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

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.