Low-temperature synthesis and characterization of rutile nanoparticles with amorphous surface layer for photocatalytic degradation of caffeine

Rutile (TiO2) nanoparticles were prepared by a low-temperature hydrothermal process from titanium(IV) isopropoxide as a precursor and without any additional calcination step. The particles were characterized with several techniques (XRD, BET, UV-vis spectrometry, TEM/HRTEM/SAED, FT-IR) and their photocatalytic efficiency was evaluated on the degradation of caffeine. The as-prepared rutile particles exhibited a rod-like morphology with a prism body and pyramidal ends. The low-temperature hydrothermal synthesis introduced an amorphous layer that was around 1-nm thick and uniformly covered the surfaces of the particles. The enhanced photocatalytic properties of the particles confirmed the positive impact of the amorphous surface layer in comparison to the fully crystallized surface of commercial rutile particles and to particles that were synthesized using a conventional high-temperature calcination route. The amorphous surface layer seems to enhance the adsorption of both oxygen and caffeine on the surface of the particles and, therefore, improves the photocatalytic activity of the rutile particles. Being the case, the electron transfer to the adsorbed oxygen is more efficient, increasing the life-time of the photogenerated holes, which contributes to the degradation of caffeine via the formation of reactive radicals and/or by direct oxidation. (C) 2013 Elsevier B.V. All rights reserved.