Organic-inorganic hybrid aerogels

A strong and porous photoactive material with a large reactive surface area could have use as a photocatalyst or as a semiconductor. Crystalline titania dioxide (TiO2) is known to have photoactive properties, but pure porous TiO2 is also known to have poor mechanical properties. Cellulose aerogel has good mechanical properties. It is strong and fairly flexible along with being very porous and thus having a high surface area. In this work, the immersion of cellulose aerogel in titania sol with subsequent heating to 250°C has shown that it is possible to impregnate aerocellulose with crystalline TiO2. Another method of preparing a hybrid aerogel by combining cellulose sol and titania butoxide sol and subjecting the combined co-sol to supercritical drying produced a material composed of TiO2 particles dispersed throughout the cellulose aerogel. Both of these methods produced interesting hybrid materials that should be studied further for possible uses. The alkaline and aqueous nature of the cellulose sol in these methods caused some difficulties in the preparation of these hybrid materials. This led to the search for a different solvent system to combining the cellulose and titania. Ionic liquids are non-aqueous solvents that have been used to dissolve cellulose and to prepare hybrid materials. Two ionic liquids that were synthesized at Texas Tech University, 1-benzyl-3-methylimidazolium chloride (BenzMimCl) and 1-benzyl-3-methylimidazolium acetate (BenzMimOAc), were investigated for use as solvents for microcrystalline cellulose (MCC) with the intention of using them in the future to prepare cellulose/TiO2 hybrid materials. BenzMimOAc easily dissolved cellulose and produced a regenerated cellulose in the expected cellulose II crystal form with a high degree of crystallinity. BenzMimCl, although more viscous, also dissolved MCC. However, the cellulose regenerated from the solution retained the cellulose Iβ crystal form. This result is highly unusual and will be studied further as more BenzMimCl becomes available.