Photocatalytic kinetics and cyclic stability of photocatalysts Fe-complex/TiO2 in the synergistic degradation of phenolic pollutants and reduction of Cr(VI).

In this paper, the kinetic characteristics and cycle stability of Fe-complex/TiO2 in the process of degradation of phenolic pollutants and reduction of heavy metal Cr(VI) were studied systematically. First, the structural characteristics and photocatalytic activities of Fe(III)-(8-hydroxyquinoline-5-carboxylic acid)-TiO2 (Fe-HQC-TiO2) nanoparticle to degrade phenolic pollutants and reduce Cr(VI) simultaneously had been investigated. Compared with the single degradation, the efficiency of synergistic degradation/reduction had been improved and the degradation/reduction rate had been obviously accelerated. In particular, the cyclic stability of Fe-HQC-TiO2 photocatalyst decreased obviously when it was used to reduce Cr(VI) alone, but it could still keep above 90% after three cycles when it was used for reduction of Cr(VI) and degradation of phenol synergistically. Second, to Fe-HQS/TiO2 nanoparticle or Fe-HQS/TiO2 nanotube (HQS (8-hydroxyquinoline-5-sulfonic acid)), the synergistic degradation/reduction (2,4-dichlorophenol/Cr(VI)) efficiencies were always greater than those of a single degradation/reduction and the time was greatly reduced. All the results indicated that there were interactions between Cr(VI) and phenol or 2,4-dichlorophenol in the photocatalytic process. The possible mechanism of synergistic accelerated degradation of phenolic compounds and reduction of Cr(VI) was proposed by analyzing and testing the surface characteristics of photocatalyst and the properties of photocatalytic system during the synergistic degradation/reduction.