Synthesis of titania-silica xerogels by co-solvent induced gelation at ambient temperature

A series of binary titania-silica mixed oxides was prepared by sol-gel synthesis at room temperature. The hydrolysis of titanium isopropoxide (Ti(ⁱOPr)₄) and tetraethylorthosilicate (TEOS) was facilitated by co-solvent induced gelation in acidic media. The resulting gels were dried, calcined, and then characterized by powder X-ray diffraction analysis, nitrogen sorption studies (at 77 K), diffuse reflectance spectroscopy, Raman microscopy, and transmission electron microscopy. The nitrogen sorption studies indicate that the porosities could be tuned when simple aromatic solvents such as toluene, p-xylene, or mesitylene were added as a co-solvent to the synthesis gel. The binary mixed metal oxide materials obtained in this study showed high activity towards the degradation of phenol, and possessed high surface areas, and large pore volumes with narrow pore size distribution without the need for additional hydrothermal synthesis or supercritical drying.     

Comparative properties of ternary oxides of ZrO2-TiO2-Y2O3 obtained by laser ablation, magnetron sputtering and sol-gel techniques

Thin films of ternary oxides of zirconium (Zr), yttrium (Y) and titanium (Ti) were obtained by the sol-gel, magnetron sputtering and laser ablation techniques. Zirconium propoxide, titanium isopropoxide and yttrium nitrate hexahydrate reagents were used as precursors in the sol-gel process. The Zr/Ti and Zr/Y molar ratios have been controlled by varying the precursors and surfactant concentration. The obtained gels were supported by dip coating on α-alumina supports, dried at 373 K and calcinated at 873 K. The powders obtained after the removal of carbon residuals were subsequently pressed and calcinated for using as targets for the magnetron sputtering and pulsed laser deposition techniques. The chemical composition was determined by Auger Electron Spectroscopy. The surface topography was investigated by Atomic Force Microscopy, while the crystallinity was evaluated from X-ray diffraction. The electrical response of the deposits to nitrogen oxides (NO_x) toxic gas is discussed according to the experimental conditions.     

Comparative study of the porosity induced by CTAB and Tween as silica templates

In this study doped-silicon polymers were synthesized using the non-ionic surfactant Tween 80 as template. The obtained material was compared with silicates doped with the cationic surfactant CTAB. Both materials were synthesized by sol–gel process with tetraethoxysilane (TEOS) as silicon source. In the synthesis procedure reported herein the main difference to previous reports is that the obtained solids were dried smoothly at 55 °C avoiding surfactant calcination. The aim of this work is to obtain new biomaterials appropriate to be used for encapsulation devices in which the surfactant kept within the silica network has two roles: (1) to improve the mechanical resistance in drying–swelling processes preventing crack formation, (2) to hold and protect the encapsulated molecules keeping intact their bioactivity during TEOS polymerization. Structural features such as pore size and surface topology were studied by means of N₂ adsorption, X-ray diffraction and AFM microscopy. The influence of surfactant net charge and molecular shape on the materials obtained is discussed.     

Preparation and characterization of selenium incorporated anodic conversion coatings on titanium surfaces for biomedical applications

An anodic spark deposition process was used for preparation of inorganic, glass-ceramic like conversion coatings. The microstructure of the layers was characterized by surface and solid state techniques such as scanning electron microscopy, electron probe microanalysis and Raman spectroscopy. The porous coatings, typically up to 8 μm thick, consist mainly of titanium oxides and amounts of incorporated electrolyte constituents like Se, Ca or P. Beside nano crystalline anatase phases, a mostly amorphous structure is proposed in which network-forming [PO₄] tetrahedras and [TiO₆] octahedras in various degrees of condensation are connected. A drastic modification of the film structure was observed when selenium was incorporated into the glassy oxide structure of the coating. In these cases no nano crystalline phases of titanium oxides or other chemical compounds were detected. First cell culture investigations show a significant improvement of the biological properties. Cell proliferation and TGF-beta-expression of these coatings in comparison with commercial pure titanium (CPT) with native titanium oxide films were examined.     

Total oxidation of volatile organic compounds on Au/Ce–Ti–O and Au/Ce–Ti–Zr–O mesoporous catalysts

Cerium–titanium mixed oxides and mesoporous cerium-modified titanium and cerium-modified titanium–zirconium mixed oxides were synthesized in order to obtain active support for gold volatile organic compound (VOC) oxidation catalysts. Ce–Ti mixed oxides were synthesized by sol–gel method. Mesoporous TiO₂ and Ti–Zr mixed oxides were prepared through the surfactant templating technique. Gold was loaded on supports by deposition-precipitation method. The catalysts were characterized by thermal analysis, XRD, N₂ analysis, TPR, DR/UV–vis and IR. The results evidenced the beneficial role of ceria modifying additive in decreasing the degree of crystallinity of mesoporous support and its particle size. A high degree of synergistic interaction between ceria and mesoporous oxide was observed. H₂-TPR revealed that the reducibility of the catalysts is greatly enhanced in the presence of gold. Considering the light off temperature, the activity of Au/mesoporous cerium-modified titanium oxide is particularly interesting for VOC oxidation comparatively to the same catalysts with a classical support. The gold particles would be more dispersed and stable. However, the sample Au/mesoporous cerium-modified titanium–zirconium mixed oxide is less interesting for VOC oxidation, particularly for toluene oxidation whose activity depends essentially on the adsorption of toluene molecule.     

The influence of surfactants on the roughness of titania sol–gel films

Substrate dipping in a composite sol–gel solution was used to prepare both smooth and rough thin films of titanium dioxide (TiO₂) on commercial fiberglass. The deposition of a composite film was done in a beaker using a solution of titanium (IV) isopropoxide as the sol–gel precursor and cetyltrimethyl ammonium bromide as the surfactant. In order to establish a correlation between experimental conditions and the titanium oxide produced, as well as the film quality, the calcined samples were characterized using Raman spectroscopy, UV–vis spectrophotometry, scanning electron microscopy and atomic force microscopy. One of the most important results is that a 61-nm TiO₂ film was obtained with a short immersion of fiberglass into the sol–gel without surfactant. In other cases, the deposited film consisted of a titanium precursor gel encapsulating micelles of surfactant. The gel films were converted to only the anatase phase by calcining them at 500 °C. The resulting films were crystalline and exhibited a uniform surface topography. In the present paper, it was found that the TiO₂ films prepared from the sol–gel with a surfactant showed a granular microstructure, and are composed of irregular particles between 1.5 and 3 μm. Smooth TiO₂ films could have useful optical and corrosion-protective properties and, on other hand, roughness on the TiO₂ films can enhance the inherent photocatalytic activity.     

Preparation of nanocrystalline MgO by surfactant assisted precipitation method

Nanocrystalline magnesium oxide with high surface area was prepared by a simple precipitation method using pluronic P123 triblock copolymer (Poly (ethylene glycol)-block, Poly (propylene glycol)-block, Poly (ethylene glycol)) as surfactant and under refluxing conditions. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET) and scanning and transmission electron microscopies (SEM and TEM). The obtained results revealed that the refluxing time and temperature and the molar ratio of surfactant to metal affect the structural properties of MgO, because of the changes in the rate and extent of P123 adsorption on the prepared samples. The results showed that the addition of surfactant is effective to prepare magnesium oxide with high surface area and affects the morphology of the prepared samples. With increasing the P123/MgO molar ratio to 0.05 the pore size distribution was shifted to larger size. The sample prepared with addition of surfactant showed a plate-like shape which was completely different with the morphology of the sample prepared without surfactant. The formation of nanoplate-like MgO was related to higher surface density of Mg ions on the (0 0 1) plane than that on the other planes of the Mg(OH)₂ crystal. The (0 0 1) plane would be blocked preferentially by the adsorbed P123 molecules during the growing process of Mg(OH)₂ nanoentities and the growth on the (0 0 1) plane would be markedly restricted, and the consequence is the generation of nanoplate-like MgO. In addition, increase in refluxing temperature and time increased the specific surface area of the prepared MgO samples.     

Effect of thermal oxidation on titanium oxides' characteristics

Nanocrystalline TiO₂, in the form of anatase or rutile, is one of the most important and used photocatalysts because of its excellent conversion efficiencies and its chemical stability. TiO₂ layers can be grown on titanium by means of anodising processes: the so-obtained oxides present either amorphous or semicrystalline structure, depending on process parameters. When a homogeneous oxide with maximum thickness of the order of hundreds of nanometres is formed, a wide range of interference colours appear on the oxide surface, showing different hues and saturations. Similar effects are obtained when the oxidation process consists of a thermal treatment. This work is aimed at the exploration of the parameters involved in thermal oxidation and of their influence on the growing oxide characteristics, with particular reference to its thickness and the contingent generation of crystal phases (anatase and rutile) responsible for photoinduced properties. Oxide characteristics are investigated by means of reflectometry and X-ray diffraction. Thermal treatments proved to be an efficient way to tune oxide thickness and structure, in order to achieve the formation of oxides showing photoactivated properties both in the UV and in the visible light range, as well as to tune their chromatic properties.     

Control of pore size distribution of silica gel through sol-gel process using inorganic salts and surfactants as additives

For control of the pore size distribution of silica gel, the gel was prepared using the sol-gel process modified by adding several kinds of inorganic salts and surfactants. The addition of any inorganic salt decreased the gel surface area and depressed the formation of mesopores. The surface area and the volume occupied by mesopores changed with the valency of the cation of the salt used. When surfactants were employed as additives, the surface area and the pore size distribution were greatly dependent on the kind of head group of the surfactant: non-ionic surfactant addition monotonously increased the surface area owing to the formation of larger mesopores; anionic surfactant addition significantly decreased the surface area because of the decrease in the volume of mesopores; cationic surfactants caused the surface area to decrease with small additions as anionic surfactants did, while further addition raised the surface area. The rise in the surface area was due to a marked formation of smaller mesopores. These results are discussed on the basis of the interfacial properties of the additives.     

Titanium oxide films produced on commercially pure titanium by anodic oxidation with different voltages

Titanium oxide films produced on commercially pure Ti by anodic oxidation with different voltages were analyzed. Anodic oxidation was carried out at room temperature using 1.4 M H₃PO₄ electrolyte and a platinum counter-electrode, in potentiostatic mode under the following conditions: 50 V, 100 V, 150 V, 200 V and 250 V. It was observed that porous titanium layers were formed at all voltage values but morphological differences were observed. Initially, the film was thin but with increasing voltage it broke down locally and porous regions became evident due to the dielectric breakdown. The porosity and the pore size increased with the increasing voltage. The surface morphology in samples formed with 200 V had substantially different porous structures than those formed with other voltage values. The anodic film surface displayed pores and craters formed on the relatively flat ground oxide surface. AFM images showed that higher voltages produced thicker titanium oxide films.     

Wetting of rare-earth element oxides by metallic melts

The results of studies on the wettability and contact interaction of rare-earth (REE) oxides and aluminium oxide (for comparison) with metallic melts are presented. Proceeding from analysis of the data obtained, a mechanism of interaction of metallic melts with rare-earth element oxides is proposed, based on the interaction of the metallic melt components with the cationic and the anionic sublattice of the oxides. The necessity to take into account the interaction of the melt metal with the cationic sublattice of oxide is determined by a high chemical affinity of the REE for quite a number of metals and by specific features of the structure of the surface of the oxides.     

Structure, morphology and fibroblasts adhesion of surface-porous titanium via anodic oxidation

Surface-porous titanium samples were prepared by anodic oxidation in H₂SO₄, H₃PO₄ and CH₃COOH electrolytes under various electrochemical conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were employed to characterize the structure, morphology and chemical composition of the surface layer, respectively. Closer analysis on the effect of the electrochemical conditions on pore configuration was involved. It can be indicated that porous titania was formed on the surface layer, and the pore configuration was influenced by electrolyte composition and crystal structure of the titania. The fibroblast cells experiment showed that anodic oxidation of titanium surface could promote fibroblast adhesion on Ti substrate. The results suggested that anodic oxidation of Ti in CH₃COOH was suitable to obtain surface-porous titanium oxides layers, which might be beneficial for better soft tissue ingrowths.     

Design and synthesis of polymetallic nanoparticles and their catalytic applications

High-temperature hydrogen reduction reactions enable the synthesis and processing of binary metal oxide composite nanoparticles starting from titanium, ruthenium, and silicon, while the use of a surface modifier and an organic surfactant enables the synthesis of catalytic thin films from binary semiconductor oxides. Surface characterization by XRD, SEM, TEM, AFM, Raman spectroscopy, and BET measurements indicate that the incorporation of binary oxide particles into the semiconductor materials altered the surface properties and morphology of the nanoparticles while the surface modifier and organic surfactant loading can be experimentally adjusted to obtain thin films of varying morphological characteristics.     

Preparation and characterization of porous ultrafine Fe2O3 particles

Porous ultrafine Fe₂O₃ particles were prepared by homogeneous precipitation method. Fe³⁺ and urea were chosen as starting materials and anionic surfactant as the template. It is shown that the reaction results in the precipitation of a gelatinous hydrous iron oxide/surfactant mixture, which gives ultrafine Fe₂O₃ particles after drying and calcinations. The products were characterized by XRD, TEM, TG/DTA and BET. Conventional XRD patterns show that the products are mixture of γ-Fe₂O₃ and α-Fe₂O₃ phase after being sintered at 350 °C, and γ-Fe₂O₃ transforms entirely to α-Fe₂O₃ when sintered at 650 °C. The low-angle XRD patterns indicate that the mesostructure can only exist between 350 and 400 °C. TEM results show that the Fe₂O₃ particles have diameters of about 30 nm and lengths ranging from 100 to 120 nm; in each particle, there are several vermiculate-like mesopores with diameter of about 20-25 nm. The BET surface areas in excess of 50 m²/g are obtained after calcinations at 350 °C. The BJH desorption average pore width is around 22 nm, which is in agreement with the TEM results. The results show that anionic surfactant and sintering temperature are important to obtain this special morphology.     

An oxygen nonstoichiometry study of barium polytitanates with hollandite structure

A series of barium titanium oxides with various Ba/Ti ratios having a hollandite structure were obtained by firing chemical synthesized oxide precursors under reducing atmosphere conditions (H₂/N₂ gas mixture flow) at temperatures of 1100°C and above. An oxygen nonstoichiometry was determined by a thermogravimetric analysis through oxidizing in air. It was shown that barium titanium hollandites may adopt both oxygen excess and oxygen-deficient stoichiometries within the structure. As a limiting case the barium titanium hollandites with only tetravalent titanium ions were obtained. The influence of oxygen nonstoichiometry on the hollandite monoclinic-tetragonal phase transition and a barium superstructure ordering was investigated and discussed. Distortion scaling rules are considered to compare this work with earlier investigations on hollandites.     

Electrochemical characteristics of nanotubes formed on Ti-Nb alloys

Titanium and Ti alloys have been used extensively as bone-implant materials due to their high strength-to-weight ratio, good biocompatibility and excellent corrosion resistance. In this work, we have investigated the effects of the β-stabilizing element Nb on the morphology of nanotubes formed on Ti-xNb alloys using 1.0 M H₃PO₄ electrolyte containing 0.8 wt.% NaF and various electrochemical methods. Oxide layers consisting of highly ordered nanotubes with a wide range of diameters (approximately 55-220 nm) and lengths (approximately 730 nm-2 μm) can be formed on alloys in the Ti-xNb system as a function of Nb content. The nanotubes formed on the Ti-Nb alloy surface were transformed from the anatase to rutile structure of titanium oxide. The titanium oxide nanotube surface was observed to have lower corrosion resistance in 0.9% NaCl solution compared to titanium oxides surfaces on Ti-xNb alloys without the nanotube morphology.     

Surface characteristics of a porous-surfaced Ti-6Al-4V implant fabricated by electro-discharge-compaction

Electro-discharge-compaction (EDC) is a unique method for producing porous-surfaced metallic implants. The objective of the present studies was to examine the surface characteristics of the Ti-6Al-4V implants formed by EDC. Porous-surfaced Ti-6Al-4V implants were produced by employing EDC using 480 F capacitance and 1.5 kJ input energy. X-ray photoelectron spectroscopy was used to study the surface characteristics of the implant materials. C, O, and Ti were the main constituents, with smaller amounts of Al and V. EDC Ti-6Al-4V also contained N. Titanium was present mainly in the forms of mixed oxides and small amounts of nitride and carbide were observed. Al was present in the form of aluminum oxide, while V in the implant surface did not contribute to the formation of the surface oxide film. The surface of conventionally prepared Ti-6Al-4V primarily consists of TiO₂, whereas, the surface of the EDC-fabricated Ti-6Al-4V consists of complex Ti and Al oxides as well as small amounts of titanium carbide and nitride components. However, preliminary studies indicated that the implant was biocompatible and supports rapid osseointegration.     

Characterization of surface oxide films on titanium and bioactivity

Biological properties of titanium implant depend on its surface oxide film. In the present study, the surface oxide films on titanium were characterized and the relationship between the characterization and bioactivity of titanium was studied. The surface oxide films on titanium were obtained by heat-treatment in different oxidation atmospheres, such as air, oxygen and water vapor. The bioactivity of heat-treated titanium plates was investigated by immersion test in a supersaturated calcium phosphate solution. The surface roughness, energy morphology, chemical composition and crystal structure were used to characterize the titanium surfaces. The characterization was performed using profilometer, scanning electronic microscopy, ssesile drop method, X-ray photoelectron spectroscopy, common Bragg X-ray diffraction and sample tilting X-ray diffraction. Percentage of surface hydroxyl groups was determined by X-ray photoelectron spectroscopy analysis for titanium plates and density of surface hydroxyl groups was measured by chemical method for titanium powders. The results indicated that heat-treatment uniformly roughened the titanium surface and increased surface energy. After heat-treatment the surface titanium oxide was predominantly rutile TiO₂, and crystal planes in the rutile films preferentially orientated in (1 1 0) plane with the highest density of titanium ions. Heat-treatment increased the amount of surface hydroxyl groups on titanium. The different oxidation atmospheres resulted in different percentages of oxygen species in TiO₂, in physisorbed water and acidic hydroxyl groups, and in basic hydroxyl groups on the titanium surfaces. The immersion test in the supersaturated calcium phosphate solution showed that apatite spontaneously formed on to the rutile films. This revealed that rutile could be bioactivated. The analyses for the apatite coatings confirmed that the surface characterization of titanium has strong effect on bioactivity of titanium. The bioactivity of the rutile films on titanium was related not only to their surface basic hydroxyl groups, but also to acidic hydroxyl groups, and surface energy. Heat-treatment endowed titanium with bioactivity by increasing the amount of surface hydroxyl groups on titanium and its surface energy.     

微米TiO-2的表面改性及其分散性研究

为提高微米TiO2的分散性,采用偶联剂(KH570)法、无机包覆(铝包覆)法、超声法、非离子表面活性剂(PEG)法、阴离子表面活性剂(月桂酸钠)法,分别对微米TiO2进行表面改性。分析了改性前后微米TiO2的亲油化度、表面形态以及粒径大小。结果表明:超声法(功率90 W、时间15min、温度40℃、分散剂质量分数0.5%)和阴离子表面活性剂法(pH为5、月桂酸钠浓度0.050mol/L、时间30min)改性微米TiO2的效果比较显著,更有利于改善其分散性。     

Silica-based aerogels as aggregates for cement-based thermal renders

Subcritically dried silica-based aerogels were synthesized by design to be used as aggregates for lightweight cement-based thermal renders. The molecular and pore structure of the aerogels and of the corresponding renders were correlated with their thermal conductivities. A subcritical hybrid aerogel proved to have advantages over a supercritical commercial one, since the particle size distribution may be controlled, it is more hydrophobic, and imparts higher specific surface areas and total pore volumes to the renders. Good stabilization of the hybrid aerogels within the aqueous cement paste, without affecting the final renders’ structure, was accomplished by using an anionic surfactant. The efficient range of aerogel contents for thermal insulation purposes (above 60 vol% of total aggregate) was optimized using an inorganic subcritical aerogel. Thermal conductivities as low as ∼0.085 W.m⁻¹.K⁻¹ and densities of 410 kg.m⁻³ were achieved by total replacement of silica sand with a designed hybrid aerogel.