Monitoring bisphosphonate surface functionalization and acid stability of hierarchically porous titanium zirconium oxides

To take advantage of the full potential of functionalized transition metal oxides, a well-understood nonsilane based grafting technique is required. The functionalization of mixed titanium zirconium oxides was studied in detail using a bisphosphonic acid, featuring two phosphonic acid groups with high surface affinity. The bisphosphonic acid employed was coupled to a UV active benzamide moiety in order to track the progress of the surface functionalization in situ. Using different material compositions, altering the pH environment, and looking at various annealing conditions, key features of the functionalization process were identified that consequently will allow for intelligent material design. Loading with bisphosphonic acid was highest on supports calcined at 650 °C compared to lower calcination temperatures: A maximum capacity of 0.13 mmol g(-1) was obtained and the adsorption process could be modeled with a pseudo-second-order rate relationship. Heating at 650 °C resulted in a phase transition of the mixed binary oxide to a ternary oxide, titanium zirconium oxide in the srilankite phase. This phase transition was crucial in order to achieve high loading of the bisphosphonic acid and enhanced chemical stability in highly acidic solutions. Due to the inert nature of phosphorus-oxygen-metal bonds, materials functionalized by bisphosphonic acids showed increased chemical stability compared to their nonfunctionalized counterparts in harshly acidic solutions. Leaching studies showed that the acid stability of the functionalized material was improved with a partially crystalline srilankite phase. The materials were characterized using nitrogen sorption, X-ray powder diffraction, and UV-vis spectroscopy; X-ray photoelectron spectroscopy was used to study surface coverage with the bisphosphonic acid molecules.     

Effect of preparative conditions on the surface characteristics of mixed zirconium and titanium oxides

The surface characteristics of mixed zirconium and titanium oxides prepared from different starting materials are investigated. One mode of preparation entailed the use of zirconium sulfate and titanium oxysulfate as starting materials and ammonium hydroxide as precipitating agent. The produced oxides were washed to different extents to obtain samples with different sulfate content. A second preparative mode used zirconium oxychloride and titanous chloride as starting materials also with ammonium hydroxide as precipitating agent. The oxidation of the titanous to the titanic form for these oxides was carried out by means of oxygen gas. Resulting samples were heat treated at 400 °C and 600 °C, and textural characteristics determined from the adsorption of N₂ at 77 K, complemented by infrared and thermal studies. The samples precipitated from the oxychloride and chloride salts of zirconium and titanium, as well as those precipitated from the sulfate and oxysulfate salts and washed free of the sulfate ions displayed quite similar textural characteristics. The unheated samples and those heat-treated at 400 °C were mesoporous, with some microporosity, and relatively large surface areas in the order of 200–300 m²/g. Heat treatment to 600 °C led to a relative decrease in surface area, in the order of 100 m²/g, and to the disappearance of microporosity. The mixed zirconium and titanium oxides with a sulfate content of ≈17% displayed significantly lower surface areas, smaller than 10 m²/g, with a prevalence of micro and mesoporosity. Infrared and thermal studies indicated the presence of differently bounded sulfato groups, which seem to have a blocking effect on the pores, resulting in the observed smaller surface areas.     

Mesoporous zirconium titanium oxides. Part 1: Porosity modulation and adsorption properties of xerogels

A series of zirconium titanium oxide mesophases containing 33 atom % Zr have been prepared using carboxylic acids of different alkyl chain lengths (Cy ) from y=4-18 through organic-inorganic polymer phase segregation as the gel transition is approached. Thermal treatment of these transparent gels up to 450 degrees C eliminated the organic template, and domain coarsening occurred affording stable worm-hole mesoporous materials of homogeneous composition and pore diameters varying from about 3 to 4 nm in fine increments. With such materials, it was subsequently possible to precisely study the adsorption of vanadium oxo-anions and cations from aqueous solutions and, more particularly, probe the kinetics of intraparticle mass transport as a function of the associated pore dimension. The kinetics of mass transport through the pore systems was investigated using aqueous vanadyl (VO2+) and orthovanadate (VO3(OH)2-) probe species at concentrations ranging from 10 to 200 ppm (0.2 to 4 mmol/L) and pH values of 0 and 10.5, respectively. In the case of both of these vanadium species, the zirconium titanate mesophases displayed relatively slow kinetics, taking in excess of about 500 min to achieve maximum uptake. By using a pseudo-second-order rate law, it was possible to extract the instantaneous and overall rate of the adsorption processes and then relate these to the pore diameters. Both the instantaneous and overall rates of adsorption increased with increasing surface area and pore diameter over the studied pore size range. However, the equilibrium adsorption capacity increased linearly with pore diameter only for the higher concentrations and was independent of pore diameter for the lower concentration. These results have been interpreted using a model in which discrete adsorption occurs at low concentrations and is then followed by multilayer adsorption at higher concentration.     

Chemical solution deposited thin films of titanium,chromium, zirconium,and tin oxides

TiO₂, Cr₂O₃, ZrO₂, and SnO₂ films with thicknesses of ～10–100 nm were produced via dipping into solution and subsequent annealing in air. The films were studied by the methods of scanning electron microscopy, elemental X-ray spectral analysis, optical spectroscopy, and X-ray diffraction. The electrical conductivity of the films in air and in a vacuum was measured. The adhesion of most of the films to the substrate was found to be high. A crystalline structure was observed for films thicker than 10 nm. The films have a specific surface resistance of 10⁸–10¹² Ω in air and 10⁹–10¹⁴ Ω in a vacuum. The films are promising as coatings for various purposes, including the development of structures of the core–shell type.     

Oxide layers with titanium and zirconium phosphates

Oxide-phosphate layers 20 to 150 μm thick were obtained on titanium by plasma electrolytic deposition in individual and mixed aqueous electrolytes with polyphosphate complexes of zirconium(IV), barium(II), and copper(II). Formation features, thickness, elemental and phase compositions, and surface morphology of the films are presented. Depending on the electrolyte composition, synthesis conditions, and temperature of annealing in air, some simple and double phosphates of titanium and zirconium are formed, including ZrP₂O₇, NaTi₂(PO₄)₃, BaTi₂(P₂O₇)₂, Zr_0.2Ti_0.8P₂O₇, and CuTi₂(PO₄)₃.     

The effect of a polypyrrole coating on the thermal stability of microporous polyethylene membranes

Microporous polyethylene (PE) membranes were coated on both sides with a polypyrrole (PPy) overlayer. PPy was deposited also on the walls of pores. Thermodeformation measurements indicate that the hard framework produced by rigid-chain PPy controls the mechanical properties of composite membranes. FTIR spectroscopy was used to detect oxidative processes in both polymer components above 200 °C. Elemental analysis showed that the nitrogen content remains at high level, even after the treatment of membranes in air at 300 °C, indicating that the decomposition involved mainly PE while PPy was much more stable. The changes in surface relief after annealing were assessed with electron microscopy. No oxidative processes were identified in the FTIR spectra of composites after annealing in vacuum, even after treatment at 300 °C.     

Fabrication of a titanium anode with an active coating based on mixed oxides of base metals

Possibility of fabricating a titanium anode with an active coating based on mixed oxides of base metals by using an asymmetric ac current was analyzed.     

Diffusion properties of bilayer membranes based on MC-40 and MF-4SC modified with silicon and zirconium oxides

MC-40 membrane samples modified with a thin MF-4SC layer containing inorganic oxide particles have been synthesized. Deposition of an MF-4SC layer raises the diffusion permeability of the membrane. Insertion of ZrO₂ or SiO₂ nanoparticles into this layer enhances the ion transport selectivity in terms of the cation transport number. The best results are obtained with oxide particles synthesized in the pores of the deposited layer.     

Mesoporous zirconium titanium oxides. Part 2: Synthesis, porosity, and adsorption properties of beads

Mesoporous zirconium titanium mixed-oxide beads having disordered wormhole textures and mole fractions of Zr (x) ranging from x=0.25 to 0.67 have been prepared. The bead preparation method combined the forced hydrolysis of mixtures of zirconium-titanium alkoxides in the presence of long-chain carboxylates with external gelation. Uniformly sized beads could be produced in the size range 0.5-1.1 mm by varying the droplet size and viscosity of the mixed-oxide sol, thus making them suitable for large-scale column chromatographic applications. The beads exhibited narrow pore size distributions with similar mean pore diameters of around 3.7 nm. The specific surface areas of the beads were linked to the Zr mole fraction in the precursor solution and were generally greater than 350 m2/g for x=0.5. A combination of scanning transmission electron microscopy and X-ray absorption fine structure analysis indicated that the pore walls of the beads were composed of atomically dispersed Zr and Ti to form a continuous network of Zr-O-Ti bonds. Mass transport in the beads was evaluated by monitoring the kinetics of vanadate and vanadyl adsorption at pH 10.5 and 0.87, respectively.     

Synthesis and structure of complex metal oxides produced by interaction of iron and nickel acetylacetonates with hydrolysis products of titanium and zirconium alcoholates

The interaction of nickel and iron acetylacetonates with hydrolysis products of titanium and zirconium alcoholates and their mixture has been studied. It was shown that chemical synthesis of organometallic gels followed by heat treatment makes it possible to form complex single-phase binary or ternary oxides. For the first time single-phase metal-containing titanate, zirconate, and titanate-zirconate oxides have been produced and their structure and magnetic and local electronic properties characterized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 295–300, February, 1991.     

Preparation and application of microporous TPX membranes

In the present work, poly(4-methyl-1-pentene) (TPX) was used to prepare hydrophobic microporous membranes, and the application of the prepared membranes to pervaporation and osmotic distillation was also investigated. The TPX/cyclohexane solution inclines to undergo solid-liquid demixing and form polymer particles at room temperature. The solid-liquid demixing is strongly related to the crystallization process. During membrane formation, the competition between solid-liquid demixing and polymer precipitation determines if particulate membranes can be prepared. By using suitable coagulant, such as propanol, the solid-liquid demixing process occurs before polymer precipitation, particulate TPX membranes with interconnected pores can thus be successfully fabricated. By adjusting the coagulation environment, the pore size of the porous TPX membrane can be tailored. Experiments were performed to evaluate the performance of the prepared membranes in pervaporation and osmotic distillation. The results indicate that the performance of the microporous TPX membranes prepared in the present work is comparable to the commercial PTFE membranes.     

Interaction of titanium tetrachloride vapors with zirconium dioxide nanocrystals

Products of interaction of the surface of zirconium dioxide nanocrystals with titanium tetrachloride as a test reagent were studied. The composition and structure of the surface of synthesized products depending on the time of treating the substrate by titanium chloride vapor were determined by a complex monitoring of both chemical conversions in the gas phase and concentrations of components in the solid-phase matrix with the help of gravimetric “in situ” measurements at various stages of the reaction.     

Permporometry characterization of microporous ceramic membranes

An evaluation of nano-order pore size of membranes was carried out using permporometry, the basic principle of which is based on capillary condensation of vapor and the blocking effect of permeation of a non-condensable gas. A computer-controlled apparatus was constructed, where liquid was injected by a syringe pump and nitrogen was used as a carrier, and was applied to the evaluation of the pore size of ceramic membranes prepared from a silica–zirconia composite. The pore size distribution, based on the Kelvin equation (Kelvin diameter), was evaluated over a range of 0.5–30 nm, using water as a condensable vapor. Vapors used in the present study were water, methanol, ethanol, isopropanol, carbon tetrachloride, and hexane. For the case of relatively large pore sizes (larger than 1 nm, based on water vapor), pore size distribution obtained by water vapor agreed very well with those by carbon tetrachloride and hexane. However, pore sizes measured using alcohols were found to be smaller than those determined by water vapor. For the case of pore sizes smaller than 1 nm, the adsorption layer before capillary condensation appears to play an important role.     

Reactions of methylaluminoxane and trimethylaluminum with zirconium and titanium tetracyclopentadienyl derivatives

Gas volumometry, gas chromatography, mass spectrometry, and ESR were used to study reactions of methylaluminoxane (MAO) and Me₃Al with Cp₄Zr, Cp₄Ti, and 2,2,6,6-tetra-methylpiperidine-1-oxyl (TEMPO). It was shown that the reaction is accompanied by evolution of methane, whose amount exceeds the initial concentration of the starting metallocene or free radical by a few hundred times, but in all the cases is no more than 15% of the starting amount of the Me??Al fragments in the organoaluminum compound. Metal-centered radicals were detected by ESR in the systems with Zr and Ti metallocene derivatives. Mechanism of the observed reactions is discussed.     

Synthesis, ethylene polymerization and dynamic features of titanium and zirconium complexes bearing chelating malonate-based enaminoketonato ligands

Synthesis of new titanium and zirconium dichloro complexes bearing malonate-based enaminoketonato (N,O) ligand is described. NMR studies of the catalyst precursors reveal that synthesized complexes have different configurational isomers in solution state and that they undergo structural change within NMR timescale. After MAO activation complexes exhibited low to moderate activities in ethylene polymerization producing bi- or multimodal polyethylenes.     

Heterobimetallic diethanolaminate complexes of titanium and zirconium with alkaline earth metals

Ti(OPr ⁱ )₄ or Zr(OPr ⁱ )₄ · Pr ⁱ OH react with hydrocarbon-insoluble complexes M{(OCH₂CH₂)NH(CH₂CH₂OH)}₂ (M = Mg, Ca, Sr, Ba) in a 2:1 molar ratio to yield hydrocarbon-soluble heterobimetallic diethanolaminate isopropoxide complexes [M{(OCH₂CH₂)₂NH}₂{M(OPr ⁱ )₃}₂] (M = Mg, Ca, Sr, Ba; M = Ti, Zr), which have been characterized by elemental analyses, molecular weight measurements and spectroscopic [i.r., n.m.r. (¹H and ¹³C)] studies.     

Gravimetric separation of titanium and zirconium from Niobium with Phenylacetylhydroxamic acid

Phenylacetylhydroxamic acid is used to separate titanium and zirconium from niobium in an oxalate medium at pH 6.5–7.5 in presence of ammonium chloride at room temperature. The method is accurate when the ratio of (TiO₂ + ZrO₂) : Nb₂O₅ is 10 : 1 to 1 : 1 ; when the niobium concentration is higher, reprecipitation is necessary. Tantalum, citrate, tartrate, lactic acid, EDTA, and a large excess of oxalate interfere.     

FTIR study of E7 liquid crystal orientations confined to cylindrical cavities of Anodisc membranes

The orientation of E7 liquid crystal (LC) confined within 200 nm diameter cylindrical cavities of Anodisc membranes was investigated by FTIR dichroism techniques. The cavity walls of the confining pores were chemically modified with different length aliphatic acids (C_nH_2n+1COOH, n=5, 6, 7, 9) at 2 and 4% concentrations. From the FTIR spectra of the aliphatic acid-treated alumina Anodsic membranes, we found salt formation between the -COOH group of the aliphatic acids and the Anodisc membranes. From the FTIR spectra of LC-filled Anodisc membranes, we found an abrupt alignment direction change, from parallel to perpendicular, of the LC molecules along the long axis of the cavities between n=6 and n=7 for the 2% concentration of aliphatic acid. However for the 4% concentration of aliphatic acid the parallel to perpendicular alignment direction of LC molecules changed between n=5 and n=6. The same trend was previously observed for ²H NMR measurements by other researchers.     

New hybrid chelating sorbents with grafted 3-aminopropionate groups based on mixed silicon,aluminum, titanium,or zirconium oxides

A series of new hybrid organo-inorganic sorbents with the 3-aminopropionate chelating group was synthesized. The synthesis includes the copolycondensation (sol—gel method) of tetraethoxysilane, 3-aminopropyltriethoxysilane, and several modifiers (MeSi(OEt)₃, EtSi(OEt)₃, Ti(OEt)₄, AlONO₃, ZrOCl₂) followed by carboxyethylation with acrylic acid. The obtained chelating sorbents were characterized by elemental analysis, FT-IR and ¹H NMR spectroscopy, and thermogravimetry. The N-carboxylated sorbents have a higher sorption capacity with respect to metal ions (0.5–0.9 mmol g⁻¹, pH 6.3, NH₄OAc, 20 °C) than the starting sorbents with the primary amino group (0.05–0.2 mmol g⁻¹) and manifest high selectivity for copper(II) ion extraction. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1783–1788, August, 2005.