An anionic Covalent Organic Framework for the removal of Al 3+ from contaminated water

Aluminum contamination in water is a critical environmental concern due to its widespread industrial usage and potential toxicity to both humans and ecosystems. Traditional aluminum removal methods such as chemical precipitation, ion exchange, and membrane filtration often present significant limitations, including high operational costs, secondary pollution, or membrane fouling. In this study, we explore the application of ionic covalent organic frameworks (iCOFs), specifically TpPa-SO₃H and TpPa-SO₃Na, as promising materials for the efficient and selective removal of Al³⁺ from aqueous solutions. These β-ketoenamine-linked COFs exhibit high chemical stability, large surface areas, and tunable porosity, making them particularly suitable for harsh water treatment environments. We report the first use of these anionic COFs for aluminum adsorption, achieving rapid uptake kinetics and high removal efficiencies under both static and dynamic conditions. Batch experiments demonstrated adsorption efficiencies exceeding 95% within minutes, while column experiments under continuous flow achieved over 99% removal for more than three hours. Recyclability tests confirmed the robustness of the material, with minimal loss of performance over five cycles. Additionally, the TpPa-SO₃Na was tested on real water samples, yielding removal efficiencies of up to 85%. The adsorption mechanism was investigated in-depth, revealing strong electrostatic interactions and selective binding with Al³⁺ ions. These findings highlight the potential of iCOFs as a sustainable and effective alternative to conventional aluminum removal technologies, advancing current water purification strategies and contributing to the development of next-generation materials for clean water applications.