Electrochemical selection of ferrous phosphide (FexP) as efficient catalyst for wastewater treatment: Performance and mechanism

Iron phosphide (FexP) has a great potential for electrochemical catalysis attributing to its outstanding electrical conductivity and activity. In the present study, a series of FexP (FeP, Fe2P and Fe3P) were carried out as catalysts for the oxidation of phenol from wastewater by the heterogeneous EF processes. Compared with FeP and Fe2P catalysts, Fe3P has shown significant two-electron oxygen reduction activity and H2O2 selectivity (90–100 %). The degradation efficiencies of phenol in Fe3P/EF (100 %) were higher than those in Fe2P/EF (91 %) and FeP/EF (67 %) upon 60-min electrochemical oxidation under pH 7. The Fe3P-CF/EF system could broaden the range of solution pH, as well the decay kinetics of phenol was enhanced by 1.5–2.4 times and the disposal cost was reduced by 33–41 % compared with FeP/EF and Fe2P/EF. Feɑ+ in Fe3P could promote the generation of •OH via accelerating Fe(II)/Fe(III) cycle and accelerating the transfer rate of electrons between Fe3P and H2O2. It was proved that •OH played a dominant role in removing phenol with the electron spin resonance (ESR) tests and trapping experiments. This work selected the most effective FexP catalyst in heterogeneous EF process and would bring new insights for organics removal from wastewater via H2O2 activation.