Photosensitization effect on visible-light-induced photocatalytic performance of TiO 2 /chlorophyll and flavonoid nanostructures: kinetic and isotherm studies

Abstract

Preparation and performance of natural dye-sensitized photocatalysts of TiO 2 are described in this study. Such sensitized nanostructures offer visible-light-reactive systems for the photodegradation of organic pollutants. Natural pigments of chlorophyll and flavonoid extracted from parsley leaves and Curcuma longa roots are grated on TiO 2 nanoparticles as photosensitizers using an incipient wetness impregnation method. The as-prepared samples are structurally characterized by combined techniques, such as X-ray diffraction, scanning electron microscopy and Fourier transform infrared. The diffuse reflectance UV–Vis spectra are also used to investigate band-gap energies. The resultant band-gap energies confirm the ability of visible light absorption and thereby the ability of more efficient generation of photoexcited charge-carriers. The photocatalytic performance of dye-sensitized nanoparticles is tested in terms of decolourization efficiency of MB dye as a function of involved operating parameters including reaction time, amount of catalyst, initial MB concentration and pH. Both samples show the excellent photocatalytic efficiencies relevant to the red shift generated and high absorption of photons in the visible region. However, the highest efficiency is obtained for TiO 2/chlorophyll catalysts (93%) compared to TiO 2/flavonoid samples (91%), which is perfectly in agreement with their band-gap energies and visible-light absorption ability. Photodegradation process kinetics is investigated by the Langmuir–Hinshelwood model, while the adsorption equilibrium is described based on Langmuir and Freundlich isotherms.