Activation of persulfate via Mn doped Mg/Al layered double hydroxide for effective degradation of organics: Insights from chemical and structural variability of catalyst

Abstract

Considerable interest has been focusing on the activation of peroxydisulfate (PDS) by layered double hydroxide (LDH) for degradation of organic pollutants. However, understanding the structure and chemistry of LDH by which the activation of PDS could achieve a high degradation efficiency of organic compounds is an unsolved and fundamental question in advanced oxidation processes (AOPs), and one which, if harnessed, could enable the rational design of LDH with desired material properties. In this work, Mg/Al-LDH was synthesized with variable structures and compositions through doping different proportions of Mn²⁺. We advanced to understand this question of how LDH by these characteristics can affect the activation of PDS for degradation of organic pollutants. At a relatively low dosage of Mn (˂ 1%) in Mg/Al-LDH, the degradation rate of phenol by LDH activated PDS increased with the increase content of Mn, which was achieved by an increase of catalytic sites in Mg/Al-LDH interlayer. Rather, higher content of Mn (˃ 1%) significantly lowered the degradation performance of phenol as the decrease of interlayer space resulted in reduction of PDS intercalation in LDH and the formation of secondary Mn-related minerals (i.e., Mn₃O₄) led to meaningless consumption of PDS. Finally, the degradation of phenol by LDH activated PDS followed a non-radical (¹O₂) mechanism. Our ability to quantify how the chemical and structural variability of LDH influence the activation of PDS for organic degradation could mark an important step toward synthesis strategies for advanced catalysts.

Keywords: Advanced oxidation process; Degradation; Mn doped LDH; Non-radical; Persulfate.