Visible light photocatalytic degradation of methylene blue and rhodamine B over silver-doped titanium dioxide nanocomposites supported on Fuller’s earth

Silver-doped-titanium dioxide nanoparticles supported on Fuller’s earth, prepared by the sol-gel method, were characterized with XRD, TGA, zeta potential, SEM, EDX, TEM, XPS, photoluminescence and UV-DRS measurements. The material, Ag-TiO₂-Fuller’s earth (AgTF), was tested for photocatalytic activity concerning the degradation of rhodamine B (RhB) and methylene blue (MB) in aqueous solution under visible light irradiation with pH, catalyst dosage, and dye concentration as the process variables. The degradation kinetics indicated pseudo-first-order kinetics with rate constant of (i) 0.55 min⁻¹with 0.12 gL⁻¹AgTF loading, 10⁻⁵ M MB at pH 9, and (ii) 0.53 min⁻¹ with 0.08 g L⁻¹ AgTF loading, 5 × 10⁻⁵ M RhB at pH 8. The methylene blue degradation was maximum (98.66%) for AgTF loading of 0.12 g L⁻¹ while the maximum RhB degradation (96.34%) was attained with AgTF loading of 0.08 g L⁻¹. With 5 × 10⁻⁶M MB concentration, the degradation achieved was 98% in 45 min and 100% in 60 min. One hundred per cent degradation of the dye, RhB (1 × 10⁻⁶ M) could be achieved in 30 min with 0.08 g L⁻¹ AgTF at pH 8. The use of Fuller’s earth, a cheap, abundant and large surface area support, increases the adsorbability of the dye on the catalyst surface and hence promotes the degradation. The catalyst could be removed easily from the reaction mixture and reused for up to five cycles without any significant decrease in activity. Scavengers such as triethanolamine (TEOA), p-benzoquinone (BQ) and isopropyl alcohol (IPA) were utilized to get some insight into the photocatalysis mechanism.