DFT and experimental study of elemental mercury (Hg⁰) removal by 2D-g-C₃N₄

Abstract

2D-g-C3N4 nanosheet was prepared and employed for the adsorption of elemental mercury (Hg0). The g-C3N4 was analyzed through X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FT-IR) methods, and the results showed that the prepared sample was well-defined 2D-nanosheet. The 2D-g-C3N4 sorbent exhibited a high Hg0 removal efficiency (> 90%) at the condition of temperature 120 °C. To investigate the mechanism of Hg0 adsorption on the 2D-g-C3N4 surface, corresponding theoretical exploration based on the first principle prediction and X-ray photoelectron spectroscopy (XPS) test was implemented. The DFT calculation results showed that Hg0 was strongly bound to the B1 site of the g-C3N4 surface with an adsorption energy change of -162.2 kJ mol−1, the equilibrium distance of Hg-C was 3.473 Å, and electron transfer between Hg and C atoms was 0.02. The results of XPS showed the main species of mercury was HgO on the surface of 2D-g-C3N4 sample and the interaction between C3N4 surface and Hg0 was physisorption. This study provides a demonstration of proof-of-concept demonstration that g-C3N4 is a promising sorbent capable of capturing Hg0, and presents in-depth understanding of Hg0 adsorption mechanism on 2D-g-C3N4 sorbent.