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.
a b s t r ac tThis article presents a novel procedure to synthesis mesoporous TiO 2 -SiO 2 structure via ultrasonic impregnation method. Mesoporous silica SBA-15 as a host structure was first prepared. Then, the prepared host structure was mixed with a homogenized solution of TiO 2 precursor under ultrasonic condition at 40°C. To understand the chemical composition and structural properties of the synthesized powder, several characterization techniques such as powder X-ray diffraction, small-angle X-ray scattering, nitrogen adsorption, X-ray photoelectron spectroscopy, transmission electron microscopy, field-emission scanning electron microscopy and energy dispersive X-ray were employed. Photocatalytic activity of the calcined materials at various temperatures (400°C, 600°C, and 800°C) was evaluated by degradation of methylene blue solution under UV light. The anatase crystals were the only detected phase until 800°C due to formation of Ti-O-Si bonds. Photo-degradation results revealed that all of synthesized samples possess much more photocatalytic activity than commercial TiO 2 . In addition, a higher photocatalytic efficiency was achieved at higher calcination temperature owing to more degree of crystallinity.
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