Effects of nickel(II) oxide on the thermal decomposition of alkali persulfates

The thermal decomposition of Na₂S₂O₈ and K₂S₂O₈ has been studied derivatographically in the presence of NiO at various molar mixtures. Experiments have proved that the first decomposition stage (persulfate into pyrosulfate) is independent of the amount of the oxide present. During the second decomposition stage (pyrosulfate into sulfate) which occurs in the melt, NiO plays the role of lowering the melting, the initial and final decomposition temperatures of pyrosulfates. The lowest melting temperatures recorded for Na₂S₂O₈ and K₂S₂O₈ are 320 and 280°C, respectively.A mechanism has been proposed to describe the catalytic action of NiO on the thermal decomposition of alkali pyrosulfates. The mechanism makes use of the semiconductivity of NiO and the availability of electron-rich centers in the pyrosulfate group to help the formation of an adsorption complex between them.NiO reacts to some extent with alkali pyrosulfates forming the yellow NiSO₄ and alkali sulfates as separate products.NiO and NiSO₄ form eutectic mixtures with alkali sulfates melting at temperatures lower than those of the pure salts.     

Determination of some kinetic parameters of the thermal decomposition of alkali persulfates from DTA curves

Using the DTA curves the thermal decomposition of alkali persulfates for the corresponding pyrosulfates is shown to be a second order reaction with activation energies of 72.7–75.6 kcal mol^?1 for sodium persulfate and 67.7–69.1 kcal mol^?1 for potassium persulfate.     

Solid-state reactions between alkali persulfates and oxides of corundum structure

The effects of three corundum structure oxides, α-Al₂O₃, α-Cr₂O₃, and α-Fe₂O₃, on the thermal decomposition of sodium and potassium peroxodisulfates (persulfates) under non-isothermal static air conditions and using various oxide/persulfate molar ratios, have been thermoanalytically investigated. Compounds such as Na₃Al(SO₄)₃, K₃Al(SO₄)₃, Cr₂(SO₄)₃, K₃Cr(SO₄₃, and Na₃Fe(SO₄)₃ are identified by X-ray diffractometry and conventional chemical analysis. The molar ratios as well as temperatures of the stoichiometric formation for these compounds have been established. At higher temperatures, α-Al₂O₃ acts as a promoter catalyst for the decomposition of pyrosulfate to sulfate, whereas α-Cr₂O₃ behaves as a retarder for the decomposition of persulfate. A eutectic mixture is formed between K₃Al(SO₄) and K₂SO₄ at 675°C. Also, K₃Fe(SO₄)₃ is identified as two crystalline phases.     

Encapsulation of titanium(IV) oxide particles in hollow silica for size-selective photocatalytic reactions

A core-shell composite of TiO2 particles encapsulated in a hollow silica was fabricated, and the core-shell composite showed size-selective photocatalytic activity for decomposition of organics without reducing the intrinsic activity of the naked TiO2 core.     

Thermal and X-Ray studies of reactions between scandium(III) oxide and sodium or potassium persulfates

TG, DTG, and DTA experiments were carried out to elucidate the influence of Sc₂O₃ on the thermal decomposition of Na₂S₂O₈ and K₂S₂O₈ under a static (air) atmosphere from ambient to 1050°C, using a derivatograph. X-Ray diffractometry has been employed to identify the intermediate and final decomposition products. Different Sc₂O₃ Na₂(K₂)S₂O₈ molar ratios were investigated and the 1 : 3 ratio found to be the one that gives stoichiometric reactions with either of these salts. Sc₂O₃ was found to react at 250 and 440°C with the thermally produced Na₂S₂O₇ yielding Sc₂(SO₄)₃. The scandium(III) sulfate was thermally stable up to 840°C. Similarly, the oxide reacts stoichiometrically at 420°C to produce KSc(SO₄)₂, a double salt which began to decompose at 840°. Moreover, three new crystalline phase-transformations were detected for Sc₂(SO₄)₃ at 640, 695, and 735°C.     

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.     

Size-selective photocatalytic reactions by titanium(IV) oxide coated with a hollow silica shell in aqueous solutions

A novel core-shell composite photocatalyst, commercially available titanium(IV) oxide (TiO(2)) particles directly incorporated into a hollow amorphous silica shell, was fabricated by successive coating of TiO(2) with a carbon layer and a silica layer followed by heat treatment to remove the carbon layer. The composite induced efficient photocatalytic reactions when relatively small substrates were used, such as methanol dehydration and decomposition of acetic acid, without any reduction in the intrinsic activity of original TiO(2), but did not exhibit efficient photocatalytic activity for decomposition of large substrates, methylene blue and polyvinyl alcohol. The unique size-selective properties of the composites are due to their structural characteristics, i.e., the presence of a pore system and a void space in the silica shell and between the shell and medial TiO(2) particles, respectively. The loading of alkylsilyl groups on the surface of the composite led to highly photostable floatability: the floated sample also induced efficient photocatalytic reaction for decomposition of acetic acid while retaining floatation at the gas/water interface.     

Thermal studies of some aryloxides of titanium(IV)

Thermal behaviour of aryloxides of titanium(IV) of composition TiCl_n(OAr)_4?n (wheren=0→3 and OAr=OC₆Bu^t-4, OC₆H₄OMe-4 and OC₆H₂-Bu ₂ ^t -2,6?Me-4) has been studied by DTA and TG analysis. Multiple decomposition steps have been indicated by thermal weight losses which are both exothermic and endothermic as shown by DTA curves. Based upon the total % loss in weight; during entire decomposition titanium dioxide has been found to be the final residue in each case.     

Rhodium(II) catalyzed multi-component reactions of aryldiazoacetates with titanium(IV) isopropoxide and imines

Rh₂(OAc)₄ catalyzed diazo decomposition of aryldiazoacetates in the presence of titanium(IV) isopropoxide generated oxonium ylide intermediates. Trapping of the oxonium ylide intermediates with imines occurred subsequently via a nucleophilic addition. The three-component reaction of aryldiazoacetates, titanium(IV) isopropoxide, and imines gave α-alkoxyl-β-amino acid derivatives with C-N/C-C bond formation in a single step. Extension of the study to a four-component reaction with in situ generated imine was also investigated.     

Mononucleating bis(beta-diketonate) ligands and their titanium(IV) complexes

Novel bis(beta-diketones) linked by 2,2'-biphenyldiyl, 2,2'-tolandiyl, and 2,2'-bis(methylene)biphenyl moieties have been prepared. All are metalated readily by titanium(IV) isopropoxide, but the nature of the complexes formed depends on the linker structure. The biphenyl-bridged ligand gives only traces of a mononuclear complex, which is thermodynamically unstable with respect to oligomerization. The tolan-bridged ligand does form mononuclear complexes, but only as a mixture of geometric isomers. In contrast, the substituted 2,2'-bis-(2,4-dioxobutyl)biphenyl ligands, R2BobH2 (R = tBu, p-Tol), react with Ti(OiPr)4 to give, initially, a mixture of monomer and oligomers, which is converted quantitatively to monomer upon heating in the presence of excess Ti(OiPr)4. Only a single relative configuration of the biphenyl and bis(chelate) titanium moieties, established by crystallography of (tBu2Bob)Ti(O-2,6-iPr2C6H3)2 to be the (R)-/(S)- diastereomer, is observed. The kinetic and thermodynamic robustness of the (R2Bob)Ti framework is confirmed by reactions with Lewis acids. For example, (Tol2Bob)Ti(OiPr)2 reacts with trimethylsilyl triflate or triflic acid to substitute one or both of the isopropoxide groups with triflates without any redistribution or loss of the diketonate ligands. Cationic complexes can be prepared by abstraction of triflate from (Tol2Bob)Ti(OiPr)(OTf) with Na[B(C6H3(CF3)2)4]. For example, in the presence of diethyl ether, the crystallographically characterized [(Tol2Bob)Ti(OiPr)(OEt2)][B(C6H3(CF3)2)4], containing a rapidly dissociating ether ligand, is formed.     

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.     

Synthesis and some properties of furylacrylates of aluminium(III) and titanium(IV)

Summary Compounds of the type [M(OPrⁱ)_m–n(FA)_n] (where m = 3 and n = 1 to 3 when M = Al; and m = 4 and n = 1 to 4 when M = Ti) have been synthesised by the reactions of aluminium and titanium isopropoxides with furylacrylic acid (HFA) in benzene. The corresponding tertiary butoxide derivatives, [M(OBu^t)_m–n(FA)_n], were also obtained by the alcohol-interchange technique. These compounds have been characterised by elemental analysis, and i.r. and p.m.r. spectra.     

Spectroscopic studies on some fluorescent mixed-ligand titanium(IV) complexes

A novel route to synthesize some titanium(IV) complexes containing acetylacetone, straight chain carboxylic acid and hydroxycarboxylic acid ligands has been investigated. Complexes with the general formula [Ti(acac)Cl(2-n)(OOCR*)(n)(OOCC(15)H(31))] (where Hacac=acetylacetone, R*COOH=hydroxycarboxylic acids and n=1 or 2) have been isolated and characterized. Molecular weight determinations indicated mononuclear nature of the complexes. LMCT bands were observed in the electronic spectra. Infrared spectra suggested bidentate nature of the ligands. Fluorescent behaviour of the complexes was noticed on the basis of fluorescence spectra. Powder XRD indicated them to be semi-crystalline having the crystallite size in 136-185 nm range. Transmission electron microscopy (TEM) indicated spherical particles of ~ 200 nm diameter. On the basis of physico-chemical studies, it is suggested that titanium is having coordination number 7 or 8 in these complexes.     

Tin(IV), titanium(IV) and hafnium(IV) complexes of some aromatic Schiff bases derived from 4-aminoantipyrine

Summary Tin(IV), titanium(IV) and hafnium(IV) chloride complexes of ligands such as salicylidene-4-aminoantipyrine (HL¹), 5-chlorosalicylidene-4-aminoantipyrine (HL²), 2,4-dihydroxybenzylidene-4-aminoantipyrine (HL³), 2-hydroxy-1-naphthylidene-4-aminoantipyrine (HL⁴) and 2-hydroxyacetophenonylidene-4-aminoantipyrine (HL⁵) have been prepared and characterized. The analytical data show that tin(IV) forms only 1:1 metal complexes when reacted with HL¹, HL³ and HL⁴, whereas it forms 1:1 and 1:2 metal complexes when reacted with HL², depending on the molar ratio. HL⁵ produces only the binuclear complex SnHL⁵Cl₄(H₂O)SnCl₄. Titanium(IV) gives only one type of complex of the general formula [Ti(HL)₂Cl₂]Cl₂-2H₂O, whilst hafnium(IV) gives HfHL³Cl₄-4H₂O and Hf(L⁵)₂Cl₂.     

Products and kinetics of non-isothermal decomposition of vanadium(IV) oxide compounds

The kinetics of dehydration and decomposition of VOSO₄·2H₂O, VOSO₄ and VOSeO₃·H₂O was studied under non-isothermal heating on a derivatograph. The stages and products of the thermal decomposition were determined. It was proved that VOSO₄·2H₂O decomposes to V₂O₅ while VOSeO₃·H₂O − to V₂O₄. A number of kinetic models and calculation procedures were used to determine the values of the kinetic parameters characterizing the process. The parameters calculated were compared and analyzed. IR-spectra of the initial substances and the solid residue after decomposition are presented.     

Synthesis and molecular structures of some new titanium(IV) aryloxides.

The coordination chemistry of model phenolic ligands (pyrocatechol, salicylic acid, and 2,2'-biphenol) that are able to form respectively five-, six-, or seven-membered rings with titanium(IV) alkoxides is investigated. With pyrocatechol, a polynuclear complex containing 10 Ti atoms was characterized with a not very common doubly bridging mu3-(O,O,O',O') coordination mode. With salicylic acid, a monomeric tris(chelate) complex was obtained. With 2,2'-biphenol, a polynuclear complex containing six Ti atoms was obtained showing both mu2-(O,O') and mu2-(O,O,O') coordination modes for the ligands. Intermolecular interactions in the solid state for these three new compounds are also quantitatively discussed using the partial charge model.     

Molecular orbitals and photoelectron spectra of some titanium(IV) organometallic compounds

The photoelectron spectra of some titanium(IV) organometallic compounds are reported, and the data and the bonding in the compounds are discussed with the aid of extended CNDO/2 calculations.     

Platinum(IV) oxide catalyzed H-D exchange reactions in arylsilanes

[reaction: see text] Arylsilanes were regioselectively labeled with deuterium by treatment with platinum(IV) oxide and deuterium oxide under hydrothermal conditions. Arylsilanols were also labeled with regioselectively under the same conditions.     

Catalysis by titanium (IV) ions of reactions forming chlorohydrins from olefins

A study was made of reactions forming chlorohydrins from cyclohexane and other olefins acted upon by H₂O₂ and HCl or H₂O₂ and TiCl₄ in alcoholic solutions. The catalyzing action of titanium (1V) was established, and possible reaction mechanisms are discussed.L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prosp. Nauki, 252039, Kiev, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 5, pp. 295—299, September–October, 1996. Original article submitted February 9, 1996.     

Nickel(II) oxide surface-modified titanium(IV) dioxide as a visible-light-active photocatalyst

The electronic modification of TiO(2) with highly dispersed NiO particles smaller than ca. 2 nm by the chemisorption-calcination-cycle technique has given rise to a high level of visible-light-activity exceeding that of iron oxide-surface modified TiO(2) simultaneously with the UV-light-activity being significantly increased.