Rsc_cc_c0cc01746a 1..3

Mesoporous silica materials have been utilized for various applications (catalysis, sensing, drug delivery, adsorption and separation) due to their uniform mesoporous features as well as high surface areas. When organic polymer layers are introduced to the mesopore walls, the physicochemical properties as well as surface nature of the silica (e.g. hydrophilicity and surface charge) can be altered. This allows for adsorbing or immobilizing a wide range of molecules/species on the mesopore walls, significantly broadening the application of mesoporous materials. In particular, if the polymer coating is conducting, it can convert the insulating mesoporous silica materials into semiconducting composites that can be used for various electrochemical applications. In order to obtain silica–polymer composites retaining uniform and accessible mesopores, a thin polymer coating should be introduced on the mesopore walls in a uniform manner without clogging the mesopore entrances. However, when monomers and initiators (e.g. oxidizing agents) are mixed with mesoporous silica particles in one reaction chamber, polymerization occurs dominantly in bulk solution or on the surface of silica particles because the diffusion of monomers or initiators into the pores is less favored. This may clog the pore entrances of the silica particles, hindering the formation of high quality composite mesoporous particles, and/or create an undesirable mixture of pure polymer particles and composite particles in solution, which calls for an additional separation step (e.g. centrifugation). In order to achieve uniform polymerization within the mesopores, several approaches have been developed, which commonly require a two-step procedure. In these two-step methods, monomers are first adsorbed within the silica mesopores, and are then moved to a different chamber to be mixed with initiators. This is to ensure that no monomers are available in the medium that contains the initiators, so that bulk polymerization can be suppressed. To date, no method has achieved selective polymerization only on the mesoporous silica walls via one pot synthesis. In this communication, we report the first synthesis strategy that enables polymerization of polypyrrole (ppy) selectively on silica mesopores in an aqueous medium containing mesoporous silica particles, pyrrole, and an oxidizing agent simultaneously. This method is based on the in situ generation of nitrosyl ion (NO) on a silica surface and using it as an oxidizing agent for polymerization. By using a silica surface as one of the reactants to generate NO ions, NO ions become available only on the silica surface. As a result, polymerization is confined to the mesoporous silica surface although no extra effort is made to localize monomers or oxidizing agents into the pores. NO ions are strong oxidizing agents and have been used for various organic reactions. However, its use for the polymerization of conducting polymers has not been explored except for one recent report in which NO ions were used to electrodeposit polypyrrole films under cathodic conditions. NO ions can be formed by the reaction of NO2 or HNO2 with H (eqn (1) and (2)). In an acidic environment amphoteric HNO2 further reacts with H + ions, which results in the generation of the NO ions (eqn (2)). NO2 + H 2 HNO2 (1)