Retarding effect of surface hydroxylation on titanium(IV) oxide photocatalyst in the degradation of phenol

Nanosized powders of TiO2 (anatase) were prepared by the hydrothermal method, acid-medium hydrolysis or by vacuum freeze-drying of sols, and annealing at temperatures <700-degrees-C. Photocatalytic activities of these powders in the mineralization of phenol, were evaluated in comparison to that of Degussa P25. Kinetic data indicated that surface hydroxylation had a retarding effect on the degradation of phenol. Formation of stable peroxotitanium species were observed on hydroxylated powders, whereas only V(Ti)-O- hole trap centres were detected by EPR on the heat treated samples. The data supports direct hole oxidation of the substrate preadsorbed on the photocatalyst, which is otherwise blocked by surface hydroxyls.

ChemInform Abstract: Slicing the Perovskite Structure into Layers: Synthesis of Novel Three- Dimensional and Layered Perovskite Oxides, ALaSrNb2M(II)O9 (A: Na, Cs)

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Study of the reactions of pyridinium poly(hydrogen fluoride) with some ternary oxides

The products of the reaction of pyridinium poly(hydrogen fluoride), PPHF, with KIO3, Na2SnO3, NaBiO3, K2CrO4, Na2MoO4 and Na2WO4 were KIO2F2; Na2SnF6; NaHF2, BiF3; K3CrF6, KHF2, (PyH)(3)CrF6; NaHF2, (PyH)(2)MoO2F4.2NaHF(2); and (PyH)(2)WO2F4.2NaHF(2), respectively, while KClO3, KBrO3 and KlO(4) react with complete decomposition to form KHF2 as the fluorinated product. This differential reactivity and mode of reaction has been discussed in terms of the oxidation state of the central atom, the nature and strength of the bonds and the complex behaviour of the formed intermediate or fluorinated products that undergo complexation or solvation with pyridine and/or hydrogen fluoride.

Metal-insulator transition in perovskite oxides: Tunneling experiments

In this paper we have investigated the composition-driven metal-insulator (MI) transitions in two ABO3 classes of perovskite oxides (LaNixCo1-xO3 and NaxTayW1-yO3) in the composition range close to the critical region by using the tunneling technique. Two types of junctions (point-contact and planar) have been used for the investigation covering the temperature range 0.4 K

Hot deformation and microstructural evolution in an alpha(2)/O titanium aluminide alloy Ti-25Al-15Nb

Deformation processing and microstructural development of an alpha(2)/O aluminide alloy Ti-25Al-15Nb (at.%) was studied in the temperature range of 950 to 1200 degrees C and strain rate range of 10(-3) to 100 s(-1). Regions of processing and instability were identified using dynamic materials model. Dynamic recrystallization (DRX) of alpha(2)/O phase and p phase were seen to occur in the region of 950 to 1050 degrees C/0.001 to 0.05 s(-1) and 1125 to 1175 degrees C/0.001 to 0.1 s(-1), respectively. Unstable flow was seen to occur in the region of 1050 to 1190 degrees C/10 to 100 s(-1). Thermal activation analysis showed that DRX of alpha(2)/O and beta was controlled by cross-slip.

Deformation behaviour of commercially pure titanium at extreme strain rates

The evolution of microstructure and texture during room temperature compression of commercially pure Ti with four different initial orientations were studied under quasi-static and dynamic loading conditions. At a low strain rate (epsilon)over dot = 3 x 10(-4) s(-1) the different initial textures yielded the same end texture, despite different microstructural evolution in terms of twin boundaries. High strain rate deformation at (epsilon)over dot = 1.5 x 10(3) s(-1) was characterized by extensive twinning and evolution of a texture that was similar to that at low strain rate with minor differences. However, there was a significant difference in the strength of the texture for different orientations that was absent for low strain rate deformed samples at high strain rate. A viscoplastic self-consistent model with a secant approach was used to corroborate the experimental results by simulation. (C) 2011 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

Processing map for the hot working of near-alpha titanium alloy 685

Using a dynamic materials model, processing and instability maps have been developed for near-alpha titanium alloy 685 in the temperature range 775-1025 degrees C and strain-rate range of 0.001-10 s(-1) to optimise its hot workability. The alloy's beta-transus temperature lies at about 1020 degrees C. The material undergoes superplasticity with a peak efficiency of 80% at 975 degrees C and 0.001 s(-1), which are the optimum parameters for alpha-beta working. The occurrence of superplasticity is attributed to two-phase microduplex structure, higher strain-rate sensitivity, low flow stress and sigmoidal variation between log flow stress and log strain rate. The material also exhibits how localisation due to adiabatic shear-band formation up to its beta-transus temperature with strain rates greater than 0.02 s(-1) and thus cracking along these regions. (C) 1997 Published by Elsevier Science S.A.

Synthesis of nanostructured titanium alloys

The synthesis of nanostructured materials is a critical step in the development elf these novel materials. The basic principles involved in the production of nanocrystals and nanocomposites by rapid solidification are dealt with. An analysis of the various factors influencing the final grain size of the nanocrystals achieved during mechanical alloying has been presented. The devitrification of amorphous phase formed during rapid solidification processing and mechanical alloying provides an alternative and attractive route. Examples of the synthesis of nanostructured materials using these three different routes are drawn from our work on titanium alloys.

Investigation of valence states in the perovskite oxides, LaAFeNbO(6) (A = Ca, Sr)

Compounds of the type, LaAFeNbO(6) (A = Ca Sr) have been synthesized to study the electrical and magnetic properties and to examine valence degeneracy. The results show that valence degeneracy is not operative and the compounds are insulating. Magnetic susceptibility data show that part of the Fe is in Fs(2+) state, thus oxidizing part of Nb4+ to Nb5+ by an internal redox mechanism. The presence of mixed valent Fe is confirmed by Mossbauer spectra. (C) 1999 Elsevier Science B.V. All rights reserved.

Thermodynamic modeling to analyse composition of carbonaceous coatings of MnO and other oxides of manganese grown by MOCVD

Equilibrium thermodynamic analysis has been applied to the low-pressure MOCVD process using manganese acetylacetonate as the precursor. ``CVD phase stability diagrams'' have been constructed separately for the processes carried out in argon and oxygen ambient, depicting the compositions of the resulting films as functions of CVD parameters. For the process conduced in argon ambient, the analysis predicts the simultaneous deposition of MnO and elemental carbon in 1: 3 molar proportion, over a range of temperatures. The analysis predicts also that, if CVD is carried out in oxygen ambient, even a very low flow of oxygen leads to the complete absence of carbon in the film deposited oxygen, with greater oxygen flow resulting in the simultaneous deposition of two different manganese oxides under certain conditions. The results of thermodynamic modeling have been verified quantitatively for low-pressure CVD conducted in argon ambient. Indeed, the large excess of carbon in the deposit is found to constitute a MnO/C nanocomposite, the associated cauliflower-like morphology making it a promising candidate for electrode material in supercapacitors. CVD carried out in oxygen flow, under specific conditions, leads to the deposition of more than one manganese oxide, as expected from thermodynamic analysis ( and forming an oxide-oxide nanocomposite). These results together demonstrate that thermodynamic analysis of the MOCVD process can be employed to synthesize thin films in a predictive manner, thus avoiding the inefficient trial-and-error method usually associated with MOCVD process development. The prospect of developing thin films of novel compositions and characteristics in a predictive manner, through the appropriate choice of CVD precursors and process conditions, emerges from the present work.

Synthesis and structure of a novel terminal imido complex of titanium

The reaction of eta(5)-Cp*TiCl3 and (LiNHBu)-Bu-t in hexanes yields a novel [eta(5)-Cp*Ti(=(NBu)-Bu-t)((NHBu)-Bu-t)(2)]Li . (NH2Bu)-Bu-t complex with a terminal tert-butylimido moiety. The synthesis and X-ray structural characterization are described. (C) 1999 Elsevier Science S.A. All rights reserved.

Synthesis of mesoporous materials based on titanium(IV)oxide and titanium nitride

Nanoparticles of titania were obtained by the controlled hydrolysis of Ti(i-OC3H7)(4) in the reverse micelles of dodecylamine derived from dodecylamine-isopropanol-water solution (water/oil microemulsion). The mesolamellar phase based on titanium nitride (TiN) was obtained by first decomposing TiN atleast partially using the 1:1 solution of acid mixture (HF and HNO3 in the ratio of 9:1) in water and then templating onto the cationic surfactant namely, cetyltrimethylammaniumbromide (abbreviated as CTAB) at 80 degrees C. The synthesis of mesolamellar phase based on TiN involves the charge matched templating approach following the counter-ion mediated pathway. The samples thus obtained were characterized by small angle x-ray diffraction using Cuk(a) radiation, scanning electron microscopy and transmission electron microscopy, which indicated some satisfactory results. (C) 1999 Acta Metallurgica Inc.

Reaction of La2CuO4 with binary metal oxides in the solid state: Metathesis, addition, and redox metathesis pathways

Investigation of the reaction of La2CuO4 with several binary metal oxides in the solid state at elevated temperatures has revealed three different reaction pathways. Reaction of La2CuO4 with strongly acidic oxides such as Re2O7, MoO3, and V2O5 follows a metathesis route, yielding a mixture of products: La3ReO8/La2MoO6/LaVO4 and CuO. Oxides such as TiO2, MnO2, and RuO2 which are not so acidic yield addition products: La2CuMO6 (M = Ti, Mn, Ru). SnO2 is a special case which appears to follow a metathesis route, giving La2Sn2O7 pyrochlore and CuO, which on prolonged reaction transform to the layered perovskite La2CuSnO6. The reaction of La2CuO4 with lower valence oxides VO2 and MoO2, on the other hand, follows a novel redox metathesis route, yielding a mixture of LaVO4/LaCuO2 and La2MoO6/Cu, respectively. This result indicates that it is the redox reactivity involving V-IV + Cu-II --> V-V + Cu-I and Mo-IV + Cu-II --> Mo-VI + Cu-0, and not the acidity of the binary oxide, that controls the nature of the products formed in these cases. The general significance of these results toward the synthesis of complex metal oxides containing several metal atoms is discussed.

Removal of As(V) by adsorption onto mixed rare earth oxides

Arsenic pollution of water is a major problem faced worldwide. Arsenic is a suspected carcinogen in human beings and is harmful to other living beings. In the present study, a novel adsorbent was used to remove arsenate [As(V)] from synthetic solutions. The adsorbent, which is a mixture of rare earth oxides, was found to adsorb As(V) rapidly and effectively. The effect of various parameters such as contact time, initial concentration, pH, and adsorbent dose on adsorption efficiency was investigated. More than 90% of the adsorption occurred within the first 10 min and the kinetic rate constant was found to be about 3.5 mg min(-1). Adsorption efficiency was found to be dependent on the initial As(V) concentration, and the adsorption behavior followed the Langmuir adsorption model. The optimum pH was found to be 6.5. The presence of other ions such as nitrate, phosphate, sulphate, and silicate decreased the adsorption of As(V) by about 20-30%. The adsorbed As(V) could be desorbed easily by washing the adsorbent with pH 12 solution. This study demonstrates the applicability of naturally occurring rare earth oxides as selective adsorbents for As(V) from solutions.

Simultaneous reduction of oxides and dissolution of alumina in stainless steelmaking slag

During stainless steelmaking, reductions of oxides, dissolution of oxides in the slag, and foam formation take place simultaneously. Each of these phenomena independently has been studied by a number of investigators, but little information is available for these phenomena acting simultaneously. Experiments have been conducted to study the simultaneous reduction of oxides of chromium, vanadium, and iron from stainless steelmaking slag by carbon along with the dissolution of alumina in the slag. The overall phenomena and the effect on the chromium oxide reduction have been studied..