Selective adsorption characteristics of g-C3N4 for Hg0 and HgCl2: A DFT study and experimental verification

Abstract

The partitioning of Hg0 and HgCl2 with selective adsorbent is an essential technology for the mercury continuous emission monitoring system (Hg-CEMS), but the existing adsorbents fail to satisfy the prolonged operational demands of Hg-CEMS due to the irreversible deactivation. This work proposed a novel regenerable selective adsorbent material, g-C3N4, and delved into the selective adsorption behaviors of Hg0 and HgCl2 on the g-C3N4 using DFT calculations and experiments. The results show that g-C3N4 has a strong affinity for HgCl2, with the binding energy of −0.843 eV, whereas Hg0 is only weakly adsorbed. The electronic structure and weak interaction analysis reveal both Hg0 and HgCl2 are coupled to g-C3N4 via van der Waals. Further, COHP calculation demonstrates that the adsorption of Hg0 and HgCl2 on g-C3N4 is essentially the consequence of polyatomic co-binding and the parallel triatomic structure of HgCl2, which binds to more C/N atoms, thereby leading to the greater binding energy. The experiments confirmed the effective capability of g-C3N4 in separating Hg0 and HgCl2, along with its thermal regeneration potential. It maintains a breakthrough rate of over 98 % for Hg0 and less than 1.6 % for HgCl2. This work updates the conventional chemical adsorption-based methods for the separation of Hg0 and HgCl2, enhances the comprehension of separating both Hg0 and HgCl2 while concurrently broadening the understanding of the interaction between g-C3N4 and small molecules.