Catalytical properties of the polyanilylin-MnO2 composite in organic dye decoloration reactions

Abstract

This work is devoted to the study of the regularities of the oxidation reactions of the dye (methyl orange) using hydrogen peroxide in the presence of a heterogeneous catalyst (PAn–MnO 2 composite), which we synthesized to increase the speed of the specified chemical reaction. When added to the reaction mixture containing H 2 O 2 and organic dye, the catalyst, which is a composite of the conjugated polymer and the transition metal oxide, can generate hydroxyl radicals, which are powerful oxidizing agents. This allows for higher rates of the dye bleaching reaction to be achieved compared to those occurring when using H 2 O 2 without a catalyst. The polyaniline–MnO 2 composite was synthesized by the method of oxidative polycondensation of aniline under the action of MnO 2 , which was dispersed in 100 ml of 1.15 mol/l aqueous sulfuric acid, the reaction was carried out at a ratio of MnO 2 : An = 1:1. In the infrared spectrum of the polyaniline–MnO 2 composite, a wide range of absorption peaks between 500 and 800 cm -1 , which are related to the vibrations of Mn–O atoms in MnO 6 octahedra, are observed; the peaks at 1 300 and 1 243 cm -1 belong to the C–N valence vibrations for the benzoid form (secondary aromatic amine), and the peak at 1 142–1 153 cm –1 belongs to the quinoid form of the doped PAn, the peak at 800 cm -1 refers to the vibrations of atoms in the C–C and C–H groups of the benzoid form. An intermolecular interaction appears to occur between the polyaniline quinoid and benzoid groups and Mn–O, which are part of the composite. We have studied the catalytic properties of the composite (PAn–MnO 2 ) and the original manganese oxide in the decolorization reactions of the MO dye under the action of H 2 O 2 . It has been shown that in the presence of manganese oxide, the oxidation of MO occurs faster than during the action of the composite (PAN – MnO2). The catalytic reaction constant in the first case has a relatively higher numerical value (1.85 × 10 -4 s -1 and 0.23 × 10 -4 s -1 , respectively). Keywords: polyaniline, composite, MnO 2 , catalysis, methyl orange