TWI405610B - Highly photosensitive titanium dioxide and process for forming the same - Google Patents

Abstract

A highly photosensitivity titanium oxide composition includes a plurality of nanosize par-ticles including titanium dioxide and titanium suboxide. The particles are substantially non-stoichiometric (TiO2-x, wherein 0. 1&lt; x&lt; 0. 3 at a surface of the particles, and in the bulk of the particles x is less than at the surface), provide a magnetic susceptibility value (&khgr; ) of at least 0. 8 10<SP>-6</SP>cm<SP>3</SP>/g at 300 K, and are least 30% by weight rutile. A related method of forming a high pho-tosensitivity titanium oxide composition includes the steps of providing a titanium chloride com-pound, such as titanium tetrachloride, an oxygen-containing gas and hydrogen, wherein a con-centration of the hydrogen is in a stoichiometric excess (H2: O2) from 2. 02: 1 to 2. 61: 1. The tita-nium chloride compound is burned in the presence of oxygen from the oxygen-containing gas and hydrogen to form plurality of ultrafine particles comprising titanium dioxide and titanium suboxide. The method can include the steps prior to the burning step of mixing the titanium chloride compound, oxygen and hydrogen and heating the same to 50 to 100 DEG C, such as from 70-100 DEG C.

Description

Highly photosensitive titanium dioxide and method of forming same

The present application claims priority to U.S. Provisional Patent Application Serial No. 60/874,536, filed on Dec.

Titanium dioxide (TiO ₂ ), also known as titania, is present in three known crystal forms (rutile, anatase, brookite). Anatase and rutile can be used in industry. There are a variety of known synthetic methods, compositional variants (including hybrids), and heat treatments that alter the defined crystalline form.

Titanium oxide is the most widely used white pigment in the dye and paint industry, ceramics, paper, rubber and plastics. Titanium oxide is also used in the manufacture of ointments and other cosmetics (especially for UV protection).

In general, photocatalytic activity is the most important feature of titanium oxide. Unlike photochemical reactions in which photo-corrosion is performed by a semi-conductive agent, the photocatalytic reaction does not cause photo-etching of the reagent and its composition remains unchanged. Photochemical reagents absorb light and promote reactions between various gas or liquid phase materials, or induce currents. Many semiconductors, including titanium oxide, exhibit such photochemical activity. Semiconducting photocatalysis is a complex phenomenon with many promising spectral-optics, thermodynamics, kinetics, electronic physics, and some other fundamental prospects. For example, titanium oxide can be used as a base material for efficient photocatalytic systems for converting, preserving, and utilizing solar energy and hazardous waste neutralization and other environmental protection solutions. The titanium oxide product is also a design and manufacture of low-tonnage chemistry, multifunctional materials (for example, materials containing thin nanoparticle precipitation layers on various substrates), optical sensors and materials with nonlinear optical properties. Come to good prospects.

These reasons promote many photocatalytic studies. Water decomposition has been reported, which occurs On the surface of titanium oxide and producing an environmentally friendly molecular hydrogen that can be used as a fuel. There are many successful research projects in the field of photocatalysis and many general studies and general work. However, the extremely low quantum yield of most photocatalytic systems is a serious drawback that limits potential applications.

A simple photocatalytic semiconducting system includes a donor (D) moiety and a acceptor (A) moiety that act on a photocatalyst (e.g., titanium oxide). Closed photocatalytic loops usually only generate electron-electron couples in light The acceptor then accepts electrons excited by the conduction band ( e ^- + A → A ^- ) and the holes are transferred to the donor ( h ⁺ + D → D ⁺ ). Further conversion of the intermediates A ^- and D ⁺ can be carried out even in the absence of light and photocatalyst. The energy properties of the photocatalytic system should correspond to each other. If the electron-hole reaction is thermodynamically acceptable, for example, the negative potential of the conduction band should be higher than the oxidation potential of D (EcB<E ^TM , Then, the reactions can be carried out. The efficiency of the reaction e ^- + A → A and h ⁺ + D → D (and the photocatalytic process itself) should be in accordance with the energy gap and Widening and rising.

Photogenerated electronics and holes can be combined. The recombination process competes with the redox mechanism described above and significantly reduces the efficiency of any semiconducting photocatalyst, including titanium oxide. Accordingly, it is preferred to modify the photocatalytic system (e.g., by inserting electron and hole carriers, depositing a metal or metal oxide on the semiconductor, using a dual semiconductor heterostructure) to reduce recombination.

Titanium oxide can be obtained in various forms and from various source compounds in crystalline or hydrated form. Hydrolysis of the aqueous Ti (IV), the vapor or gaseous hydrolysis colloid, Ti (IV) alcoholate of the thermal decomposition of a compound or complex of TiCl ₄ pyrohydrolysis and a method for producing the most widely used titanium oxide. There are many industrial processes for the manufacture of titanium oxide.

Titanium oxide can be used as a photosensitive component of an optical layer and a dielectric material or as a photocatalyst for some redox reactions. These compounds generally provide high photocatalytic activity and dispersibility.

Most of the industrial samples of titanium oxide contain coarsely dispersed particles with low photocatalytic activity. There are some methods of producing finely divided titanium oxide having relatively high photosensitivity. However, such methods are often inconvenient and laborious.

There is a method for producing ultrafine titanium dioxide disclosed in British Patent No. 1,052,896, which discloses the combustion of titanium tetrachloride (preheated to 350 ° C) in a gas mixture containing oxygen (or carbon dioxide) and hydrogen at 1200 ° C to 1400 ° C. . The oxygen content in the gas mixture is revealed to be a slight stoichiometric excess relative to the hydrogen content in the gas mixture. In this way, fine titanium dioxide of the rutile type is obtained. However, the photosensitivity of the resulting product is very low and its photocatalytic activity (determined by methylene blue reduction reaction) is only about 2.5 to 3.0 x 10 ^-5 mg/ml at room temperature. Min. m ² .

A highly photosensitive titanium oxide composition comprises a plurality of nanosized particles comprising titanium dioxide and titania. The composition of the particles is substantially non-stoichiometric and the composition provides a magnetic susceptibility value (χ) of at least 0.8 x 10 ^-6 crrr ³ /g at 300 K and is typically at least 30% by weight rutile. As used herein, ''substantially non-stoichiometric TiO ₂ ' comprises TiO _2-x wherein 0.1<x<0.3 on the surface of the particles and x is less than the surface value in the bulk of the particles) .

In one embodiment, the crucible is between 0.8 x 10 ^-6 cm ³ /g and 2.4 x 10 ^-6 cm ³ /g at 300K. The average size of the particles is typically from 10 nm to 40 nm, such as from 10 nm to 20 nm. In one embodiment, the rutile comprises at least 40% of the composition, and the remainder of the composition is substantially all anatase (such as 45 to 55% rutile and the balance being anatase).

The concentration of chlorine on the surface of the particles is lower than the concentration of chlorine in the bulk of the particles, and the concentration of chlorine on the surface of the particles is typically at least one order of magnitude lower than the concentration of chlorine in the bulk of the particles. The surface of the particles may have an x value of 0.15 < x < 0.3, and in the bulk of the particles, x may be less than 0.1 (such as 0.08 to 0.1). The photocatalytic activity of the particles can be 1.4 to 3.0 mg/ml as measured by a methylene blue reduction reaction at room temperature. Min. m ² .

A method of forming a highly photosensitive titanium oxide composition comprising the steps of providing a titanium chloride compound such as titanium trichloride or titanium tetrachloride, and an oxygen-containing gas (e.g., air) and hydrogen, wherein the concentration of hydrogen is 2.02: A stoichiometric excess (H ₂ : O ₂ ) of 1 to 2.61:1 (such as 2.12:1, 2.22:1, 2.32:1, 2.42:1 or 2.52:1). The titanium chloride compound is burned in the presence of oxygen and hydrogen from an oxygen-containing gas to form a plurality of ultrafine particles comprising titanium dioxide and titania. The method may include the steps of mixing a titanium chloride compound, oxygen, and hydrogen and heating the titanium chloride compound, oxygen, and hydrogen to a temperature of from 50 ° C to 100 ° C (such as from 70 ° C to 100 ° C) prior to the burning step.

The steady state temperature during the combustion step is typically from 700 ° C to 1100 ° C, such as 800 ° C, 850 ° C, 900 ° C, 950 ° C, 1000 ° C or 1050 ° C. The method may further comprise the step of steam treating the particles at 150 ° C to 220 ° C to promote the desorption of chlorine from the surface of the particles (such as in the temperature range of from 170 ° C to 200 ° C).

The molar ratio of titanium tetrachloride compound to H ₂ is usually in the range of 1:4 to 1:2. The median size of the particles is usually in the range of 10 nm to 40 nm (coagulation), while the size of individual primary particles is usually 2 nm to 8 nm. The photocatalytic activity of the particles can be 1.4 to 3.0 mg/ml as measured in the methylene blue reduction reaction at room temperature (300 K). Min. m ² .

A method of forming a highly photosensitive titanium oxide composition comprises the steps of providing a titanium chloride compound such as titanium trichloride or titanium tetrachloride, an oxygen-containing gas such as air, and hydrogen (H ₂ ). The hydrogen concentration is a stoichiometric excess (H ₂ : O ₂ ) of 2.02:1 to 2.61:1. The titanium chloride compound is burned in the presence of oxygen and hydrogen from an oxygen-containing gas to form a plurality of ultrafine (nano) particles. Such secondary particles comprise titanium oxide and titanium dioxide, but simply referred to as "the present invention comprises the TiO ₂ particles" or "composition" present invention "herein. The resulting present invention comprises the TiO ₂ particles to provide at least 300K The magnetic susceptibility value (χ) of 0.8×10 ^-6 cm ³ /g is at least 30% by weight of rutile, and the rest is basically anatase. The enthalpy may be 0.8×10 ^-6 cm ³ at 300K / g between 2.4 and 10 ^-6 cm ³ /g. The extremely high paramagnetic susceptibility of the composition of the invention is its high photocatalytic activity (such as room temperature photosensitivity of 1.4 to 3.0 mg/ml.min.m ² ) The index, which is several orders of magnitude higher than the photosensitivity provided by the conventional industrial titanium oxide pigment product (2.5 to 3.0 x 10 ^-5 mg/ml.min.m ² at room temperature).

The oxygen-containing gas such as air is usually pre-dried and heated, for example, to 70 ° C to 100 ° C. The combustion process typically takes place at temperatures ranging from 700 °C to 1100 °C. The flame hydrolysis temperature (700 ° C to 1100 ° C) generally defines the rate of hydrolysis and structure of the final product. The treatment rate is significantly slowed down and the hydrolysis is usually not completed at temperatures below 700 ° C. It has been found that this photocatalytic activity of the reduced product Sex. On the other hand, the optimum ratio between the anatase form and the rutile form is shifted toward the rutile form at a temperature higher than 1100 ° C. The inventors have found that the specific surface area and photocatalytic activity of the final product are Negative Effects. The final product can be subjected to steam treatment at 170 ° C to 200 ° C.

The reaction conditions determine the composition of the final product, its photocatalytic activity and its crystalline nature (anatase or rutile or mixtures thereof) by varying the temperature, the ratio between the source components or by adding from about 0.001 to 3.0. The mass % is selected from a mixture of W (VI), V (V), Bi (III), Al (III), Zn (II), Zr (IV), Hf (IV) compounds. Regardless of whether TiCl ₃ or TiCl _{4 is} used as the titanium source compound, the reaction conditions are substantially unchanged.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a special spherical-elongated quartz ampoule 100 used by the inventors to measure the photocatalytic activity of the compositions of the present invention. In a typical experiment, 16 mg of the composition of the invention was loaded into the spherical portion 105 of the ampoule, and 0.6 ml of a 0.2 g/l methylene blue solution was placed in the elongated portion 110 together with 0.6 ml of a 38% formaldehyde solution. The capillary 115 is inserted into the ampoule, and an inert gas (argon or nitrogen) containing no oxygen is pumped through the capillary 115 until the oxygen content falls below 4.0.10 ^-5 vol.%. The ampoule 100 is then sealed and placed in a manner to mix the composition of the invention with the solutions. The mixture is mechanically agitated and irradiated with a lamp such as a mercury lamp (not shown) which provides ultraviolet radiation having a peak at typically from 310 nm to 400 nm. The distance between the spherical portion 105 and the lamp is typically about 20 cm. The measurement time at which the reaction mixture completely faded was measured. The shorter the time elapsed until fading, the higher the photocatalytic activity exhibited by the sample containing TiO ₂ .

As described herein, the photocatalytic activity is calculated using the formula:

Wherein the initial concentration of c ₀ -methylene blue (mg/ml); τ _1/2 - the time of semi-fading (min); S - specific surface area (m ² /g) (measured by the BET method); m-containing TiO sample ₂ of the mass (mg).

When the composition of the present invention is embodied as a composite comprising the composition of the present invention and other oxide materials or polymers, the experimental method can also be used to measure the photocatalytic activity of the composition of the present invention.

2 shows a simplified reactor apparatus 200 that can be used to make particles having the compositions of the present invention. The source material includes an oxygen-containing gas such as air, hydrogen, and titanium tetrachloride as a titanium chloride compound. The source material is typically heated to 70 ° C to 100 ° C and the material is piped to a combustor / combustor 210 where the materials are mixed with one another, wherein a stoichiometric excess of H _{2 is provided} . The source material is then piped from the orifice to a flame tube 215 where the air-hydrogen mixture is combusted at 700 ° C to 1100 ° C to hydrolyze titanium tetrachloride: TiCl ₄ + 2 H _{. 2} + O ₂ → TiO ₂ +4 HCl .

The primary particles of titanium dioxide are formed in this reaction. The size of the initial particles is usually from 2 nm to 8 nm.

Another process can also be carried out together: 4 H Cl + O ₂ → 2 H ₂ O + 2 Cl ₂

The secondary particles of the TiO ₂ -containing material of the present invention are ultimately formed into agglomerates in the condenser. The coalescence size is usually 10 nm to 40 nm. This final product can also be steam treated at 170 ° C to 200 ° C to remove surface adsorbed chlorine.

Ultrafine fumed particles comprising TiO ₂ having a non-stoichiometric composition are the end products of the process of the invention. The compositions of the invention are obtained in the form of a mixture of two different crystal modifications, anatase and rutile. This makes the material highly defective, which usually causes high paramagnetic susceptibility and photosensitivity. X-ray analysis by the inventors has demonstrated that the resulting product is a mixture of individual anatase particles and rutile particles alone. However, a very small percentage of the particle system may include mixed anatase and rutile.

This process should normally be maintained within the specified temperature range. The mixture of TiCl ₄ (or TiCl ₃ ) with other reactant gases is most effectively homogenized at 70 ° C to 100 ° C. This condition ensures homogeneity and fine dispersion (small particle size) of the flame hydrolysate. The TiCl ₄ vapor does not reach the desired concentration at temperatures below 70 ° C, which results in lower product homogeneity. Temperatures above 100 °C can result in the formation of large chunks in the final product.

Heating to 70 ° C to 100 ° C helps to avoid condensation of TiCl ₄ vapor during pipe transport. Heating also promotes a more stable and more uniform reaction mixture. The temperature of the reaction mixture is preferably higher than the boiling point of the titanium chloride compound, such as 140 ° C for TiCl ₄ (boiling point of about 138 ° C). Thus, it should normally be prevented (e.g., at 70 deg.] C to 100 deg.] C) is added to the evaporator of an air conveyor in TiC1 ₄ at a temperature of TiCl ₄ vapor condensation. The line between the evaporator and the burner should also be heated to avoid condensation in the vapor. If condensation occurs, a new droplet phase appears in the gas mixture, which can significantly change the state of the combustion process. This change usually results in obtaining a coarsely dispersed and polydisperse titanium oxide powder.

The flame hydrolysis should generally be maintained at 700 ° C to 1100 ° C because the process is too slow at temperatures below 700 ° C and the hydrolysis oxidation reaction is not complete, which significantly reduces the photosensitivity of the product. On the other hand, at a temperature higher than 1100 ° C, the ratio between the anatase phase and the rutile phase deviates from the optimum value, which lowers the specific surface area and photosensitivity of the product. The flame hydrolysis temperature can be measured using a thermocouple detector.

The ratio of TiCl ₄ (or TiCl ₃ ) to H ₂ is usually in the range of 1:4 to 1:2. Beyond this range in excess of a hydrogen system generally disadvantageous because it causes an additional consumption of hydrogen and TiO generally do not provide any significant dispersibility improvement and ₂ of the photocatalytic activity. Insufficient hydrogen below this range generally results in poor dispersibility and a decrease in photocatalytic activity of TiO ₂ .

Steam treatment at temperatures below 150 °C generally also reduces the photosensitivity of the product, while treatments at temperatures above 200 °C generally do not produce any significant increase in photosensitivity, but require additional energy consumption.

Steam treatment of TiO ₂ -containing powders in accordance with the present invention is generally a useful step. The steam treatment helps eliminate 'acid' gas (about 0.1 to 0.15 mass% of HCl, Cl _2), the acid gas can be adsorbed on the surface comprising particles of TiO ₂ of the great affinity .TiO ₂ with steam, so that from this elimination of the active surface of the TiO ₂ (desorption temperature) becomes possible HCI and Cl _2. the product containing TiO ₂ of the steam treatment with air, the air pre-distilled water of 400 deg.] C steam wetting.

The titanium oxide powder product can also be treated with steam in a "boiling bed" unit. The "boiling bed" is formed by a flow of inert gas (nitrogen) installed in a heated quartz tube in a cylindrical vertical device. The steam treatment temperature should be no higher than 690. °C to 700 ° C, because higher temperature can reduce the photocatalytic activity and dispersibility of the product.

Various modifications of the titanium oxide of the present invention (anatase, rutile or a mixture of various ratios of anatase and rutile) can be obtained by changing the reaction conditions (temperature, ratio between source compounds, etc.). The physical and chemical properties of these deformations are given in Table 1 below.

Instance

It is to be understood that the following examples are provided for illustrative purposes only and are not intended to limit the scope of the invention in any way.

In the framework of the present invention, the titanium oxide of the present invention can be produced in a continuous process according to the following scheme.

The dry air is heated to 70 ° C to 100 ° C and saturated with TiCl ₄ vapor. This saturation can be achieved with hot TiCl ₄ in the surface evaporator. The mixture is then mixed with hydrogen and then piped to a combustion apparatus. This process produces TiO ₂ which is subjected to steam treatment.

Example 1

The air at 100 nm ³ was dried and heated to 100 ° C, then air was mixed with 10 l of TiCl ₄ and 40 nm ³ of hydrogen and piped to the combustion equipment. Combustion occurred at 1100 ° C and the product was treated with water vapor at 180 °C. The photosensitivity of the obtained product was determined by a reduction reaction of methylene blue. The product contains particles of 0.01 to 0.02 μm, having a specific surface area of 80 m ² /g and 3.0 mg/ml. Min. Photocatalytic activity of m ² .

Example 2

The air at 100 nm ³ was dried and heated to 70 ° C, then mixed with 10 l of TiCl ₄ and 40 nm ³ of hydrogen and piped to a combustion apparatus. The combustion took place at 1100 ° C and the product was treated with steam at 200 ° C. The obtained product containing TiO ₂ has a specific surface area of 80 m ² /g and 2.9 mg/ml. Min. Photocatalytic activity of m ² .

Example 3

The air of 100 nm ³ was dried and heated to 100 ° C, then mixed with 20 l of TiCl ₄ and 40 nm ³ of hydrogen and piped to a combustion apparatus. The combustion took place at 700 ° C and the product was treated with water at 200 ° C. The obtained product containing TiO ₂ has a specific surface area of 50 m ² /g and 2.0 mg/ml. Min. Photocatalytic activity of m ² .

Example 4

The product comprising TiO ₂ obtained in Example 3 was treated with water vapor at 150 °C. The obtained product containing TiO ₂ has a specific surface area of 50 m ² /g and 0.9 mg/ml. Min. Photocatalytic activity of m ² .

Based on the experimental data presented, it was found, compared to other known or available titanium oxide composition of the present invention comprises the TiO ₂ particles to provide a significantly higher photocatalytic activity. Higher photosensitivity allows for performance improvements in a variety of applications including, but not limited to, as a framework for additive technology for various redox processes, for the manufacture of photosensitive materials, for the manufacture of printed boards, and many other applications. Medium photocatalyst.

The invention has been described in connection with the preferred embodiments thereof, and the foregoing description and the following examples are intended to illustrate and not to limit the scope of the invention. Other aspects, advantages, and modifications within the scope of the invention will be apparent to those skilled in the art.

100‧‧‧Spherical-elongated quartz ampoule

105‧‧‧ spherical part

110‧‧‧Elongation

115‧‧‧Capillary

200‧‧‧Simplified reactor unit

210‧‧‧burner/combustion chamber

215‧‧‧flame tube

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a spherical-elongation quartz ampule used by the inventors to measure the photocatalytic activity of the TiO ₂ -containing particles of the present invention.

Figure 2 shows a simplified reactor apparatus that can be used to make the titanium oxide particles of the present invention.

100‧‧‧Spherical-elongated quartz ampoule

105‧‧‧ spherical part

110‧‧‧Elongation

115‧‧‧Capillary

Claims (25)

A highly photosensitive titanium oxide composition comprising: a plurality of nanosized particles comprising titanium dioxide and titania, said particles being substantially non-stoichiometric, having at least 0.8 x 10 ^-6 cm ³ at 300K / The magnetic susceptibility value of g (χ) is at least 30% by weight of rutile. The composition of claim 1, wherein the oxime is between 0.8 x 10 ^-6 cm ³ /g and 2.4 x 10 ^-6 cm ³ /g at 300K. The composition of claim 1, wherein the particles have an average size of from 10 nm to 40 nm. The composition of claim 1 wherein the rutile is at least 40% and the remainder of the composition is substantially all anatase. The composition of claim 1 wherein the composition comprises from 45% to 55% of the rutile, the anatase comprising the remainder. The composition of claim 1 wherein the surface of the particles has a chlorine concentration that is lower than a concentration of chlorine in the bulk of the particles. The composition of claim 6 wherein the concentration of the chlorine on the surface of the particles is at least one order of magnitude lower than the concentration of chlorine in the body of the particles. The composition of claim 1, wherein the composition comprises TiO _2-x , wherein 0.15 < x < 0.3 on the surface of the particles and x is less than x of the surface in the bulk of the particles. The composition of claim 8 wherein the x in the body of the particles is less than 0.1. The composition of claim 8 wherein the x in the body of the particles is from 0.08 to 0.1. The composition of claim 1, wherein the photocatalytic activity of the particles is from 1.4 to 3.0 mg/ml as measured in the reduction reaction of methylene blue. Min. m ² . A method of forming a highly photosensitive titanium oxide composition comprising the steps of: providing a compound comprising titanium chloride, an oxygen-containing gas, and hydrogen, wherein the concentration of the hydrogen is a stoichiometric excess of 2.02:1 to 2.61:1 (H) ₂ : O ₂ ), and burning the titanium-containing compound in the presence of oxygen from the oxygen-containing gas and the hydrogen to form a plurality of ultrafine particles comprising titanium dioxide and titania. The method of claim 12, further comprising mixing the titanium chloride-containing compound, the oxygen and hydrogen, and heating the titanium chloride-containing compound, the oxygen and hydrogen to 50 ° C to 100 ° C before the burning step step. The method of claim 13, wherein the heating temperature is from 70 ° C to 100 ° C. The method of claim 12, wherein the steady state temperature during the burning step is from 700 ° C to 1100 ° C. The method of claim 12, further comprising the step of steam treating the particles at 150 ° C to 220 ° C to promote the desorption of chlorine from the surface of the particles. The method of claim 16, wherein the steam treatment has a temperature of from 170 ° C to 200 ° C. The method of claim 12, wherein the titanium chloride-containing compound and the H ₂ molar ratio are in the range of 1:4 to 1:2. The method of claim 12, wherein the compound comprising titanium chloride comprises titanium tetrachloride. The method of claim 12, wherein the photocatalytic activity of the particles is from 1.4 to 3.0 mg/ml as measured in a methylene blue reduction reaction at room temperature. Min. m ² . A highly photosensitive titanium oxide composition comprising a plurality of nanosized particles comprising titanium dioxide and titania, said particles being substantially non-stoichiometric, having at least 0.8 x 10 ^-6 cm ³ at 300K / a magnetic susceptibility value (χ) of at least 30% by weight of rutile, the particles being formed by a method comprising the steps of: providing a compound comprising titanium chloride, an oxygen-containing gas, and hydrogen, wherein the concentration of the hydrogen a stoichiometric excess (H ₂ : O ₂ ) of from 2.02:1 to 2.61:1; and combustion of the inclusion at a steady state temperature of from 700 ° C to 1100 ° C in the presence of oxygen from the oxygen-containing gas and the hydrogen A compound of titanium chloride is formed to form a plurality of ultrafine particles comprising titanium dioxide and titania. The composition of claim 21, further comprising the step of steam treating the particles at 150 ° C to 220 ° C to promote the desorption of chlorine from the surfaces of the particles. The composition of claim 22, wherein the steam treatment has a temperature of from 170 °C to 200 °C. The composition of claim 21, wherein the titanium chloride-containing compound and the H ₂ molar ratio are in the range of 1:4 to 1:2. The composition of claim 21, further comprising mixing the titanium chloride-containing compound, the oxygen and hydrogen, and heating the titanium-containing compound, the oxygen and hydrogen to 70 ° C to 100 ° C prior to the burning step The steps.