Synthesis, Characterization and Photocatalytic Activities of Fly Ash-TiO2 Nanocomposites for the Mineralization of Azo Dyes in Water

Abstract

Approximately 15 Mt/year of solid by-products (fly ash, bottom ash) are being produced by the lignite combustion in West Macedonia and Peloponnesus in Greece. The utilization of lignite byproducts, which are atmospheric dust components, is demanded to be significantly increased in the future. Potential environmental applications of these or some of these, by-products would make them a resource rather than a waste. In order to use fly ash as a resource, we synthesized TiO₂-fly ash nanocomposites in two different mass ratios (70%–30% and 80%–20% respectively). The nanocomposites were prepared using fly ash from Megalopoli (Peloponnese) by depositing TiO₂ in the form of anatase on the fly ash components using titanium isopropoxide as a precursor under mild hydrothermal conditions at 180 °C. Mineral as well as amorphous phase composition, particle morphology and physical properties of the prepared nanocomposites were characterized by XRD, SEM, SEM-EDS and N₂-sorption/desorption isotherms. Their photocatalytic activities in mineralising azo dyes in water were measured. An acidic (orange G) and a basic (yellow 28) azo dye were used in order to compare the activities of the nanocomposites and determine the parameters affecting the decomposition of dyes. The characterization of the nanocomposites showed that anatase nanoparticles are well dispersed on fly ash surface. More importantly both nanocomposites proved to be more effective in the photocatalytic decomposition of acid orange 10 indicating that they are more promising for use in decomposing acid than base azo dyes in water.