Titanium dioxide nanoparticles with a diameter in the 5 nm range were prepared by the sol-gel method, in an acidic environment, under several finely tuned experimental conditions. The titanium dioxide nanoparticles prepared were subjected to hydrothermal treatment and calcination. Using absorption spectrophotometry, X-ray diffraction, dynamic light scattering, and transmission electron microscopy permitted the assessments of the diameters of the nanoparticles and their composition (in terms of percentages of anatase, rutile, and amorphous phases). One of the methods of preparation led to samples that contained 72.4 wt % anatase and 27.6 wt % amorphous phase. Using montmorillonite and hectorite clay mineral platelets and titanium dioxide nanoparticles, nanocomposites were also prepared and calcinated under a variety of experimental conditions. Two major experimental conditions were employed. Method A involved the preadsorption of the titanium alkoxides into/onto the clay mineral platelets and their subsequent hydrolysis and calcination. In method B previously crystallized titanium dioxide nanoparticles and clay mineral platelets were heterocoagulated and calcinated. All the samples were characterized by absorption spectrophotometry (to assess their optical band gaps), by X-ray diffractometry (to determine the basal spacing of the clay mineral platelets in the nanocomposite as well as the diameters of the titanium dioxide nanoparticles), by transmission electron microscopy (to image the structures of the nanocomposites), by thermoanalytical measurements (to observe the structural changes that accompanied calcination), and by BET gas adsorption analysis (to determine the specific surface areas). Calcination was found not to be necessary for the preparation of titanium dioxide-clay mineral nanocomposites that had high specific surface areas and well-crystallized anatase contents and thus could be used as an efficient photocatalyst.