Kinetics and mechanism of exchange reaction of [Y(APTA)] (APTA=o-aminophenol-N,N, O-triacetic acid) with copper(II)

Summary The kinetics of the exchange reaction between [Y(APTA)] and Cu^II have been investigated over a range of [H⁺] from 2.5×10^–5 to 7.5×10^–4 mol dm^–3 at 30°C and ionic strength 0.2 mol dm^–3 KNO₃. The results show that the exchange reaction proceeds via both self-and proton-catalyzed dissociation of [Y(APTA)] and also by the direct attack of Cu^II on [Y(APTA)]. The corresponding rate constants k_d, k _h and k_Cu have been evaluated as 6.3s^–1, 8.4×10⁴ mol^–1 dm³ s^–1 and 416mol^–3 dm³ s^–1 respectively. The possible intermediates are discussed in terms of the structure of APTA. The complex-formation rate constants of Y^III with APTA^3- and HAPTA^2- were also obtained.     

Immobilization of yttrium over crystalline titania

A co-precipitation method was adopted for the immobilization of yttrium radioactive waste over crystalline titania. A high uptake of⁹¹Y was observed over the preformed hydrous titania. Weighable quantity of Y was coprecipitated with Ti(IV) hydroxide and a maximum of 38 wt% was found to be adsorbed. Mixed masses were calcined separately at 800 and 1000°C for 20 hours, and soxhlet leach tests at 97°C, repeated 7 times at an interval of 24 hours, showed the release of yttrium in the order of 10^–1 and 10^–2 g·m^–2·d^–1, respectively. X-ray powder diffraction analysis revealed that the yttrium was immobilized in the titania crystal lattice which suffered some structural changes with the formation of new mineral phase Y₂Ti₂O₇ which is accompanied by rutile and little quantity of anatase form of titania at 800°C, and only rutile form of titania at 1000°C.     

Ultrasound-assisted synthesis of titania hydrosols

0.0021–0.44 M TiO₂ hydrosols have been prepared by an ultrasound-assisted method using titania hydrogel precipitated from TiCl₄ solution. The hydrosols contain amorphous primary titania particles ～5 nm in size, combined into aggregations having average sizes of 22–51 nm.     

Aerosol-assisted synthesis of mesoporous titania nanoparticles with high surface area and controllable phase composition

Mesoporous titania nanoparticles (denoted as MTN) with high surface area (e.g., 252 m² g⁻¹) were prepared using tetrapropyl orthotitanate (TPOT) as a titania precursor and 10–20 nm or 20–30 nm silica colloids as templates. Co-assembly of TPOT and silica colloids in an aerosol-assisted process and immediate calcination at 450 °C resulted in anatase/silica composite nanoparticles. Subsequent removal of the silica colloids from the composite by NaOH solution created mesopores in the TiO₂ nanoparticles with pore size corresponding to that of silica colloids. Effects of silica colloids’ contents on MTN porosity and crystallites’ growth at a higher calcination temperature (e.g., 1000 °C) were investigated. Silica colloids suppressed the growth of TiO₂ crystallites during calcination at a higher calcination temperature and controllable contents of the silica colloids in precursor solution resulted in various atomic ratios of anatase to rutile in the calcinated materials. The mesostructure and crystalline structure of these titania materials were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), differential thermal analysis (DTA)-thermo-gravimetric analysis (TGA), and N₂ sorption.     

Facile preparation of transparent monolithic titania gels utilizing a chelating ligand and mineral salts

Highly homogeneous transparent titania gels have been successfully prepared from titanium alkoxide by a sol–gel method utilizing chelating agent, ethyl acetylacetate (EtAcAc), in the presence of strong acid anions. Only catalytic amount of a strong acid anion suppress the rapid hydrolysis of titanium alkoxide by blocking the nucleophilic attack of HO⁻ and H₂O, and the resultant moderate sol–gel reactions thus afford homogeneous gelation, leading to transparent monolithic titania gels. Gelation time can be widely controlled by changing amounts of water, chelating agent and salt. The ability of salts to suppress the too abrupt sol–gel reactions is strongly dependent on the electronegativity of anions and valence of cations. With employing NH₄NO₃ as a suppressing electrolyte, the obtained titania gels can be converted to pure TiO₂ by simple washing and heat-treatment, and transformations to anatase and rutile structures were found to start at 400 and 600 °C, respectively.     

Complexes of iron(III) with cyclopropanecarbo- and cyclohexyl-acetohydroxamic acids

Summary Cyclopropanecarbohydroxamic acid (CPAH) and cyclohexylacetohydroxamic acid (CHAH) were synthesized, characterized and their pK _a's determined spectro-photometrically as 9.80 and 9.85, respectively, at 25 °C and in buffers of 0.1 mol dm^–3 ionic strength (I). A spectroscopic investigation of their reactions with Fe^III in aqueous solutions revealed the sole formation of the 1:3 complexes at equilibrium. Stability constants (log ₃ at 25 °C and I = 0.1 mol dm^–3 are 34.80 and 34.22 for [Fe(CPA)₃] and [Fe(CHA)₃], respectively. Spectral and magnetic studies of the isolated complexes indicate octahedral coordination via the O atoms of the hydroxamate group.     

Preparation of Lead-Calcium Hydroxyapatite Solid Solutions by a Wet Method Using Acetamide

Lead-calcium hydroxyapatite solid solutions with different Pb/(Pb+Ca) molar ratios (X_Pb) were prepared by a wet method using acetamide (AA). The crystal phase and structure of the products depended on the aging period (t_a), Pb/(Pb+Ca) molar ratio ([X_Pb]), and AA concentration ([AA]) of the starting solution. At [AA]=1.6 mol dm⁻³ and t_a=6 days, the large needle-like PbCaHap particles were formed from solutions at [X_Pb]=0-0.6 and 0.9-1. Under the other AA concentrations and aging periods, pure PbCaHap particles could be obtained in a narrower region of [X_Pb]; e.g., PbCaHap was formed from solutions at [AA]=0.8 mol dm⁻³, t_a=6 days, and [X_Pb]= 0-0.1, 0.4-0.5, and 0.9-1.     

Influence of hydrofluoric acid on extraction of thorium using a commercially available extraction chromatographic resin

The dependence of Th recovery on hydrofluoric acid (HF) concentration in nitric acid (HNO₃) solutions (1–5 mol/dm³) containing 1 × 10⁻⁶ mol/dm³ of Th and various concentrations of HF and the elution behavior were studied using a commercially available UTEVA (for uranium and tetravalent actinide) resin column. Thorium recovery decreased with an increase in HF concentration in the sample solutions. The concentration of HF at which Th recovery started to decrease was ∼1 × 10⁻⁴ mol/dm³ in 1 mol/dm³ HNO₃ solution, ∼1 × 10⁻³ mol/dm³ in 3 mol/dm³ HNO₃ solution, and ∼1 × 10⁻² mol/dm³ in 5 mol/dm³ HNO₃ solution. When Al(NO₃)₃ (0.2 mol/dm³) or Fe(NO₃)₃ (0.6 mol/dm³) was added as a masking agent for F⁻ to the Th solution containing 1 × 10⁻¹ mol/dm³ HF and 1 mol/dm³ HNO₃, Th recovery improved from 1.4 ± 0.3% to 95 ± 5% or 93 ± 3%. Effective extraction of Th using UTEVA resin was achieved by selecting the concentration of HNO₃ and/or adding masking agents such as Al(NO₃)₃ according to the concentration of HF in the sample solution.     

A simple method to synthesize N-doped rutile titania with enhanced photocatalytic activity in sunlight

This study demonstrates a simple route for the synthesis of nanocrystalline N doped rutile titania by calcination of acidified TiCl₃ in presence of urea. Urea was used as a source of nitrogen. The N doped rutile titania was yellow in colour and showed excellent photocatalytic activity in sunlight.     

Kinetics and mechanism of the base hydrolysis of thecis-chlorobis(ethylenediamme)(benzimidazole)cobalt(III) cation

Summary The hydrolysis ofcis-[CoCl(en)₂(bzmH)]²⁺ (en=ethylenediamine, bzmH=benzimidazole) has been studied over the pH range 8.31–11.58 at I=0.1 mol dm^–3 and 25°. Potentiometric titration of aqueous solutions of the [Co(en)₂(bzmH)OH₂]³⁺ complex obtained by silver(I) catalysed aquation of the chloro-complex give pK₁=5.81 and pK₂ = 8.84 for Equilibria (1) and (2) at 25° and I=0.1 mol dm^–3. Spectrophotometric titration of the hydroxy complex also gives a value of pK₂=8.88 for the ionisation of the coordinated benzimidazole. The kinetic data can be interpreted in terms of base hydrolysis ofcis-[CoCl(en)₂(bzmH)]²⁺ (k_OH=220 dm³ mol^–1s^–1) andcis-[CoCl(en)₂(bzm)]⁺ (k_OH=14.9 dm³ mol^–1s^–1). Comparisons with the corresponding imidazole and pyridine complexes are made.     

Process optimization of preparing spherical titania colloids with uniform distribution using artificial neural networks

Optimal operating variables for preparing submicron uniform titania colloids were estimated using the artificial neural networks (ANN) modeling and the process optimization algorithms. Titania colloids were synthesized by a sol–gel method using mixture recipes of titanium tetraisopropoxide (TTIP), NH₃, and H₂O with ethanol/acetonitrile under temperature-controlled conditions. Different sets of the operating variables, such as [NH₃], [H₂O], and reaction temperature, were selected within an operating range to carry out Design of Experiment to evaluate the prepared particle size (PS) and the particle size distribution (PSD) data. The relationship between the operating variables and PS and PSD of the prepared samples can be constructed by an ANN modeling approach. The built ANN model was then used to predict PS and PSD values corresponding to the operating variables. The optimal operating conditions to fabricate different PS values with narrow PSD were determined by the ANN model with the optimization method. Meanwhile, the monodispersed colloids between 150 and 400 nm were fabricated using the determined optimal operating conditions.     

Mixed-ligand complexes of nickel(II) involving sulphur-containing ligands and diaminocarboxylic acids

Summary Stability constants for mixed-ligand complexes of the types [NiABH₂], [NiABH] and [NiAB] formed by Ni^II with l-cysteine (cys), d-penicillamine (pen) or l-cysteic acid (cya) as ligand A and dl-2,3-diaminopropionic acid (dapa), dl-2,4-diaminobutyric acid (daba) or dl-ornithine (orn) as ligand B have been determined by the computerbased analysis of pH titration data obtained at 37 °C and I = 0.15 mol dm^–3 (NaClO₄). In the [NiABH] species, for all three secondary ligands (B), when A = pen or cya the labile proton appears to be attached to the terminal amino group of ligand B, whereas when A = cys it is not clear where the proton is located. In all the systems in the [NiABH₂] species, one proton resides with the primary ligand (A) and the other with the secondary ligand (B). In the [NiAB]-type complexes, cys and pen chelate through the amino and thiolato groups, while cya binds in a glycine-like mode and the secondary ligands (B) coordinate in a terdentate manner.Author to whom all correspondence should be directed.     

Preparing titania aerogel monolithic chromatography columns using supercritical carbon dioxide

The search for a method to fabricate monolithic inorganic columns has attracted significant recent attention due to their unique ability in separation applications of various biomolecules. Silica and polymer based monolithic columns have been prepared, but titania and other metal oxide monoliths have been elusive, primarily due to their fragility. This article describes a new approach for preparing nanostructured titania based columns, which offer better performance over conventional particle packed columns for separating a wide variety of biomolecules including phosphopeptides. TiO₂ monolithic aerogels were synthesized in separation columns using in situ sol‐gel reactions in supercritical carbon dioxide (scCO₂) followed by calcination, and compared to those prepared in heptanes. The characterization results show that scCO₂ is a better solvent for the sol‐gel reactions, providing lower shrinkage with the anatase TiO₂ monolith composed of nanofibers with very high surface areas. The monolithic columns show the ability to isolate phosphopeptides with little flow resistance compared to conventional titania particle based microcolumns.     

Synthesis,characterization and electrocatalytic properties of carbon nitride nanotubes for methanol electrooxidation

In this paper, carbon nitride nanotubes (CNNTs) have been synthesized with porous anodic aluminum oxide membrane as template by the thermal polymerization of sol–gel precursors for the first time. Field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis and X-ray photoelectron spectroscopy were applied to characterize the morphology and composition of the as-prepared nanotubes. The electrocatalytic activity and stability of CNNTs, towards methanol electrooxidation in 0.5 mol/dm³ H₂SO₄ solutions containing 1 mol/dm³ CH₃OH are presented at room temperature.     

New hierarchically porous titania monoliths for chromatographic separation media

Separation media based on hierarchically porous titania (TiO₂) monoliths for high‐performance liquid chromatography (HPLC) have been successfully fabricated by the sol–gel process of titanium alkoxide in a mild condition utilizing a chelating agent and mineral salt. The as‐gelled TiO₂ monoliths were subjected to a simple solvent exchange process from ethanol (EtOH) to H₂O followed by drying and calcination. The resultant monolithic TiO₂ columns consist of anatase crystallites with the typical specific surface area of more than 200 m²/g. The resultant monolithic TiO₂ column calcined at 200 and 400°C exhibited a good separation performance for organophosphates as well as for polar benzene derivatives in the normal‐phase mode.     

Acid dissociation kinetics of the copper(II) complex of a 15-membered mixed N3O2 donor macrocycle

Summary The kinetics of the acid dissociation of the copper(II) complex of the 15-membered N₃O₂ donor macrocycle [prepared by reaction of 2,6-bis(2-aminophenoxymethyl)-pyridine with glyoxal in the presence of a manganese(II) template followed by reduction of the two imine linkages with NaBH₄] was studied over an acidity range (0.01–0.5 mol dm^-3 [H⁺]) at 25 °C and I = 1.0 mol dm^-3 by stopped-flow methods. A biphasic reaction was observed at 752 nm, the first reaction being complete within 20 ms at 25 °C and too rapid to study in detail. The second reaction shows a good first order dependence on the hydrogen ion concentration over the whole acidity range and k _obs=k0+k _H[H⁺], where k ₀ = 0.52 s^-1 and k _H = 40.2 dm³ mol^-1 s^-1 at 25 °C. The k ₀ term represents a small but significant solvolytic reaction. The mechanism of the acid-catalysed dissociation is discussed.     

Inorganic Sol-Gel Preparation of Medium Sized Microparticles of Li2TiO3 from TiCl4 as Tritium Breeding Material for Fusion Reactors

Microspheres of Li₂TiO₃ were fabricated by a classical, inorganic sol-gel process from commercially available TiCl₄. Elaborated process consists of the following main steps: (1) dissolving of TiCl₄ in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl₄ by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li₂TiO₃ microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier.     

Synthesis of Spherical Titanium Dioxide Particles by Homogeneous Precipitation in Acetone Solution

Titania powders were synthesized by thermal hydrolysis of titanium tetrachloride in a mixed solvent was studied. The dielectric constant was tuned by regulating the acetone/water volume ratio (R/H ratio) and temperature of the solvent. Hydroxypropyl cellulose (HPC) was used as a steric dispersant. The synthesis were carried out at R/H ratios of 0–4, temperatures of 70–90°C, TiCl₄ concentrations of 0.05–0.2 M, HPC concentrations of 0–5 × 10^–3 g/cm³, and synthesis times of 15–60 min. The TiO₂ particles obtained at an R/H ratio of 0, i.e., pure water system, were fine and agglomerated. In contrast, the TiO₂ particles prepared at an R/H ratio of 3 were uniform and spherical. The TiO₂ particle size increased with increasing TiCl₄ concentration. The synthesis temperature did not influence the particle size, but greatly influenced the morphologyof the TiO₂. Adding HPC to the solution yielded more uniform and spherical particles. In addition, the synthesis time should be longer than 30 min to obtain the most uniform and spherical particles. The dielectric constant of the acetone-water mixed solvent at 28 gave the most uniform and spherical TiO₂ particles. The powders prepared at the condition of 0.1 M TiCl₄, R/H ratio of 3, HPC concentration of 0.001 g/cm³, temperature of 70°C, and synthesis time of 1 h exhibited the most uniform and spherical morphology. The as-synthesized powder was anatase and retained the phase below 400°C. It transformed to the rutile phase after calcination at 700°C.     

Photocatalytic properties of Ru-doped titania prepared by homogeneous hydrolysis

Nanocrystalline titania particles doped with ruthenium oxide have been prepared by the homogenous hydrolysis of TiOSO₄ in aqueous solutions in the presence of urea. The synthesized particles were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction (SAED) and Nitrogen adsorption-desorption was used for surface area (BET) and porosity determination (BJH). The photocatalytic activity of the Ru-doped titania samples were determined by photocatalytic decomposition of Orange II dye in an aqueous slurry during irradiation at 365 nm and 400 nm wavelengths.      

Photocatalytic destruction of catechol on illuminated titania

First-order kinetics was found for the photocatalytic oxidation of catechol on TiO₂. Kinetic constants calculated from the Langmuir-Hinshelwood equation are: k=2.03x10^-8 mol dm^-3 s^-1; K_ads=1.63x10⁴ dm³ mol^-1. Full catechol mineralization is a multistep reaction, 1,2,4-benzenetriol and glycol are the main intermediates. This revised version was published online in August 2006 with corrections to the Cover Date.