856 Journal of Chemical Engineering of Japan Copyright © 2015 The Society of Chemical Engineers, Japan Journal of Chemical Engineering of Japan, Vol. 48, No. 10, pp. 856–861, 2015 Effect of Addition of Surfactant to the Surface Hydrophilicity and Photocatalytic Activity of Immobilized Nano-TiO 2 Thin Films Eden G. Mariquit 1 , Winarto Kurniawan 1 , Masahiro Miyauchi 2 and Hirofumi Hinode 1 1 Department of International Development Engineering, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8550, Japan 2 Department of Metallurgy and Ceramics Science, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8550, Japan Keywords: Sol–Gel Method, Surface Hydrophilicity, TiO 2 Photocatalysis, TiO 2 Thin Films We study the effect of adding cetrimonium bromide (CTAB) as a surfactant to titanium dioxide (TiO 2 ) solution for im- mobilizing TiO 2 on glass substrates. The thin films are deposited by the dip-coating technique. After dipping into the TiO 2 sol, the films are calcined and a pure anatase crystal phase is obtained. The thickness of the thin film is changed by vary- ing the number of the dip-and-calcine cycles. The prepared films are characterized using FE-SEM, TG-DTA, and XRD, and samples’ photocatalytic performances are tested with regard to the degradation of methylene blue dye. Aside from the photocatalytic performance, the photoinduced hydrophilicity of thin TiO 2 films surface is also studied. Characterization results show that the addition of surfactant gives rise to characteristic patterns on the surface of the TiO 2 thin film, which also affects the photocatalytic activity. The addition of CTAB to the TiO 2 dipping solution has a negative effect because the calcination temperature is not sufficiently high to burn all the surfactants off. As for surface wettability, the addition of surfactant has a positive effect on the photoinduced surface hydrophilicity of the TiO 2 films under UV light. Introduction Recent research has shown that semiconductor pho- tocatalysis can potentially be utilized towards addressing environmental problems (Young, 1964). Titanium dioxide (TiO 2 ) is the most commonly used photocatalyst in semi- conductor photocatalysis because of its stability and high photocatalytic efficiency (Zhao and Miyauchi, 2008). Since the discovery of the Honda–Fujishima effect, which shows the strong oxidation and reduction capability of titanium dioxide irradiated with UV light (Honda and Fujishima, 1972), there have been several studies on the possibility of the use of TiO 2 in environmental applications to degrade harmful pollutants in air and water (Frank and Bard, 1977). Tis has prompted more research on the photocatalytic degradation of different pollutants and has spawned many studies on the photocatalytic reactions of TiO 2 related to environmental purifcation (Ireland et al., 1993; Anpo, 1997; Nakata and Fujishima, 2012). In these processes, titanium dioxide is ofen used in the powder form and it require an additional process to remove the TiO 2 from the water afer treatment (Černigoj et al., 2006). To address this issue, TiO 2 has been coated on various materials such as tiles, glass, ce- ramics, steel, polymer, and activated carbon (Sopyan et al., 1994; Bideau et al., 1995; Yao et al., 2009). Tere are several approaches for immobilizing photocatalysts on a substrate (Akpan and Hameed, 2010), but the sol–gel method is the most frequently used method to immobilize TiO 2 because of its relatively low cost, fexibility, good homogeneity and optical properties, and low-temperature requirement for processing. Further, the method allows coating of large areas (Liu et al., 2008). It has also been observed that TiO 2 -coated materials possess self-cleaning abilities through the photo- induced hydrophilicity of TiO 2 immobilized on the surface (Wang et al., 1998). Here, we remark that the mechanisms for the photo- catalytic degradation of environmental pollutants and the surface wettability of TiO 2 under UV light appear to be governed by the different material properties of TiO 2 . Te photocatalytic properties of TiO 2 arise from the photogen- erated charge carriers that are produced when TiO 2 absorbs UV light corresponding to the band gap (Fujishima et al., 2000), while the photoinduced superhydrophilicity of TiO 2 is caused by changes in the chemical conformation on its surface when it is irradiated with UV light (Wang et al., 1997, Sakai et al., 2003, Takeuchi et al., 2005). Te photo- catalytic oxidation capability of TiO 2 is more dependent on the bulk properties while the hydrophilicity of TiO 2 under UV light is postulated as an inherent interfacial property (Lee et al., 2003). Te photoinduced hydrophilicity of TiO 2 thin flms has led to numerous practical applications such as self-cleaning materials, anti-beading, and anti-fogging glass (Fujishima et al., 2000). Received on December 30, 2014; accepted on March 24, 2015 DOI: 10.1252/jcej.14we421 Correspondence concerning this article should be addressed to E. G. Mariquit (E-mail address: egmariquit@yahoo.com). Research Paper