Effect of dopant (Co, Ni) concentration and hydroxyapatite compositing on photocatalytic activity of titania towards dye degradation

In this study, different concentrations of cobalt- and nickel-doped titania nanopowders were synthesized via non-aqueous sol-gel method and comprehensively characterized by several techniques. The photocatalytic activity of samples was evaluated by the photodegradation test of 10 mg L-1 of methylene blue solution under UV irradiation. The photocatalytic efficiency was enhanced by the presence of Co and Ni as dopants in TiO2 lattice compared to undoped titania (97.7%, 98.9%, and 88.0% for 0.05 mol% cobalt doped, nickel-doped, and undoped titania, respectively). FE-SEM images explained that samples had a uniform spherical shape, with the exception of 2 mol% dopant concentration, which were agglomerated. Furthermore, to suppress agglomeration problem, biphasic composite photocatalysts consisting 2 mol% doped titania and hydroxyapatite (HAp) were prepared by the precipitation of HAp in the presence of doped TiO2. FE-SEM, TEM images and BET results revealed that the composite samples suppressed TiO2 nanoparticles from agglomeration and increased specific surface area. The average size of nanoparticles was 20 nm. Also, higher photocatalytic activity and reaction rate constant were observed for 2 mol% cobalt- (91.0%) and 2 mol% nickel- (67.0%) doped titania/HAp nanocomposites compared to corresponding non-composited samples (58.5% and 49.9% for 2 mol% cobalt and nickel doped titania, respectively) as a result of better adsorption of dye molecules via HAp. The composite samples show photostability even after 4 cycles. (C) 2017 Elsevier B.V. All rights reserved.