An integrated catalyst of Pd supported on magnetic Fe3O4 nanoparticles: simultaneous production of H2O2 and Fe2+ for efficient electro-Fenton degradation of organic contaminants.

A novel electro-Fenton process based on Pd-catalytic production of H2O2 from H2 and O2 has been proposed recently for transforming organic contaminants in wastewaters and groundwater. However, addition of Fe(II) complicates the operation, and it is difficult to recycle Pd catalyst after treatment. This study attempts to synthesize an integrated catalyst by loading Pd onto magnetic Fe3O4 nanoparticles (Pd/MNPs) so that H2O2 and Fe(2+) can be produced simultaneously in the electrolytic system. In an undivided electrolytic cell, phenol, a probe organic contaminant, is degraded by 98% within 60 min under conditions of 50 mA, 1 g/L Pd/MNPs (5 wt% Pd), pH 3 and 20 mg/L initial concentration. The degradation rate peaks at pH 3, increases with increasing Pd loading and electric current and decreases with increasing initial concentration. A distinct mechanism, reductive dissolution of solid Fe(III) in Fe3O4 by atomic H chemisorbed on Pd surface, is responsible for Fe(2+) production from Pd/MNPs. The efficiency of phenol degradation can be sustained at the same level for ten times of repeated treatment using the Pd/MNPs catalyst. The variations of main crystal structure and magnetic property of catalysts are minimal after treatment, but low concentrations of Pd leached, which needs further evaluation.