Preparation and model construction of novel 2D nanocomposite of Zn-P-GCNN and its mechanisms of synergistic adsorption for Cu(II) and methylene blue

In this study, a novel two-dimensional (2D) ultrathin Zn-P-g-C3N4 nanocomposite (Zn-P-GCNN) with a large specific surface area was synthesized by using graphitic carbon nitride (GCN) as the raw material and P, Zn as the dopants. The physicochemical properties of the synthesized nanocomposite were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet–visible (UV) spectroscopy, fluorescence (PL) spectroscopy, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and first-principles calculations. The results revealed that compared with GCN, the thickness of Zn-P-GCNN decreased from 22 to 5 nm, and the specific surface area increased from 26.98 to 96.85 g/m2. The adsorption capacity of Zn-P-GCNN for Cu(II) and methylene blue (MB) reached 114.68 and 265.50 mg/g, respectively, under the optimal adsorption conditions (25 mg adsorbent, pH 5.8, 25 °C, 60 min). To explore the synergistic adsorption effect of Cu(II) and MB, the adsorption kinetics, isothermal curves, and regeneration performance of Zn-P-GCNN were investigated. Even after five cycles, the adsorption rates of MB and Cu(II) remained above 94.0% and 57.0%, respectively. This indicated the potential of Zn-P-GCNN as a cost-effective and convenient adsorbent. Further, first-principles calculations based on the density functional theory (DFT) were utilized to establish an adsorption model, which can accurately predict the distribution, conformational changes, and adsorption energy of MB and Cu(II) on the adsorbents. The adsorption energy of one MB molecule on Zn-P-GCNN was lower than that on GCN, due to which the adsorption capacity of Zn-P-GCNN was improved. Overall, this study proposed a novel 2D Zn-P-GCNN, which can be potentially used for the treatment of environmental pollutants such as heavy metals and organic dyes in sewage environments.