*2.6. Oil*/*Solvent Absorption Capacity Measurements*

The absorption capacity of SCA for various oils and organic solvents was determined by dipping a piece of SCA directly into the liquid (oil or solvent) for a certain time. The wet sample was then removed from the liquid and weighed after the aerogel surface has been blotted with filter paper to remove the excess surface oil/solvent. The test was repeated several times until the absorption process reached equilibrium. The absorption capacity (Q) was calculated from the mass gain using

$$Q\left(^{\circ}\text{\textquotedblleft}\right) = \frac{\mathcal{W} - \mathcal{W}\_0}{\mathcal{W}\_0} \times 100\tag{2}$$

where *W*<sup>0</sup> and *W* are the weights of the SCA before and after absorption, respectively.

The pseudo-first-order model (Equation (3)) and pseudo-second-order model (Equation (4)) were used to evaluate the absorption kinetics, where *k*<sup>1</sup> (h−1) and *k*<sup>2</sup> (g·g−1·%−1·h−1) are the adsorption rate constants of the pseudo-first-order equation and the pseudo-second-order equation, respectively. In addition, both *Qm* and *Qt* are absorption capacities at equilibrium conditions and at time *t*, respectively.

$$\ln \frac{Q\_m}{Q\_m - Q\_t} = k\_1 t \tag{3}$$

$$t\frac{t}{Q\_t} = \frac{1}{Q\_{\text{m}}}t + \frac{1}{k\_2 Q\_{\text{m}}^2} \tag{4}$$

To examine their reusability, the oil/organic swollen samples were squeezed by hand to remove the absorbed solvent. The weights of the aerogels before organic adsorption, after adsorption, and after squeeze for removal of organic were measured during each cycle. Five samples were tested for each experiment.
