Functionalization of titanium dioxide through dye-sensitizing method utilizing red amaranth extract for phenol photodegradation

Abstract

In this work, red amaranth (RA) extract was utilized as the source of the natural pigments for dye-sensitizing of the TiO2. The natural pigments were isolated from the RA leaves through a maceration technique to obtain the RA extract as a red powder. Since photocatalytic efficiency of titanium dioxide (TiO2) under visible light is negligible, further modification such as by addition of dye-sensitizer is required. The TiO2 was sensitized using the natural pigments contained in the RA extract using (3-aminopropyl)trimethoxysilane (APTMS) as the linker agent through an impregnation method to give the dye-sensitized TiO2 composite (RA-APTMS/TiO2). After dye-sensitizing, new absorption peaks at 1632-1030 cm-1 were detected in the Fourier transform infrared (FTIR) spectra, which were corresponded to the functional groups of chlorophyll originated from the RA extract. Furthermore, the appearance of a new absorption peak at 665 nm in the diffuse reflectance ultraviolet-visible (DR UV-vis) spectra also supported the successful sensitization of the TiO2 by the RA extract. Photocatalytic tests showed that while the unmodified TiO2 could not degrade phenol under visible light, the RA-APTMS/TiO2 composites exhibited photodegradation ability in 9, 13, 22 and 7 % when using 5, 10, 20 and 30 % mass ratio of the RA extract, respectively.