Iron(III) photoinduced degradation: Catalytic method for 4,4'-diaminostilbene-2,2'-disulfonic acid removal from water

The Fe(III)-photoinduced degradation of 4,4′-diaminostilbene-2,2′-disulfonic acid (DSD), used as a model compound of fluorescent whitening agents, was investigated in aqueous solution. The mixing of DSD and iron(III) solutions immediately led to DSD degradation into two oxidation products 5-amino-2- formyl-benzene sulfonic acid (1) and DSD epoxide (2) together with the formation of Fe(II). The behaviour of the latter solution was investigated under monochromatic excitation at 365 nm. The irradiation of the solution resulted in a photoredox process that yielded Fe(II) and HO• radicals; [Fe(H2O)5(OH)]2