Persulfate enhanced photoelectrocatalytic degradation of cyanide using a CuFe2O4 modified graphite felt cathode

In order to remove cyanide (CN-) from wastewater, a photoelectrocatalytic (PEC) system was constructed using TiO2 nanorods (NRs) anode and CuFe2O4 modified graphite felt (CuFe2O4/GF) cathode. With the addition of persulfate (PS), the performance of PEC for the removal of CN- with an initial concentration of 0.9mM was increased from 31.10% to 98.21% in 120 min and the pseudo- first- order rate constant was calculated to be 0.0314 min(-1). The removal rate of CN- was accelerated with the decrease of initial CN- concentration and the increase of PS dose. The optimal bias potential for the removal of CN- and the recovery of Cu was 1.00 V. Results of radical quenching experiments and electron spin resonance analysis suggested that center dot OH and SO4 -center dot were generated by a Fenton- like process in the PEC/PS system. As proved by the XPS analysis, Cu(II) in CuFe2O4 cathode was dissolved by CN- into solution and then partially transformed to Cu(I). When CN- was removed, dissolved Cu ions were deposited onto the surface of CuFe2O4 cathode forming Cu2O. In addition, the dissolved Cu ions can also be deposited on TiO2 photoanode forming CuO. Cu(I) ions reacted with PS through a Fenton- like reaction, generating SO4 -center dot, which enhanced the oxidation ability of the PEC/PS system. The results provided a promising way to treat the industrial cyanide effluents efficiently.