Synthesis of porous α-Mn2O3 and its catalytic performance for activating peroxymonosulfate to degrade methylene blue solution

Abstract

Porous α-Mn2O3 with irregular granular morphology stacked from microplates was synthesized through thermal decomposition of oxalate, and its performance as a catalyst to activate peroxymonosulfate(PMS) for degradation of simulated dyestuff wastewater with methylene blue(MB)as main component was explored. Influences of calcination temperature, catalyst addition, PMS dosage and anion species on MB degradation efficiency were investigated.The results show that the product obtained at 450℃ exhibits the most excellent catalytic ability. The degradation ratio of MB is 75.88% in the system of α-Mn2O3/PMS, while its counterpart is only 22.19% and 5.72% for PMS or α-Mn2O3 alone, respectively.The optimization reaction additions for degradation of MB of 500 mL with a concentration of 10 mg/L are: 3 mL of PMS (0.1 mol/L), 0.05 g of α-Mn2O3. At this condition, a MB degradation ratio of 83.55% can be achieved in 50 min. In addition, it is found that introduction of C2O42- or PO43- has a negative effect on MB degradation, whose inhibition rate is 49.11% and 10.27%, respectively. However, Cl- has no inhibitory effect for MB degradation. Furthermore, the active species in the reaction system are identified by the quenching experiments and electron paramagnetic resonance(EPR) tests.The results confirm that there are ·OH, SO4-·, ·O2- and 1O2 in the reaction system, and 1O2 is the most important active intermediate involved in the direct oxidation degradation of MB.Kinetic analysis demonstrates that the degradation of MB solution with PMS catalyzed by α-Mn2O3 is a secondary reaction, and the kinetic reaction rate constant is 3.53 L·mmol-1·min-1.

Keywords

• oxalate route
• α-mn2o3
• peroxymonosulfate
• methylene blue
• singlet oxygen