Water Purification in Dark Conditions Using PhotocatalyticLight-leakage Type Plastic Optical Fiber Haruki Nagakawa, 1 Takuya Sato, 1 Goki Takahashi, 1 Tsuyoshi Ochiai, 2,3 Rei Furukawa, 4 and Morio Nagata* 1 1 Department of Industrial Chemistry, Graduate School of Engineering, Tokyo University of Science, 12-1 Ichigayafunagawara-cho, Shinjuku-ku, Tokyo 162-0826, Japan 2 Materials Analysis Group, Kawasaki Technical Support Department, Local Independent Administrative Agency Kanagawa Institute of Industrial Science and TEChnology (KISTEC), Kanagawa 213-0012, Japan 3 Photocatalysis International Research Center, Tokyo University of Science, Chiba 278-8510, Japan 4 The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan E-mail: nagata@ci.tus.ac.jp In this study, we fabricated a device that can be used for water purification in dark areas by combining a light-leakage type plastic opticalfiber with a photocatalyst. The light-leakage type fiber was prepared by adding a scattering agent to the fiber core, and the titanium dioxide photocatalyst was composited by a two-layer coating method. Photocatalytic decomposition of methylene blue was performed by introducing light into the fiber without direct light irradiation. Keywords: Plastic optical fiber | Photocatalyst | Water purification Photocatalytic reactions continue to attract attention as clean processes because they use light energy to advance various chemical reactions. The range of photocatalysis applications iswide, and it has been put into practical use and researched in many fields such as water splitting for energy production, 1,2 self-cleaning, 3 and environmental purification. 4,5 The first step in a photocatalytic reaction is to irradiate a semiconductor with light. Carriers excited by the light energy then diffuse to the semiconductor surface and cause a chemical reaction to occur. Therefore, the introduction of light is essential for photocatalysis. Due to this limitation, photocatalytic technology is rarely used in locations that cannot be reached by light. However, there are many dark environments that require long- term and continuous cleanliness, such as for the purification of contaminated water, water pipes, and storage tanks. Therefore, methods for employing photocatalytic reactions in unlit areas are in demand. To introduce light into a dark place, one approach is to install a light source. However, if the light source requires power, energy is consumed when light is irradiated, and thus the meritof using photocatalysis is lost. Therefore, the introduction of sunlight and ambient light has been studied instead. Composites of opticalfibers have been devised as one such method. Thus far, reported photocatalystopticalfiber composite devices have consisted of asilica core fiber coated with a photocatalyst. 68 In particular, it has been confirmed that light leakage realized by damaging the cladding portion of the fiber 9 or using side-growing opticalfibers 10 can advance photocatalytic reaction. However, silica fiber has limitations such as weakness to bending, small core diameter, poor propagation oflarge amounts of light, and difficult processing. In order to overcome these drawbacks, H. Joo et al. combined a plastic opticalfiber (POF) with a photocatalyst. 11 They realized light leakage from POF by dissolving the cladding with acetone and used the resulting fiber for photocatalytic reactions. However, this method causes an increase in device manufacturing steps and controlled immersion time in an organic solvent. To resolve these issues, we aimed to develop a method for realizing light leakage with the cladding remaining and applying it to photo- catalytic reactions. First, a POF was fabricated using a method we reported previously. 12 The light-leakage type plastic optical fiber (L-POF) was then prepared by adding a light-scattering agent to the core of the POF, and finally, the photocatalytic L-POF was prepared by applying a photocatalyst to the fiber surface. By using the POF, we have succeeded in fabricating a device that has the advantages of easy processing, low cost, large core diameter, and the ability to propagate large amounts of light. In addition, it was confirmed that methylene blue decomposition proceeded in the dark owing to the introduction of light through the photocatalytic L-POF. Therefore, a device that combines the L-POF and a photocatalyst is suitable for organic matter decomposition in dark places. Since the photo- catalyst coated on the POF is irradiated with light from inside the fiber, the light absorption is not blocked even when the contaminant is adsorbed. In addition, the fiber shape of the photocatalytic device provides a larger reaction area. The L-POF was prepared by applying a previously reported method. 12 Methyl methacrylate (179 g, MMA, Mitsubishi Chemical) was polymerized into a tubular geometry with a closed end (inner/outer diameter, 14.7/22.0 mm; length, 600 mm). Polymerization was performed at 70 °C using 854 ¯Lof t- butyl peroxy-2-ethylhexanoate (Wako Pure Chemical Industries) and 561 ¯Lof 1-butanethiol (NOF Corporation) as the polymer- ization initiator and chain transfer agent, respectively. A poly- MMA (PMMA) tube was obtained by spinning the container during polymerization. This PMMA tube was later used as the fiber cladding. A solution of 70g of MMA and 7.42 g of diphenyl disulfide (Tokyo Chemical Industry) was prepared as the core material. The solution was placed in the center cavity of the PMMA tube prepared in advance and then polymerized at 70 °C in a 0.6MPa nitrogen atmosphere. Di-t-butyl peroxide (14 ¯L, Wako Pure Chemical Industries) and 231 ¯Lof 1- dodecanethiol (NOF Corporation) were used as the polymeriza- tion initiator and chain transfer agent, respectively. Furthermore, 3.87 mg of titanium dioxide (TiO 2 ) powder (P25, Nippon Aerosil), a material having a high refractive index, was added to the solution as the scattering agent. The obtained preform was heat-drawn ina furnace with a maximum internal temperature of Received: October 23, 2019 | Accepted: December 13, 2019 | Web Released: December 19, 2019 CL-190788 Chem. Lett. 2020, 49, 199–202 | doi:10.1246/cl.190788 © 2020 The Chemical Society of Japan | 199