Journal of Colloid and Interface Science 238, 267–272 (2001) doi:10.1006/jcis.2001.7504, available online at http://www.idealibrary.com on Characterization of Pore Structure and Coordination of Titanium in TiO 2 and SiO 2 –TiO 2 Sol-Pillared Clays Z. Ding, H. Y. Zhu, P. F. Greenfield, and G. Q. Lu 1 Department of Chemical Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia Received August 29, 2000; accepted February 27, 2001 Titania sol-pillared clay (TiO 2 PILC) and silica–titania sol- pillared clay (SiO 2 –TiO 2 PILC) were synthesized by the sol–gel method. Supercritical drying (SCD) and treatment with quaternary ammonium surfactants were used to tailor the pore structure of the resulting clay. It was found that SCD approach increased the ex- ternal surface area of the PILCs dramatically and that treatment with surfactants could be used to tailor pore size because the meso- pore formation in the galleries between the clay layers follows the templating mechanism as observed in the synthesis of MCM-41 ma- terials. Highly mesoporous solids were thus obtained. In calcined TiO 2 PILC, ultrafine crystallites in anatase phase, which are active for photocatalytic oxidation of organics, were observed. In SiO 2 – TiO 2 PILCs and their derivatives, titanium was highly dispersed in the matrix of silica and no crystal phase was observed. The highly dispersed titanium sites are good catalytic centers for selective oxi- dation of organic compounds. C  2001 Academic Press Key Words: titania sol; silica sol; pillared clays; supercritical dry- ing; surfactant templating. INTRODUCTION Pillared clays (PILCs) have been a new and interesting fam- ily of microporous materials since the late 1970s (1–3). PILC is constituted of silicate layers intercalated with metal oxides and is thermally stable. The extent of the pore opening of the interlay- ers of PILCs is dependent on the type of metal oxides used. Var- ious oxide pillars such as Ti (4, 5), Si (6, 7), Al (8), Fe (9), Zr (3), have been used. Because of the activity of some of these metal oxide pillars in catalytic reactions, combined with the porous structure and surface acidity properties, PILCs show great poten- tial either as promising supports or directly applied as catalysts. In this study, PILCs containing titanium are of particular in- terest. It is widely reported that Ti is active in many processes. Titanium oxide in anatase crystallite form is the most attrac- tive material in photocatalytic oxidation of organic compounds (10, 11) in both the gas phase (12) and the liquid phase (13), and complete mineralization can be obtained. Noncrystallite or isolated Ti species in a matrix of other oxides are also active in 1 To whom correspondence should be addressed. E-mail: maxlu@cheque. uq.edu.au. dehydrogenation of alcohols to ketones with (14) or without UV illumination (15, 16). Obviously, when they are applied as cata- lysts, the most important properties for the titanium-containing PILCs are the form of the titanium and the pore structure of the PILCs. Generally, microporous structure is dominant in these TiO 2 -containing PILCs and this feature restrains their applica- tion to small organic compounds (14). In addition, for reactions involving light beams, those active sites in interlayers are hard to activate. On the other hand, the form in which Ti exists in silica–titania sol-pillared clay has not been investigated com- prehensively. In this study, we aim to tailor the pore structure and to inves- tigate the state of Ti in PILCs and their derivatives. The study will provide insights into the catalytic properties of the PILC products. EXPERIMENTAL PILCs Synthesis and Modification Two types of clays, sodium montmorillonite and sodium ben- tonite, supplied by Commercial Minerals, Australia, were used. The cation-exchange capacity (CEC) is 75 meq/100 g of clay. Pillared samples were labeled PILM and PILB for montmoril- lonite and bentonite, respectively. TiO 2 PILC and SiO 2 –TiO 2 PILC were synthesized following a traditional sol–gel method (4, 7). For TiO 2 PILC, a TiO 2 sol was first prepared by hydrolysis of titanium isopropoxide (TTIP) in a solution of 1 M HCl. After being stirred for 3 h, the clear solution of TiO 2 sol was added to 1 wt% of clay suspension and stirred for another 3 h. The solid in the resulting mixture was separated by centrifugation and washed with deionized water until no Cl − was detected. The molar ratio for TTIP/HCl/CEC was 1/4/0.05. The wet cake of TiO 2 PILC thus obtained was ready for SCD treatment. For SiO 2 –TiO 2 PILC, a TiO 2 sol was prepared similarly to the above procedure, while a SiO 2 sol was prepared by hydrol- ysis of tetraethoxide orthosilicate (TEOS) at a ratio of 41.6 g TEOS/10 ml of 2 M HCl /12 ml ethanol. After being stirred for 3 h, the two sol solutions were mixed for 30 min and then added into 1 wt% of clay suspension. The molar ratio of Si/Ti/CEC was 30/3/1. After 6 h of stirring the solid in the suspension was 267 0021-9797/01 $35.00 Copyright C  2001 by Academic Press All rights of reproduction in any form reserved.