van der Waals pressure assisted synthesis of solid state nanomercury from mercury salts under ambient conditions: a sustainable approach for effortless Hg(<scp>ii</scp>) removal from wastewater and safe storage thereof

The synthesis and characterisation of stable solid mercury nanoparticles (HgNPs) face significant hurdles, as the physical properties of the material under ambient conditions limit the fabrication and characterisation of the element in the nanoregime. Extremely stringent conditions (1.2 GPa or -38 °C) are mandatory for achieving mercury in the solid state. Here crystalline mercury stabilized in turbostratic nitrogen-doped graphenic matrix (t-NG) is achieved from aqueous Hg²⁺ at room temperature, using a simple procedure involving N-doped graphene oxide quantum dots (NGOQDs). Solid crystalline nanomercury formation in graphenic layers is verified by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), which is further backed by Raman spectral analysis. The solid mercury lattice exhibited rhombohedral α-phase and showed considerable crystallinity at room temperature. Excellent stability of the HgNPs lasting for months under ambient laboratory conditions warrants the scope of the system for further applications. Furthermore, the strategy furnishes a novel and efficient method for the detection and removal of the highly soluble mercury ions Hg(II) from waste water using NGOQDs. The method also offers a provision for safe storage of the species in the solid state, thus claiming advantage over traditional adsorptive removal methods, where the management of adsorbed ions remains a hurdle.