Adsorption of sulfur into an alkynyl-based covalent organic framework for mercury removal

Highly efficient removal of Hg(II) has been previously achieved through the adsorption by functionalized covalent organic frameworks (COFs). Among these COFs, thioether groups need to be deliberately introduced into the pores of COFs through either a bottom-up synthesis or post-synthesis strategy. Herein, we report a simple mercury removal strategy that used a stable alkynyl (-C equivalent to C-) based covalent organic framework (TP-EDDA COF) as an adsorbent for Hg(II) removal. Sulfur vapor was first adsorbed by the TP-EDDA COF due to the van der Waals interaction between adsorbed sulfur and alkynyl groups. The Hg(II) removal capability was then evaluated for the sulfur loaded TP-EDDA COF. Our results exhibited a good Hg(II) removal performance for the sulfur loaded TP-EDDA COF. It was deduced that s center dot center dot center dot pi interaction between sulfur atom and the alkynyl groups of the COF skeleton caused an increase in the electron density of sulfur and the electronegative sulfur atoms acted as a soft acid to accept soft-basic Hg(II). This strategy provides a convenient platform for COFs to cope with environmental issues.