Effects of CTAB and SDS on the nucleation and growth of MnO2 and Ag-doped MnO2 nanoparticles formation

Abstract

Permanganate (MnO4−) redox reaction with cysteine and sodium borohydride (NaBH4) were studied spectrophotometrically in absence and presence of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulphate (SDS) surfactants. Water soluble dark brown color MnO2 was formed as the stable product with CTAB and SDS. Absorbance of MnO4− at 526 nm increases with CTAB concentrations. The order of mixing of CTAB and reducing agents (cysteine and NaBH4) have significant effect on the redox reactions of MnO4−. The MnO4− purple color was not decolorized in a reaction system containing CTAB + MnO4− + NaBH4. These observations can be rationalized due to the strong MnO4− and BH4− electrostatic interactions with the ionized CTAB. Such type of observations were not noticed with SDS. Cationic and anionic head groups of CTAB and SDS were responsible to the incorporation as well as exclusion of MnO4−, cysteine, and BH4− from the Stern-layer of both micelles. Ag-Doped MnO2 was prepared using seedless and seed growth methods with SDS and CTAB. Morphology of MnO2 and Ag-Doped MnO2 were determined with SEM, EDX, XRD, and FTIR.