High adsorption and high catalyst regeneration kinetics observed for Flyash-Fe3O4-Ag magnetic composite for efficient removal of industrial azo reactive dyes from aqueous solution via persulfate activation

The degradation of industrial azo reactive dyes (Corafix Red ME4B, Corazol Golden Yellow, and Corazol Black BX) has been demonstrated via the activation of persulfate (S2O82-) by using the Flyash (FA)-Fe3O4, FA-Fe3O4-Ag, and FA-Fe3O4-Ag-Cu magnetic composites as the activators. No significant dye decomposition has been observed for the thermal (30 degrees C) activation process and with the use of FA as an activator which involve no anchoring of the dye on the catalyst-surface. Nevertheless, FA-Fe3O4-Ag catalyst (100 g L-1) shows the maximum catalytic activity (98.6%) for the degradation of Corafix Red ME4B at the initial dye concentration of 0.3 g L-1 which has been attributed to its largest adsorption capacity (29.6 mg g(-1)) and the highest catalyst regeneration kinetics. Former is the result of pore-filling sorption process involving the electrostatic attraction mechanism caused by the presence of the highest surface oxygen-ion vacancy concentration and the largest pore volume (0.1654 cm(3) g(-1)). The mechanism of dye degradation via the activation of S2O8 center dot- involves the generation of SO4 center dot- and (OH)-O-center dot which are responsible for the dye decomposition and the catalyst regeneration respectively. The kinetics of catalyst regeneration is enhanced by the relatively higher pore volume of catalyst and smaller change in its oxidation state.