Nanosized Titanium Dioxide Powder Research Articles

Factors to control the alignment of surface-treated titanium dioxide powders to maximize performance of sunscreens.

Titanium dioxide powders are contained in a large class of colour cosmetics and sunscreen formulas. When they are used, the formation of a uniform functional powder layer on the skin is an important factor to show their functionality, such as aesthetic and UV protection. Attempts were made to extract the factors that affect the UV shielding ability of the deposited powder layer. Seven kinds of surface treatments were conducted on nano-sized titanium dioxide powder to modify the surface characteristics. Dispersion samples were prepared by mixing these powders with liquids, such as mixed solutions of cyclopentasiloxane, isododecane, coconuts alkane and dimethicone using a disperser and a bead mill. The dispersions were applied using an applicator on cellulose triacetate film, polycarbonate film and polymethyl pentene film. Laser microscope observation and micro-gloss glossmeter analysis were carried out to assess the flatness of the deposited powder layers, and the UV shielding ability was evaluated using SPF analyser. Factors whose influences on the structure and UV shielding ability of the deposited powder layer being analysed were pseudo-HLB of the powders, liquids for preparing the dispersions and material of the substrates. Higher UV shielding ability was attained when powders having pseudo-HLB at around 6 were employed independent from the kinds of liquids and substrates. Flatness of the deposited layer was found to enhance the UV shielding ability of the UV-B region, while that of the UV-A region was scarcely influenced by the flatness. Employing lower surface tension liquids for preparing the dispersions and materials exhibiting lower polar components of surface free energy as substrates tended to enhance the UV shielding ability. Surface treatments conducted on the powders in this study were found to change UV shielding ability, especially UV-B shielding ability, and the relation between pseudo-HLB and UV shielding ability was scarcely influenced by the kinds of liquids. Both surface tension of liquids and the polar component of surface free energy of substrates affected the UV shielding ability. It was suggested that pseudo-HLB calculated based on chemical structure becomes useful information to choose optimum surface treatment to make uniform powder alignment independent from the surrounding environment.

Grain growth and phase transformation of nano-sized titanium dioxide powder during heat treatment and spark plasma sintering

The control of nanostructures is crucial for enhancing the thermoelectric properties of materials. In this work, the grain growth and phase transformation of different nano-sized titanium dioxide (TiO2) powders were investigated during heat treatment and spark plasma sintering. First, the thermal behaviors of TiO2 powders with different particle sizes during heat treatment, such as grain growth, phase transformation, and adsorption properties, were studied. The results showed that the phase transformation of 7 nm anatase TiO2 occurred more easily, and the rutile phase content increased with increasing heat treatment temperature. The grain growth of 7 nm anatase TiO2 occurred at low temperature (i.e., 873 K), even the grain size increased by 13-fold at 1123 K (i.e., the phase transformation temperature). Thermogravimetry results suggested that the 7 nm anatase TiO2 powder had a greater adsorption characteristic owing to its large specific surface area. Moreover, TiO2 compacts with and without graphite were fabricated using spark plasma sintering. The results indicated that a lower sintering temperature was beneficial for maintaining the nanostructure, whereas the addition of graphite powder promoted grain growth. Furthermore, the thermal conductivity was reduced owing to the nanostructure, and the phonon thermal conductivity accounted for a dominant proportion of the total thermal conductivity. Consequently, the lowest thermal conductivity was 1.1 Wm−1K−1 at 973 K for the nanostructured compact sintered at 1073 K, which is approximately 50% lower than that of the microstructured compact sintered at 1273 K.

Effects of nano-sized titanium dioxide powder and ultraviolet light on superficial veins in a rabbit model.

Titanium dioxide (TiO2) is widely used in many fields such as food, cosmetics, and paper industries. Studies on the photocatalytic properties of TiO2 on living tissue are limited. To examine the histopathological effects of TiO2 solution on the marginal veins of rabbit ears under ultraviolet (UV) light. In this study, 4 groups of rabbits (8 rabbits per group) were used: the 1st group was the control group, the 2nd group received 20% of nano-TiO2 only, the 3rd group received UV light only, and the 4th group received nano-TiO2 and UV light, simultaneously. The study lasted for 14 days and samples were taken from the marginal ear vein on the 15th day. The ear tissues of rabbits in the control and TiO2 groups showed a normal histological appearance. In the UV group, the results showed severe chronic inflammation due to mononuclear cells around the hair follicles and perivascular areas. However, these findings decreased in the UV/nano-TiO2 group. The method applied in this study can be used in the treatment of telangiectasia in the future. However, this study investigating the effects of nano-TiO2 on vascular structures under UV light had a predominantly histological and observational nature. Further studies involving genetic, cytogenetic, biochemical, histochemical, and immunohistochemical analyses need to be performed to test the theories we proposed.

Paramagnetism and super paramagnetism of nanocrystalline titanium dioxide powders

Studies of magnetization of undoped and Mn-doped nanosized titanium dioxide powders showed that its dependence on the magnetic field can be approximated by the function that is a linear combination of two Langevin functions with different parameters. The linear part along with the diamagnetic contribution typical for metal oxides is due to the contribution of two types of paramagnetic centers. The first one is present in both undoped and doped powders. As follows from the published models, the centers are complex lattice defects Ti+3 ions + O− vacancies. The second is the vast majority of the manganese ions (and related oxide vacancies) in the doped powders that are uniformly distributed over all nanoparticles. The nonlinear part, even present in the undoped samples, is caused by the contribution of a small number of regions with a high magnetic moment (ferromagnetic clusters). These regions do not interact magnetically, and the powder as a whole exhibits superparamagnetic behavior. According to our estimates, the introduction of Mn into the TiO2 lattice mainly leads to the predominance of the paramagnetic contribution to the magnetization over the diamagnetic contribution characteristic of the TiO2 lattice and a small increase in the number of the ferromagnetic clusters.

Study of a Nanostructured Anatase Coating on the Rutile Surface

Nanosized titanium dioxide allows solving complex engineering problems. One such a problem is the development of materials and coatings that reduce the probability of nosocomial infections of the surface of orthopedic structures, including implant systems. This article presents the results of studying anatase ceramic coatings deposited according to the sol–gel technology on a sintered material based on nanosized titanium dioxide powder (rutile modification) by the Raman spectroscopy, X-ray diffraction analysis, and scanning electron microscopy. The resulting coating has a complex layered structure, which almost completely consists of titanium dioxide in the anatase phase according to the Raman spectroscopy data. The simultaneous occurrence of both phases is fixed in a coating. The identification of rutile in X-ray diffraction patterns is apparently associated with the fact that rutile with a varied peak intensity is preferentially formed at the first deposition stages of the coating on the polycrystalline rutile surface. The fact that nonstoichiometric phases are also present in X-ray diffraction patterns makes it possible to assume that the phase composition of the coating over the thickness is nonidentical and presented by a gradual layerwise transition from rutile to anatase. The coating thickness is 60 ± 15 μm. It is presented by lamellar blocks of various sizes. The thickness of a separate plate is in the limits of 60–80 nm. This procedure allows the deposition of an anatase coating not only on the ceramic samples based on titanium dioxide, but also on the surface of titanium implants when preliminarily forming the titanium dioxide layer in the form of rutile on the metal surface. The experiments on the investigation into the antibacterial properties and morphological characteristics of bone tissue contacting with the implant are performed at the Department of the Prosthetic Dentistry at the Perm State Medical University.

Optimization of Synthesis of Nanosized Titanium Dioxide Powder Materials from Peroxo Titanium Complex

A green-chemistry method of sol-gel synthesis of nanosized titanium dioxide powder materials using a step of the formation of a peroxo titanium complex was optimized. The developed method reduces energy and reactant consumption, rules out the production of toxic wastewater contaminated with organic substances, and improves the environmental performance of the process as a whole. The obtained powder materials are nanosized, and their photocatalytic activity is higher than that of similar materials.

THE STUDY OF NANOSTRUCTURED ANATASE COATINGS ON THE SURFACE OF RUTILE

Nanosized titanium dioxide allows solving complex engineering problems. One of such tasks is the creation of materials and coatings that reduce the likelihood of nosocomial infections on the surface of orthopedic structures including implant systems. The paper presents the results of the Raman spectroscopy, X-ray diffraction analysis and scanning electron microscopy of anatase ceramic coatings deposited by sol-gel technology on a sintered material based on a nanosized titanium dioxide powder (rutile modification). The resulting coating has a complex layered structure, which is almost completely represented by titanium dioxide in the anatase phase according to the Raman spectroscopy data. The simultaneous existence of both phases in the coating was recorded. The identification of rutile on diffractograms seems to be due to the fact that modified peak intensity rutile is mainly formed during the first stages of coating application on the polycrystalline rutile surface. The fact that non-stoichiometric phases also present in the diffractograms suggests that coating phase composition is not the same in thickness and is represented by a gradual layerwise transition from rutile to anatase. The coating thickness is 60 ± 15 μm. The coating is represented by lamellar blocks of various sizes. The thickness of a single plate in the coating is 60–80 nm. The developed technique makes it possible to apply the anatase coating not only on samples of titanium dioxide ceramics but also on the surface of titanium implants with the preliminary formation of a titanium dioxide layer in the form of rutile on the metal surface. Experiments on the study of antibacterial properties and morphological characteristics of bone tissue in contact with the implant were carried out at the Department of Prosthetic Dentistry at the PSMU.

Effect of synthesis conditions on the photocatalytic activity of titanium dioxide nanomaterials

The photocatalytic activity of nanosized titanium dioxide powders synthesized by thermal treatment of the precursor phases precipitated from aqueous solutions on the degradation of methylene blue in a solution under the action of UV radiation has been studied. The dependence of the photocatalytic activity on pH of the medium used to precipitate precursor phases in combination with temperatures and duration of their thermal treatment has been found. The selected synthesis conditions allowed to obtain titanium dioxide materials that appear to be at least two times more active than the commercial catalyst Degussa P25. It is found that the materials based on anatase modification of titanium dioxide obtained from the phases precipitated at pH 7–9 and calcined at 600°C for 1–2 h show the highest photocatalytic activity. It is shown that under UV radiation 25 min is enough for almost complete destruction of methylene blue dye in the solution with an initial concentration of 20 mg/L.

Distribution of Nanoparticle Number Concentrations at a Nano-TiO2 Plant

Nanoparticle number concentration distributions were measured at various sites in a plant manufacturing nano-sized titanium dioxide powder. It was found that aerosol nanoparticles suspended in the air were mainly in the form of agglomerated particles, and had the average diameters of 124.2 nm and 524.4 nm, respectively. The number concentration of aerosol particles increased with source height, but decreased with distance from the source. The concentration was highly affected by the dispersive forces of the discharging port, and the suspension and the agglomeration of particles. The aerosol particles accumulated after a long working time, and the concentration was reduced at large suspending distances. In contrast, the concentration of primary particles was higher for a working time of less than 2 hours, and returned to normal levels after 3 hours, due to the accumulation and agglomeration effects experienced by the primary particles. Motivated by these findings, an aerosol enclosure was developed in this study, and it showed excellent control over the distribution of aerosol particles, including the agglomerated and primary particles. This is thus a promising approach to achieve effective and efficient personal protection in the workspace.

Inhibition effect of phosphate on the crystal grain growth of nanosized titania

The inhibitory effect of phosphate on the crystal grain growth of nanosized titania during high temperature calcination was investigated. Nanosized titanium dioxide powders prepared by hydrolysis of titanium tetrachloride were soaked in phosphate solutions with different concentrations. The obtained powders calcined at various temperatures were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectronic spectroscopy (XPS). The grain size of the samples without phosphate treatment increased quickly when calcined at high temperatures, while the grain size of the samples with phosphate modification increased slowly when calcined at the same temperature. This phenomenon implies that phosphate treatment plays an important role in inhibiting the crystal grain growth of titania. The possible mechanism of the inhibition effect of phosphate on titania is discussed.

Detonation synthesis of nanosized titanium dioxide powders

Utilizing titanyl sulfate as a TiO2 source, via a novel synthesis method—the detonation method—nanosizedTiO2(n-TiO2) powders were prepared. The results showed that the as-preparedn-TiO2 powders did not have enough time to grow into large and fine crystallites, and that thecharacteristics of high temperature, high pressure and high cooling were helpful in the synthesisof nanosized materials. The anatase phase appeared to be the stable form of nanocrystallineTiO2 at small crystallite sizes to some extent and part of the rutile phase couldtransform to the anatase phase when the detonation products were oxidizedto eliminate the impurities via the combined action of chromic anhydride(CrO3) and concentrated nitric acid. The main reason resulting in the reversal of stability ofanatase and rutile could be the differences in the surface energy of anatase and rutile atsmall crystallite sizes.

Capability of coupled CdSe/TiO 2 for photocatalytic degradation of 4-chlorophenol

The photocatalytic process using TiO 2 and coupled semiconductor in the photodegradation reaction of 4-chlorophenol (4-CP) was investigated. Nanosized titanium dioxide powder was synthesized via the sol–gel procedure and modified via the coupled photocatalysts. The microstructural and chemical properties of TiO 2 and coupled CdSe/TiO 2 were also examined. For CdSe/TiO 2 samples, the specific surface area was 7.0 m 2/g and the deposition proportion of CdSe was approximately 27.6%. In the photocatalysis results, higher photodegradation efficiency of 4-CP was observed at higher pH values. In the UV 254 nm system, the degradation efficiency of 4-CP and TOC with sol–gel produced TiO 2 (TiO 2(SG)) powder was higher than with commercial TiO 2(RdH) powder. For the coupled semiconductor system (CdSe/TiO 2), the apparent first-order rate constants were 1.35 × 10 −2, 4.33 × 10 −2, 2.0 × 10 −3 and 1.9 × 10 −3 min −1 at the conditions of pH 7 (254 nm), pH 11 (254 nm), pH 7 (365 nm), and pH 11 (365 nm). The disappearance of 4-CP under CdSe/TiO 2(RdH) photoreaction at pH 7 and 365 nm condition is better than that of TiO 2(RdH) system, with 30% versus 22% 4-CP reduction in 180 min. In the same condition, CdSe/TiO 2(RdH) provided more photomineralization efficiency than that of TiO 2(RdH) in terms of TOC reduction. Both 4-CP and TOC reduction were significant for systems illuminated at 254 nm. Considering the direct photolysis effect at 254 nm where 4-CP reduction is near 100% and TOC removal is nil, CdSe/TiO 2(RdH) exhibits a 50% photomineralization efficiency and a nearly four times faster reaction rate than the single TiO 2(RdH) semiconductor.

Influence of titanium dioxide nanopowder addition on microstructural development and hardness of tin–lead solder

This paper presents the microstructure and hardness of composite solders obtained by the addition of nanopowders of titanium dioxide to a conventional solder. Titanium dioxide powders-reinforced lead (Pb)–tin (Sn) composite solders were prepared by thoroughly blending nano-sized titanium dioxide powders with powders of a eutectic solder and using a water-soluble flux. The blended solder paste was melted and allowed to re-solidify in a crucible placed on a hot plate and maintained at a constant temperature. Optical microscopy observations revealed that for additions of titanium dioxide up to 1 wt.%, the grain size and width of the grain boundary decreased. For the addition of 2 wt.% of titanium dioxide, nanopowders microporosity was observed both at and along the grain boundary regions coupled with the presence of second-phase particles. Microhardness measurements revealed that the addition of titanium dioxide nanopowders is helpful in enhancing the overall strength of the eutectic solder.

Effects of Calcination on the Microstructures and Photocatalytic Properties of Nanosized Titanium Dioxide Powders Prepared by Vapor Hydrolysis

Ultrafine titanium dioxide powders are produced in an aerosol reactor using vapor hydrolysis of titanium tetraisopropoxide (TTIP) at 260°C and higher temperatures (600°, 700°, 800°, and 900°C). The effect of calcination on the microstructure characteristics and the photoactivity is studied. The powders are characterized using Brunauer‐Emmett‐Teller (BET) surface area, X‐ray diffraction (XRD), and transmission electron microscopy (TEM) analyses. The photocatalytic activity of the powders is also studied using degradation of phenol in water as a test reaction. The powder produced at 260°C is calcined at 500° to 900°C while those produced at higher temperatures are calcined at 600°C for 3 h. Raw powder produced at 260°C is amorphous but becomes crystalline after calcination. As the calcination temperature increases, the surface area decreases but the rutile‐to‐anatase ratio and the anatase and rutile crystallite sizes increase. The photoactivity increases as calcination temperature increases to 900°C, when the powder becomes densified and the surface area drops significantly because of sintering. Powders produced at higher temperatures are predominantly anatase and are generally more photoactive. Calcination of the powders at 600°C for 3 h results in little loss of surface areas and enhances the photoactivity. Among the factors examined, large surface area and good dispersion of the powders in the reaction mixture are favorable to photoactivity. Conversely, prolonged calcination at high temperatures is detrimental to photoactivity. However, surface area, crystallite size, anatase‐to‐rutile ratio, and dispersity of the powders alone cannot account for the observed trend of photoactivity. The role of crystallinity needs to be investigated.

Surface property control of semiconducting metal oxide nanoparticles

The comprehension of the underlying mechanism attributing either a reducing or oxidizing effect to humidity on the metal oxides used in gas sensors is still a challenge as the literature on this subject shows contradictory results. The high surface-to-bulk ratio of nanosized powders conferring them a much higher surface reactivity compared to their micronsized counterpart, clearly helps in a better understanding of the gas-surface interactions. A thorough FTIR surface study of a nanosized titanium dioxide powder subjected to various sequences of carbon monoxide and mixtures of carbon monoxide and water vapor is reported. The effect of acetic acid and hexamethyldisilazane grafting on TiO 2 is studied under the same conditions. It is found that water molecules have a reducing or oxidizing effect, depending on the acido-basicity of the metal oxide. Our study clearly shows that a thorough knowledge of the surface reactivity of metal oxides is a prerequisite for further major gas sensing optimization.