cm7b04482_si_001.pdf (558.57 kB)
Model for the Synthesis of Self-Assembling Template-Free Porous Organosilicas
journal contribution
posted on 2018-03-09, 00:00 authored by Brian K. Peterson, Mobae Afeworki, David C. Calabro, Quanchang Li, Simon C. WestonHigh surface area
solids are important materials in science and
in many industrial applications but often are produced from expensive
and inefficient combinations of materials and processes. New principles
for the selection of molecular precursors that yield high surface
area solids in simple and efficient sol–gel processes would
be useful. Focusing on organosilicas, we show that an index based
on rigidity theory can be used to quantify the relative strength of
the gel and the level of condensation at which it is able to withstand
the capillary stresses imposed by drying, thereby preventing loss
of surface area. This index correctly orders precursors according
to the surface area of the solid materials produced from them and
provides, when correlated to a few data points, a predictive relationship
between the index and the surface area. Precursor features leading
to early formation of a highly connected rigid network include high
ratios of nonhydrolyzing (e.g., methylene) to hydrolyzing (e.g., oxy)
groups bridging silicate moieties, large SiOH/Si ratios in the hydrolyzed
precursors, and low numbers of noncondensing terminal groups (e.g.,
methyl). These features explain the extremely high surface areas obtained
from 1,1,3,3,5,5-hexaethoxy-1,3,5-trisilacyclohexane and high surface
areas obtained by similar materials in aqueous, nontemplated syntheses,
as shown in a related publication (DOI: 10.1021/acs.chemmater.7b04480).