TiO2-Coated Cenospheres as Catalysts for Photocatalytic Degradation of Methylene Blue, p-Nitroaniline, n-Decane, and n-Tridecane under Solar Irradiation

Fly ash cenosphere particles generated in coal-fired thermal power plants were coated with TiO2 using the sol-gel technique. Thus prepared photocatalysts were used for the degradation of methylene blue (MB), nitro-aromatic compound p-nitroaniline (PNA), and photocatalytic oxidation of n-decane and n-tridecane from aqueous solution under solar light irradiation. The morphology, composition, and crystallinity of both pristine and TiO2-coated cenospheres were studied. The UV-visible spectroscopic analysis was used to monitor the progress of the reaction for MB and PNA. The decrease in the amount of n-decane and n-tridecane was determined by gas chromatographic analysis. The decrease in the concentration for a 25 ppm initial concentration of MB and PNA was observed to be 99 and 26%, respectively, after 3 h of reaction time. This demonstrates that MB is more amenable toward degradation and mineralization as it acts as a sensitizer. Decreases up to 51 and 36% for n-decane and n-tridecane were observed with initial amounts of 3-12 mL, respectively, after 6 h. The coated cenosphere catalyst could be recovered by filtration and reused. The coating was found to be stable even after three uses of the catalyst in the photocatalytic degradation reaction of MB and PNA. The mineralization of dye and nitro-aromatic compound was confirmed by the chemical oxygen demand analysis. Cenospheres, because of their light weight, would make the catalyst particles float on the aqueous surface and hence could be directly activated by sunlight.