Crystalline TiO2 Particles Research Articles

Evaluation of weathering resistance of cross-laminated timber blocks surface-treated with TiO2 nanoparticles by liquid-precursor flame spray pyrolysis

Wood is a versatile and renewable resource utilized in a wide range of applications, including tools, furniture, construction, and advanced engineering structures. However, certain inherent properties of wood, such as moisture and ultraviolet (UV) degradation, impose limitations on its long-term durability and dimensional stability for outdoor applications. This research investigates the weathering durability of cross-laminated timber (CLT) blocks surface-treated with titanium dioxide (TiO2) nanoparticles synthesized via liquid-precursor flame spray pyrolysis (FSP), directly deposited onto the surface of CLT blocks, and thereby resulting in a porous TiO2 coating. This coating endows the CLT surface with superhydrophobic properties evidenced by a water contact angle of ≥150°. Results from scanning electron microscopy and X-ray diffraction show the coating to be comprised of crystalline, sub-100 nm individual and aggregated TiO2 particles with significant porosity. Even after an 8-week accelerated weathering test, a portion of the crystalline TiO2 particles remains on the CLT surface. The TiO2-treated CLT demonstrates enhanced resistance to discoloration and gloss change over 8-weeks of accelerated weathering conditions, which are evidenced by a total color difference (ΔE) that is 3–4 times lower than that of the untreated CLT in the initial two weeks, and 58% lower after 8 weeks of weathering. Furthermore, the TiO2-treated CLT exhibits fewer weathering defects, such as splits and cracks, than the untreated CLT. The enhanced weathering durability of the TiO2-treated CLT is attributed to reduced lignin degradation, which is supported by the Fourier-transform infrared spectroscopy analysis. The findings of this study suggest that the TiO2 coating by FSP offers a viable and cost-effective method for modifying engineered wood products for improving hydrophobicity and protecting against the deteriorating effects of UV irradiation and moisture exposure.

Red anatase TiO2 microspheres with exposed major {0 0 1} facets and boron-stabilized hydrogen-occupied oxygen vacancies for visible-light-responsive water oxidation

In pursuit of efficient solar energy to chemical energy conversion through band engineering of wide-bandgap photocatalysts such as TiO2, a compromise occurs between a narrow bandgap and high-redox-capacity photo-induced charge carriers, which impairs the potential advantages associated with the widened absorption range. The key to this compromise is an integrative modifier that can simultaneously modulate both the bandgap and band edge positions. Herein, we theoretically and experimentally demonstrate that oxygen vacancies occupied by boron-stabilized hydrogen pairs (OVBH) serve as an integrative band modifier. Compared to hydrogen-occupied oxygen vacancies (OVH), which require the aggregation of nanosized anatase TiO2 particles, oxygen vacancies coupled with boron (OVBH) can be easily introduced into large and highly crystalline TiO2 particles, as shown by density functional theory (DFT) calculations. The coupling with interstitial boron facilitates the introduction of paired hydrogen atoms. The red-colored {001} faceted anatase TiO2 microspheres with OVBH benefit from the narrowed bandgap of 1.84 eV and the down-shifted band position. These microspheres not only absorb long-wavelength visible light up to 674 nm but also enhance visible-light-driven photocatalytic oxygen evolution.

Photocatalytic activity and antibacterial efficacy of titanium dioxide nanoparticles mediated by Myristica fragrans seed extract

The synthesis of semiconductor metal/metal oxide nanoparticles (NP) via the green synthesis routes is desirable due to its effectiveness, economical, and eco-friendly nature of the products. The present study aims to synthesize the titanium dioxide (TiO2) NP via the green synthesis route, using Myristica fragrans plant extract as the reducing agent, where the photocatalytic activity was evaluated. The physicochemical and morphological properties of TiO2 NP have been analyzed using spectroscopic and electron microscopic techniques. From the analysis, the powdered X-ray diffraction (XRD) indicated the formation of very well crystalline TiO2 particles in the anatase phase, while the Fourier transform infrared (FTIR) spectroscopy confirmed the presence of TiO bonds, and UV–Vis spectroscopy proofed the optical properties. The field emission scanning electron microscopy (FESEM) analysis provided the surface morphological characteristics and the formation of spherical shape particles; and the electron diffraction X-ray analysis (EDX) indicated the elemental composition. The photocatalytic activity of the TiO2 NP was evaluated based on the degradation rate of two aqueous dye solutions, i.e. methylene blue (MB) and congo red (Con-R) using the 8 W Xenon lamp as the light source for the visible irradiation. The degradation activity of the Con-R dye is slightly higher (99% degradation in 45 min) than that of the MB dye (97% degradation in 60 min). Both degradations activity followed the first-order kinetic model. The high activity of TiO2 NP on both dyes was supported by the increased absorption of light, associated charge separation efficiency, and specific surface area as provided by the UV–Vis DRS analysis. The plant extract mediated the synthesis of TiO2 which formed stable particles without losing the semiconducting and photocatalytic properties, where the holes (h+) and superoxide radicals (O2−) contributed to the enhanced degradation of dye. The antibacterial activity of the TiO2 NP (50 and 100 µg/mL; 6 h) synthesized was evaluated by testing against two different bacterial cultures of K. pneumoniae and S. aureus. The results proved that the particles became active only in the presence of UV light exposed and no significant differences in bacterial inhibition efficiency between the two cell types (79% and 72%) as observed. The antibacterial activity of the TiO2 NP was proven by the epifluorescence microscopic analysis, total viable count (TVC), and zone of inhibition (ZOI).

SORPTION PROPERTIES OF RUTILE PHASE TiO2 NANOPARTICLES

There are many scientific studies on phenol adsorption. Sorption of phenol in the presence of activated carbon, graphite oxide and other adsorbents is very common. This article is the first to study the sorption properties of TiO2nanoparticles with a rutile phase; TiO2 nanoparticles with a rutile phase were synthesized by the sol-gel method and used as an adsorbent. Later the process of adsorption of a 1 mgL-1 phenol solution in the presence of rutile TiO2 nanoparticles was studied. The adsorption process lasted 2 hours at a temperature of 25°C.Although the rutile TiO2 phase is a very good photocatalyst it has been shown to be a weak adsorbent. Nano crystalline TiO2 particles of the rutile phase were characterized by powder X-ray diffraction (XRD).The course of adsorption was studied on the device "Varian Cary 50". Based on the curves plotted on the “Varian Cary 50” it was determined that adsorption was incomplete. At the end of the process judging by the graph we can say that the amount of phenol in the solution decreased but phenol still remained which indicates incomplete adsorption. Mathematical modeling of the process has been developed using both logistic and exponential methods. Keywords: nano-TiO2, phenol, adsorption, XRD, TEM.

Morphology regulation of TiO2 thin film by ALD growth temperature and its applications to encapsulation and light extraction

As a multi-functional material, TiO2 thin film has been widely studied and applied in display, photocatalysis, solar cells and other fields. In this work, TiO2 thin films were prepared using atomic layer deposition, and their morphology was successfully regulated by the growth temperature. It was found that TiO2 film prepared at low temperature was amorphous, uniform and dense, with great barrier property, which can be used for encapsulation. Crystalline TiO2 nanoparticles with anatase phase appeared at higher temperature than 150 °C, whose amount increased with the growth temperature. The crystalline TiO2 particles can be used as templates to prepare randomly textured nano-patterns, which were proved to be able to improve the light extraction efficiency of photoelectric devices. Specifically, the luminance efficiency of the QLED with the nano-patterns formed by the crystalline TiO2 particle prepared at 200 °C and 250 °C were increased by 24.07% and 30.44%, respectively.

Sintering a Mixture of Powders in the Al2O3–SiO2–β-SiAlON–TiC–Dy2O3 System by the Spark-Plasma Method with High Compaction Loading

The effect of the addition of 2 and 5 mol.% Dy2O3 during spark-plasma sintering at a compaction loading of 60 MPa in the range of 1200 – 1600°C on phase composition, microstructure, relative density, open porosity, linear shrinkage, physicomechanical properties, and linear correlation of the elastic modulus and fracture toughness of mullite–sialon–TiC samples is shown. The synthesized powders of sialon and TiC are characterized by corresponding intensive crystallization. The increase in the content of Dy2O3 from 2 to 5 mol.% in the sintered composition to produce β-SiAlON/TiC = 70/30 mol.% promotes intensive mullitization, active growth of sialon and less intensive growth of TiC in the range of 1200–1600°CC, and also leads to the formation of less densely sintered crystalline microstructures in the sample, containing round crystalline TiO2 particles, pores and glassy phase at the boundaries of the regions in mullite–sialon–TiC solid solution composites at 1500°CC. Asample containing 5 mol.% Dy2O3 has lower values of relative density, linear shrinkage, physical and mechanical properties in the range of 1200 – 1600°CC, lower crack resistance with the formation of microcracks at 1500°CC and a slightly larger linear correlation of the elastic modulus and impact toughness in the range of 1200 – 1600°C.

Influence of calcination on the morphology and crystallinity of titanium dioxide nanofibers towards enhancing photocatalytic dye degradation

The development of titanium dioxide (TiO2) nanostructures with superior morphology and crystallinity is crucial for the photocatalytic degradation of textile dyes. This study highlights the evolution in the morphology and crystallinity of electrospun TiO2 nanofibers using polyvinylpyrrolidone (PVP) support in relation to applied calcination temperature, and their influence towards the photocatalytic dye degradation performance of the material. Results showed distinct differences in the thermal decomposition patterns of (PVP) on the fiber surface and the inner core, where it is dependent on the presence of oxygen. These differences drastically affect the morphology of the obtained fibers especially its surface area and porosity. Crystallinity of the embedded TiO2 particles increases with higher calcination temperature which contributes to higher photocatalytic performance. Highly mesoporous nanofibers with crystalline anatase TiO2 particles, together with fiber diameter of 118.3 ± 6.30 nm and surface area of 72.3219 m2 g−1 are obtained at 500 °C. The combination of these properties produced the best photocatalytic dye degradation rate constant of 0.080 29 min−1 and 0.0543 min−1 for methylene blue and methyl orange respectively. The performance can be attributed to a combination of high particle crystallinity and fiber porosity and surface area.

Acid acting as redispersing agent to form stable colloids from photoactive crystalline aqueous sol–gel TiO2 powder

In this work, the redispersion of three nanocrystalline TiO2 colloids is studied: one pure and two Fe-doped titania. These three colloids are produced by an easy aqueous sol–gel synthesis using precipitation-acidic peptization of Ti precursor. For the two Fe-doped TiO2, one is doped during synthesis (primary doping) and the other is doped after the synthesis (secondary doping). The initial colloids are composed of crystalline TiO2 particles around 7 nm with good photocatalytic properties, tested on PNP degradation under visible light (wavelength >390 nm). The powders obtained by air drying of these three colloids are redispersed in water to produce colloids, which are compared to the initial colloid produced. For each colloid, five cycles of drying redispersion are achieved. The colloids are characterized by dynamic light scattering, zeta potential measurements, inductively coupled plasma–atomic emission spectroscopy, X-ray diffraction, nitrogen adsorption–desorption measurements, Mossbauer spectroscopy, diffuse reflectance spectroscopy, and photocatalytic tests. The results show that similar products are obtained between the cycles, maintaining homologous properties of colloids. This property of redispersion is mainly due to the acid (HNO3, HCl, or H2SO4) which protonates the surface of the TiO2 nanoparticle leading to high-surface charges and electrostatic repulsions between aggregates. This property can be very useful for industrial applications of this synthesis, especially as it allows the volume and weight to be reduced for transportation and storage. Moreover, results show that the pure TiO2 powder can be doped during its redispersion step. The redispersion of the TiO2 developed here is possible without surface functionalization or multiple step processes, contrary to commercial Degussa P25. A 2-year stability study of all the produced colloids has been performed by following the evolution of the macroscopic aspect and the physicochemical properties of these sols. This study showed high stability of the produced colloids.

Design and Fabrication of TiO2/Lignocellulosic Carbon Materials: Relevance of Low‐temperature Sonocrystallization to Photocatalysts Performance

AbstractWe present a facile and green approach to produce crystalline TiO2 nanoparticles on a surface of different carbonaceous materials derived from lignocellulosic biomass such as STARBON‐800® obtained by carbonization at 800 °C and biochar‐SWP700 (Soft Wood Pellets (SWP) obtained by pyrolysis at 700 °C) via novel low‐temperature ultrasound‐promoted green methodology coupled with citric acid as a cross‐linking agent. In comparison to other methods, the developed method has several significant benefits such as simplicity, great ability to get crystalline TiO2 particles (elimination of high‐temperature treatment (material calcination at >300 °C) needed in the conventional sol‐gel method, which is extremely important in transforming amorphous TiO2 into a photoactive crystalline phase) elimination of risky chemicals and oxidizing agent, and also ability to change some parameters (e. g. ultrasound intensity). Prepared materials were characterized by XRD, DR UV−vis, N2 physisorption, HR‐XPS, XRF, HR‐TEM, FT‐IR and subsequently tested for their photocatalytic activities both in photocatalytic phenol degradation (in water) and oxidation of methanol (in air) under UV and visible light irradiation.

Spray pyrolysis-deposited nanoengineered TiO 2 thick films for ultra-high areal and volumetric capacity lithium ion battery applications

Abstract Energy storage technologies are sensitively dependent on electrode film quality, thickness and process scalability. In Li-ion batteries, using additive-free titania (TiO2) as electrodes, we sought to show the potential of spray pyrolysis-deposited nanoengineered films with thicknesses up to 135 μm exhibiting ultra-high areal capacities. Detailed electron microscopic characterization indicated that the achieved thick films are composed of highly crystalline anatase TiO2 particles with sizes on the order of 10–12 nm and porous as well. A 135 μm thick film yielded ultra-high areal and volumetric capacities of 3.7 mAh cm−2 and 274 mAh cm−3, respectively, at 1C rate. Also the present work recorded high Coulombic efficiency and good cycling stability. The best previously achieved capacities for additive-free TiO2 films have been less than 0.25 mAh cm−2 and With additives, best reported areal capacity in the literature has been 2.5 mAh cm−2 at 1C rate, but only with electrode thickness as high as 1400 μm. Formation of through-the-thickness percolation of Ti3+ conductive network upon lithiation contributed substantially for the superior performance. Spray pyrolysis deposition of nanoparticulate TiO2 electrodes have the potential to yield volumetric capacities an order of magnitude higher than the other processes previously reported without sacrificing performance and process scalability.

ZrO2/TiO2 films prepared by plasma electrolytic oxidation and a post treatment

ZrO2/TiO2 films with high surface area and improved catalytic structures were prepared by the combination of plasma electrolytic oxidation technology with a sulfuric acid acidification and calcinations post treatments. The metal oxides composition, metal oxides phase and morphologies of the obtained films were determined by X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. The post treatment conditions had significant influence on the phase composition and morphologies of the films. Both anatase and rutile phases of TiO2 in the film were observed by XRD. After the post processing, the surface of the film was covered by high crystalline TiO2 particles and the film surface is rough, leading to an increased surface area. With the increase of sulfuric acid concentration, the crystal form of the TiO2 particles transformed from cubic to spindle-like. Moreover, a tendency to form a multilevel structure was displayed with the increase of the calcinations temperature. The degradation of methylene blue under ultraviolet radiation indicated that the film with a post treatment showed a high photocatalytic activity. When catalyzed by the film prepared with a 750°C calcination temperature, the degradation of the methylene blue reached 93.18%. Meanwhile, the regeneration experiments showed the prepared film catalyst had a good reusability.

Characterization of Interfacial Charge‐Transfer Photoexcitation of Polychromium‐Oxo‐Electrodeposited TiO2 as an Earth‐Abundant Photoanode for Water Oxidation Driven by Visible Light

Polychromium-oxo-deposited TiO2 (CrIII x Oy /TiO2 ) electrodes were fabricated by a simple electrochemical technique by using different TiO2 basal electrodes (anatase, rutile, and mixed polymorphic phases P25) as earth-abundant photoanodes for visible-light-driven water oxidation. The high-resolution transmission electron microscopy (HR-TEM) observation illustrated that an CrIII x Oy layer with approximately 2-3 nm thickness was formed on the surface of the crystalline TiO2 particles. Upon visible-light irradiation of the electrodes, the photoanodic current based on water oxidation was generated at the CrIII x Oy /TiO2 electrodes. However, the wavelength (below 620 nm) for photocurrent generation at CrIII x Oy /TiO2 -rutile was longer than that (below 560 nm) at CrIII x Oy /TiO2 -P25 by 60 nm, which is in agreement with the difference (0.2 eV) in the conduction band (CB) edge energy between rutile and anatase TiO2 . This gives a quantitative account for the photocurrent generation based on interfacial charge transfer (IFCT) from Cr 3d of the deposited CrIII x Oy layer to the TiO2 CB. The photocurrent generated for CrIII x Oy /TiO2 -rutile was higher than that for CrIII x Oy /TiO2 -anatase, which is ascribed to 1) more effective CrIII x Oy deposition on the rutile particles, 2) a larger electrolyte/CrIII x Oy interface for water oxidation as a result of smaller rutile particles (ca. 30-40 nm) compared with larger P25 particles (ca. 40-80 nm), and 3) more effective use of visible light owing to the low energy IFCT transition of rutile.

A facile method for the structure control of TiO2 particles at low temperature

Crystalline and amorphous TiO2 particles have important potential applications in photocatalysis, structural ceramics, solar batteries and nanoglasses. Hence controlling the structure of TiO2 particles is of practical importance. Crystalline TiO2 particles are usually prepared by calcination of their amorphous precursor. Here a facile method was developed to control the structure of TiO2 particles at a low temperature. TiO2 particles were prepared by sol–gel method; and it was found that during the washing process, the TiO2 particles washed with water are crystalline whereas the TiO2 particles washed with ethanol are amorphous. Further analyses indicate that ethanol washing may introduce an organic cover layer on the TiO2 particles which hinders the crystallization of amorphous TiO2 particles. Therefore, the structure of TiO2 particles, amorphous or crystalline (anatase), can be controlled just by changing the washing medium, water or ethanol. This method seems a common method for controlling the (amorphous or crystalline) structure of metal oxides and hydroxides and was verified in the preparation of ZrO2, FeO(OH), and Al(OH)3 particles.

Effect of Ce conversion underlayer coating on the photo-catalytic activity of TiO2 sol–gel film deposited on hot-dip GI

In the present work, a photocatalytic titanium dioxide (TiO2) thin film was prepared by dip coating using an alkoxide sol–gel solution that included crystalline nano-sized TiO2 particles (P-25) on hot-dip galvanized steel (GI). A cerium (Ce) conversion coating was used as an interface layer between the steel substrate and TiO2 film to improve the photocatalytic activity and anti-corrosion performance of the film. The Ce conversion coatings were deposited on the GI via the sol–gel dip coating process using a Ce nitrate/hydrogen peroxide solution. The properties of the coating layers were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), UV–vis light absorption spectroscopy, and electrochemical impedance spectroscopy (EIS). The thickness of the TiO2 sol–gel film and Ce conversion coating were approximately 150nm and 30nm, respectively. It was clearly demonstrated that the addition of nano-sized TiO2 particles in the sol–gel film significantly enhanced the film's photocatalytic activity. The higher quantity of nano-sized TiO2 particles induced a higher absorption of UV light and improved photocatalytic activity. In particular, the photocatalytic activity was improved further by applying the Ce conversion coating because in most cases, the crystalline CeO2 interlayer reduced the band gap energy of the coating layer from 3.2eV to 2.8eV. In addition, the EIS measurements indicated that the Ce conversion coatings improved the anti-corrosion property of the coating layer on the hot-dip galvanized steel.

Molecular selective photocatalytic decomposition of alkylanilines by crystalline TiO2 particles and their nanocomposites with mesoporous silica

Molecular selective photocatalytic decomposition of alkylanilines in water was investigated by using crystalline TiO2 particles (P-25) and their nanocomposites with mesoporous silica. In the nanocomposites, pre-formed TiO2 particles were embedded into surfactant-templated mesoporous silica with tuned pore sizes (1.4–5.3 nm) as described in our previous reports (Chem. Commun. 2005, 2131–2133; J. Mater. Chem. 2011, 21, 12117–12125). Contrary to the generally accepted knowledge of TiO2 photocatalysts, pristine TiO2 particles showed molecule selective photocatalysis: decomposition of 4-n-heptylaniline (NHA) was much faster than that of 4-n-butylaniline (NBA) or p-toluidine (4-methylaniline, PT) in a mixed aqueous solution. After NHA had almost disappeared, decomposition of NBA accelerated. When the TiO2 particles were surrounded by mesoporous silica, the molecular selectivity was strongly modified: the nanocomposites showed high molecular selectivity for NBA decomposition and the reaction of PT was considerably suppressed. The origin of molecular selectivity can basically be ascribed to preferential molecular adsorption, and the difference in selectivity between alkylanilines and alkylphenols is discussed in terms of the interaction of the molecules with the nanocomposite surfaces.

Nanocomposites of crystalline TiO2 particles and mesoporous silica: molecular selective photocatalysis tuned by controlling pore size and structure

Preformed well-crystallized TiO2 particles (P-25, 20–30 nm in diameter) were directly embedded into surfactant-templated mesoporous silica having tuned pore sizes (1.4–5.3 nm). These nanocomposites (containing as much as 60 wt% TiO2) demonstrated molecular-selective photocatalysis toward the decomposition of mixed alkylphenols in water. Even in the presence of highly concentrated phenol, the nanocomposite decomposed dilute nonylphenols (NP) and heptylphenol (HP) completely, which is in contrast to pristine TiO2, highlighting the importance of the nanocomposite structure. The molecular selectivity could be tuned by systematically controlling the pore size: catalysts having large pores (2.7–5.3 nm) decomposed NP and HP at similar fast rates due to their preferential adsorption onto the catalysts. Catalysts having small pores (1.4–1.9 nm and smaller micropores) decomposed HP faster than NP because of their different diffusion rates. Furthermore, it was found that the nanocomposite structures were significantly improved by TiO2 particle surface alkyl-grafting: SEM and TEM images of the nanocomposite prepared from surface alkyl-grafted TiO2 particles revealed that the TiO2 particles were almost completely surrounded by mesoporous silica, whereas in the case of unmodified TiO2 particles, parts of them were left uncovered with the mesoporous silica. The nanocomposite prepared from alkyl-grafted TiO2 particles showed much higher molecular selectivity and activity than that prepared from unmodified TiO2.

Qualitative investigations of the photocatalytic dye destruction by TiO2-coated polyester fabrics

The preparation of TiO2-coated polyester fabrics for purposes of photocatalytic water purification requires coating agents with crystalline TiO2 particles preferably in the anatase modification. The resulting coatings should exhibit a high water resistance and high photocatalytic activity according to reaction with structurally different dyestuffs. For this, the synthesis of anatase sols by hydrolysis of tetraisopropyltitanate in acidic medium under reflux was optimized. By precoating or addition of polymeric epoxysilanes a good adhesion on the polyester support could be realized. The photocatalytic activity was tested with different dyestuffs as: Methylene blue, Rhodamine B and the azo dyes AcidOrange 7 and C.I. Reactive red 158. The rate of photodestruction depends strongly on the type of used dye and its structure. Surprisingly, no differences in photodegradation were found in case of investigations with Rhodamine B, if the photoreaction is performed under exposure with UV or with visible light. A possible explanation of the similar behavior of photoreaction under different light sources could be a photodestruction by electron transfer from Rhodamine B to TiO2. Therefore, Rhodamine B seems to be generally not suitable for the evaluation of the photoactivity of TiO2 under irradiation with visible light.

Growth Behavior of TiO2 Particles via the Liquid Phase Deposition Process

TiO2 particles were obtained from aqueous solutions by the liquid phase deposition (LPD) method. The crystalline anatase TiO2 particles could be prepared below 100°C directly from aqueous solutions. The growth behavior of TiO2 particles via the LPD process was investigated by dynamic light scattering (DLS) measurement and transmission electron microscopy (TEM). From DLS measurement, the particle growth process shows a sigmoidal curve and can be divided into three stages, i.e., the initial stage, the acceleration stage, and the completion stage. TEM measurements revealed that the primary particles with a diameter of ca. 50 nm were deposited at the initial stage. At the acceleration stage, these primary particles were assembled to form raspberry-like particles with a diameter of ca. 300 nm. Finally, the particles were precipitated by further aggregation with the micro-meter size at the completion stage.

Sedimentation Properties of TiO<sub>2</sub> Nanoparticles in Organic Solvents

In this study, the colloidal stability and sedimentation behavior of crystalline TiO2 particles (∼300nm) in various organic solvents have been investigated by means of a backscattered light flux profile (Turbiscan) and a zeta potential measurement. The backscattered light flux profiles revealed that the TiO2 nanoparticles were readily sedimented in water, methyl alcohol, and ethyl alcohol due to a flocculation-induced particle growth, while a particle coalescence and a sedimentation of the TiO2 nanoparticles were hardly observed in isopropyl alcohol. The measured ζ potentials verified the differences of the colloidal stabilities of the TiO2 particles in the organic solvents, showing a good correlation with the migration velocity.

Dispersion Stability of TiO<sub>2</sub> Powder Synthesized by Homogeneous Precipitation Process at Low Temperatures

Crystalline TiO2 particles with a diameter of 300nm were obtained from aqueous TiOCl2 solution with 0.67M Ti4+ concentration, diluted by TiCl4 solution using the homogeneous spontaneous precipitation process. Dispersion stability of rutile TiO2 powder with acicular typed primary particles has been investigated in both aqueous and organic media. In this paper, we focus on the TiO2 suspension stability in aqueous and organic media using a recently developed optical analyzer(Turbiscan) and Zeta potential analyzer. The surface potentials of TiO2 particles were greatly modified by dispersion medium and valance of the ionic species, which governs the colloidal behavior of TiO2 particles virtually.