Riken Technos and Niihama College Establish New Evaluation Method for Water Treatment Photocatalysts Using Deep UV Absorbance

Riken Technos Corp. (Headquarters: Chiyoda-ku, Tokyo; President: Kazuaki Tokiwa), through joint research with Niihama National College of Technology (Niihama City, Ehime Prefecture; Principal: Akihiro Tokai), has established a new evaluation method to more accurately assess the performance of water treatment photocatalysts.

While developing iron oxide photocatalysts supported on porous bodies, the team discovered that conventional evaluation—relying solely on 'decolorization' (decrease in visible light absorbance)—could fail to accurately judge the decomposition of organic substances. To address this, they introduced an evaluation of absorbance changes in the deep ultraviolet region (around 230nm), allowing for a multi-faceted assessment of both color disappearance and the actual decomposition of organic frameworks or the formation of intermediates.

### 1. Research Background In water treatment technologies using photocatalysts, decolorization (reduced absorbance in the 400–700nm range) has been the standard for judging material decomposition. However, many persistent organic pollutants possess stable organic structures like aromatic rings. Even if only part of the chromophore changes, decolorization can occur while the toxic organic skeleton remains in the water. This posed a challenge for accurately judging the true degree of decomposition.

### 2. Features of the New Evaluation Method - **(1) Dual-Indicator Evaluation (Visible & Deep-UV)**: In addition to visible light, changes in absorbance in the deep-UV range (200–250nm) are evaluated. This range corresponds to π–π* transitions of aromatic rings and low-molecular-weight organics, making it effective for tracking skeletal residue. - **(2) Distinguishing Decolorization from Decomposition**: If only visible absorbance drops without changes in deep-UV, it is judged as mere decolorization. A drop or shift in the deep-UV range suggests structural changes in the organic framework or the progress of decomposition. - **(3) Validation through Joint Research**: Verification using multiple photocatalysts and persistent dyes confirmed that this method can clearly distinguish differences in material performance.

### 3. Significance of the Method This achievement enables essential performance evaluation independent of superficial changes. It facilitates the comparison of true decomposition capabilities between different materials, serving as a vital foundational technology to enhance R&D quality and practical implementation in the water treatment sector.

### 4. Future Outlook Using this evaluation method as a foundation, Riken Technos aims to develop photocatalysts and treatment processes with even higher performance, striving for the advancement and social implementation of water treatment technologies.