Simultaneous removal of two industrial dyes by adsorption and photocatalysis on a fly-ash–TiO2 composite
•Two industrial dyes are simultaneously removed using a fly-ash–TiO2 composite.•The adsorption kinetics depends on the dyes molecular structure and flexibility.•The azo dye removal involves parallel adsorption and photocatalysis mechanisms.•The anthraquinone dye removal involves concurrent adsorption and photocatalysis.
A novel composite was obtained in mild hydrothermal conditions using fly ash, TiO2 and a cationic surfactant (HTAB). The components were involved in extensive re-structuring processes, evidenced by XRD, FT-IR, SEM, AFM, BET and surface energy measurements. The composite was used as adsorption substrate and as photocatalyst for the simultaneous removal of two commercial dyes (Bemacid Red, BR; Bemacid Blue, BB). The experimental tests were run at the natural pH of the suspension, which was alkaline (pH 10.6). In the experimental conditions electrostatic interactions due are less extensive, and the data can be directly linked to the substrate’s morphology and dyes molecular structure and size. It was found that adsorption efficiency is strongly influenced by the micro-pores on the substrate and the kinetics mainly depends on the dyes flexibility. For the azo dye (BR), photocatalysis was found to run independent from adsorption while for the anthraquinone dye (BB) the process proves to be more complex. Under UV irradiation, the removal efficiencies reached after 240 min were of 93% for BR and of 77% for BB.
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Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 306, 15 June 2015, Pages 21–30