A novel unsupported hydrophobic cobalt-doped silica membrane
was derived from the sol–gel process by the acid-catalyzed
hydrolysis and condensation of TEOS with MTES and cobalt nitrate
salt. The surface properties as well as thermal stability of the novel
unsupported silica membrane were enhanced by cobalt-doping
within the organic templated silica material (hybrid silica). The novel
material showed a hydrophobic behavior after heat treatment
in air at 400 C. Moreover, the novel silica material is thermally stable
up to 560 C in oxidizing atmosphere and inert atmosphere as
well. This enhancement could be attributed to the presence cobalt
as covalently bound cobalt strongly interacting with the silica matrix
forming Si–O–Co as well as tiny crystal of Co3O4 as confirmed
by FTIR where tiny small bands at 570 and 660 cm1 were assigned
to Co3O4. These two bands appeared after the calcination
process whereas they were no present before calcination process.
In addition to these results, the N2 and CO2 isotherms confirmed
the formation of microporous material with a narrow pore size distribution
centered at 1.1 nm, i.e. the novel silica membrane material
exhibited trend toward micropores formation. This is in a good
agreement with solid-state 29Si MAS NMR results where the resonances,
Q3 and Q2, were observed. These two resonances results in
silica matrix with smaller pore sizes. The objective of the present
study was to demonstrate the development of a novel unsupported
organic templated silica membrane. The results obtained concerning
the Hyd–Co–Si membrane material are in a good agreement
with what have been reported in the literature concerning the B–
Si, Co–Si and Hyd–Si. Therefore, a novel hydrophobic microporous
silica membrane material, with high thermal stability, have been
achieved which can be a precursor material for molecular sieve silica
membranes applications.