Comparative analysis on optical and photocatalytic properties of chlorophyll/curcumin-sensitized TiO2 nanoparticles for phenol degradation

In thiswork, natural-dye-sensitized photocatalysts (NDSPs) of TiO2 were prepared by a simplewetness impregnation method, in which natural pigments of chlorophyll and curcumin were initially extracted from fresh parsley leaves and long roots of dried turmeric, respectively. The as-prepared NDSPs were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and UV-vis diffuse reflectance (DRS) spectroscopy. XRD and SEM studies verified intact structural and morphological properties for NDSPs of TiO2 compared to non-sensitized nanostructures, while FT-IR and DRS analyses confirmed the presence of dye pigments on the surface of TiO2 photocatalysts after the photosensitization process. A red-shift towards longer wavelengths was observed in band-gap energies of dye-sensitized samples. These NDSPs indicated efficient photocatalytic performances towards decomposing phenol in visible light irradiation. Phenol degradation experiments are systematically conducted to optimize four key operating parameters, including irradiation time, initial pH of the reaction mixture, dye-sensitized TiO2 dosage and initial phenol concentration. Dye-sensitization using chlorophyll pigments results in the highest phenol degradation rate (85%) compared with that of samples sensitized with curcumin pigments (75%), which is perfectly in agreement with the corresponding band-gap energies. Photodegradation processes were modelled by the Langmuir-Hinshelwood kinetics, while the adsorption equilibrium was investigated based on Langmuir and Freundlich isotherms. Lastly, possible mechanisms involved in the process of phenol photodecomposition were proposed.