Preparation of cobalt/zinc bimetallic porous oxides and its performance in activating peroxymonosulfate for methylene blue degradation

Abstract

Cobalt/zinc bimetallic porous oxide composites were prepared by the oxalate-pyrolysis method and used as a catalyst for activating peroxymonosulfate(PMS) to degrade methylene blue(MB) solution. Taking Co(NO3)2·6H2O and Zn(NO3)2·6H2O as metal ion sources and oxalic acid as precipitant, cobalt-zinc oxalate precursor was first obtained through simultaneously precipitating Co2+ and Zn2+. The porous Co3O4/ZnO composite oxide catalysts with different Co/Zn molar ratios were attained by calcining the oxalate precursor. The results show that the Co1Zn5 composite with an initial Co/Zn raw material ratio of 1∶5 has the best catalytic activity. When the catalyst dosage is 0.02 g·L-1 and PMS concentration is 0.6 mmol·L-1, MB degradation rate of 98.49% can be reached. Electron paramagnetic resonance (EPR) results identify that the degradation of MB by Co1Zn5/PMS follows both free radical and non-free radical mechanisms. Moreover, it is found that more exposure of active component Co3O4 in the Co1Zn5 composite, which is resulting from the partial dissolution of ZnO in the weak acidic environment caused by PMS, is mainly responsible for the boosting catalytic performance due to the increase of reaction chances between Co3O4 and PMS.

Keywords

• oxalate-pyrolysis method
• bimetallic oxide
• peroxymonosulfate
• heterogeneous catalysis
• advanced oxidation process