Effect of pH on formation of γ-MnO2 from Zn-bearing MnSO4 solution

Abstract

Manganese dioxide has attracted much attention owing to its distinctive properties. A facile method was developed to synthesis γ-MnO2 by the reaction of Na2S2O8 with Zn-bearing MnSO4, keeping the molar ratio of Mn to S as 1:2-4. The oxidation of Mn2+ increased from 62.3% to 99.9% with the increase of the final solution pH from 0.55 to 4.45. The needlelike γ-MnO2 particles with a length of 200-500 nm and a diameter of 10-30 nm were synthesized in the initial solution pH range of 3.5-4.0. γ-MnO2 particles with poor crystallinity and porous morphology were synthesized in the initial solution pH range of 6.0-6.5. The Zn2+ adsorption capacities of the γ-MnO2 formed at initial pH=3.5 and pH=6.0 were 131.8 mg.g -1 and 527.4 mg.g-1, respectively.