The influence of metal ions, such as Fe2+ , Fe3+ , Cu2+ and Mn2+ , on 4-CP degrada- tion was investigated in an aqueous pulsed discharge plasma system with or without the addition of a TiO 2 photo-catalyst. From an analysis of the pseudo first-order rate constant (k CP ) and energy efficiency (G 50% ) for 4-CP degradation, the experimental results show that the degradation of 4-CP is much enhanced in the presence of ferrous ions at the optimal concentration of 0.2～0.8 mmol/L or 0.2 mmol/L in an aqueous pulsed discharge plasma without or with the TiO2 system, respectively, and the enhancement is ascribed to plasma induced Fenton and photo-Fenton reactions. Meanwhile, the rank of such metal ions for catalytic effect on 4-CP degradation was Fe2+ > Fe3+ > Cu2+ > Mn2+ and Fe2+ > Fe3+ > Mn2+ > Cu2+ for the former and the latter systems, respectively, and the reasons behind this were discussed through the analysis of active species, especially hydrogen peroxide.
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