Shifting mechanisms in the initial stage of dye photodegradation by hollow TiO2 nanospheres
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Hollow TiO2 (HT) sphere aggregates were prepared using carbon spheres as templates. The photocatalytic activity of HT was determined by degradation of two nitrogen-containing dyes, methylene blue (MB) and methyl orange (MO). The adsorption isotherms and the photocatalytic degradation kinetics of the two dyes were studied and compared using different concentrations of dyes for the pure, isopropanol-added, and KI-added systems. Isopropanol was used as a OH• radical scavenger, while KI was added as a valance band hole scavenger. The results showed that the reaction mechanism of the photocatalytic process of MB was first governed by OH• radicals, and then by valence band holes, whereas holes played a major role in the whole photodegradation process of MO. The photocatalytic adsorption constant K V has a positive correlation with the reaction constant k ov in all systems. The photodegradation efficiencies of the dyes were discussed considering the surface characteristics of HT and the structure of the dyes with different catalyst loads (0.25–2 g L−1) and under different pH (3–10) conditions. Compared with solid TiO2, HT exhibited enhanced performance in photocatalytic degradation of both MB and MO.
KeywordsMethylene Blue Total Organic Content Photocatalytic Activity Photocatalytic Degradation Methyl Orange
The authors gratefully acknowledge financial support from the Foundation of State Key Laboratory of Pollution Control and Resource Reuse of China, the Natural Science Foundation of China (No. 51008154), the Jiangsu Natural Science Foundation (No. SBK201022682), the Research Fund for the Doctoral Program of Higher Education of China (No. 20090091120007), the Fundamental Research Funds for the Central University (No. 1112021101), the Jiangsu Cultivation of Innovative Engineering for Graduate Students (CXZZ12_0063), the Scientific Research Foundation of Graduate School of Nanjing University (No. 2012CL10), and the China Postdoctoral Science Foundation funded project (No. 2012M511254).