Porphyrin COF and its mechanical pressing-prepared carbon fiber hybrid membrane for ratiometric detection, removal and enrichment of Cd2

Abstract

A nitrogen (N), oxygen (O)-rich porphyrin-based covalent organic framework (COF), in which interlayer porphyrin molecules are vertically stacked, is prepared and characterized. As-prepared N,O-rich TpTph COF shows a high adsorption capacity for Cd²⁺ due to the abundant coordination sites. More interesting, it is found that the formation of COF enlarges the porphyrin ring center space, thus facilitating the Cd²⁺coordination, and the resulting optical signal changes make the ratiometric detection of Cd²⁺ possible. Furthermore, using carbon fiber (CF) filaments, which are obtained from low cost and easy-to-obtain actived carbon mask, as support, porphyrin COF-based CF@TpTph membrane is prepared through in-situ growth of COF on the support followed by simple mechanical pressing. The CF@TpTph membrane is demonstrated to work well for both Cd²⁺ removal and enrichment from soil and water samples, and shows the advantages of ease of handling, robust stability, reduced secondary pollution risk to samples, and good reusability. This work provides a powerful tool for Cd²⁺ removal and enrichment, exhibits that preparing porphyrin-based COFs is a feasible way to promote the interactions between porphyrin ring and Cd²⁺, and demonstrates that mechanical pressing is a promising strategy for the design of COF-based monolithic materials to promote the practical applications of COFs.

Keywords: COF membrane; Cd(2+); Porphyrin COF; Ratiometric detection; Removal and enrichment.