Alekseev S. Silicas modified with alkylsulfonic acid: synthesis, thermochemical behavior, grafted layer structure and properties

Method of covalent modification of amorfous and hexagonal MCM-41 type silica surface by alkylsulphoacidic groups by free-radical addition of NaHSO3 to vinyl group was developed. The influence of reaction conditions, carrier type and grafted layer structure on the composition and nature of surface groups, appearing in this reaction, were analyzed. The mechanismes of thermal decomposition for synthesised matherials were studied and kinetic parameters of observed processes were calculated. The key role of the interaction between silanols and bonded organic groups during decomposition process was prooved. Using dielectric relaxation spectroscopy and H2O adsorbtion we found 2 types of supramolecular structures formed by hydrogen bonded Si-OH groups: small finite clasters and infinite one-dimencional chains - elements of hydrogen bonds net. The substitution of silanols by trimethylsilyl groups leads to broke of hydrogen bonded silanols net, so to the excluding of part of the silanols from the interaction with the sulfoacidic groups. In it's turn this leads to the increasing of the acidity and so to the increasing of catalytic activity in the reaction of EtOH with i-C4H8 for trimethylsilylated alkylsulphosilicas in comparison with raw alkylsulphosilica.