Influence of TiO2 Surface Properties on Water Pollution Treatment and Photocatalytic Activity

Nowadays, waste water with color is plentifully generated from many industries including textile, leather, paper, print-ing, dye stuff, plastic and so on.1-3 Degradation and removal of dye materials from contaminated water is very important, because the water quality is severely reduced by even quite slight color. Methyl orange (MO, C14H14N3NaO3S) is one of the well-known anionic dyes, and has been widely used in textile, printing, paper, food and pharmaceutical industries and research laboratories.2 Methylene blue (MB, C16H18NSCl) is one of the most common dying materials for wood, silk and cotton.2,3 The structures of MO and MB are shown in Table 1. The degradation and removal of MO and MB from waste water is very important due to their toxicity and even carcinogenicity. The high photocatalytic activity of titanium oxide (TiO2) has been well-documented in many literatures and widely used in purification of waste water.1-5 The TiO2 (110) surface structures are shown in Figure 1 and it is believed that the surface structure is the most primitive and essential property that functions in photocatalytic activity.5,6 The studies on TiO2 photocatalytic reactions have shown that the overall kinetics depend on both amount of adsorbed substrate on the surface be reduced or oxidized by photoexcited electron (e−) or positive hole (h+), respectively, and rate of geminate re-combination of e − and h+.4-6 Therefore, the different electric charge’s influence of dye in aqueous heterogeneous suspen-sions may be complicated by possible competing reactions of direct photocatalyzed oxidation, dye photosensitized catalysis, and photolysis of the adsorbed dye.2,4,7-10 In this research, the dyes of MO and MB for reasons stated above were selected, respectively representing anionic dye and cationic dye, to study the TiO2 photocatalytic reactions pro-perties