Adsorption of typical dyes in water by sponge based covalent organic frameworks: Pore size and mechanism

This study addressed the ambiguity surrounding the relationship between the pore size of covalent organic frameworks (COFs) and their adsorption capacity and rate. To achieve this, we synthesized COFs with five distinct pore sizes (COF1-COF5) and conducted a comprehensive analysis using kinetic models. Our findings indicated that the adsorption capacity and rate of methyl orange (MO) increased linearly with the pore size of COFs, from 1.25 nm to 2.57 nm. Notably, COF3, with a pore size of 2.57 nm, exhibited the highest adsorption performance for MO, boasting an impressive capacity of 43.07 mg/g. Furthermore, we tackled the challenge of COFs powder recovery by employing a one-pot synthesis method to create SP-COFs, where COFs powder was loaded onto polyurethane sponge. Through rigorous adsorption and analytical experiments, we demonstrated that SP-COF3 achieved rapid recovery while efficiently adsorbing MO, maintaining a high removal efficiency of over 95% even after 8 reuse cycles. The mechanism underlying MO adsorption on SP-COF3 was attributed to electrostatic interaction and hydrogen bonding, with the possibility of π-π interaction also being considered. Overall, this study provides valuable new insights into the tailored synthesis of COFs with specific structures and functionalities, shedding light on the crucial relationship between pore size and adsorption behavior. The development of SP-COFs presents a promising approach to enhance the practical application of COFs as highly efficient adsorbents.