Soluble and supported hematin as a catalyst for decolourization of anthraquinone textile dyes: A kinetic modelling validation study

Hematin-catalysed decolourizations of alizarin red S solutions were carried out in order to validate a peroxidatic model in competition with pseudo-catalatic routes. Absorbance and dissolved oxygen were followed with time and hematin was used in solution or immobilized onto chitosan. Initial rates decreased with increasing dye concentration. Modelled dye concentration profiles properly reproduced experimental data. Optimized rate constants indicated that immobilization reduced hematin activity, emphasized dye inhibition and promoted the pseudo-catalatic pathway. The increase in H2O2 concentration increased oxygen evolution rates whereas the increase of dye concentration depleted them, which agree with the kinetic model proposal. These findings were also discussed considering some additional reactions which consume or evolve oxygen. UV-visible stack spectra of reacting systems allowed to propose some degradation products, whose molecular weights decreased with the increase of hydrogen peroxide to dye molar ratio. This is consistent with accumulation of inorganic radical-s proposed by the pseudo-catalatic mechanism.

Automated summary

The hematin-catalysed decolourization of alizarin red S solutions was studied in this research to understand the competition between peroxidatic and pseudo-catalatic routes. Absorbance and dissolved oxygen were measured over time, with hematin either in solution or immobilized onto chitosan. The experimental data were properly reproduced by the modelled dye concentration profiles, and the optimized rate constants showed that immobilization reduced hematin activity, emphasized dye inhibition, and promoted the pseudo-catalatic pathway. The findings were supported by the changes in oxygen evolution rates with H2O2 and dye concentrations, and the UV-visible stack spectra allowed the proposal of degradation products.