Selective betalain impregnation from red amaranth extract onto titanium dioxide nanoparticles

Abstract

In the present work, we reported a selective impregnation of betalain from the red amaranth extract onto titanium dioxide (TiO2) nanoparticles with the help of (3-chloropropyl)trimethoxysilane (CPTMS) as the organic linker. At first, the red amaranth was extracted using a free-solvent method and encapsulated with maltodextrin. The CPTMS was then used as a linker agent to prepare the composite TiO2 material containing the red amaranth extract (0.05, 0.10, and 0.20% (w/w)) by an impregnation method in ethanol. After the impregnation, the filtrate color was green while the composite material was obtained as a purplish solid. The diffuse reflectance ultraviolet-visible (DR UV-Vis) spectra of the composite materials showed the absorption peaks at 540 and 665 nm, showing the presence of the betalain pigment. Furthermore, the Fourier-transform infrared (FTIR) spectrum of the composite material confirmed the betalain functional groups, i.e. O-H and N-H (3680-2980 cm−1), C-H sp3 (2924 cm−1), C=O (1632 cm−1), C=C, C=N (1385 cm−1), C-O, C-N (1030-1024 cm−1) and Ti-O-Ti (800-500 cm−1). These results demonstrated that selective impregnation of betalain onto the TiO2 material could be achieved by using CPTMS as the linker agent.