Enhance the photocatalytic activity for the degradation of organic contaminants in water by incorporating TiO₂ with zero-valent iron

Titanium dioxide (TiO₂) has become the most popular photocatalyst in treating persistent organic pollutants. The main disadvantage of TiO₂ is the diminishing photocatalytic activity over time due to the electron-hole pair recombination. Many studies have aimed to prolong the photocatalytic life of TiO₂. Among them, incorporation of zero-valent iron (ZVI) is one of the approaches. In this study, a novel nano TiO₂/Fe⁰ composite (NTFC) was synthesized from a nano neutral TiO₂ sol and a nano zero-valent iron (nZVI), both prepared in our laboratory. The structure, composition and physical property of the NTFC are characterized. The photocatalytic activity of the NTFC was evaluated by the reductive decolourization of an azo dye, Acid Black-24 (AB-24), and was found superior to those of nZVI and nano neutral TiO₂ sol. Evidence suggests that the enhanced activity of NTFC is highly correlated to the ratio of ferrous to ferric ion in the system. The quantities of ferrous and ferric ions in the nZVI and NTFC systems were monitored separately. In the nZVI system, the concentration of ferric ions decreased significantly with time while a high level of ferrous ions was maintained in the NTFC suspension. The ferrous/ferric ratio of the NTFC suspension was substantially increased after irradiation by UV. Evidence from EPR analysis suggests that the excited electrons in the conduction band of the TiO₂ can be trapped by the half reaction of Fe³⁺/Fe²⁺, reducing the probability of electron-electron hole pair recombination and sustaining the catalytic life of TiO₂. Corrosion tests further proved that by incorporating TiO₂ with zero-valent iron the surface oxidation of nZVI can be effectively prevented.