Mesoporous titania was prepared employing a modified sol-gel method using titanium(IV) tetraisopropoxide (TTIP) in a deep eutectic solvent (DES) consisting of choline chloride and phenol. Monodisperse mesopores formed because of the low hydrolysis rate of TTIP in the highly viscous DES and the slow diffusion of water vapor into the DES. However, the removal of the DES from the titania gel using methanol washing caused the titania framework to shrink during calcination, resulting in washed titania with low pore volume. By contrast, the DES in the unwashed precursor contributed to preventing the shrinking of the framework. As a result, the pore volume and Brunauer-Emmett-Teller (BET) specific surface area of the unwashed titania were higher than those of the washed titania. The adsorption separation of gold nanoparticles (GNPs) using unwashed and washed titania calcined at 500 degrees C was investigated. Washed titania lacked the ability to adsorb GNPs due to its low pore volume. High pore volume unwashed titania could capture GNPs with sizes of 10 nm or smaller, while the 15 nm GNPs were not adsorbed due to the sieve effect of the monodisperse mesopores.