Reduction of MnO4− Ions and Selective Deposition of Sodium-Manganese Spinel Nanocrystals on the Surface of Hierarchically Structured Carbon Films in Aqueous Solutions.

The paper presents an investigation into the reduction and adsorption performance of hierarchically structured carbon films (HSCFs). The HSCFs are synthesized from glucose using a molten magnesium catalyst under a layer of molten salts during their reaction with an aqueous sodium permanganate solution at pH values from 1 to 14 and temperatures from 20 to 80 °C. By increasing the temperature from 20 to 80 °C, the reduction and adsorption of Mn (VII) on the HSCFs is accelerated by a factor of 150; moreover, the reaction products are not temperature-dependent. According to Raman and photoelectron spectroscopy data, synthesis in the neutral and basic sodium permanganate solutions produces an "HSCF-sodium-manganese spinel" nanocomposite, the greater part (≈ 80%) of whose manganese is in a tetravalent state, while the remainder is in a trivalent state. The predominant precipitation of manganese spinel nanocrystals on the developed side of the carbon film may be related to the full disappearance of the sp hybridized carbon peak on the XPS spectra. It is shown for the first time that the reactivity of carbon varies with its valence state. Of the three hybridized states of carbon, sp hybridized carbon is demonstrated to have the highest reactivity. It is confirmed that 100% reduction and adsorption from 0.01 to 0.1 M sodium permanganate solutions occur in neutral and basic media. The adsorption capacity of the hierarchically structured carbon film interacting with 0.1 M sodium permanganate solution is more than 450 mg/g, representing a high adsorption performance as compared to other carbon nanomaterials investigated earlier. [ABSTRACT FROM AUTHOR]