Synthesis of mesoporous amorphous silica via silica-polyviologen hybrids prepared by the sol-gel route

A range of polyviologens synthesized by the Menshutkin reaction have been successfully incorporated into silica hybrids using the hydrolytic sol-gel route. Transparent hybrids can be obtained with up to 75% polyviologen content, indicating a likely nanoscale morphology. Hybrids were calcined at 650 degrees C to remove the polymer, forming porous amorphous silica products. Nitrogen adsorption-desorption studies have been undertaken on the hybrids and the calcination products, and the results are analyzed by the modeless method of Brunauer et al. for mesopore size distributions and a micropore analysis method based on t-curves. The hybrids are mostly mesoporous solids, but porosities are very low at high polymer contents. Calcination leads to silicas which are mainly mesoporous with varying degrees of microporosity depending on the nature and concentration of the polyviologen (PV) used. Poly(hexyl viologen ditosylate) produces high surface area silicas with > 98% mesoporosity. The results may provide evidence for an influence of the PV on the structure of the forming silica, which is proposed to occur through electrostatic interactions between the quaternary nitrogen atoms of the polymer and the silanol oxygen atoms in the growing silica network.