Surface modification of a mesoporous tungsten- and bismuth-promoted titania-silica nanocomposite was conducted by a silylation method using hexamethyldisilazane (HMDS) as the silylation reagent to overcome the low adsorption capacity of TiO2-based photocatalysts for organic dyes, which subsequently enhances photodegradation of the organic dyes under visible light irradiation. The performance of the nanocomposites was evaluated by photodegradation of Rhodamine B (RhB) dye under visible light irradiation in a triple-walled immersion well reactor. The synthesized nanocomposites were characterized by N2 adsorption-desorption, FE-SEM, XRD, SAED pattern, HR-TEM, EDX, FTIR, UV-Vis DRS, PL spectroscopy, TGA, and water contact angle measurement to determine the bulk structure and surface properties before and after surface silylation. The results revealed that surface hydroxyl groups were successfully replaced by the silyl groups via the silylation process, without significant alterations in the structure and textural properties of the nanocomposite. In addition, silylation of the nanocomposite surface significantly enhanced the adsorption capacity of RhB molecules due to increased surface hydrophobicity, which accelerated the photocatalytic degradation of RhB in water. The results of the photocatalytic degradation experiments demonstrated that although all the synthesized nanocomposites were able to remove all RhB molecules from water after 240 minutes of the reaction, the optimized silylated sample with 0.15 g of HMDS (TSWBi-Sil3) was able to remove 92% of the RhB after only 90 minutes, while it was only 79% for the unmodified nanocomposite.