MoS₄-LDH: A dual centre Fe-based layered double hydroxide catalyst for efficient atrazine removal and peroxymonsulfate activation

The Fe-based materials were considered very attractive for the treatment of wastewater using peroxymonosulfate (PMS) activation. However, the difficulties to restore the active Fe²⁺ oxidation state restrict them to attained sustainable efficiency. In this work, a new strategy was introduced to accelerate the regeneration of Fe²⁺ state through constructing an electron-rich MoS₄²⁻ centre in the inter-layers of FeMgAl layered double hydroxide (MoS₄-LDH) catalyst. The dual centre MoS₄-LDH catalyst was found more efficient as clear from the observed atrazine (ATZ) degradation rate of 0.117 min⁻¹, 100 times higher than the Fe³⁺/PMS or 25–50 times higher than the Fe based single centre NO₃-LDH/PMS, CO₃-LDH/PMS or S₂O₄-LDH/PMS systems, respectively. This boosted efficiency was related to the electron-rich MoS₄²⁻ centre which allows the constant electron transfer to reduce the electron-deficient Fe³⁺ center at MoS₄-LDH surface and thereby accelerating the Fe²⁺/Fe³⁺ redox cycle during reaction. Furthermore, the MoS₄-LDH/PMS system exhibited a broader effective pH (3.0–9.0), good stability and minimum influence of background electrolyte or organic matter. The degradation pathway of ATZ based on free radical (SO₄[rad]^– and [rad]OH), involving the redox cycles of Fe³⁺/Fe²⁺ and Mo⁶⁺/Mo⁴⁺ was proposed for the activation of PMS. This work highlighted the essential role of MoS₄²⁻ moiety, to accelerate the Fe³⁺ reduction at the surface of the LDH catalyst through the continuous feeding of electrons.