This chapter investigates the photocatalytic deterioration of Eriochrome Black-T dye by titanium dioxide (TiO₂) nanoparticles prepared by the sol-gel method. The synthesized nanoparticles were characterized using FTIR, XRD, and SEM to confirm their anatase crystalline structure, nano-sized morphology, and high photocatalytic activity. Degradation efficiency was measured in sunlight and focused on the impact of operational parameters like pH, dye concentration, and adsorbent dosage. Optimal degradation of 92.7% was found at a pH of 2, a dye concentration of 100 ppm, and a catalyst loading of 0.5 g. Adsorption studies investigated the interaction between the adsorbent and the dye molecules. The Langmuir isotherm model best fits the experimental data, with a maximum adsorption capacity (Qmax) of 198.41 mg/g and a regression coefficient of 0.99, indicating monolayer adsorption on a homogeneous surface. The Temkin isotherm also showed good fitting with constants that indicated significant adsorbent-adsorbate interactions and a gradual reduction in the heat of adsorption with increased coverage. These results suggest that TiO₂ nanoparticles have good adsorption capacity and are applicable in wastewater treatment.