Environmental Engineering Reference
In-Depth Information
cosolvent and tetrabutylammonium luoride as a catalyst. Before drying, the wet gels are
rinsed to remove unreacted silane, water, and catalyst. Rinsing is followed by derivatiza-
tion of the residual silanol groups using a chlorosilane reagent such as trimethylchlorosi-
lane. Capping the silanol groups prevents cross-linking during the drying of the wet gel,
which would limit the lexibility of the matrix. The identity of the silanol capping reagent
has no effect on the swelling behavior.
14
However, derivatization is required to produce a
material that swells. A chlorosilane possessing an alkane functional group is preferred
for produced water applications as the surface becomes hydrophobic and is well suited
to absorb dissolved and neat uncharged organic compounds. In addition to absorbing
large amounts of nonpolar substances from the neat liquid phase, adsorption of nonpolar
organic molecules is also possible from the gas phase or from aqueous solution. Because of
these unique properties, there are a number of potential applications for Osorb, including
the removal of dissolved organics from water.
8.2.1 Physical Characteristics
One of the most unusual aspects of Osorb is that it appears macroscopically glass-like, yet
has the ability to swell up 5 mL/g upon addition of organic liquids, but does absorb water.
Swelling occurs in <1 s (Figure 8.3), and there is no loss in the degree of swelling behavior
when the material is cycled through many steps of absorption (swell) and evaporation
(shrink). Remarkably, the swelling resulting from absorption of neat liquids is so energetic
that the material expands with forces in excess of 500 N/g, which allows the material to
Time = 5 s
Time = 10 s
Time = 0 s
Dry
Partially swollen
Fully swollen
200 nm
200 nm
150 nm
FIGURE 8.3
(Top) Photographs of Osorb swelling upon dropwise addition of acetone. (Middle) Scanning electron micro-
scope images of the nanoporous organosilica matrix (left) in the dry collapsed form; (center) partially swol-
len state captured by swelling the matrix with a poly(2,2,3,3,4,4,4-heptaluorobutylmethacrylate) solution and
allowing the solvent to dry leaving the polymer entrapped; and (right) fully expanded as captured by swollen
in ethanol followed by critical point drying. (Bottom) Cartoon representing the arrangement of organosilica
nanoparticles in the corresponding swollen states.
