Synthesis and characterization of lignite fly ash ceramic substrates coated with TiO2 slurry, and evaluation in environmental applications

Abstract

The novel valorization of lignite combustion fly ashes in the development of ceramic substrates modified with ΤiΟ2 photocatalyst, with environmental benefits, was investigated. Disc-shaped compacts from fly ashes (either calcareous or siliceous) were sintered (1000 °C, 2 h), then coated with TiO2 slurry, and further thermally treated (400 and 500 °C, 1 h) to acquire TiO2 consistency onto the ceramic substrate. The ceramic microstructures were examined by XRD and SEM-EDAX. Their photocatalytic activity was examined in aqueous solutions of two organic dyes, methylene blue and methyl orange using visible and UV irradiation, with encouraging results. A synergistic effect between ash ceramic substrates and ΤiΟ2 enhances the properties of the final activated product. Pores occurring on the non-activated ash surface are to some extent covered by TiO2. As a result, the photocatalytic activity, rather than simple dye adsorption onto the surface of the coated substrates, is promoted leading to efficient dye decolorization. Higher dye removal is achieved in the case of methylene blue under cool daylight compared to methyl orange under UV (blacklight and blacklight blue). A major advantage of the process is the immobilization of TiO2 onto a cheap porous substrate, which can provide an alternative for the photocatalytic treatment of industrial effluents.