Synergistic activation of peroxydisulfate with magnetite and copper ion at neutral condition

•Cu2+ can synergistically activate PDS with magnetite to generate radicals.•Synergistic activation of PDS is effective to degrade contaminants in groundwater.•The adsorbed Cu2+ is reduced by the structural Fe(II) to generate Cu+.•Stability of Cu+ is enhanced on magnetite surface at pH 7 and higher.•The generated Cu+ on magnetite surface contributes to PDS activation. Magnetite is known to exhibit high catalytic reactivity in Fenton-like reactions merely at low pH conditions. Here we report the association of Cu2+ ion can significantly enhance peroxydisulfate (PDS) activation with magnetite under environmental aquatic conditions (near neutral pH). Cu2+ is able to synergistically activate PDS with magnetite to generate radicals, e.g., SO4·−, at neutral or slightly alkaline pH, and such synergistic activation of PDS is promising to degrade various contaminants in groundwater. In-depth study reveals Cu2+ ion adsorbed on magnetite plays a crucial role in PDS activation. The adsorbed Cu2+ is labile to be reduced by the structural Fe(II) on magnetite to generate Cu+, which is relatively stable in the presence of magnetite at neutral or alkaline pH, but extremely unstable at acidic pH. The generated Cu+ on magnetite surface, rather than Cu2+, contributes to PDS activation in the reaction system, and the recycling of Cu+/Cu2+ sustains continuous activation of PDS. This study is among the first to report the synergistic activation of PDS by magnetite and Cu2+ ion at neutral pH, and unambiguously discern the role of Cu+ in PDS activation. The new mechanistic knowledge provides a more accurate understanding of PDS activation by natural minerals in environmental remediation.