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.

This work focuses on the photocatalytic removal of recalcitrant organic pollutants in water treatment. Based on facile precipitation reaction, we fabricated a photocatalyst (PbCrO₄) in single crystals that present evident response to visible light and employed the catalyst in the photocatalytic decomposition of microcystin-LR (MC-LR). In the degradation test using the nanorods with prepared PbCrO₄ photocatalyst, a 100% removal efficiency (27 min reaction) and a kinetics constant of 0.1356 min⁻¹ were achieved. Such a high performance of PbCrO₄ in photocatalytic conversion of MC-LR was ascribed to its high carrier separation efficiency, positive valence band (VB) position, and good delocalization of VB and conduction band (CB). The test of electron spin-resonance resonance (ESR) demonstrated that excessive free [rad]OH radicals were produced during the PbCrO₄ photocatalysis of MC-LR. The density functional theory (DFT) and LC/MS/MS technology were employed to ascertain the intermediates during the MC-LR photocatalytic degradation. The major intermediates were resulted from the attack of hydroxyl radicals to the ADDA side chains of MC-LR structure. This study provides a proof-of-concept strategy to develop effective photocatalysts to efficiently produce [rad]OH radicals for the visible-light induced photocatalytic degradation of MC-LR in water.

To guarantee drinking water security, removal of bromate (BrO₃ ⁻) has garnered plenty of attention in water treatment. In current study, we have developed a novel conjugated donor-acceptor (D-A) photocatalyst (4,4′'-bis(diphenylamino)-[1,1′:4′,1′'-terphenyl]-2′,5′-dicarbaldehyde, BDTD) with supramolecule architecture assembling via intermolecular C–H···O hydrogen bonds and C–H···π interactions. Both diffuse reflectance spectrum (DRS) and density functional theoretical (DFT) calculations gave the bandgap of E_g = 2.21 eV, clearly indicating the visible-light response of BDTD supramolecule. The calculations showed that BDTD supramolecule could induce nearly 100% removal of BrO₃ ⁻ stably at pH-neutral condition driven by visible light, accounting for a first-order kinetic constant being one order of magnitude higher than most of the photocatalysts previous reported. As demonstrated by our electron scavenger experiment and DFT calculations, the BDTD supramolecule should undergo the photocatalytic reduction of BrO₃ ⁻ through direct reduced by the lowest unoccupied molecular orbital of conduction band (potential of −1.705 V versus standard hydrogen electrode) electron. The BDTD supramolecule may serve as an attractive photocatalyst by virtue of response to visible light, efficient charge transfer and separation as well as high photocatalytic activity, which will make the removal of BrO₃ ⁻ in water much easier, more economical and more sustainable.