Photocatalytic degradation of azo dye in aqueous solution by a novel TiO2/FeO composite

摘要

The major obstacle of zerovalent iron (Fe_) application is the limit of the efficiency as time due to the formation of a surface oxide layer. However, the electrode potential of photocatalyzed TiO2 could be possibly used to transform ferric to ferrous and therefore improve the efficiency of Fe_. Therefore, we synthesized a novel TiO2/Fe_ composite (NTFC) with nanoscale size to improve the degradation performance by retarding the formation of surface oxide layer. This novel composite was synthesized by mixing TiO2 and Fe_ nano-particles by applying a special chemical treatment. Both TiO2 and Fe_ particles were also prepared in the lab by a neutral sol-gel process and wet precipitation method, respectively. The surface characteristics of the novel composite were investigated by using FE-SEM, XRD, XPS and chemical analysis techniques. The results from XPS and XRD analysis indicated that the laboratory-prepared NTFC material was mainly composed of Ti and Fe. The degradation of target compound (azo dye) in a reactor full of suspended NTFC nano-particles with UV illumination was conducted at room temperature and atmospheric pressure. The degradation rate of azo dye solution (25 mg/L) in this photocatalytic reactor was 99.0% for color and 50% for TOC in 2.0 h. The result shows that Fe_ can produce higher concentration of ferrous ions than NTFC at pH 3 during the initial reaction period. But after long-term reaction, the situation has been changed. The concentration of ferrous ion decreased significantly in the Fe_ suspension, allowing NTFC suspension maintained its double concentration of Fe 2+ than Fe_ suspension. Besides, the ferrous/ferric ratio was about 30 in the NTFC suspension after UV illumination, which represents that the NTFC with UV illumination is more effective to degrade azo dye. The evidence indicates that the superior redox ability of this novel NTFC shows a promising competitive future in the application of photocatalytic materials.