Development of evaluation method for photocatalytic ability by ion chromatography combined with a flow-type reactor: Application to immobilized photocatalyst materials prepared by double-layer coating method

Abstract In this study, an inline method to effectively utilize photocatalytic materials for water-purification, comprising a flow reactor (FR) connected to an ion chromatography (IC) system, denoted as FR-IC, has been developed to accurately evaluate the performance of photocatalyst-coated substrates. This system is essential for determining not only indicator decomposition, but also byproduct behavior. Small portions (30 μL) of the 50-mL test solution were collected from the FR using a flow cell input and automatically injected into the IC for chromatographic analysis at regular intervals. The stable photocatalytic ability of materials comprising TiO2 photocatalyst coated onto substrates, such as glass beads, glass plate, and stainless-steel wire mesh, have also been demonstrated using the FR-IC system. These materials were prepared using the double-layer coating (DLC) method developed in our laboratory. The performances of these materials were evaluated by FR-IC using dimethyl sulfoxide (DMSO) as the radical scavenger and index pollutant. FR-IC enabled monitoring of the UV-light-induced decomposition of DMSO and the formation of byproducts, such as methane sulfonate (MSO) and sulfate (SA). Durability testing of the photocatalyst substrates prepared by the DLC method over ten repeat cycles of MSO formation from DMSO decomposition showed stable reactions, compared with a TiO2 monolayer-coated substrate. These materials showed stable photoactivity for water purification. Furthermore, this system showed that the substrate-immobilized photocatalyst adsorbed the derivatives during UV irradiation. Therefore, the selection of substrate coated with the photocatalyst was related to the water purification performance.