Abstract
Soluble colloidal MnO2 was prepared by the reduction of KMnO4 by three reducing agents as MnSO4, Na2S2O3 and HCOOH in neutral aqueous solutions at 25A degrees C. Under suitable conditions, these solutions were dark brown in color and found to remain stable and transparent for several weeks. The obtained colloid was characterized by spectrophotometric and coagulation methods. The spectral behavior of soluble colloidal MnO2 was studied. The lambda(max) was 390 nm when MnO2 was prepared by the reduction of KMnO4 by MnSO4. Both the lambda(max) and the molar extinction coefficient depended on the method of preparation of colloidal MnO2. The formation of MnO2 was confirmed by the determination of the oxidation state of Mn-species in MnO2. The behavior of as-prepared colloidal solution obeys Beer Lambert law, if the concentrations of the colloidal particles are assumed to be equal to [MNO (4) (-) ](0). Both spectral analysis and that using Rayleigh's law confirmed the existence of colloidal MnO2. The observed coagulating efficiency depends not only on the concentration of electrolyte but also on the charge carried by the cation of the electrolyte. Stability of the colloidal particles in the aqueous solutions is determined by the negative charge on the surface of the colloidal particles.