Preparation of macroporous silica and its application on polysaccharide derivative based chiral stationary phase

In order to prepare 100-nm macroporous silica, spherical silica (5 μm in particle size, 10 nm in pore diameter) was treated by hydrothermal or baking methods. During hydrothermal treatment, 22 g/L NaF was added, which efficiently promoted the enlargement of pore diameters. By this method, the average pore diameter of silica reached 100 nm after heating for 48 h at 160℃ in an autoclave, but showed a poor size distribution. In the baking method, pore diameter enlargement was controlled by modifying the baking temperature, time, and the amount of double salt LiCl-NaCl added. The addition of 1.125 g LiCl·H2O and 0.75 g NaCl per 10 g silica and baking at 500℃ for 3-5 h yielded silica with 100-nm pore diameters. This method was more efficient, easier, and better in the product pore diameter distribution than hydrothermal treatment. The obtained silica was very similar to commercial Fuji-1000 gel. The macroporous silicas obtained from the hydrothermal and baking treatments were both modified with aminopropyl silane and coated by cellulose tri(3,5-dimethylphenyl carbamate) to prepare chiral stationary phases (CSPs). The CSP based on the baking-treated silica exhibited much better selectivity and resolution for enantiomers.