In Situ Oxidation of Alkanethiol Groups and Proton Transfer in Nanopores of Sodium Borosilicate Glasses

Porous glasses with 4 nm diameter pores were prepared utilizing a spinodal-type phase separation of Na2O-B2O3-SiO2 glass, and the surface was modified by using mercaptoalkyltrimethoxysilane with different alkyl chain length ((CH3O)(3)Si(CH2)(n)-SH, n = 1, 3, 6, 10). The thiol groups (-SH) were oxidized with H2O2 to obtain -SO3H groups. The amount of the introduced silane coupling agents and the reactivity with H2O2 inside the nanopores drastically changed by changing the alkyl chain length (n). The molecular structures, charge distributions, bond overlap populations (BOP) between Si and alkyl chains, as well as net charges of thiol groups were calculated based on a density functional theory and a first-principle theory (DVX alpha). The charge distribution calculations suggest that oxygen atoms on pores affect significantly for both the net charge of S and BOP, and the BOP values were directly related with the in situ oxidation reactivity of silane coupling agents. ne porous glasses modified with the silane coupling agent with n = I showed high proton conductivity of 1 x 10(-2) S/cm at 80 degrees C and 90% relative humidity.