reached an optimum because of their crosslinking nature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2021–2027, 1997     

Supported Nano-Gold Catalysts for Epoxidation of Styrene and Oxidation of Benzyl Alcohol to Benzaldehyde

Nano-gold particles supported on different alkaline earth oxides (viz. MgO, CaO, BaO and SrO), Gr. IIIa metal oxides (viz. Al₂O_3, Ga₂O_3, In₂O₃ and Tl₂O₃), transition metal oxides (viz. TiO_2, Cr₂O_3, MnO_2, Fe₂O_3, CoO_x, NiO, CuO, ZnO, Y₂O₃ and ZrO₂), rare earth metal oxides (viz. La₂O_3, Ce₂O_3, Nd₂O_3, Sm₂O_3, Eu₂O_3, Tb₂O_3, Er₂O₃ and Yb₂O₃) and U₃O₈ [all prepared by depositing gold on corresponding metal oxide support by deposition precipitation (DP) and/or homogeneous deposition precipitation (HDP) method] were evaluated for their catalytic performance in the liquid phase epoxidation of styrene by tert-butyl hydroperoxide (TBHP) to styrene oxide and also in the solvent-free benzyl alcohol-to-benzaldehyde oxidation (by molecular oxygen or TBHP) reactions. For the epoxidation, the catalytic performance (styrene oxide yield) of the most promising nano-gold catalysts prepared by the HDP method was in the following order: Au/MgO > Au/Tl₂O₃ > Au/Yb₂O₃ > Au/Tb₂O₃ > Au/CaO (or TiO₂). However, for the oxidation of benzyl alcohol to benzaldehyde by molecular oxygen, the order of choice for the most promising catalysts (based on benzaldehyde yield) was Au/U₃O₈ > Au/Al₂O₃ > Au/ZrO₂ > Au/MgO. Whereas, when TBHP was used as an oxidizing agent for the benzyl alcohol oxidation, the order of choice for the most promising catalysts was Au/U₃O₈ > Au/MgO > Au/TiO₂ > Au/ZrO₂ > Au/Al₂O₃. The catalytic performance of a particular supported nano-gold catalyst was thus found to depend on the reaction catalysed by them. Moreover, it is strongly influenced by a number of catalyst parameters, such as the metal oxide support, the method of gold depositon on the support, the gold loading and also on the catalyst calcination temperature. Nano-gold particles-support interactions seem to play an important role in controlling the deposition of gold (amount of gold deposited and size and morphology of gold particles), formation of different surface gold species (Au⁰, Au¹⁺ and Au³⁺) and electronic properties of gold particles and, consequently, control the catalytic performance (both the activity and selectivity) of the supported nano-gold catalysts in the reactions. The nano-gold catalysts prepared by the HDP method showed much better catalytic performance than those prepared by the DP, coprecipitation or impregnation method; in general, the HDP method provided supported gold catalysts with much higher gold loading and/or smaller size gold particles than that achieved by the DP and other methods.     

Kinetics of the carbothermal synthesis of Mo carbide catalyst supported on various semiconductor oxides

Molybdenum carbide synthesized by temperature-programmed carburization of MoO₃ supported on various semiconductor oxides (10 wt.% Mo) with a H₂/C₃H₈ mixture have been characterized and evaluated for Fischer-Tropsch synthesis. The carburization reaction appeared to be a 2-stage process involving formation of intermediate oxycarbide phase, which was further carburized to the metal carbide form. Both α-MoC_1 − x and β-MoC_1 − x phases were detected in all Mo carbide catalysts and MoO₃ was converted completely to molybdenum carbide during carburization. The carburization rate depended on the C₃H₈ composition in the feed and attained an optimum at a H₂:C₃H₈ ratio = 5 for all four supports (Al₂O₃, TiO₂, SiO₂, and ZrO₂). Carbide formation rate increased with Mo loading although it reached a ‘plateau’ at Mo loading beyond 15 wt.% Mo. The existence of a compensation effect and isokinetic relationship for both oxycarbide and carbide phases suggested that the conversion of Mo oxide to oxycarbide and oxycarbide to carbide phase was governed by the same topotactic mechanism. Mo carbide catalysts were evaluated for CO hydrogenation activity and Fischer-Tropsch specific reaction rate decreased in the order; MoC_1 − x/TiO₂ > MoC_1 − x/SiO₂ > MoC_1 − x/ZrO₂ > MoC_1 − x/Al₂O₃ parallel to the trend for Mo carbide production rate.     

Enhancement of hydrogen-storage properties of Mg by reactive mechanical grinding with oxide, metallic element(s), and hydride-forming element

In order to improve the hydrogen-storage properties of magnesium, oxides, metallic element(s) and a hydride-forming element were added to Mg by grinding under a hydrogen atmosphere (reactive mechanical grinding). As the oxides, Fe₂O₃ purchased, Fe₂O₃ prepared by spray conversion, MnO purchased, SiO₂ prepared by spray conversion, and Cr₂O₃ prepared by spray conversion were chosen. As the metallic elements, Ni, Fe, and Mo were selected. In addition, as the hydride-forming element, Ti was selected. Samples with the compositions of Mg-10 wt%oxide, 76.5 wt%Mg-23.5 wt%Ni, 71.5 wt%Mg-23.5 wt%Ni-5wt% Fe₂O₃, 71.5 wt%Mg-23.5 wt%Ni-5 wt%Fe, and Mg-14 wt%Ni-2 wt%Fe-2wt%Ti-2 wt%Mo were prepared. The hydrogen-storage properties and changes in phase and microstructure after the hydriding-dehydriding cycling of the prepared samples were then investigated.     

Dehydration of 2,3-butanediol into 3-buten-2-ol catalyzed by ZrO2

Vapor-phase catalytic dehydration of 2,3-butanediol was investigated over metal oxides such as CeO₂, La₂O₃, Yb₂O₃, ZrO₂, Al₂O₃, TiO₂, ZnO, Fe₂O₃, NiO, and Cr₂O₃. In the dehydration of 2,3-butanediol, 3-buten-2-ol was preferentially produced over monoclinic ZrO₂ along with major by-products such as butanone and 3-hydroxy-2-butanone. Over ZrO₂ calcined at 900 °C, 3-buten-2-ol was produced with a maximum selectivity of 59.0% at 300 °C without producing 1,3-butadiene.     

Preparation of synthetic rutile and metal-doped LiFePO4 from ilmenite

The synthetic rutile and metal-doped LiFePO₄ are prepared from the high-titanium residue and iron-rich lixivium, which are obtained from the ilmenite by a mechanical activation and leaching process. ICP results show that the rutile contains 92.01% TiO₂, 1.59% Fe₂O₃, 0.034% MnO₂ and 0.60% (MgO + CaO), which meet the requirement of the titanium dioxide chlorination process. The results also reveal that small amounts of Al³⁺, Ca²⁺ and Ti⁴⁺ precipitate in the FePO₄·xH₂O precursor. XRD and Rietveld-refine results show that the metal-doped LiFePO₄ is single olivine-type phase and well crystallized, and Ti⁴⁺ occupy M1 site, Ca²⁺ occupy M2 site and Al³⁺ occupy both sites, which indicates the formation of cation-deficient solid solution. The sample exhibits a capacity of 123 mAh g⁻¹ at 5C rate, and retains 94.3% of the capacity after 100 cycles.     

Mechanistic investigation of chemical looping combustion of coal with Fe2O3 oxygen carrier

The reaction of three Chinese coals with Fe₂O₃ oxygen carrier (OC) was performed in a thermogravimetric analyzer (TGA), with special focuses on the effects of varying heating rate and coal rank on reactivity. Fourier transform infrared spectroscopy (FTIR) was used to in situ detect the emitted gases from TGA. Field scanning electron microscopy/energy-dispersive X-ray spectrometry (FSEM-EDX) was used to study the morphology and elemental compositions of the reaction residues collected from TGA and the related phase evaluation was further identified by X-ray diffraction (XRD). Through all these experiments, it was found that the pyrolysis of coal samples without Fe₂O₃ OC under N₂ atmosphere underwent the dehydration and the ensuing primary and secondary pyrolysis stages. The increasing heating rate shifted the characteristic temperature (T_m) of the primary pyrolysis to a higher temperature and favored a more rapid generation of volatile matters. When the three coals reacting with Fe₂O₃ OC, TGA results demonstrated even over 200 °C, the reaction still experienced the partial pyrolysis at the relatively low temperature and the ensuing two reactions of Fe₂O₃ with the pyrolysis products at the primary and secondary stages. The coal of low rank with high volatile content should be preferred for the full conversion of coal into CO₂. Furthermore, the activation energy of Fe₂O₃ OC reacting with PDS at its primary pyrolysis stage was the largest, more than 70 kJ/mol. Finally, SEM-EDX and further XRD analysis of the residues from the reaction of PDS with Fe₂O₃ OC indicated the reduced counterpart of Fe₂O₃ was Fe₃O₄, and some inert iron compounds such as Fe₂SiO₄ and FeAl₂O₄ were also generated, which might deteriorate the reactivity of Fe₂O₃ OC.     

Synthesis,characterization and magnetic properties of glass ceramics containing nanoparticles of both Ba-hexaferrite and Zn-ferrite

Differential thermal analysis, X-ray diffractometry and transmission electron microscopy were used to study the crystallization behavior of glass ribbons with a composition of 35% BaO, 35% Fe₂O₃, 20% B₂O₃ and 10% TiO₂ (mol.%). Replacement of different amounts of BaO by ZnO was studied. Heat treatment was applied at both 700 and 1000 °C for 1 h with heating rate 3 °C/min. Both Ba-hexaferrite and Zn-ferrite, with crystallite size 2–7 nm, were detected by XRD and TEM. The magnetic properties of ribbons prepared via cooling the melts between steel rollers were measured with a vibrating sample magnetometer. Magnetization saturation (Ms) was increased by increasing ZnO, while coercivity (Hci) increased by increasing BaO. Partial replacement of Ba by Zn revealed preparation of samples contains both Zn ferrite and Ba hexaferrite which give wide range for engineering application.     

Synthesis and analysis of multi-walled carbon nanotubes/oxides hybrid materials for polymer composite applications

Nanotubes-based nanocomposites to be used as polymer reinforcing/flame-retardant additives are synthesized by decomposition of isobutane at 600 °C. Catalytic chemical vapor deposition (CCVD) is carried out over 17 wt%Fe-catalysts supported on various oxides (Al₂O₃, MgO, CaO, SrO or BaO) reduced at 600 °C. Catalysts utilized and carbonaceous deposits obtained are systematically characterized by the use of several analysis techniques, in order to investigate the influence of catalyst specifics on reaction yield, selectivity and characteristics (crystallinity and purity) of the grown nanotubes. The results show that the support greatly influences the catalyst performance. The lack of metallic iron renders Fe/SrO- and Fe/BaO-catalysts inactive. Fe/Al₂O₃ catalysts exhibit the highest catalytic activity, but give rise to scarce selectivity and large metallic impurity contents. Contrarily, using Fe/MgO and Fe/CaO catalysts leads to lower yields, but allows reducing impurities and remarkably improving selectivity and nanotube crystallinity.     

Aldol Addition of Acetone,Catalyzed by Solid Base Catalysts: Magnesium Oxide,Calcium Oxide,Strontium Oxide,Barium Oxide,Lanthanum (III) Oxide and Zirconium Oxide

Aldol addition of acetone was studied over alkaline earth oxides, La₂O₃, ZrO₂, SiO₂Al₂O₃ and Nb₂O₅ at 0°C to elucidate the nature of active sites. The activities of catalysts on a unit surface area basis were in the order: BaO > SrO > CaO > MgO > La₂O₃ > ZrO₂ ≫ SiO₂Al₂O₃ > Nb₂O₅. The reaction is base-catalyzed, and the oxides of stronger basic sites promote the reaction effectively.The effects of preadsorption of water, ammonia, pyridine and carbon dioxide were investigated with MgO and CaO. For MgO, addition of water and ammonia caused marked increase in activity and selectivity to diacetone alcohol, while pyridine had little effect on the catalytic behavior. Preadsorption of carbon dioxide scarcely inhibited the reaction. For CaO, the effects of preadsorption were small compared with those on MgO. Basic OH⁻ ions, which are either retained on the surfaces or formed by dehydration of diacetone alcohol, are proposed as active sites for aldol addition of acetone.     

Effect of different nucleation catalysts on the crystallization of Li2O–ZnO–MgO–Al2O3–SiO2 glasses

Based on local raw materials, a range of LiZnMg aluminosilicate glasses were prepared to investigate the influence of TiO₂, Cr₂O_3, and ZrO₂ on the crystallization behaviour and thermal expansion characteristics. Differential thermal analysis showed that the crystallization propensity increases in the order TiO₂ > Cr₂O₃ > ZrO₂. Virgilite, β-spodumene ss, gahnite, enstatite and cristobalite were formed in the prepared glass-ceramics. The microstructure of glass-ceramic samples showed growths of rounded and subrounded grains in the base sample, whereas, somewhat rod-like and accumulated growths appeared in samples containing ZrO₂. However, a rather homogeneous texture of accumulated growths was developed in glass-ceramics containing TiO₂ and Cr₂O₃. The coefficient of thermal expansion of parent glasses was sensitive to the type of nucleating agent added (Cr₂O₃ > TiO₂ > ZrO₂) varying from 24.8 × 10⁻⁷ to 65.1 × 10⁻⁷ °C⁻¹ being almost unchanged with the heat-treatment. The microhardness values of glass-ceramic samples were in the 763–779 kg/mm² range.