Synthesis of titania-pillared montmorillonite via intercalation of titanium alkoxide dissolved in supercritical carbon dioxide

A new method for the synthesis of pillared clays using supercritical carbon dioxide (scCO2) has been developed. This scheme consists of two steps: (1) the hydrophobitization of the clay interlayer space, using an organic ion exchange method with interlayer cations in aqueous solution, and (2) the intercalation of a metal alkoxide dissolved in scCO2 followed by hydrolysis with adsorbed water present in the interlayer space. This method is expected to be advantageous in the structural and chemical design of pillared clays by allowing specific tailoring of the organic ions and metal alkoxides used during preparation. In this work, the synthesis of titania-pillared clay using montmorillonite (MNT) and titanium isopropoxide was investigated. Alkyltrimethylammonium cations were used to study the effect of organic ions on the clay structure. Titania pillared MNT were successfully prepared with the presence of hydrophobic interlayer ions, whereas intercalation was not successful on MNT without hydrophobitization of the interlayer space. Nano-sized anatase was observed on the calcined samples and the titania content was related to the hydrophobic nature of the organic ion used. The intercalated samples have both meso- and microporous structures and the microporosity was considered to be a factor related to the variety of organic ion used. An optimised pillared clay sample showed potential as a catalytic adsorbent for toxic volatile organic compounds in air.