Thio-groups decorated covalent triazine frameworks for selective mercury removal

Covalent triazine frameworks (CTFs) as a kind of covalent organic framework (COF) materials show great potential for practical application by virtue of their high stability and facile large-scale synthesis. In this work, we developed three CTFs (MSCTF-1, MSCTF-2, and xSCTF-2) of different pore size decorated with S-groups using different functionalization methods for achieving selective Hg2+ removal from aqueous solutions. The material structures were comprehensively studied by gas adsorption, IR and XPS, etc. Among them, the MSCTF-2 with 24.45% S content showed the highest Hg2+ adsorption capacity of 840.5 mg g(-1), while MSCTF-1 exhibiting much larger distribution coefficient of 1.67 x 10(8) mL g(-1) renders an exceptionally high efficiency for reducing the concentration of Hg2+ contaminated water to less than 0.03 mu g L-1. Moreover, the MSCTFs show distinct features of: (i) high selectivity toward Hg2+ over various transition metal ions; (ii) high stability over a wide pH range from pH 1 to 12; and (iii) good recyclability with 94% of Hg2+ removal over five consecutive cycles. The Hg2+ adsorption on functionalized CTFs followed pseudo-second-order kinetics and Langmuir isotherm. Our results revealed the material structure-performance relationship that the adsorption capacities depend on the binding site density whereas the distribution coefficient is essential to the removal efficiency.

Automated summary

In this study, three Covalent Triazine Frameworks (CTFs) decorated with S-groups were developed for selective removal of Hg2+ from aqueous solutions. Among them, MSCTF-2 showed the highest Hg2+ adsorption capacity, while MSCTF-1 exhibited exceptional efficiency for reducing Hg2+ concentration. The adsorption process followed pseudo-second-order kinetics and Langmuir isotherm, with adsorption capacities dependent on binding site density and distribution coefficient being essential to removal efficiency.