Synthesis of conjugated microporous polymers rich in sulfonic acid groups for the highly efficient adsorption of Cs+

Conjugated microporous polymers (CMPs) with extended π-conjugated systems and permanent microporous scaffolders have broad application prospects in the treatment of radionuclides in nuclear wastewater. Herein, the Sonogashira–Hagihara coupling process was employed to generate three CMPs, called CMP1–3. CMP1S–3S with different degrees of sulfonation were produced and employed for Cs+ ion adsorption by adjusting the sulfonation time using chlorosulfonic acid as the sulfonating agent. This is the first attempt to apply CMPs containing sulfonic acid groups to Cs+ ion adsorption, which show excellent adsorption properties. CMP1S-48 with the highest surface sulfonic acid group density exhibited the fastest adsorption rate, and it reached adsorption equilibrium on Cs+ ion in an aqueous solution under 1 min. The adsorption process corresponded to the Freundlich isotherm model of multilayer adsorption, with an adsorption capacity of up to 288.1 mg g−1. Compare with CMP2S-48 and CMP3S-48, CMP1S-48 with more sulfonic acid groups shows the highest adsorption capacity. Moreover, the selectivity of CMP1S-48 adsorbing Cs+ ion was exceeded high. Notably, the adsorption mechanism of Cs+ ion by CMP1S–3S involved ion exchange with H+ in the sulfonic acid groups, as well as its complexation and electrostatic attraction with the sulfonic acid groups. This work opens up a new way for CMPs rich in sulfonic acid groups to treat Cs+ ion-contaminated water sources.