WO2008033227A2

WO2008033227A2 - Optically clear nanoparticle colloidal suspensions and method of making thereof

Info

Publication number: WO2008033227A2
Application number: PCT/US2007/019157
Authority: WO
Inventors: Partha Dutta
Original assignee: Applied Nano Works, Inc.
Priority date: 2006-09-11
Filing date: 2007-08-31
Publication date: 2008-03-20
Also published as: WO2008033227A3

Abstract

A method of making a nanoparticle colloid composition includes mixing a chloride compound with an acid to form a mixture and adding an oxygen containing material to the mixture to form an oxide nanoparticle colloid composition which can be used in a UV blocking coating, a CMP slurry or a structural composite.

Description

OPTICALLY CLEAR NANOP ARTICLE COLLOIDAL SUSPENSIONS AND

METHOD OF MAKING THEREOF

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims benefit of United States provisional application 60/843,506, filed September 11, 2006, which is incorporated herein by reference in its entirety.

BACKGROUND

It has been known for over 100 years that reacting TiCl₄ with water results in Tiθ₂ by the following reaction (see BJ. Harrington, Trans. Royal Soc. (Canada), [2], 1, 3

(1895)):

TiCl₄ + 2H₂O -> TiO₂ + 4HCl

As noted in the Encyclopedia of Chemical Reactions, vol. 7, page 404 "[rjutile crystals are obtained by the action of water vapor upon volatile titanium chloride." The above reaction has been used by the TiO₂ producing industries to produce bulk TiO₂ powders in large quantities. As used herein, bulk powder means a powder having an average particle size of greater than 100 nm, such as 1 micron or greater. Furthermore, titanium based sols can be manufactured by reacting TiCU with a variety of reagents for specific applications.

However for a wide range of commercial applications, colloids with one or more following properties are desirable: (a) nanoparticles which can be dispersed in both water as well as organic solvents, (b) maintaining a high optical transparency in the visible range (400-700 nm) and high UV absorption (wavelength below 400 nm) while tuning pH of the colloid from extreme acidity to basic (for example, a pH of 0.1 to 1 1), (c) maintaining the optical properties described in (b) above, while increasing particle loading density in the colloid beyond few weight percentage, such as beyond 5-10 weight percent, (d) absence of undesirable additives, such as surfactants, which are used to keep particles from agglomerating in the colloid, and (e) absence of a shell of different material on the nanoparticles to allow the nanoparticles to link or chemically bond with solid matrix materials, such as polymers. The present inventor believes that a single prior art TiO₂ based colloid fails to meet all the above criteria, which limits the scope of application of the prior art colloids.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1 , 3 and 4 are UV- Visible absorption spectra OfTiO₂, ZnO and CeO₂ colloids, respectively, with different particle concentrations.

Figures 2 and 5 are PCS plots of size distribution of TiO₂ and SiO₂ nanoparticles, respectively, in exemplary colloids.

DETAILED DESCRIPTION

One embodiment of the invention provides a nanoparticle containing composition, such as a colloid, which contains one or more of the following properties: (a) nanoparticles which can be dispersed in both water as well as organic solvents, (b) maintaining a high optical transparency in the visible range (400-700 nm) and high UV absorption (wavelength below 400 nm) while tuning pH of the colloid from extreme acidity to basic (for example, a pH of 0.1 to 11), (c) maintaining the optical properties described in (b) above, while increasing particle loading density in the colloid beyond few weight percentage, such as beyond 5-10 weight percent, (d) absence of undesirable additives, such as surfactants which are used to keep particles from agglomerating in the colloid, and/or (e) absence of a shell of different material on the nanoparticles to allow the nanoparticles to link or chemically bond with solid matrix materials, such as polymers. Preferably, the composition contains all of the above described properties. The terms colloid and colloidal suspension are used interchangeably herein.

The term nanoparticles includes particles having an average size between about 2 and about 100 nm, preferably particles having an average size between about 2 and about 50 nm. Most preferably, the nanoparticles have an average size between about 2 and about 10 nm. Preferably, the first standard deviation of the size distribution is 60% or less, preferably 40% or less, most preferably 10 to 25% of the average particle size. Preferably, the nanoparticles comprise oxide nanoparticles, such as metal or semiconductor oxide nanoparticles, such as titanium oxide, silicon oxide, cerium oxide, aluminum oxide, zirconium oxide or zinc oxide nanoparticles. Specifically, the nanoparticles may comprise titania, silica, ceria, alumina, zirconia or zinc oxide nanoparticles, which in their pure, stoichiometric state can be expressed by the following respective chemical formulas: TiO₂, Siθ2, CeO₂, Al₂O₃, ZrO₂ and ZnO. However, other nanoparticle compositions may be used.

Another embodiment of the invention provides a two step method for synthesizing oxide nanoparticle based, optically clear colloidal suspensions with greater than 80% transparency for wavelengths in the visible range (i.e., greater 400 ran, such as 400 run to 700 nm) and tunable UV absorption strength below 400 nm. The colloidal suspension can be water or organic solvent based with a tunable pH ranging between 0.1 and 11. Any suitable organic solvents, such as ethanol, methanol, toluene, etc. may be used.

The first step of the method comprises mixing a metal or semiconductor chloride compound with an acid to form a mixture. The metal or semiconductor element of the chloride compound is chosen based on the type of metal or semiconductor element that is desired to be included in the nanoparticles. For example, SiCl₄, TiCU, CeCU, AlCl₃, ZrCU, and ZnCl₂ chloride compounds may be used. Any suitable acids may be used. Preferably, weak carboxylic acids, such as acetic acid, for example glacial acetic acid, may be used. For example, pure TiCl₄ liquid is mixed with glacial acetic acid. Preferably, a ratio of the chloride compound to acid in the mixture ranges from 1 :1 to 1 :30, such as 1 :1 to 1 :20, for example 1 :1 to 1 :10.

The second step of the method comprises slowly adding an oxygen containing material to the mixture of the acid and the chloride compound to form a metal or semiconductor oxide nanoparticle colloid composition. Preferably, the oxygen containing material comprises water. However, other oxygen containing materials, such as dry or moist air or organic compounds may be used. The air may be bubbled through the mixture. The oxygen containing compound, such as water, converts the chloride compound in the mixture to oxide nanoparticles via a chemical reaction. For example, for TiCl₄ and water, the reaction comprises TiCl₄ + 2H₂O ^"> TiO₂ + 4HCl (g). The HCl gas bubbles out of the colloid and is collected by a fume hood. The water is added to the mixture sufficiently slow to prevent nanoparticles from quickly precipitating from the mixture and clumping, thus causing the mixture to become opaque. For example, water is added to the mixture at a rate of 1 to 20 ml per minute, such as about 5 to 15 ml per minute, for example 10 ml per minute. Thus, the present inventor unexpectedly found that when the water is slowly added to the mixture of the acid and the chloride compound, the nanoparticles form but do not precipitate, thus forming an optically clear and transparent colloid. In contrast, if the chloride compound is added to a mixture of water and acid, then large oxide particles precipitate and turn the liquid opaque. Furthermore, if water is mixed with titanium chloride without the acid, then a bulk titania powder is formed as in the prior art methods.

The addition of the water causes oxide nanoparticles to form in the solvent (i.e., acid and water). Preferably, the nanoparticles comprises titania, silica, ceria, alumina, zirconia or zinc oxide nanoparticles and have an average size between 2 and 10 nm. More preferably, all nanoparticles detectable by Photon Correlated Spectroscopy (PCS) in the composition have a diameter of 10 nm or less. The nanoparticle diameter can be controlled by controlling a ratio of the acid to water and chloride compound. The higher the amount of acid compared to amount of water and chloride compound, the smaller the resulting nanoparticle size.

After the synthesis, the pH of the colloid is extremely low (such as a pH of less than 1 , for example). Thus, if a mildly acidic, neutral or basic colloid is desired, then the pH of the colloid is increased by adding a weak base or a mixture of a weak acid and a strong base to the colloid. The post synthesis pH modification is preferably conducted in a step by step fashion to avoid agglomeration of the colloid that leads to precipitation of the nanoparticles which turns the colloid white and optically opaque. The present inventor believes that changing pH by usual acid-base titration process by adding a strong base to the colloid is not suitable for maintaining the optical clarity of the colloid because it causes the agglomeration and precipitation of the nanoparticles.

Thus, either a weak base, such as a base having a pH of between 7.1 and 9, or a mixture of a weak acid (having a pH between 5 and 6.9) and a strong base (having a pH greater than 9, such as 10-14), where the mixture has an overall pH above 7.1, is added to the colloid while maintaining the optical clarity (i.e., such that the colloid remains optically transparent in a visible wavelength range) and UV absorption properties of the colloid. Preferably, a mixture of a carboxylic acid, such as acetic acid, and a strong base, such as NaOH, is added to the colloid. Other acid-base mixtures, such as acetic acid and sodium bi-carbonate, or sodium acetate and NaOH, dispersed in water in different ratios is suitable for changing the pH of the colloid without affecting its optical properties. The acid and the base are preferably mixed before being introduced into the colloid. Thus, the colloid pH may be low, such as 0.1 to 1 without adjustment, or it may be increased to about 2 to about 1 1 by adding the acid-base mixture.

Without wishing to be bound by a particular theory, the present inventor believes that the use of a carboxylic acid, such as the acetic acid, either during the first step of nanoparticle formation and/or during the third step of pH adjustment, causes the formation of a carboxylic acid residue, such as an acetic acid residue, on nanoparticle surface. The residue may include CH₃CO- carboxyl groups and/or reactive COOH groups. For example, the residue may include CH₃COO groups in which the oxygen covalently binds to a metal or Si site, such as a Ti site on the nanoparticle surface. These groups may passivate the nanoparticle surface and prevent or reduce nanoparticle agglomeration. However, a complete shell of different material (such as a core-shell nanoparticle configuration) is preferably not present on the nanoparticles. Furthermore, as noted above, the colloid does not require undesirable additives, such as surfactants, which are used to keep particles from agglomerating in the colloid. However, a surfactant may be added if desired. Thus, for nanoparticles formed by a reaction of a tetrachloride, such as silicon or titanium tetrachloride, with a carboxylic acid, such as acetic acid, the final composition may contain silica or titania nanoparticles with acetic acid residue on their surface, hydrochloric acid, acetic acid and water. The nanoparticles may be separated from this composition in a subsequent step.

The nanoparticle compositions, such as colloids, are suitable for a wide range of applications, including, but not limited to, refractive index modifier additive to optical devices, abrasion or scratch resistant coating, coating which provides a tunable mechanical hardness, a UV blocking coating, solar cell layer, paint additive, composite material, such as a nanoparticle-polymer composite, etc. The nanoparticles are preferably incorporated from the solvent of the colloid into a solid matrix material, such as a polymer layer, for uses such as the UV blocking and scratch resistant thin film on a glass window or windshield. The colloid solvent, such as water, is evaporated from the solid matrix material. However, the nanoparticles retain their optical properties in the solid matrix, especially if the matrix material is optically transparent. If desired, the nanoparticles may be incorporated into a gel or viscous liquid matrix, such as an optically clear sunscreen or cosmetic composition with UV absorbing properties. The nanoparticle compositions maintain their optical properties even in organic solvents, such as ethanol, methanol, toluene, etc., and thus can be incorporated into organic solvents and matrixes without substantial loss of optical properties.

In another embodiment, the nanoparticle composition is used in a polishing slurry. One example of a polishing slurry is a chemical mechanical polishing (CMP) slurry which is used for chemical mechanical polishing of semiconductor and other solid state devices. The nanoparticles form the abrasive portion of the polishing slurry. Preferably, silica nanoparticles, such as amorphous silica nanoparticles, are used in the slurry.

As noted in U.S. Patent 6,749,488, incorporated herein by reference in its entirety, there are two general types of layers that can be polished. The first layer is interlayer dielectrics (ILD), such as, silicon oxide and silicon nitride. The second layer is metal layers, such as, tungsten, copper, aluminum, etc., which are used to connect the active devices. In the case of CMP of metals, the chemical action is generally considered to take one of two forms. In the first mechanism, the chemicals in the solution react with the metal layer to continuously form an oxide layer on the surface of the metal. This generally requires the addition of an oxidizer to the solution, such as, hydrogen peroxide, ferric nitrate, etc. Thereafter, the mechanical abrasive action of the particles continuously and simultaneously removes this oxide layer. In the second mechanism, no protective oxide layer is formed. Instead, the constituents in the solution chemically attack and dissolve the metal, while the mechanical action is largely one of mechanically enhancing the dissolution rate by such processes as continuously exposing more surface area to chemical attack, raising the local temperature (which increases the dissolution rate) by the friction between the particles and the metal, enhancing the diffusion of reactants and products to and away from the surface by mixing, and by reducing the thickness of the boundary layer.

For example, a number of systems for chemical-mechanical polishing of copper have been disclosed. The above mentioned U.S. Patent 6,749,488 lists several examples, such as a slurry that contains glycerol and abrasive alumina particles, slurries based on either ammonium hydroxide or nitric acid that may contain benzotriazole (BTA) as an inhibitor of copper dissolution, alumina-ferric nitrate slurries that contain polymeric surfactants and BTA, and slurries that contain either alumina or silica particles, nitric acid or ammonium hydroxide, with hydrogen peroxide or potassium permanganate as an oxidizer.

Thus, the nanoparticles, such as silica or alumina nanoparticles, made according to the embodiments of the present invention may be used as an abrasive component in any suitable polishing slurries that contain other chemical components, including oxidizers and components which chemically attack or etch the semiconductor device layer(s), such as metal, insulator or semiconductor layer(s). Such chemical components include glycerol, ammonium hydroxide, nitric acid, ferric nitrate, BTA, hydrogen peroxide and/or potassium permanganate, etc. The nanoparticles for the polishing slurry may have any suitable size, such as 10 to 100 nm, for example 20 to 50 nm. The nanoparticle size is controlled by controlling a ratio of the acid to oxidizer, such as a ratio of acetic acid to water during nanoparticle fabrication.

In another embodiment, the nanoparticles are used in a composite material, such as a structural composite material, having an organic and/or an inorganic matrix. For example, the nanoparticles may be added to cement to add strength to the cement.

Specific Examples

After the colloid synthesis, the optical transmission and absorption of the colloid was evaluated using a Cary 500 UV-Visible spectrometer (from Varian Corporation). The particle size measurements were carried out using the photon correlation spectroscopy (PCS) technique. The Beckman Coulter's Particle Size Analyzer (model N5) was used for the PCS measurements.

Figure 1 shows the UV-visible data (i.e., a plot of absorbance versus wavelength) of various titania colloids synthesized according to the methods of the embodiments of the invention. The optical path length for all the measurements was 1 cm. In Figure 1 , an absorbance of 10 on the y-axis represents complete 100% absorption or absorbance, while absorbance of 0 means 100% optical transparency or 0% absorption or absorbance. Various curves in Figure 1 have been obtained by diluting the colloid to result in different nanoparticle concentration in the colloid. The curves shown in figure 1 have been recorded with TiO₂ particle concentration of 6, 4, 3, 2.5, 1, 0.5, 0.25, 0.1 and 0.01 weight percentages. As the TiO₂ concentration was reduced in the colloid, the onset for absorption shifted towards shorter wavelengths as shown in Figure 1. This is consistent with the absorption coefficient of the TiO₂ and effective absorption length of light in TiO₂. The initial colloid (the light green curve exhibiting an absorption edge around 380 nm) consisted of TiO₂ nanoparticles constituting 6 weight percentage dispersed in water along with acetic acid and hydrochloric acid. The colloid was prepared by adding water to a mixture of acetic acid and TiCU. The pH of the resulting colloid (Colloid A) was less than 1. The particle size analysis (shown in figure 2) of this colloid was found to be less than 10 nm. The rest of the absorption curves shown in figure 1 was recorded on colloids prepared by mixing water with the original colloid (Colloid A) in different ratios to yield the final TiO₂ weight percentages as indicated above. The pH of all the colloids was less than 2. The nanoparticle loading density in the colloid may be greater than 5 weight percent, such as up to 80 weight percentage. Slow evaporation of the water from the colloid, preferably at low temperature (close to room temperature) can result in clear gel or paste with high particle density.

Figure 2 shows a typical titania nanoparticle size distribution of a colloid with pH less than 2. All the colloids with different particle loading listed above showed similar particle size range (between 2 - 9 nm). For the PCS measurements, each colloid was diluted with water until the optical signal strength was within the measurable limit of the N 5 equipment. The specific curve shown in Figure 2 was taken from colloid A when diluted with water adequately to yield the optical signal suitable for the PCS measurement. As can be seen, all the PCS detected particles are less than 10 run, thereby making the colloid optically clear (no visible light scattering).

In another example, a ZnO nanoparticle composition was formed by the following method. 10 grams of ZnCl₂ powder was mixed in a 20 ml solution of acetic acid. After that, 50 ml of water was added to the mixture and the powder was dissolved using a magnetic stirrer at room temperature. Then, a solution containing ammonium hydroxide and acetic acid mixture in water with a pH of 8.5 was added to the above mixture until the pH was raised to 6.2. The UV- Vis spectrum of the colloid is shown in Figure 3. The oscillations at wavelengths below 200 ran are believed to be detector artifacts. Particle size analysis of the colloid using PCS indicated particles having a size in a range of 3-5 ran in the colloid.

In another example, a cerium oxide nanoparticle composition was formed by the following method. 8.5 grams of CeCb powder was mixed in a 15 ml solution of acetic acid. After that 65 ml of a water (95 % by volume)-hydrogen peroxide (5 % by volume) mixture was added to the above solution, the powder was dissolved using a magnetic stirrer at room temperature. Then a solution containing ammonium hydroxide and acetic acid mixture in water with a pH of 7.6 was added to the above mixture until the pH was raised to 3.5. The UV- Vis spectrum of the colloid was recorded and is shown in Figure 4 (curve with longest wavelength cut-off around 450 ran). Dilution of the above colloid with pure water led to decreasing CeO₂ concentration in the colloid. The on-set of the absorption curves shifted continuously with decrease in particle concentration in the colloid (corresponding to 7, 6, 3, 1, 0.5 and 0.1 weight %) as depicted by the curves shown in Figure 4. The oscillations at wavelengths below 450 nm are believed to be detector artifacts.

Thus, the nanoparticle containing composition, such as a titania nanoparticle containing colloid or solid matrix has a low absorbance in the visible range and a high absorbance in the UV range, such as an absorbance of 20% or less in a wavelength range between 400 nm to 700 nm and an absorbance of 80% or greater in a wavelength range of 220 nm or less, as shown in the Figures. For example, the composition is UV blocking and optically transparent and has an absorbance of 80% or greater in a wavelength range of 380 nm or less, such as an absorbance of 90% or greater in a wavelength range of 220 ran or less and an absorbance of 10% or less in the wavelength range between 400 nm to 700 nm. Preferably, the composition has an absorbance of between 0 and 5% in the wavelength range between 400 nm to 700 nm and an absorbance of between 99 and 100% in a wavelength range of 340 nm or less. For titania compositions, if a high absorbance throughout the UV range is important, then the composition may have an absorbance of between 99 and 100% in a wavelength range of 380 nm or less, with an absorbance between 5 and 20% in the visible range. In contrast, if a low absorbance in the visible range is important, then the composition may have an absorbance of between 0 and 5% in the wavelength range between 400 nm to 700 nm, and an absorption edge at around 340 nm or less. In general, the composition has an absorbance of 20% or less, such as 10% or less in at least one point in the visible wavelength range and an absorbance of 80% or greater, such as 90% or greater, in at least one point in the UV wavelength range.

The absorption edge of the composition can range from 220 nm to 700 nm, depending on the composition. As can be seen in Figure 1, the absorption edge for titania compositions can be shifted to various wavelengths in the UV range from about 240 nm to about 380 nm by varying the nanoparticle concentration and/or size. The absorption edge can also be shifted, such as into the visible range or deeper into the UV range, by varying the nanoparticle composition. For example, for ceria nanoparticlcs, the absorption edge is in middle of the visible range, such as at about 550 nm. Thus, ceria containing compositions may be used in applications where it is desirable to transmit longer wavelength visible radiation, such as orange and red light, but to absorb shorter wavelength visible radiation, such as violet and blue light. In contrast, for zirconia nanoparticles, the absorption edge lies deep in the UV range, such as at about 220 nm. Thus, zirconia compositions may be used in applications where it is desired to transmit visible light and long wavelength UV radiation, but to block short wavelength UV radiation. Thus, the absorbance of the composition is a function of nanoparticle composition, concentration and size, and can be tailored by selecting the desired nanoparticle properties. The nanoparticle properties, such as composition, size and concentration, are controlled by selecting desired starting materials (i.e., the desired chloride compound), acid to chloride plus water ratio, and ratio of solvent to nanoparticles, respectively. In another example, samples of colloidal SiO₂ were prepared by adding water to a mixture of acetic acid and SiCl₄ at room temperature. Sample (a) in Figure 5 was prepared by first adding 5 ml of SiCl₄ to 50 ml of acetic acid and then bubbling air through the solution for 5 minutes. The particle size analysis (shown in Figure 5) of this colloid shows a peak with particle size around 10 nm. Sample (b) shown in Figure 5 was prepared by bubbling air in an acetic acid-SiCU mixture (50 ml: 5 ml) for 10 minutes. The peak in particle size distribution is around 15 nm. Sample (c) shown in Figure 5 was prepared by adding 5 ml of water slowly (drop by drop) while vigorously mixing the acetic acid-SiCl₄ mixture (50 ml: 5 ml) using a magnetic stirrer. The peak in particle size distribution is around 40 nm. Sample (d) shown in Figure 5 was prepared by adding 10 ml of water slowly (drop by drop) while vigorously mixing the acetic acid-SiCU mixture (50 ml: 5 ml) using a magnetic stirrer. The peak in particle size distribution is around 60 nm. The pH of the resulting colloids (samples a-d in Figure 5) was less than 2. The long tail in the particle size distribution is attributed to inadequate mixing during the colloidal synthesis process that lead to rapid hydrolysis and bigger particle formation. The particle size distribution did not change with time indicating no agglomeration after the colloid has been synthesized.

^"Nanoparticle loading density in the colloid, such as greater than 5 weight percent, such as 5 to 50 weight percent, may be achieved by slow evaporation of the liquid from the colloid, preferably at low temperature (close to room temperature). This may also result in clear gel or paste with high particle density (such as 80 weight percent). The pH of the colloid can be conveniently varied in the range of 2-11 by adding a base, such as NH₄OH.

The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The drawings and description were chosen in order to explain the principles of the invention and its practical application. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.

I l

Claims

1. A composition comprising nanoparticles, wherein the composition has an absorbance of 20% or less in a wavelength range between 400 nm to 700 nm and an absorbance of 80% or greater in a wavelength range of 220 ran or less.

2. The composition of claim 1, wherein the composition has an absorbance of 80% or greater in a wavelength range of 380 nm or less.

3. The composition of claim 1, wherein the composition has an absorbance of 10% or less in the wavelength range between 400 nm to 700 nm and an absorbance of 90% or greater in the wavelength range of 240 nm or less.

4. The composition of claim 3, wherein the composition has an absorbance of between 99 and 100% in a wavelength range of 380 nm or less.

5. The composition of claim 1, wherein the composition has an absorbance of between 0 and 5% in the wavelength range between 400 nm to 700 nm.

6. The composition of claim 1, wherein the composition has an absorbance of between 0 and 5% in the wavelength range between 400 nm to 700 nm and an absorbance of between 99 and 100% in a wavelength range- of 340 nm or less, and the nanoparticles comprise titania nanoparticles.

7. The composition of any one of claims 1-6, wherein the composition comprises a colloid comprising a solvent and oxide nanoparticles having an average diameter between 2 and 10 nm.

8. The composition of claim 7, wherein the nanoparticles comprise titania, silica, ceria, alumina, zirconia or zinc oxide nanoparticles.

9. The composition of claim 7, wherein all nanoparticles detectable by PCS in the composition have a diameter of 10 nm or less.

10. The composition of any one of claims 7-9, wherein the nanoparticles comprise non-agglomerated nanoparticles containing a carboxylic acid residue on nanoparticle surface.

1 1. The composition of any one of claims 7-10, wherein the solvent comprises water or an organic solvent.

12. The composition of any one of claims 1-6, wherein the composition comprises a composite material comprising the nanoparticles in a matrix material.

13. The composition of claim 12, wherein the composition comprises a thin film and the solid matrix material comprises an optically transparent polymer matrix.

14. A method of making a nanoparticle colloid composition, comprising: mixing a metal chloride or semiconductor chloride compound with an acid to form a mixture; and slowly adding an oxygen containing material to the mixture to form a metal or semiconductor oxide nanoparticle colloid composition.

15. The method of claim 14, wherein the oxygen containing material comprises water.

16. The method of claim 14, wherein the oxygen containing material comprises air.

17. The method of claim 14, wherein the acid comprises a carboxylic acid.

18. The method of claim 17, wherein the acid comprises acetic acid.

19. The method of claim 14, wherein the chloride compound is selected from a group consisting of SiCl₄, TiCl₄, CeCl₃, AlCl₃, ZrCl₄, and ZnCl₂.

20. The method of claim 19, wherein the nanoparticles comprise titania, silica, ceria, alumina, zirconia or zinc oxide nanoparticles having an average size of between 2 and 10 ran.

21. The method of any one of claims 14-20, wherein: a ratio of the chloride compound to the acid ranges from 1 :1 to 1 :10; and water is added to the mixture at a rate of 1 to 20 ml per minute.

22. The method of any one of claims 14-21, further comprising controlling nanoparticle diameter by controlling a ratio of the acid to the water and the chloride compound.

23. The method of any one of claims 14-22, further comprising increasing a pH of the colloid by adding a weak base or a mixture of a weak acid and strong base to the colloid.

24. The method of claim 23, wherein the step of increasing the pH comprises adding a mixture of a carboxylic acid and a strong base.

25. The method of claim 24, wherein the step of increasing the pH comprises adding a mixture of at least one of acetic acid and sodium acetate and at least one of sodium bicarbonate and sodium hydroxide.

26. The method of any one of claims 14-20, further comprising providing the nanoparticles into a chemical-mechanical polishing slurry.

27. The method of claim 26, wherein the nanoparticles comprise amorphous silica nanoparticles having an average diameter between 10 and 100 nm.

28. The method of any one of claims 14-20, further comprising providing the nanoparticles into a structural composite material.

29. The method of claim 28, wherein the structural composite material comprises cement.

30. A composition comprising nanoparticles, wherein the composition has an absorbance of 20% or less in at least one point in a visible wavelength range and an absorbance of 80% or greater in at least one point in an UV wavelength range.

31. The composition of claim 30, wherein an absorption edge of the composition ranges from 220 nm to 700 nm.

32. The composition of claim 30, wherein: the composition comprises a colloid comprising a solvent and oxide nanoparticles having an average diameter between 2 and 10 ran; the nanoparticles comprise titania, silica, ceria, alumina, zirconia or zinc oxide nanoparticles; and wherein the solvent comprises water or an organic solvent.

33. A composition comprising metal oxide or semiconductor oxide nanoparticles, wherein the nanoparticles comprise non-agglomerated nanoparticles containing a carboxylic acid residue on nanoparticle surface

34. The composition of claim 33, wherein the composition comprises a colloid comprising a solvent and nanoparticles having an average diameter between 2 and 100 nm.

35. The composition of claim 33 or 34, wherein the nanoparticles comprise titania, silica, ceria, alumina, zirconia or zinc oxide nanoparticles.

36. The composition of any one of claims 33-35, wherein the composition comprises a composite material comprising the nanoparticles in a matrix material selected from an optically transparent polymer matrix, a cement matrix or a chemical mechanical polishing slurry matrix.

37. A method of increasing a pH of a nanoparticle colloid, comprising adding a mixture of a weak acid and a strong base to an acidic nanoparticle colloid.

38. The method of claim 37, wherein the step of adding comprises adding a mixture of a carboxylic acid and a strong base to an optically transparent colloid containing metal or semiconductor oxide nanoparticles such that the colloid remains optically transparent in a visible wavelength range.

39. The method of claim 37, wherein the step adding comprises adding a mixture of at least one of acetic acid and sodium acetate and at least one of sodium bicarbonate and sodium hydroxide.

40. A method of making a nanoparticle colloid composition, comprising: mixing one of SiCl₄, TiCl₄, CeCl₃, AlCl₃, ZrCl₄, and ZnCl₂ with acetic acid in a ratio from 1 : 1 to 1 : 10 to form a mixture; slowly adding water at a rate of 1 to 20 ml per minute to the mixture form titania, silica, ceria, alumina, zirconia or zinc oxide nanoparticles in the mixture, which results in the nanoparticle colloid composition; and increasing a pH of the nanoparticle colloid composition by adding a mixture of a carboxylic acid and a strong base to the nanoparticle colloid composition.