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 center dot- and (OH)-O-center dot), 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.