Highly efficient degradation of azo dyes by palladium/hydroxyapatite/Fe3O4 nanocatalyst

Highlights: ► Pd/HAP/Fe3O4 catalyst was fabricated for highly efficient degradation of azo dyes. ► There is no need for the addition of an adulterant or application of light irradiation. ► The catalyst is easily recovered from reaction mixture by external magnet. ► The catalyst has excellent recyclability and stability. ► A synergistic mechanism for the azo dyes degradation in Pd/HAP/Fe3O4 systems is proposed. - Abstract: Palladium/hydroxyapatite/Fe3O4 (Pd/HAP/Fe3O4) nanocatalyst was synthesized and evaluated for its catalytic activity towards the degradation of azo dyes (methyl red, methyl orange and methyl yellow) selected as test dye species. The Pd/HAP/Fe3O4 was employed as a novel catalyst that offers high catalytic activity, magnetic separateability and good stability. It was found that catalytic activity of this catalyst was significantly enhanced under acidic conditions. The degradation mechanism is proposed to be due to the reaction of Pd/HAP/Fe3O4 with dissolved oxygen with the assistance of acid to form a Pd hydroperoxide, which oxidizes azo dyes under HAP catalysis. This in turn shows the clear importance of HAP as the support for the Pd nanocatalyst. The concentrations of dyes change exponentially with time and high rate constants were obtained for the degradation of these dyes. The pseudo-first-order equation was shown to fit degradation kinetics in most cases. Therefore, the Pd/HAP/Fe3O4 nanostructures are considered as a highly efficient and promising catalyst in degradation systems and they can be effectively recovered after use.