Method of making titanium dioxide particles
The disclosure provides a process for preparing nanocrystalline titanium dioxide, in particular rutile nanocrystalline titanium dioxide, comprising: (a) precipitating a mixture comprising hydrated titanium oxide and a separable filtering agent; (b) filtering the precipitated mixture to form a filter cake comprising the precipitated hydrated titanium dioxide and a separable filtering agent, (c) calcining the precipitated hydrated titanium oxide and separable filtering agent at a temperature of greater than about 300° C.; and (d) removing the separable filtering agent thereby recovering titanium dioxide particles.
1. A process for preparing nanocrystalline titanium dioxide, comprising the following steps:
(a) forming a mixture by combining starting materials comprising
(i) an aqueous titanium oxychloride,
(ii) a MOH, where M is selected from the group consisting of NH 4 , Na, K, Li, and Rb, and mixtures thereof, and
(iii) a solvent comprising an alcohol or an aqueous salt solution that is capable of precipitating a filtering agent and a hydrated titanium oxide in the mixture;
wherein the mixture has a pH less than about 3 and a precipitate comprising the filtering agent having a formula MCl and a hydrated titanium oxide;
(b) filtering the precipitate to form a filter cake;
(c) calcining portions of the filter cake at a temperature greater than about 300° C. to form a calcined mixture comprising titanium dioxide,
(d) removing the filtering agent from the calcined mixture, and
(e) recovering nanocrystalline titanium dioxide.
2. The process of claim 1 wherein the solvent is selected from the group consisting of an alcohol and an aqueous salt solution.
3. The process of claim 1 wherein the pH of the mixture is less than about 2.
4. The process of claim 1 wherein the pH of the mixture is about 1.
5. The process of claim 1 wherein the nanocrystalline titanium dioxide has a primary particle size that does not exceed about 100 nm.
6. The process of claim 1 wherein step (c) and step (d) occurs simultaneously.
7. The process of claim 1 wherein the filtering agent is NH 4 Cl.
8. The process of claim 1 further comprising in step (d) removing the filtering agent from the calcined material by washing the calcined material with water or a solution comprising water.
9. The process of claim 1 wherein the nanocrystalline titanium dioxide is predominantly rutile.