Rutile Phase Content Research Articles

Tailoring the crystalline and amorphous phase ratios of TiO2 through the use of organic additives during hydrothermal synthesis

The photocatalytic properties of TiO2 are primarily determined by its crystallinity and crystalline phase ratios. To improve the photocatalytic properties of TiO2, greater control over the formation of crystalline and amorphous phases during synthesis is therefore required. In this study, we demonstrate how the addition of minute amounts of three organic compounds (isopropanol, acetone and acetic acid) during hydrothermal treatment affects the amorphous and crystalline phase ratios: the addition of isopropanol or acetone accelerates the phase transition from anatase and brookite to rutile, whereas the addition of acetic acid inhibits the transformation of anatase to rutile, increasing the content of amorphous phase compared to samples where no organic compound was added. We show that the combination of the organic compound added, along with the duration of the hydrothermal treatment, can be used to tailor the phase composition of TiO2, so as to obtain either: i) TiO2 with a high content of both rutile and amorphous phase, ii) TiO2 with a high rutile content and iii) TiO2 with different ratios of all four phases, when the duration of synthesis is short (2–4 h). The materials synthesized exhibited high photocatalytic activity (in most cases higher than P25), which is attributed to the beneficial phase composition and high specific surface area.

Boosting the visible-light-driven photocatalytic efficiency in porous Cu/TiO2 ceramic coatings

In this study, we examined how current density, sodium phosphate concentration, and the addition of copper sulfate to the supporting electrolyte affect PEO coatings on pure titanium. The chemical composition, morphology, and optical behavior of PEO coatings were extensively analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV–Vis diffuse reflectance spectroscopy (DRS). With an increase in current density from 6 to 18 A/dm2, the coating's pore size enlarges and the rutile phase content within the coatings increases. The coating created at 12 A/dm2 shows the highest photocatalytic activity and triggers a unique three-stage behavior in the voltage-time diagram. Adding 4 g/l of CuSO4 to the electrolyte resulted in the formation of an unwanted Cu-based precipitates, causing electrolyte instability. To stabilize it, potassium hydroxide was removed, and the base electrolyte concentration was adjusted. To address this issue, potassium hydroxide was eliminated from the supporting electrolyte. Subsequently, the concentration of the base electrolyte was optimized. Also, the synergistic influence of CuSO4 addition (4 g/l) to the supporting electrolyte at different concentrations of 5, 10, and, 15 g/l of trisodium phosphate on PA was investigated. The superior photocatalytic performance of the optimum coating created in the electrolyte containing 5 g/l trisodium phosphate and 4 g/l CuSO4 is attributed to its enhanced porous structure, along with the heterojunction between the anatase and rutile phases. These features significantly boost the available surface area and facilitate the efficient separation and transfer of photogenerated charge carriers. Ultimately, a mechanism for MB photodegradation was proposed based on the findings from Mott-Schottky analysis and DRS.

The effect of TiO2 crystal phase on CH3Br catalytic combustion over Ru/TiO2 catalyst

Supported Ru catalysts over TiO2 with various crystal phases were prepared, which involved rutile, anatase, and their mixed phase. And their catalytic activities for CH3Br complete oxidation were investigated. Results showed Ru/TiO2-700-4 that TiO2-700-4 is sourced from anatase TiO2 calcined at 700 °C for 4 h is the most active catalyst among these catalysts. The content of rutile phase on the surface is lower than the bulk. Strong metal support interaction occurs owing to lower lattice mismatch between RuO2 and rutile TiO2. It was further verified by H2-temperature programmed reduction, ultraviolet-Raman and transmission electron microscopy. Especially mixed-phase TiO2 is more conductive to higher dispersion of RuO2 than pure phase TiO2, which is easier to form epitaxial growth. The catalytic activity for CH3Br complete oxidation was not in exact accord with the dispersion of Ru. It is possibly attributed to the combination of arguably favorable physico-chemical properties of more Ru active sites, electron transfer, and appropriate surface acidity. At the low reaction temperature, more Ru active sites are beneficial for the total oxidation of CH3Br. With the increase of temperature, higher activity is prone to strong surface acidity and electron transfer, as was confirmed by X-ray photoelectron spectra and NH3-temperature programmed desorption analysis.

Microstructural evolution and biological properties of PEO coating on SLM-prepared NiTi alloy

Selective laser melting (SLM)-prepared NiTi alloy is considered to have great application potential in the fabrication of complex-structured metal implant materials. However, the SLM-NiTi alloy still suffers from some disadvantages, such as poor bio-corrosion resistance, bio-compatibility, and health hazards caused by the release of nickel ions. In order to improve the surface biological properties of SLM-NiTi alloys, bio-active coatings rich in Ca and P elements were prepared on SLM-NiTi alloys by PEO process in this work. Confocal laser scanning microscopy, SEM, EDX, XRD, and XPS were utilized to feature the micro-structure, thickness, element information, and composition of SLM/PEO coatings at different oxidation times. The adhesion strength was determined using scratch testing. A potential polarization test and a simulated body fluid (SBF) immersion test were applied to assess the corrosion resistance and detect the biological activity of SLM/PEO coatings at varied oxidation periods, respectively. The results showed that the growth of SLM/PEO coatings was hindered due to the overflow of Ni elements at the spark discharge stage (stage II). However, with the PEO process, the inhibition effect of Ni element was gradually eliminated. The pore size, thickness and the TiO2 rutile phase content of the SLM/PEO coatings gradually increased over time. However, the coating density, roughness and adhesion strength increased first and then decreased, and the SLM/PEO coatings were maximized at 15 min. The main composition of SLM/PEO coatings was TiO2, CaO, CaHPO4 and Ca3(PO4)2, and hydroxyapatite (HA) was gradually formed in the coating with time. The SLM/PEO-15 min coating with high thicknesses and rutile phase content, as well as optimum density provided optimum corrosion resistance (1.615 × 10−6 A cm−2). Meanwhile, the SLM/PEO-15 min coating possessed the best surface roughness and higher active element content, providing an excellent nucleation point and growth environment for the deposition of apatite. And the Ni element on the SLM-NiTi alloy substrate surface (oxidation time from 0 to 20 min) was significantly reduced from 12.49 % to 0.52 % after immersing in SBF solution for 24 h. Therefore, the PEO process can effectively improve the corrosion resistance and biological activity of SLM-NiTi alloy and inhibit the release of Ni elements.

Hollow TiO2/Poly (Vinyl Pyrrolidone) Fibers Obtained via Coaxial Electrospinning as Easy-to-Handle Photocatalysts for Effective Nitrogen Oxide Removal.

Herein, we present a method for fabricating hollow TiO2 microfibers from Ti (OBu)4/poly (vinyl pyrrolidone) sol-gel precursors and their effects on denitrification as a photocatalyst for air purification. Various sizes of hollow TiO2 fibers were developed using coaxial electrospinning by controlling the core flow rate from 0 to 3 mL h-1. At higher flow rates, the wall layer was thinner, and outer and core diameters were larger. These features are correlated with physical properties, including specific surface area, average pore diameter, and crystalline structure. The increase in the core flow rate from 0 to 3 mL h-1 leads to a corresponding increase in the specific surface area from 1.81 to 3.95 µm and a decrease in the average pore diameter from 28.9 to 11.1 nm. Furthermore, the increased core flow rate results in a high anatase and rutile phase content in the structure. Herein, hollow TiO2 was produced with an approximately equal content of anatase/rutile phases with few impurities. A flow rate of 3 mL h-1 resulted in the highest specific surface area of 51.28 m2 g-1 and smallest pore diameter size of ~11 nm, offering more active sites at the fiber surface for nitrogen oxide removal of up to 66.2% from the atmosphere.

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.

Influence of organic acids on the phases and physical characteristics of titanium dioxide synthesized by sol–gel for air depollution through heterogeneous photocatalysis

AbstractBACKGROUNDAir pollution in big cities is becoming a global problem due to its negative consequences on human health and the ecosystem. Currently, some materials available promise successful gases pollutants removal, by reacting with them through photocatalysis when sunlight irradiates them. The most studied and applied material is TiO2; due to its chemical stability and availability, it is widely incorporated into cements, bricks, coatings, etc.RESULTSIn this study, powders of titanium dioxide were synthesized through the sol–gel method using tetraisopropoxide with and without organic acids. Their photocatalytic activity was determined by the colorimetric method, following the standard UNI‐11259, and by the NO abatement test using the international standard ISO‐22197‐1. The results of the colorimetric test indicate that all the samples are photoactive according to the criteria stablished in the standard. Additionally, a similar photocatalytic performance was evidenced in the NO abatement tests for all the samples despite the differences in their particle sizes and in their crystalline phase distributions obtained without and with the different organic acids used in the synthesis process.CONCLUSIONThe particles synthesized show that the use of organic acids influences the decrease in particle size; moreover, in the case of citric acid, a favourable effect on the appearance of the rutile phase is perceived.All the samples were photoactive and their photocatalytic performance, evaluated under a NO atmosphere, were not negatively affected by the largest particle size (150 nm) nor by the rutile phase content (42 wt.%). © 2022 Society of Chemical Industry (SCI).

Fabrication of Adsorbed Fe(III) and Structurally Doped Fe(III) in Montmorillonite/TiO2 Composite for Photocatalytic Degradation of Phenol

The Fe(III)-doped montmorillonite (Mt)/TiO2 composites were fabricated by adding Fe(III) during or after the aging of TiO2/Ti(OH)4 sol–gel in Mt, named as xFe-Mt/(1 − x)Fe-TiO2 and Fe/Mt/TiO2, respectively. In the xFe-Mt/(1 − x)Fe-TiO2, Fe(III) cations were expected to be located in the structure of TiO2, in the Mt, and in the interface between them, while Fe(III) ions are physically adsorbed on the surfaces of the composites in the Fe/Mt/TiO2. The narrower energy bandgap (Eg) lower photo-luminescence intensity were observed for the composites compared with TiO2. Better photocatalytic performance for phenol degradation was observed in the Fe/Mt/TiO2. The 94.6% phenol degradation was due to greater charge generation and migration capacity, which was confirmed by photocurrent measurements and electrochemical impedance spectroscopy (EIS). The results of the energy-resolved distribution of electron traps (ERDT) suggested that the Fe/Mt/TiO2 possessed a larger amorphous rutile phase content in direct contact with crystal anatase than that of the xFe-Mt/(1 − x)Fe-TiO2. This component is the fraction that is mainly responsible for the photocatalytic phenol degradation by the composites. As for the xFe-Mt/(1 − x)Fe-TiO2, the active rutile phase was followed by isolated amorphous phases which had larger (Eg) and which did not act as a photocatalyst. Thus, the physically adsorbed Fe(III) enhanced light adsorption and avoided charge recombination, resulting in improved photocatalytic performance. The mechanism of the photocatalytic reaction with the Fe(III)-doped Mt/TiO2 composite was proposed.

Systematically evaluate the physicochemical property and hemocompatibility of phase dependent TiO2 on medical pure titanium

In recent years, TiO2 nanotube has presented great potentials in blood-contacting implants. However, considering the reliability and safety of the application and complexity of coagulation mechanism, the physicochemical property and hemocompatibility of phase dependent TiO2 still need to be investigated deeply. In this research, the wettability, electrochemical properties, mechanical properties, and whole blood coagulation response of phase dependent TiO2 nanotubes were systematically evaluated. First, the surface topography and crystal phase of regular self-ordering TiO2 nanotubes arrays were characterized, some significant changes including fracture, collapse and micropores appeared with the increase of annealed temperature, which mainly caused by transformation of crystal structure. Secondly, the physicochemical properties were analyzed, which presented that the superhydrophilicity, hardness, elastic modulus, adhesive strength of TiO2 nanotubes gradually decrease with the increase of annealed temperature; the mean coefficient of friction increases when the crystal phase of TiO2 nanotubes transferred from amorphous into anatase, whereas it decreases with the increase of rutile phase content; and the rutile phase displays excellent resistant element precipitation due to the increase of grain boundary density and close packed crystal structure. Finally, the whole blood was applied to evaluate the hemocompatibility of phase dependent TiO2 nanotubes by in vitro experiment. The deteriorative surface morphology and lower interfacial tension of nanotubes array composed of rutile phase can effectively avoid adhesion and activation of platelets. This research can provide a useful guide to design the TiO2-nanotube-based blood compatible biomaterials.

The critical role of Tween 80 as a ‘green’ template on the physical properties and photocatalytic performance of TiO2 nanoparticles for Rhodamine B photodegradation

A popular non-toxic surfactant, Tween 80 (T80), is widely used in foods, cosmetics, and pharmaceuticals. This eco-friendly surfactant should be promising to be utilized as a non-ionic template in the preparation of TiO2 nanoparticles. Moreover, few studies deal with Tween 80 as a template in the synthesis of various nanoparticles. Different concentrations of T80/isopropanol solutions (0–50%) were used in a modified template-assisted sol–gel route, where the synthesized xerogels were denoted by x%T80-TiO2. Different techniques such as DRS, XRD, SEM, HR-TEM, and N2 adsorption–desorption isotherms were utilized to characterize the as-prepared x%T80-TiO2 catalysts. The obtained results showed that the whole physical properties, such as crystalline parameters, optical properties, micromorphology, nanomorphology, and surface parameters, were affected by the concentration of T80 (T80%). In addition, T80% significantly changed the photoactivity of the synthesized samples toward the photodegradation of Rhodamine B (RB) as a pollutant model. 5%T80-TiO2 nanoparticles were the most reactive catalyst referring to its unique rod structure and existence of a small content of Rutile phase. Finally, tetra (4-carboxyphenyl) porphyrin (TCPP) was anchored on TiO2 nanorods to be used as a visible antenna to enhance its photocatalytic activity toward the visible light irradiation. Briefly, TCPP-sensitized T80-TiO2 nanoparticles showed an enhanced performance toward the degradation of RB under various light sources.

Effect of HVOF Process Parameters on TiO2 Coatings: An Approach Using DoE and First-Order Process Maps

High-velocity oxy-fuel deposition stages of titanium oxide coatings were analyzed and reported here. For the first stages of deposition, process maps were used to evaluate the influence of deposition parameters such as stand-off distance (SOD), powder feed rate (PFR) and fuel/oxygen ratio (F/O) on velocity and temperature of in-flight particles. These parameters were then combined with particle size distribution (PSD) to further optimize the deposition process considering the spray trace width and the area covered by splats and non-molten particles as responses. Furthermore, the structural, morphological and mechanical characteristics either of single splats, clusters of semi- and/or non-molten particles or coatings were obtained by, x-ray diffraction, Raman spectroscopy, scanning electron microscopy and nanoindentation. During coating build-up, lower PFR and F/O induce more splat particles and fewer clusters of semi- and/or non-molten particles, whereas the PSD affects the width of the spray trace. The combination of F/O and SOD upper levels was related to a high percentage of TiO2 splat deposition. Finally, the proposed methodology allowed to obtain dense TiO2 coatings with a higher content of rutile phase and an average thickness of 65 µm.

Sol-Gel Synthesis of SnO<sub>2</sub>-TiO<sub>2</sub> System - Morphologic, Photocatalytic and Antibacterial Properties

SnO2-TiO2 sol-gel coatings on soda-lime silicate glass heat treated at 500 °C and xerogel specimens also heat treated at 500 °C were investigated in this study. The morphology of 1, 3, 5 and 7 mol% SnO2 doped titanium oxide coatings were evaluated with a scanning electron microscope (SEM), an atomic force microscope (AFM) and an UV-VIS light spectrophotometer, whilst xerogel structure was analysed with X-ray diffraction spectroscopy (XRD). The physicochemical properties of the TiO2-SnO2 systems depended mainly on the Sn-to-Ti ratio. The surface morphology of the layer was compact and homogeneous with no visible cracks. Anatase and rutile phase was found in the tested 1, 3, 5, 7 and 10 mol% SnO2 doped and heat treated xerogel specimens. Rutile phase content in the heat treated xerogel was reduced, if Sn4+ content was increased. Photocatalytic activity and antibacterial properties were evaluated as well.

Study of the structure and characteristics of mesoporous TiO2 photocatalyst, and evaluation of its factors on gaseous formaldehyde removal by the analysis of ANOVA and S/N ratio.

This study differs from previous studies of TiO2/SiO2 in that 0.5–10 μm microsized TiO2-rutile based catalysts (TR catalysts) with varying proportions of titanium and silicon were synthesized using a one-step modified hydrothermal method. At Ti/Si = 1/9, a two-dimensional channel-structured catalyst with a morphology resembling that of SBA-15 was obtained. In contrast, at Ti/Si = 3/7 or 5/5, a three-dimensional porous structure was formed, and Ti–O–Si–C bonds appeared. The structure of the TR catalyst transformed due to the decrease in C–Si bond content and the increase in C–C bond content with increasing Ti/Si ratio. The results indicated that the rutile phase was the main crystal phase of the TR catalyst. The small crystal size and large rutile phase content of the mesoporous TR catalyst contributed to the low band gap energy below 3.0 eV. Under 2 × 10 W lamp irradiation with either UVA or visible light, the three TR catalysts showed better formaldehyde (HCHO) removal efficiency than P25. Furthermore, the Taguchi method was employed to evaluate the catalytic factors by analysis of variance (ANOVA) and S/N ratio. The results revealed the contributions of each of the three factors to HCHO removal efficiency over TR catalysts to be as follows: space velocity (62%), Ti ratio (32%), and time on stream (5%). The TR catalyst with Ti/Si = 1/9 showed good HCHO removal efficiency with a high SBET (787.1 m2 g−1) and large pore volume (0.95 cm3 g−1) for a residence time of over 2.29 × 10−1 s under visible light irradiation. Microwave-assisted EG reduction was successfully applied to dope a TR catalyst with nanosized Pt particles in a short synthesis time. After Pt doping, the removal efficiency in the stream improved and stabilized. The Pt particles were Pt0 and proved effective for improving the photocatalytic removal of HCHO over the TR catalyst by prolonging the separation time of the electron–hole pairs. Overall, the Pt/TR catalyst is a potential material for pollutant removal and can be easily separated from the pollutant removal system since the catalysts are microsized.

Heterojunctions of mixed phase TiO2 nanotubes with Cu, CuPt, and Pt nanoparticles: interfacial band alignment and visible light photoelectrochemical activity

Anodically formed, vertically oriented, self-organized cylindrical TiO2 nanotube arrays composed of the anatase phase undergo an interesting morphological and phase transition upon flame annealing to square-shaped nanotubes composed of both anatase and rutile phases. This is the first report on heterojunctions consisting of metal nanoparticles (NPs) deposited on square-shaped TiO2 nanotube arrays (STNAs) with mixed rutile and anatase phase content. A simple photochemical deposition process was used to form Cu, CuPt, and Pt NPs on the STNAs, and an enhancement in the visible light photoelectrochemical water splitting performance for the NP-decorated STNAs was observed over the bare STNAs. Under narrow band illumination by visible photons at 410 nm and 505 nm, Cu NP-decorated STNAs performed the best, producing photocurrents 80% higher and 50 times higher than bare STNAs, respectively. Probing the energy level structure at the NP–STNA interface using ultraviolet photoelectron spectroscopy revealed Schottky barrier formation in the NP-decorated STNAs, which assists in separating the photogenerated charge carriers, as also confirmed by longer charge carrier lifetimes in NP-decorated STNAs. While all the NP-decorated STNAs showed enhanced visible light absorption compared to the bare STNAs, only the Cu NPs exhibited a clear plasmonic behavior with an extinction cross section that peaked at 550 nm.

Effect of Annealing Temperature on Structural, Electrical and Optical Properties of TiO2 Nanopowder

TiO2 nanopowder is prepared by simple sol-gel method using starting material as titanium isopropoxide with methanol and annealed at 600°C, 700°C and 800°C for 1 hour in air. X-ray diffraction pattern revealed the presence of both anatase and rutile phase in TiO2 specimens annealed at different temperatures. It is observed that the content of rutile phase and crystallite size increases with increase in annealing temperature. Scanning electron microscopy (SEM) is used to study surface morphology of TiO2 specimens annealed at different temperatures. Using Tauc plot it is observed that energy band gap decreases with increase in annealing temperature. I-V curve of TiO2 specimen shows that current increases with increase in annealing temperature. The preparation method is optimized by changing the concentration of titanium isopropoxide which leads to mixed phase (anatase and rutile) TiO2 nanopowder with a lower energy band gap value which may play an important role in gas sensing applications.

Improved light-induced cell detachment on rutile TiO2 nanodot films

Anatase TiO2 nanodot films have been found to be able to release cells under light illumination with excellent efficiency and safety. In the present study, we investigated the effects of rutile contents in TiO2 nanodot films on such light induced cell detachment behavior. The results showed that TiO2 nanodot films with different contents of rutile phase have been prepared successfully. The content of rutile phase increased with the increase in calcination temperature. All films possessed good cell adhesion but there was a decrease in cell proliferation with the increasing content of rutile phase. Single cell detachment assay showed that the films with high rutile contents (calcined at 900°C and 1100°C) showed better cell detachment performance. That was ascribed to the changes of the secondary structure of extracellular proteins adsorbed on the nanodot surface after ultraviolet (365nm, UV365) illumination. In addition, cell sheets detached through UV365 illumination maintained high activity and could be further used in tissue engineering. The present work showed that the existence of rutile phase is helpful in cell detachment behavior and it could be utilized to optimize light-induced cell detachment behavior. Statement of SignificanceThis work discovers that the presence of rutile phase in TiO2 nanodot films could improve the light-induced cell detachment behavior, although rutile phase is inferior to anatase phase on light induced superhydrophilicity. That strongly supported that the behaviors of adsorbed proteins are crucial in acquiring cell sheet with light illumination. In fact, the state and behavior of adsorbed protein greatly affect the interaction between biomaterials and living cells. Therefore, we consider this work is not only important in harvesting cells or cell sheets through light illumination, but also helpful in further understanding of interaction between biomaterials and cells.

Effects of morphology and crystal phase of sulfated nano-titania solid acids on catalytic esterification

In this work, sulfated TiO2 nanostructures with different morphology structures and anatase/rutile phase ratios were synthesized by a hydrothermal method followed by calcination. The nanotube, nanorod and nanoparticle morphologies were obtained by varying the hydrothermal and/or annealing temperatures, and the anatase/rutile phase ratio was adjusted by controlling the annealing temperature. The characterization indicated well dispersed bidentate SO4 2− linked to the TiO2 surface. The catalytic activity of the synthesized sample was evaluated by the esterification of acetic acid with n-butanol. It was shown that the prepared sulfated titania possessed different catalytic activity. Effects of different reaction conditions were discussed. The catalytic activity was dominated by the concentration of surface acid sites of the catalyst. Hence, with the help of TEM, SEM, XRD and BET analyses, the concentration of surface acid sites per unit area of sulfated TiO2 was correlated with the type of morphology and increased linearly with the rutile phase content. The nanoparticle morphology and high rutile phase ratio were favorable for the catalytic activity per unit area of sulfated TiO2 in our experiments.

Using ethanol for preparation of nanosized TiO2 by gaseous detonation

A method of preparing nanosized titanium dioxide by gaseous detonation by using ethanol, hydrogen, and oxygen as an explosion source and titanium tetrachloride as a precursor is described. The results indicate that the rutile phase content of the obtained products is high, and the pure rutile phase can be produced by adding a small amount of hydrogen. Most of the particles obtained under the two different synthesis conditions are spherical (or sphere-like) with small and even particle sizes, generally about 30 nm, and has a very good size dispersion.

Effect of thermal treatment on the structural phase transformation of the detonation-prepared TiO2 mixed crystal nanoparticles

Nanopaticles of TiO2 mixed crystals (anatase phase and rutile phase) are prepared by detonation method. Morphologies and structural phase transformation behaviors of the as-prepared TiO2 nanopaticles are investigated for different annealing temperatures (600 ℃ and 720 ℃) and durations of annealing time (1, 2, 3.5, and 5 h). The structural phase transformation process and transformation mechanism are also discussed within the framework of the thermodynamic theory. Results show that with the increase of the annealing temperature and annealing time, the particle size of the detonation-prepared TiO2 nanoparticles increases gradually and the relative content of rutile phase in the TiO2 mixed crystal nanopaticles is improved. Compared with the TiO2 nanoparticles prepared by the conventional methods, the mean growth rate of rutile phase is obviously slower than that of anatase phase at the same annealing temperature and annealing time. It is obvious that the temperature at which the anatase phase completely changes into the rutile phase is lower than that of the TiO2 nanoparticles prepared by using other methods. These results are helpful for realizing the control of particle size and phase transformation of TiO2 nanoparticles. Meanwhile, the results can also provide us the theoretical and experimental bases for mass production of TiO2 nanoparticles in the future.

Preparation and Photocatalytic Activity of Shape- and Size-Controlled TiO<sub>2</sub> Films on Silica Glass Slides

TiO2 films consisting of rod-like to sphere-like TiO2 particles on glass slides were synthesized by assembly technique. The results showed that the shape and size of TiO2 particles could be manipulated using different concentrations of polyethylene glycol 20000. By increasing of PEG, the shapes of the TiO2 particles transformed from rod-like to sphere-like, the size of TiO2 particles became gradually smaller. The size became bigger when an excess amount of PEG was added. With the adding of PEG，the amount of the TiO2 , the hydroxyl content, and the rutile phase content on the surface of TiO2 films increased, respectively. The photocatalytic activity of TiO2 films added PEG was higher than that of unadded samples.