Sodium dodecyl sulphate-assisted synthesis, optical properties and catalytic activities of silver/manganese dioxide nanocomposites

A sodium dodecyl sulphate (SDS)-assisted approach was used for the synthesis of α-MnO2 nanorods by aerial oxidation of MnCl2 in the presence of NaOH. The mixing order of reactants (Mn2+ + OH−, Mn2+ + SDS, Mn2+-OH− + SDS and Mn2+-SDS + OH−), their molar ratios and pH have significant impacts on the pseudo-first-order kinetics of the redox system. Use of SDS decreases the Mn2+ reduction potential and avoids the formation of Mn(OH)2 as an intermediate in alkaline medium. α-MnO2 nanorods were further used in the preparation of Ag@MnO2 nanocomposites by a wet chemical method. The morphologies of α-MnO2 and Ag-doped MnO2 were determined by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDX), X-ray diffraction (XRD) and dynamic light scattering (DLS) measurements, which show that the α-MnO2 nanorods are successfully converted into Ag-doped MnO2. The complex formation constant, KC = 26 mol−1 dm3, and difference in absorption, ∆ε = 5.5 mol−1 dm3 cm−1, were calculated. The optical band gap energy was calculated and found to be 2.4 and 2.0 eV for MnO2 and Ag@MnO2, respectively.