Effect of KMnO4 on the Structure and Adsorption Behavior of Hydrous Manganese Dioxide Toward Pb(II) and Cd(II)

Four kinds of hydrous manganese dioxide (HMO) with different morphologies are synthesized by one-pot method in this work. The effect of KMnO4 on structure and adsorption behavior of HMO has been thoroughly investigated by XRD, SEM, TEM, BET, and zeta potential analysis. The HMOs prepared are all delta-MnO2, and a higher concentration of KMnO4 leads to a disordered, lower crystallinity structure, and higher absolute zeta potential values of HMO in the same condition, which exhibits a better adsorption capacity of 478.2 mg g(-1) for Pb(II) and 135.2 mg g(-1) for Cd(II). The addition of KMnO4 after reaction can also affect structure and adsorption capacity of HMO, it is characterized by higher crystallinity, fewer lattice defects, and higher adsorption capacity. The SEM and TEM analyses indicate that the possible formation is divided into two steps, involving the nucleation and shell growth, in a higher concentration of KMnO4: the first step is the reaction of KMnO4 and Mn2+, the second is KMnO4 decomposition with H+. In contrast, there is only the nucleation step in insufficient KMnO4. The addition of KMnO4 after reaction also involves two steps.