Novel activation of persulfate by its intercalation into Mg/Al-layered double hydroxide: Enhancement of non-radical oxidation

Persulfate based advanced oxidation processes have been well investigated, with the generation of radical species via various activation methods. This study reports an activation pathway of peroxydisulfate (S2O82−, PDS) without radical production, achieved by the intercalation of PDS into Mg/Al-layered double hydroxide (LDH). Physical characterization indicated that the LDH was intercalated by PDS with the interlayer distance increasing to 0.917 nm. Approximately 93.9% of the phenol was decomposed by a LDH-PDS composite containing 0.4 mmol/g PDS, whilst no removal of phenol was achieved in the control group with PDS. Moreover, sulfate from decay of PDS was likely kept in the layers of LDH for no sulfate leakage in solution was observed. This is in accordance with the occurrence of characteristic peaks assigned for sulfate in FT-IR spectrum of LDH-PDS after reaction. Interestingly, radicals were not recorded by electron spin resonance measurement or radical scavenger tests during the oxidation process. The reactivity of PDS was likely improved by the basic sites on the LDH laminate, which provided OH to activate the OO bond in PDS. Further, the limited space of LDH layers reduce the bond cleavage of intercalated PDS and thus the generation of radicals. Therefore, the results proposed a non-radical reaction between phenol and PDS in the interlayer of LDH and developed a novel activation pathway for PDS in the elimination of organic contaminants.