Hydrated titanium(IV) oxide as a granular inorganic sorbent for removal of radiostrontium

The sorption of radiostrontium on hydrated titanium(IV) oxide was studied in batch equilibration experiments. The strontium uptake capacity was determined. Batch distribution coefficients were measured as function of solution pH as well as strontium and sodium concentration. The effect of electron beam irradiation on strontium sorption was also examined. The results are of significance in connection with the removal of radiostrontium traces from alkaline sodium salt-loaded wastes of reprocessing plant origin.     

Coordination of nitrogen(II) oxide by metal prophyrins

The equilibrium constants have been determined for the extra coordination of nitrogen(II) oxide and its metabolite formed in biochemical reactions (the nitrite ion) by cobalt complexes of porphyrins with various structures in ethanolic and aqueous solutions with near-physiological pHs. The far higher values of the thermodynamic stability constants of (NO)CoP nitrosyl complexes compared to those for nitrite complexes argue for a considerable covalence of the Co-NO bond.     

Ultrathin functional films of titanium(IV) oxide

Chemistry and physics of thin semiconducting layers of various types are subjects of intense research. Especially when nanotechnology methods such as self-assembly are involved, amazing structural and/or functional properties may appear. Also modern physical methods using variously organized plasma arrangements are able to produce uniform structures with distinctive functionality. In this review, based virtually on our own work, discussions on the preparation, structure, morphology, and function of titanium(IV) oxide nanoscopic thin films are presented. It was shown that structurally and functionally similar titanium(IV) oxide films can be prepared via completely different preparation techniques. Function tests were arranged as “primary”, covering the assessment of the light induced charge separation efficiency, and “secondary”, based on photocatalytic surface oxidations.     

Photocatalytic reaction of neat alcohols by metal-loaded titanium(IV) oxide particles

The photocatalytic reaction (excitation wavelength, greater than 300 nm) of neat alcohols (ethanol or 2-propanol) by metal-loaded titanium(IV) oxide (TiO₂) was conducted under argon at room temperature. The dehydrogenation products hydrogen (H₂) and acetaldehyde (or acetone in the case of 2-propanol) were found in the absence of additives. The corresponding acetals, ethers, and alkanes were obtained by the addition of concentrated hydrochloric acid (HCl). The measurement of the product yields during the post-irradiation dark reaction in the presence of photocatalyst (TiO₂) loaded with platinum(IV) oxide (PtO₂) revealed that the production of ether and ethane and the regeneration of ethanol proceed by the hydrogenation of acetal over loaded metal, presumably via a hemiacetal intermediate. X-ray diffraction (XRD) analyses showed that the loaded PtO₂ is reduced to platinum metal during the course of the photocatalytic reaction. For the production of ether from HCl-acidified ethanol, Pd-loaded catalysts, especially prepared by precipitation—reduction, exhibit the highest activity of several metal-loaded TiO₂ catalysts. From XRD and X-ray photoelectron spectroscopy studies of Pd-loaded TiO₂ particles, it was shown that the smaller the size of the Pd particles, the higher the selectivity for ether production from the acidified ethanol suspension. The application of this photocatalytic O-alkylation to the synthesis of cyclic ethers was demonstrated.     

Sorption behavior of germanium(IV) on titanium dioxide nanoparticles

Titanium dioxide nanoparticles were employed for the sorption of Ge(IV) ions from aqueous solution. The process was studied in detail by varying the sorption time, pH, and temperature. The sorption process was found to be fast, equilibrium was reached within 3 min. A maximum sorption could be achieved from solution when the pH ranges between 4.0 and 11.0. Sorbed Ge(IV) ions can be completely desorbed with 2 mL of 0.3 mol L⁻¹ K₃PO₄-1.0 mol L⁻¹ H₂SO₄ mixture solution. The kinetic experimental data properly correlate with the second-order kinetic model (k ₂ = 0.88 g mg⁻¹ min⁻¹ (25°C)), Reichenberg equation and Morris-Weber model. The estimated E _a for Ge(IV) adsorption on nano-TiO₂ was 19.66 kJ mol⁻¹. The overall rate process appears to be influenced by intra-particle diffusion. The sorption data could be well interpreted with the Langmuir and Dubinin-Radushkevich (D-R) type sorption isotherms. The D-R parameters were calculated to be K = −0.00321 mol₂ kJ⁻², q _m = 0.59 mmol g⁻¹ and E = 12.48 kJ mol⁻¹ at room temperature. Furthermore, the thermodynamic parameters were also determined, and the ΔH ⁰ and ΔG ⁰ values indicated a spontaneous exothermic behavior.     

Reductions by titanium(II) as catalyzed by titanium(IV)

The cobalt(III) complexes, [(NH3)5CoBr]2+ and [(NH3)5CoI]2+ are reduced by Ti(II) solutions containing Ti(IV), generating nearly linear (zero-order) profiles that become curved only during the last few percent of reaction. Other Co(III)-Ti(II) systems exhibit the usual exponential traces with rates proportional to [Co(III)]. Observed kinetics of the biphasic catalyzed Ti(II)-Co(III)Br and Ti(II)-Co(III)I reactions support the reaction sequence: [Ti(II)(H20)n]2+ + [Ti(IV)F5]- (k1)<==>(k -1) [Ti(II)(H2O)(n-1)]2+ + [(H2O)Ti(IV)F5]-, [Ti(II)(H2O)(n-1)]2+ + Co(III) (k2)--> Ti(III) + Co(II) with rates determined mainly by the slow Ti(IV)-Ti(II) ligand exchange (k1 = 9 x 10(-3) M(-1) s(-1) at 22 degrees C). Computer simulations of the catalyzed Ti(II)-Co(III) reaction in perchlorate-triflate media yield relative rates for reduction by the proposed active [Ti(II)(H2O)(n-1)]2+ intermediate; k(Br)/k(I) = 8.     

Titanium-based mixed oxides from a series of titanium(IV) citrate complexes

The isostructural hexaaquatransition-metal/titanium citrate complexes (NH₄)₂[M(H₂O)₆][Ti(H₂cit)₃]₂·6H₂O [M(II)=Mn 1, Fe 2, Co 3, Ni 4, Cu 5, and Zn 6] (H₄cit=citric acid), which were synthesized by reacting titanium(IV) citrate with divalent metal salts in the 1.0-3.5 pH range, adopt hydrogen-bonded chain motifs. The crystal structures feature three bidentate citrate anions that chelate to the titanium atom through their negatively charged α-alkoxy and α-carboxy oxygen atoms; the chelation is consistent with the large downfield shifts of ¹³C NMR for carbon atoms for complex 6. The thermal decomposition of the complexes furnishes mixed metal oxides. The main-group magnesium analog when heated at 600 °C yielded MgTi₂O₅ that is of the pseudobrookite type; the particle size is approximately 30 nm.     

Rapid synthesis of tin (IV) oxide nanoparticles by microwave induced thermohydrolysis

Tin oxide nanopowders, with an average size of 5 nm, were prepared by microwave flash synthesis. Flash synthesis was performed in aqueous solutions of tin tetrachloride and hydrochloric acid using a microwave autoclave (RAMO system) specially designed by the authors. Energy dispersive X-ray analysis (EDX), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, nitrogen adsorption isotherm analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM), were used to characterize these nanoparticles. Compared with conventional synthesis, nanopowders can be produced in a short period (e.g. 60 s). In addition, high purity and high specific surface area are obtained. These characteristics are fundamental for gas sensing applications.     

Chromatographic behaviour of metal ions on tin(IV) and titanium(IV) antimonate papers

Summary The chromatographic behaviour of 49 metal ions has been studied on papers impregnated with Sn(IV) and Ti(IV) antimonates in aqueous HNO₃ and mixed solvent systems containing dimethyl sulphoxide. Numerous separations have been achieved and the Alberti equation, for Sn(IV) and Ti(IV) antimonate papers, in the modified form: –nloga K⁺=R_M + constant (a K⁺=activity of K⁺), has been verified. The effect of the concentration of impregnating reagents on these papers has been determined and compared with other papers. The effect of pH on R_f, R_i, log R_f and R_M values of metal ions has also been examined in aqueous systems.     

Friedel-Crafts alkylation of indoles with epoxides catalyzed by nanocrystalline titanium(IV) oxide

Friedel-Crafts alkylation of indoles with epoxides to afford 3-alkyl indole derivatives at room temperature with moderate to good yields and high regioselectivity using nanocrystalline titanium(IV) oxide catalyst is described.     

A green process for coupling manganese oxides with titanium(IV) dioxide

MnO(2) nanoparticle-loaded TiO(2) prepared by a green process capable of removing harmful MnO(4)(-) ions from water exhibits catalytic activity for a test reaction, H(2)O(2) decomposition, in the dark with its activity enhanced by UV light irradiation.     

Photocatalytic disproportionation of nitrite to dinitrogen and nitrate in an aqueous suspension of metal-loaded titanium(IV) oxide nanoparticles

Photocatalytic reaction of a nitrite ion in aqueous suspensions of bare and metal-loaded TiO(2) particles was examined without electron and hole scavengers under irradiation of UV light. In the bare TiO(2) system, disproportionation of NO(2)(-) to N(2) (or N(2)O) and NO(3)(-) with nitrogen balance (NB) and redox balance (ROB) close to unity within experimental errors was observed, although the reaction was slow. Palladium (Pd)-loaded TiO(2) particles exhibited an extraordinarily large rate of disproportionation of NO(2)(-) in their aqueous suspension, i.e. NO(2)(-) was almost completely converted to N(2) (or N(2)O) and NO(3)(-) even after only 3 h of photoirradiation, both the values of NB and ROB being close to unity. This result suggests that Pd loaded on TiO(2) particles acted as storage sites for photogenerated electrons and effectively transferred the electrons to NO(2)(-) and, therefore, that the reduction process in the photocatalytic disproportionation of NO(2)(-) was accelerated by Pd loaded on TiO(2). Effects of the amount of Pd and pH of the suspension on the reaction rate were also examined.     

Selective photocatalytic reduction of nitrate to nitrogen molecules in an aqueous suspension of metal-loaded titanium(IV) oxide particles

Nitrate was photocatalytically reduced to nitrogen molecules with a high selectivity in a basic aqueous suspension of palladium and copper-loaded titanium(IV) oxide powders in the presence of oxalate anion as a hole scavenger.     

Synthesis,structure, and photocatalytic properties of titanium(IV) oxide modified with silver oxide nanoparticles on a boron-containing mesoporous support

A method for the synthesis of TiO₂–B₂O₃–Ag composite has been proposed. The composite structure and phase composition have been determined by X-ray diffraction analysis, IR spectroscopy, and scanning as well as transmission electron microscopy. The introduction of boron oxide in the TiO₂–Ag composite enhances catalytic activity of the samples in the reactions of methyl orange photodecomposition.