The Catalytic Degradation Of Congo Red Simulated Dying Waste Water By Nanostructured Manganese Oxides

Congo Red is one of the most wildly used azo dyes in dying industry. Wastewater containing azo dyes is hard to be degraded with the traditional physical,chemical and biological methods. The present project investigates nanostructuredmanganese oxides as catalysts respectively to accelerate the oxidation anddecomposition of high concentrations of Congo Red solutions with small amountsof catalysts and good recyclability.In this dissertation, β-MnO₂nanorods were synthesized by thermaldecomposition of MnOOH nanorod precursor. α-MnO₂nanorods were synthesizedfrom the reaction of KMnO₄and MnSO₄in water-bath. Mn₃O₄nanoparticles weresynthesized by solvothermal reaction between KMnO₄and ethanol. The sampleswere characterized by the X-ray powder diffraction （XRD） and transmissionelectron microscopy （TEM）. The β-MnO₂sample is composed of nanorods withdiameters of about200nm and length of tens of micrometers, α-MnO₂sampleconsists of nanorods of about50nm in diameter and1μm in length, and Mn₃O₄sample exists in nanoparticles with average particle size of100nm.The as-prepared nanostructured manganese oxides were used as catalystsrespectively to degrade Congo Red simulated dying waste water with the presenceof H₂O₂and showed good catalytic performance. The results indicated that β-MnO₂nanorods had higher catalytic activity than α-MnO₂nanorods and Mn₃O₄nanoparticles. With β-MnO₂nanorods and Mn₃O₄nanoparticles as the catalystsrespectively, the effects of the reacting conditions on the decoloration rate ofCongo Red solution were investigated, such as initial Congo Red concentration,H₂O₂concentration, catalyst dosage and reaction time.Further research showed that with β-MnO₂nanorods as the catalyst thedecoloration rate of Congo Red solution followed2.44-order kinetics and thereaction rate constant was0.002834（mol/L）^-1.44min^-1, while with Mn₃O₄nanoparticles as the catalyst the decoloration rate followed first-order kinetics andthe reaction rate constant was0.01276min^-1. UV-vis and FTIR results indicate thatCongo Red could have been decomposed into smaller organic compounds as well asCO2and others.