Investigation of the intermediates formed during the degradation of Malachite Green in the presence of Fe3+ and H2O2 under visible irradiation

The photodegradation of Malachite Green (MG) was investigated in the presence of Fe3+ and H2O2 under visible irradiation (λ > 470 nm) and the intermediates produced during the degradation were determined by FTIR, GC-MS and 1H NMR. The mineralized products of nitrogen atoms in the dye molecule were analyzed by ammonia ion-selective electrode and ion chromatography. N,N-dimethylaniline, 4-dimethylamino phenol, 4-methylamino benzophenone, 4-dimethylamino benzophenone, benzeneacetic acids and 4-hydroxybenzoic acid were found during the photodegradation of MG. It can be concluded that the dye underwent two different principal degradation pathways in the initial period of the photodecomposition, one is that the dye molecule is splittingly decomposed into small species by attack of HO• radicals on the central carbon, another is that the N-methyl groups are oxidized by HO• radicals, leading to demethylation. Nitrogen atoms in the dye molecules are finally transformed into ammonium ions. A possible degradation mechanism is proposed.