Solar Photocatalytic Methods for Dyes Treatment in Water: from Oxidative Degradation to Conversion into Useful Products

Here is provided a facile solution for realizing together wastewater purification and photocatalytic conversion of a waste (discharged dye) into useful products (such as sulfanilic acid used again for synthesis of new azo dyes). FTO/TiO2/CdS slides used as photocatalytic system have many advantages: use of visible light (CdS is the only photoactive material), overcoming the use of suspended powders, ease in handling and recovery, good stability and recyclability. The comparison between FTO/TiO2/CdS and FTO/ZrO2/CdS points out the synergic effect of TiO2 and CdS that causes a longer lifetime of the separated charges resulting in greater efficiency in the reductive cleavage of the N=N bond.