Preparation and photocatalytic activity of Nd-modified TiO2 photocatalysts: Insight into the excitation mechanism under visible light

Titanium dioxide (TiO2) nanoparticles (NPs) modified with neodymium (Nd) in the range between 0.1 and 1.0 mol% were prepared via the hydrothermal method. The samples obtained were characterized by diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), X-ray fluorescence (EDX), Brunauer-Emmett-Teller (BET) method, X-ray powder diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). The photocatalytic activity of the obtained samples was evaluated by photodegradation of phenol in aqueous solution under ultraviolet-visible (UV-Vis, lambda > 350 nm) and visible (Vis, lambda > 420 nm) irradiation. Experimental results showed that the photocatalysts exhibited high photocatalytic activity under Vis light. The sample showing the highest photoactivity under Vis irradiation was in the form of anatase; its surface area equalled 124 m(2)/g (1.16 times larger than that of pristine TiO2). The average crystal size was 10.9 nm, and it was modified with 0.1 mol% of Nd3+ (28% of phenol was degraded after 60 min of irradiation). The photocatalytic tests of phenol degradation in the presence of scavengers confirm that e(-) and O-2(center dot-) were responsible for the visible light degradation of organic compounds in the aqueous phase. Action spectra analysis revealed that although Nd-modified TiO2 could be excited under visible light in the range of 400-480 nm, the up-conversion process is not responsible for the degradation of phenol under Vis irradiation. (C) 2017 Elsevier Inc. All rights reserved.