Preparation of colloidal manganese dioxide and their stability investigation under different conditions

The colloidal form of MnO2 is widely used as catalyst in various organic and inorganic reactions in many industries. In the present study soluble colloidal MnO2 is prepared by the reduction of KMnO4 by Na2S2O3 in neutral aqueous solution at 25°C. Under suitable condition, these solutions were dark brown in color and found to remain stable and transparent is for several weeks. Stabilization of the colloidal MnO2 may occur in two different ways; decreasing the polarity of particles at the colloid surface and endowing the colloidal particles with a negative electrostatics charge. The application of micellar system using cationic, anionic, and non-ionic surfactants on this observation may provide the information for proper understanding of the stability and improve our knowledge about the effect of micelle on the stability of the MnO2 colloidal solution. The stability investigation was carried out in absence and presence of various anionic (sodium dodacylsulfate), cationic (cetyltrimethyl-ammonium bromide) and nonionic (Triton X-100) surfactants, to make an attempt to correlate the stability of the colloidal MnO2 solution and characteristics of the surfactants as well as with their organized media. From these correlations and survey of previous literature, the stability of this colloid was proposed. Different stability condition for miceller was available in the literature which applied on the reaction and an effort was made to establish the stability of the colloidal in different organized media (micelle of TX-100, SDS and CTAB). The micellar effect of this colloid was also used to facilitate the stability of colloid with different concentrations of micelle of TX-100, SDS and CTAB. Finally, the combination of all these observation of different condition and surfactants provided a better understanding about the preparation of MnO2 and stability of the colloidal solution. The above study provides the knowledge about the condition of this colloid which proved the information in future for understanding the different reaction mechanism.

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