The role of fly ash in solar photocatalytic water treatment

To investigate the possibility of using waste material in the water purification, fly ash (FA0) was modified and built-in within composite TiO2-FA. In that purpose, titanium dioxide (TiO2) was prepared in-situ by sol-gel synthesis in the presence of FA. The morphology, surface, structure and optical properties of obtained composite were compared to those of pure TiO2, synthetized by the same procedure as TiO2-FA. Both photo catalysts were then used in solar driven treatment of reactive azo dye Reactive Red 45 (RR45), exploring the influence of following process parameters: initial pH, photo catalyst dosage and initial RR45 concentrations, on the overall effectiveness. The reusability of TiO2-FA and TiO2 has also been explored. Modification of FA0 significantly increased its surface area. Synthetized TiO2 was highly crystalline and of anatase phase only, regardless the presence of FA. Band gap of TiO2-FA is slightly lower than that of TiO2, indicating that composite might have higher activity under solar irradiation. However, it was found that TiO2 is more effective, except at extreme conditions tested (the lowest pH and highest photo catalyst dosage), presumably because composite had 16 wt% less photo catalytically active component. On the other hand, composite underwent easier separation after the treatment that facilitated its reuse more efficiently.