Industrial dye pollution remains one of the most persistent and hazardous challenges in global wastewater management. The dyes from textile and chemical manufacturing sectors are difficult to remove, non-biodegradable, and can be toxic to plants, animals, and humans. However, conventional treatment technologies for dyes often fail to efficiently purify the wastewater without significant tradeoffs.
To remedy this issue, researchers from Tohoku University developed a three-dimensional covalent organic framework (COF), TU-123, that enables highly efficient and selective removal of anionic dyes from contaminated water. The highly porous COF acts like a sponge - trapping dyes for easier separation. This work establishes a new structural blueprint for constructing highly connected imidazole-linked three-dimensional COFs. Furthermore, it opens sustainable pathways for advanced wastewater purification technologies. The study was accepted and published in the Journal of the American Chemical Society on January 23, 2026.
An emerging solution for removing dyes from wastewater is the use of porous adsorbents that can selectively capture hazardous dye molecules. COFs are attracting increasing attention as a promising solution because of their crystalline order, tunable pore structures we can tailor to our exact specifications, and chemical robustness. Most COFs explored for wastewater remediation are two-dimensional (2D), but three-dimensional (3D) COFs offer much more benefits such as enhanced structural rigidity and isotropic pore connectivity. The reason they haven't been used extensively despite their value lies in how difficult it is to construct highly connected 3D COFs with chemically stable linkages.
The research team faced this challenge head on and developed a 3D COF called TU-123. It is the first 12+3-connected three-dimensional imidazole-linked COF with aea topology, using a two-component cyclocondensation strategy between aldehyde and amine building blocks. The result is a highly ordered, permanently porous, and chemically resilient 3D network perfect for dye treatment in wastewater.
"By moving beyond the traditional multicomponent Debus-Radziszewski reaction, we have established a new route to build highly connected and chemically robust 3D imidazole-linked COFs," explains Junior Associate Professor Saikat Das (Institute of Multidisciplinary Research for Advanced Materials, Tohoku University).
The researchers put TU-123 to the test at removing a hazardous anionic dye called Acid Orange 7. They found that under neutral conditions, it exhibited the strong electrostatic capture of this dye with a maximum adsorption capacity of 495.07 mg g⁻1 and a removal efficiency exceeding 86%. The material also demonstrated rapid adsorption kinetics, excellent recyclability, and high durability in complex aqueous environments. Importantly, TU-123 also demonstrated effective dye removal from real industrial effluent samples, confirming its practical relevance for wastewater treatment applications.
"This work establishes a new structural blueprint for constructing high-connectivity imidazole-linked 3D COFs and opens sustainable pathways for advanced water purification technologies," remarks Yuichi Negishi (Institute of Multidisciplinary Research for Advanced Materials).