Synthesis of bimodally porous titania powders by hydrolysis of titanium tetraisopropoxide
- PDF / 296,986 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 85 Downloads / 159 Views
Bimodally porous titania powders with controlled phase composition and porosity were made by hydrolysis of titanium tetraisopropoxide (TTIP) and calcination. The extent of calcination was followed by thermogravimetric differential thermal analysis and Fourier transform infrared spectroscopy. The specific surface area (SSA) of the powders ranged from 10 to 500 m2/g as determined by nitrogen adsorption. The SSA increased by decreasing either the water concentration during hydrolysis or the calcination temperature. The pore size distribution was bimodal with fine intraparticle pore diameters at 1–6 nm and larger interparticle pore diameters at 30–120 nm as determined by nitrogen adsorption isotherms. The particle phase composition as determined by x-ray diffraction ranged from amorphous to crystalline anatase and rutile largely proportional to the calcination temperature and to a lesser extent on the initial H2O/TTIP molar ratio.
I. INTRODUCTION
Titania powders are widely used as a white pigment, an adsorbent, and a major component in many electronic devices (e.g. capacitors and varistors) and have recently become of interest as functional materials such as a photosemiconductor and a photocatalyst.1–5 The most common procedures of preparing the titania powders have been based on the hydrolysis of acidic solutions of Ti(IV) salts6,7 or by gas-phase oxidation reaction of TiCl4 at high temperatures.3,8 Recently, however, methods of vapor-phase hydrolysis,9 pyrolysis,10 and sol-gel synthesis2,11 of organic precursors (e.g., titanium tetraisopropoxide, TTIP) have been developed to synthesize titania nanoparticles with high purity. Sol-gel synthesis provides a way to make nanoparticles by a chemical reaction in solution starting with metal alkoxides as a precursor. An advantage of the solgel synthesis is that it is possible to obtain large amounts of powder with a high level of chemical purity.12 In this sol-gel synthesis two simultaneous reactions—hydrolysis and polycondensation—take place when TTIP reacts with water.13 These two reactions are sensitive to water concentration, pH, type and amount of solvent, reaction temperature, and mixing conditions. Among the reaction
a)
On leave from Konyang University, Nonsan, South Korea. Address all correspondence to this author. e-mail: [email protected]
b)
2322
http://journals.cambridge.org
J. Mater. Res., Vol. 15, No. 11, Nov 2000 Downloaded: 15 Mar 2015
variables, especially the water concentration significantly influences the properties of the titania powders as TTIP reacts quickly with water. Ding et al.15 synthesized titania powders from titanium tetrabutoxide (TTB) by controlling the water concentration during hydrolysis. They reported that the grain size of powders prepared at low H2O/TTB molar ratios was smaller than that of powders made at high molar ratios. As a result, the anatase to rutile phase transformation temperature for powders made at low H2O/TTB molar ratios was less than that of powders at high H2O/ TTB ratios. Sasamoto et al.16 also prepare
Data Loading...
