Kinetics of peroxide bleaching of azorubin in the presence of polyaniline-mangane oxide composite (IV)

Abstract

Purification of aquatic ecological systems from residues of synthetic dyes used in the textile and printing industry is an urgent problem. Researchers are successfully studying the possibilities of using Fenton and Raff reagents to decolorize aqueous solutions of dyes, they offer various compounds of metals with variable valence, whose ions can serve as catalysts for the decomposition of H 2 O 2 to HO • radicals, which are powerful oxidants. However, the separation of such homogeneous catalysts after interaction with industrial dyes is technically and economically impractical, so there is a need to create insoluble solid catalysts with high adsorption capacity, as exemplified by polymer composites polyaniline - MnO 2 . After the process of purification of water from the dye residues, the solid phase catalyst together with the adsorbed purification products is removed by filtration. We investigated the kinetics of oxidative decolorization of the synthetic dye azorubin in the presence of an adsorbent agent–polyaniline, which was used in the form of its composite with manganese (IV) oxide. The catalytic action of MnO 2 causes the decomposition of hydrogen peroxide to HO• radicals, with their participation the oxidation of dye molecules takes place, products that have almost no color are formed. The polyaniline–MnO 2 composite was synthesized by oxidative polycondensation by adding aniline to a reaction vessel containing a certain amount of MnO 2 powder, which was ground in an aqueous solution of sulfuric acid, the molar ratio of MnO 2 :An = 1:3. Infrared spectroscopy showed that the composition of the polyaniline–MnO 2 composite includes quinoid and benzoid groups of polyaniline and groups of atoms (Mn–O). A number of adsorption absorption peaks between 500 and 800 cm -1 are attributed to the oscillations of Mn–O atoms in MnO 6 octahedra, valence oscillations for quinoid and benzoid forms of PAN are traced at 1 575 and 1 495 cm -1 , peaks at 1 300 and 1 243 cm -1 belong to C–N valence oscillations of the benzoid form (secondary aromatic amine), and the peak at 1 142–1 153 cm -1 is attributed to the quinoid form of doped PAN, the peak at 800 – to the oscillations of atoms in the C–C and C–H bonds of the benzoid form of polyaniline. The kinetics of oxidative decolorization of the dye solution in the presence of equal amounts of the synthesized composite (PAN–MnO 2 ) or mechanical mixtures of the original manganese oxide with pure polyaniline (PAN+MnO 2 ) was studied by UV spectroscopy. It is shown that the rate constants of catalytic decolorization of azorubin with hydrogen peroxide (T = 20 C) when using such catalysts have numerical values of the same order (≈ 10 -5 c -1 ). Increasing the content of PAN in the mechanical mixture from (MnO 2 :PAN = 1:3; k 1 = 6,67 10 -5 s -1 ) to (MnO 2 :PAN = 1:30; k 2 = 8.17 10 -5 s -1 ) leads to some increase in the rate constant of azorubin decolorization reaction, however, in the case of the synthesized composite (MnO 2 :PAN = 1:3; k 3 = 3,17 10 -5 s -1 ) the catalysis efficiency decreases. This fact can be explained by the restriction of access of reagents to the catalytic centers on the surface of manganese oxide particles during the encapsulation of MnO 2 inside the polyaniline matrix during the synthesis of the composite. Keywords : polyaniline, composite, MnO 2 , catalysis, dye azorubin