Application of TiO2 nanoparticles sensitized with natural chlorophyll pigments as catalyst for visible light photocatalytic degradation of methylene blue

This study investigated the application of chlorophyll (chl) sensitized TiO2 (chl/TiO2) nanoparticles in visible light photocatalytic degradation of methylene blue (MB) with blue LED illumination. The novel chlorophyll sensitized catalyst was characterized through X-ray diffraction (XRD), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), and UV-vis diffused reflectance spectroscopy. The average crystallite size of the chl/TiO2 particles was in the range of 15-18 nm with a bandgap of 2.83 eV. An optimum degradation of 85 % was achieved with 2.5 g L-1 of 0.1 wt% chl/TiO2, initial pH of 6, and initial MB concentration of 20 ppm with 2 h of visible blue LED irradiation. The photocatalytic degradation of MB followed pseudo-first-order kinetics. The degradation products were identified using Liquid chromatography-mass spectrometry (LC/MS) analysis, and a degradation pathway was proposed following the N-demethylation process. The effect of secondary treated real domestic wastewater matrix on the degradation efficiency, as well as the recovery and reuse potential of the catalysts, was also investigated. Further, a plausible degradation mechanism for MB degradation by chlorophyll sensitized TiO2 under visible light irradiation was proposed.