The Mechanism Of CUCO2O4 And ZN-CU Binary Metal Oxides To Activate Potassium Persulfate To Degrade Phenol

Bimetallic catalysts with the formula of A_xB_3-xO₄,such as CuFe2O₄,CoFe2O₄ and CoMn2O₄ have been paid more attention for their good catalytic activities in peroxymonosulfate?PMS?activation to degrade organic contaminants.However,to the best of our knowledge,bimetallic catalysts used for activating the more cost-effective and oxidative persulfate?PS?have been scarecely reported so far.In addition,identification of the respective contributions of each metal species in PMS/PS activation is still a problem that constrains our understanding on the catalytic mechanisms by bimetallic catalysts.'In this study,CuCo₂O₄ and Zn-Cu oxides show high catalytic activities to activate PS under alkaline conditions,and their catalytic activities increase with increasing pHs.At pH 11.0,100.0 mg L^-1 phenol can be completely removed in 30 min by 1.0 g L^-1 PS in the presence of 1.0 g L^-1 CuCo₂O₄ or 1.0 g L^-1 Zn1Cu₂ with the pseudo-first order rate constant k of 1.64×10^-1 and 6,72 ×10-2 min^-1,respectively.Although SO₄·-and ·OH radicals have been proved to play important roles in organic degradation in previous studies,more than 60%phenol can still be removed in the presence of 5.0 M methanol,a strong scavenger for both SO₄·-and ·OH radicals.EPR analysis also confirms the absence of oxidative radicals,indicating that a non-radical mechanism largely contributes to phenol degradation in the CuCo₂O₄ and PS system.XPS results further suggest that PS can directly oxidize Co???and Cu???to the respective Co???and Cu???,which later oxidize phenol via a non-radical degradation mechanism.In order to distinguish the respective contributions of Co???and Cu???to phenol degradation,a series of ligand-promoted experiments,as well as XPS and Raman analyses were designed.The results suggest that either reduction of Co???by L-cysteine or complexation of Co???by EDTA significantly decreases the catalytic activity of CuCo₂O₄,whereas complexation between F-and Cu???does not significantly affect the degradation rate of phenol,revealing the more importance of Co???than Cu???in phenol degradation.In the ZnCu₂ and PS system,SO₄·-and ·OH radicals can still be detected after 60 min in the presence of 5.0 M ethanol as suggested by EPR analysis,indicating the importance of these active radicals in phenol degradation.When Zn was replaced by Mg???or Ca???,Mg1Cu₂ and CaCu₂ could also catalyze PS to effectively degrade phenol.Given that Mg???and Ca???have no catalytic activities towards PS,we believe that the primary catalytic contribution of Zn1Cu₂ should come from Cu???instead of Zn???.XPS analysis further indicates the presence of Cu???and 'Zn???'on Zn1Cu₂ after PS activation,and 'Zn???represents the intermediate formed between Zn???and-O-O-.The ligand-promoted experiments further confirm the more significant contribution of Cu???than that of 'Zn???'.This is the first study to report that CuCo₂O₄ and Zn1Cu₂ can effectively activate PS in the degradation of organic contaminants under alkaline conditions,which opens a new avenue for the treatment of alkaline organic wastewater.Moreover,this study enriches our understanding on the activation pathways of PS under alkaline conditions.