Preparation and characterization of polyaniline/manganese dioxide composites and their catalytic activity

This paper is devoted to the preparation of polyaniline/MnO 2 (PANI/MnO 2) composites via chemical oxidation of aniline in H 2SO 4 medium using β-MnO 2 as an oxidant. The parameters affecting the polymerization reaction are considered. These parameters are [aniline], amount of β-MnO 2, stirring time, and polymerization temperature. SEM, FT-IR, XRD, and TGA techniques are used to characterize the resulting composites. XRD measurements reveal the distortion of the crystal structure of β-MnO 2 after the polymerization reaction. Thus, the XRD pattern of PANI is predominating. The crystalline composites are obtained using higher molar ratio of [Ox]/[ANI] and at higher temperature. Increasing the amount of β-MnO 2 led to an increase in the acidic character of the obtained composites due to adsorption of excess H + on the oxide surface. The thermal stability of the composites decreased with increasing both [aniline] and stirring time, while it increased with increasing amount of β-MnO 2. The applications of the composites in the oxidative degradation of Direct Red 81, Acid Blue 92, and Indigo Carmine dyes exhibited good catalytic activity in the presence of H 2O 2 as an oxidant. The reactions followed first-order kinetics and the rate constants were determined. The degradation reaction involved the catalytic action of the PANI counterpart of the composite toward H 2O 2 decomposition, which can lead to the generation of HO ⋅ radicals as a highly efficient oxidant attacking the target dyes. The detailed kinetic studies and the mechanism of these catalytic reactions are under consideration in our group. Well-characterized PANI/MnO 2 composites exhibited a good catalytic activity for the oxidative degradation of the target dyes using H 2O 2 as an oxidant.