Graphitic carbon nitride nanosheet as an excellent compound for the adsorption of calcium and magnesium ions: theoretical and experimental studies

In this work, the removal of calcium (Ca2+) and magnesium (Mg2+) ions were studied using graphitic carbon nitride (g-C3N4) nanosheet as an adsorbent from aqueous solutions. In experimental studies, the effects of various adsorption parameters were investigated by batch method culture including pH, initial Ca2+ and Mg2+ concentrations, temperature, time, and adsorbent mass. The best results were obtained at pH=8.50, 0.05 g of g-C3N4, 90 min, 10 ppm of ion concentration, 23.80 mg g-1 of maximum adsorption capacity for Ca2+, and pH=9, 0.05 g of g-C3N4, 60 min, 15 ppm of ion concentration, 40.00 mg g-1 maximum adsorption capacity for Mg2+ ion. The adsorption of calcium and magnesium ions obeyed the Langmuir model on adsorbent. In theoretical study, g-C3N4 nanosheet as an interesting material was studied by first-principle calculation using the Quantum Espresso package. The Ca2+ and Mg2+ ions were located at different positions on g-C3N4 nanosheet to obtain the stable configuration. The Eads, HOMO, LUMO, Eg, band structure, DOS and PDOS plots were investigated at stable configuration of g-C3N4 nanosheet. The adsorption energy (Eads) was calculated -15.55 and -26.24 eV for Ca2+ and Mg2+ ions, respectively. Further, the results indicated that Mg2+can be located at the center of the porous g-C3N4 nanosheet, which the adsorption of Mg2+ on surface of g-C3N4 nanosheet was stronger than that of Ca2+ ion. Theoretical and experimental data confirmed each other’s findings. The adsorption of Ca2+ and Mg2+ ions was shown to be simple, high-yield, eco-friendly, and economical performance from aqueous solutions using g-C3N4 nanosheet