Heterogeneous photocatalysis has the potential to offer significant benefits with respect to energy, size, and reliability compared to traditional technologies. Although much research has been devoted to photocatalysis for environmental applications, the testing and application of these systems beyond the bench-scale is limited. Photocatalytic systems for treatment of gas-phase contaminants typically employ a thin film of titania (TiO2) on, for example, reactor walls, wire mesh, or glass beads. These systems may not lend themselves well to scale up due to their low adsorption capacity, mass transfer limitations, and problems with catalyst immobilization or durability. Systems for treatment of aqueous-phase contaminants often employ a nanoparticle slurry, which leads to problems with catalyst recovery. In order to overcome these issues, a nano-structured silica-titania composite (STC) was developed. This work centered on the optimization and scale-up of photocatalytic reactors employing the STC for two applications: (1) degradation of VOCs to improve air quality and (2) recovery of mercury emitted from water and air streams at chemical manufacturing facilities.