CTAB assisted evaporation-induced self-assembly to construct imidazolium-based hierarchical porous covalent organic polymers for ReO4-/TcO4-removal

Evaporation-induced self-assembly method (EISA) was a facile and reliable method to synthesize porous materials. Herein, we report a kind of hierarchical porous ionic liquid covalent organic polymers (HPnDNH2) under cetyltrimethylammonium bromide (CTAB) assisted by EISA for ReO4- /TcO4- removal. Unlike covalent organic frameworks (COFs), which usually needed to be prepared in a closed environment or with a long reaction time, HPnDNH2 in this study was prepared within 1 h in an open environment. It was worth noting that CTAB not only served as a soft template for forming pore, but also induced ordered structure, which was verified by SEM, TEM, and Gas sorption. Benefit from its hierarchical pore structure, HPnDNH2 exhibited higher adsorption capacity (690.0 mg g-1 for HP1DNH2 and 808.7 mg g-1 for HP1.5DNH2) and faster kinetics for ReO4- /TcO4- than 1DNH2 (without employing CTAB). Additionally, the material used to remove TcO4- from alkaline nuclear waste was seldom reported, because combining features of alkali resistance and high uptake selectivity was not easy to achieve. In this study, in the case of HP1DNH2, it displayed outstanding adsorption efficiency toward aqueous ReO4- /TcO4- in 1 mol L-1 NaOH solution (92%) and simulated Savannah River Site High-level waste (SRS HLW) melter recycle stream (98%), which could be a potentially excellent nuclear waste adsorbing material.

Automated summary

Evaporation-induced self-assembly method (EISA) is a reliable and efficient technique for synthesizing porous materials. In this study, we successfully prepared hierarchical porous ionic liquid covalent organic polymers (HPnDNH2) for the removal of ReO4- /TcO4- using CTAB-assisted EISA. The CTAB not only acted as a soft template for pore formation, but also induced an ordered structure in the material. The HPnDNH2 showed higher adsorption capacity and faster kinetics compared to 1DNH2, and exhibited outstanding efficiency in removing ReO4- /TcO4- from alkaline nuclear waste.