Enhancement of the photocatalytic activity of decatungstate, W10O324-, for the oxidation of sulfasalazine/sulfapyridine in the presence of hydrogen peroxide

The degradations of sulfasalazine and also sulfapyridine have been investigated by using the sodium decatungstate Na4W10O32 as a photocatalyst in the presence of hydrogen peroxide as a sacrifial agent. The selective irradiation of decatungstate, W10O324-, in the presence of the pollutants at 365 nm and at pH = 4.0 leads to the reduction of hydrogen peroxide via a Fenton like reaction involving the reduced species, W10O325-. Such process represents an efficient way for the formation of the highly reactive species, namely the hydroxyl radicals. The process appears then to be highly efficient for the oxidation of the pollutants sulfasalazine and sulfapyridine. Under our experimental conditions, the process was optimized in terms of concentrations of the photocatalyst, hydrogen peroxide and pollutant concentrations and also in term of pH. For both pollutants, the analysis of the generated by-products, using HPLC/MS, shows that the degradation proceeds primarily through three and common chemical processes: i) hydroxylation ii) desulfurization and iii) scission at the azo group -N = N-. The attack of the hydroxyl radical is clearly the main species for the degradation processes. As clearly demonstrated by the TOC experiments, the combination of W10O324-/H2O2/h nu system permitted a total mineralization of the solution indicating its high efficiency for the a potential application of water depollution.

Automated summary

The degradation of sulfasalazine and sulfapyridine was efficiently achieved using the photocatalyst Na4W10O32 and hydrogen peroxide, leading to the formation of highly reactive hydroxyl radicals. By analyzing the generated by-products, it was found that the degradation primarily involved hydroxylation, desulfurization, and scission processes. The total mineralization of the solution demonstrated the high efficiency of this system for water depollution applications.