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

Abstract

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.