Application of polyaniline/manganese dioxide composites for degradation of acid blue 25 by hydrogen peroxide in aqueous media

The kinetics of catalytic degradation of acid blue 25 dye (AB-25) by hydrogen peroxide using polyaniline/manganese dioxide (PANI/MnO2) composites was investigated. To optimize the degradation kinetics of the dye, several parameters have been varied: (i) parameters varied during the preparation of PANI/MnO2 composites include: aniline concentration, acid concentration, acid type, amount of β-MnO2, stirring time and polymerization temperature and (ii) kinetic variables include: [H2O2], dye concentration, amount of composite, pH, addition of salt, and UV-light irradiation. The catalytic activity of the composite is obtained when it has (i) high % PANI content, (ii) high degree of crystallinity, and (iii) high doping ratio. The reaction obeyed second-order kinetics with respect to [H2O2], attains a maximum, and decreases thereafter. The degradation decreased when the dye concentration increased. Additionally, the effect of salts on the degradation rate was also studied. The rate of reaction decreases with increasing pH of the medium due to (i) the conversion of ES form of PANI into EB form and (ii) protonated form of the dye is more facial to be oxidized than the deprotonated form. Degradation rate was increased in the presence of UV/H2O2 compared to H2O2 alone. Mechanism was proposed for the catalytic degradation reaction which is in agreement with the experimental data.