Contribution of the lamellar morphology to the photocatalytic activity of alkaline-hydrothermally treated titania in rhodamine B photodegradation

Abstract

TiO₂ particles with a specific morphology are essential for their accessibility and photoactivity. The present study shows that NH₄OH-based alkaline-hydrothermal treatment affects the transformation of their particle morphology. We investigated the effect of NH₄OH by varying the synthesis route. We observed that the TiO₂ particles with an open channel pore structure only resulted in the alkaline-hydrothermally treated and calcined samples. Based on Raman and XRD analyses, we figured out the titanate layers as an intermediate phase resulting from the alkaline-hydrothermal treatment of the amorphous particles. The hydrothermal treatment changed the particle surface morphology into a lamellar structure with a high specific surface area. These are the anatase precursors with {200} planes that transform into the anatase phase after calcination. The calcination followed by alkaline-hydrothermal treatment converted the crystallinity without significantly changing their morphology. We found that the morphology of TiO₂ particles can be modified via hydrothermal treatment using NH₄OH as long as the particles remain uncrystallized. We suggested the modification of particle morphology through the swelling and phase segregation process by alkaline-hydrothermal treatment. All final products have been used for the photodegradation of rhodamine B. S-HT-500 and A-HT-500 show the best photocatalytic activity with their rate constants (k) of 47.9 and 30.9 × 10⁻² min⁻¹, and their surface area-normalized rate constants (k_sa) of 6.5 and 2.6 × 10⁻³ L m⁻² min⁻¹, respectively, and have a photocatalytic efficiency of 90.93% and 67.78%, respectively, after 10 minutes of UV irradiation. This activity is approximately 3.5 times and 1.5 times higher than that of Degussa P25; 30 times and 20 times higher than that without a photocatalyst.