Highest photocatalytic activity observed for nanocrystalline anatase-titania having lowest crystallinity

Abstract

The nanocrystalline anatase-TiO2, a well-known photocatalyst, has been synthesized via the conventional sol-gel method involving an alkoxide-precursor. The nanocrystalline anatase-TiO2 has also been processed via the modified sol-gel technique involving the phosphoric acid (H3PO4) as an acid-catalyst. The different samples have been characterized using the various analytical techniques such as the transmission electron microscope (TEM), selected-area electron diffraction (SAED), energy dispersive X-ray (EDX), X-ray diffraction (XRD), and Fourier Transform Infrared (FTIR) spectroscope. The realtive concentrations of free-hydroxyl radicals (OH•) generated by these samples, under the ultraviolet (UV)-radiation exposure, has been qualiatively measured via the OH•-trapping experiments using the photoluminescence (PL) spectrofluorometer. The photocatalytic activity of different samples has been measured under the UV-radiation exposure using the methylene blue (MB) as a model catalytic dye-agent. The maximum photocatalytic activity has been exhibited by the nanocrystalline anatase-TiO2 processed via the modified-sol-gel method, which has the lowest crystallinity among all the investigated samples. This has been primarily attributed to the presence of PO43- anions on the surface, which help adsorb relatively large amount of MB dye in the dark-conditon and subsequently take part in the generation of superoxide-ions (O2-), which along with the OH• produced, attack and degrade the surface-adsorbed MB dye.