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[Display omitted] • A novel g-C 3 N 4 is developed as efficient selective adsorbent for HgCl 2 and Hg0. • EDD and DOS reveals the binding of g-C 3 N 4 with HgCl 2 and Hg0 is not chemical interaction. • QTAIM and IRI prove the binding depends on van der Waals force. • COHP confirms polyatomic co-binding is responsible for the separation of HgCl 2 and Hg0. • g-C 3 N 4 possesses potential for thermal regeneration. The partitioning of Hg0 and HgCl 2 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-C 3 N 4 , and delved into the selective adsorption behaviors of Hg0 and HgCl 2 on the g-C 3 N 4 using DFT calculations and experiments. The results show that g-C 3 N 4 has a strong affinity for HgCl 2 , 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 HgCl 2 are coupled to g-C 3 N 4 via van der Waals. Further, COHP calculation demonstrates that the adsorption of Hg0 and HgCl 2 on g-C 3 N 4 is essentially the consequence of polyatomic co-binding and the parallel triatomic structure of HgCl 2 , which binds to more C/N atoms, thereby leading to the greater binding energy. The experiments confirmed the effective capability of g-C 3 N 4 in separating Hg0 and HgCl 2 , along with its thermal regeneration potential. It maintains a breakthrough rate of over 98 % for Hg0 and less than 1.6 % for HgCl 2. This work updates the conventional chemical adsorption-based methods for the separation of Hg0 and HgCl 2 , enhances the comprehension of separating both Hg0 and HgCl 2 while concurrently broadening the understanding of the interaction between g-C 3 N 4 and small molecules. [ABSTRACT FROM AUTHOR]