Large-scale preparation of N-doped microporous-dominated carbon-based adsorbents for efficient removal of Chromium(VI): The synergistic effect of different nitrogen configurations

Carbon-based adsorbents with abundant resources, environmental friendliness, and sufficient adsorption sites have broad application prospects for efficient removal of Chromium (Cr(VI)) in aquatic environment. Pursuing a heavy metal adsorption material and advancing it from the laboratory to the actual water environment are of great importance. Herein, we developed a general synthesis strategy for large-scale preparation of N-doped microporous-dominated carbon-based adsorbents (NC-s) via a direct pyrolysis process of ethylene diamine tetraacetic acid tetrasodium. The NC-s samples had abundant microporous, different nitrogen configurations and large specific surface area (503 m2 g-1). Due to these advantages, the NC sample prepared at 800 °C (NC-800) possessed high adsorption capacity toward Cr(VI) (167.3 mg g-1) toward Cr(VI), fast adsorption process (180 min), and good reusability. Through specific experiments and density functional theory (DFT) calculations, we proposed that the adsorption mechanism of NC-s samples was primarily determined by the ion exchange/electrostatic attraction-reduction-complexation synergy, and the mechanism included adsorption-reduction of Cr(VI) and immobilization of Cr(III). Graphitic-N and pyridinic-N adsorbed Cr(VI) in solution mainly by electrostatic attraction, while pyrrolic-N mainly reduced the toxicity primarily by reducing Cr(VI) to Cr(III). These insights prove that the nitrogen-doped porous carbon-based adsorbents prepared in this study can effectively reduce Cr(VI) pollution in water environment.