Stabilization of Pickering emulsion with surface-modified titanium dioxide for enhanced photocatalytic degradation of Direct Red 80

Surface modification of titanium dioxide (TiO₂) was carried out with salicylic acid (SA) to generate an efficient Pickering emulsion (PE)-based photocatalytic system. The PE was stabilized with 0.5 and 1.0 mg mL⁻¹ of TiO₂ and SA-TiO₂ by using cyclohexane and a synthetic aqueous Direct Red 80 (DR 80) solution (0.4:1) as the oil and water phases, respectively. The photocatalytic activity of solution-dispersed TiO₂ was compared with that of the PE-based photocatalytic system for DR 80 degradation. In almost all PE-based photocatalytic systems, 100% color removal of DR 80 was observed within 15–60 min, compared to 76% and 100% color removal, achieved after 120 min, using 0.5 and 1.0 mg mL⁻¹ solution-dispersed TiO₂, respectively. The estimated reaction rates of the PE-based photocatalytic system, as calculated using the Langmuir–Hinshelwood kinetics model, were almost double to those obtained for solution-dispersed TiO₂. However, the addition of a free oil phase adversely affected the photocatalytic activity, and the lowest DR 80 degradation percentage was observed using 0.5 or 1.0 mg mL⁻¹ TiO₂. The results demonstrated that a functional PE was successfully stabilized with SA-TiO₂, and enhanced photocatalytic degradation of the azo dye was achieved in an effective and novel way.