An enhanced method of hydroxyl radical generation was studied to lead a better understanding of the catalytic mechanism of α-FeOOH in UV-Fenton system. The catalyst was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption–desorption isotherms and scanning electron microscope. The Orange II degradation and hydroxyl radical concentration under different conditions were studied in detail. The results showed that the hydroxyl radical was mainly oxidizing species for Orange II degradation. And the hydroxyl radical generation included both homogeneous and heterogeneous UV-Fenton processes. In heterogeneous UV-Fenton system, the additional oxalate could increase the ratio of homogeneous UV-Fenton process for hydroxyl radical generation. In oxalate enhanced system, the peak value of hydroxyl radical concentration would increase to 11.314 μmol/L which was nearly twice as it in heterogeneous UV-Fenton system (5.978 μmol/L). The k values of Orange II discoloration and mineralization increased to 0.386 min −1 and 0.044 min −1 , which were 1.169 and 0.692 times as that in heterogeneous UV-Fenton system (0.178 min −1 and 0.026 min −1 ). After treatment, the total iron ions concentration decreased to 2.357 μmol/L in oxalate enhanced system. The results indicated that additional oxalate was a promising enhanced method for hydroxyl radical generation in heterogeneous UV-Fenton system with α-FeOOH as catalyst.
Chen Wang,Yubei Liu,Mingjie Huang,Wei Xiang,Tao Zhou,Xiaohui Wu,Juan Mao
It was demonstrated in this study that appropriate concentrations of oxalate (Ox) would lead to greatly accelerated electro-generation of Fe 2+ but obviously lower power consumption in the Fered-Fenton system. Depending on the Ti electrode with pristine TiO 2 layer, effects of important parameters on the SMX degradation were investigated in the Fered-Fenton-Ox system. It was found that the heterogeneous interfacial electrochemically reduction of Fe III was critical in the Fered-Fenton-Ox system relying on the surface hydroxyl bonding Fe III -Ox and formation of Fe O Ti bonds. A heterogeneous-homogeneous reaction mechanism was therefore proposed. It included the heterogeneous interfacial electrochemical generation of Fe II -Ox and the heterogeneous-homogenous Fenton oxidation of pollutants. The promotional role of Ox would be also homogenous and heterogeneous, i.e. maintaining ferric at higher pH and forming specific Fe III -Ox complex as well as accelerating the solid-liquid interfacial heterogeneous iron cycle. Furthermore, a continuous-flow pilot study was conducted in treating a printing and dyeing industrial wastewater. As compared to conventional Fenton and Fered-Fenton systems, the Fered-Fenton-Ox system could achieve more efficient COD removal with a relative low cost/△COD, suggesting great advantages in its practical applications for treating real industrial complex wastewaters.
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