Direct synthesis of N-doped porous carbon materials from EDTA dipotassium salt for the rapid adsorption of hexavalent chromium from aqueous solutions

Abstract

The development of versatile, sustainable, and efficient N-doped porous carbon materials for the removal of trace contaminants has attracted considerable interest. Traditional methods for preparing porous carbon materials often involve the use of potent and hazardous activating agents such as KOH, H₃PO₄, and ZnCl₂, which not only restrict the choice of production equipment but also pose environmental hazards. In this study, we introduce a self-activating method to synthesize N-doped porous carbon materials specifically designed for the removal of hexavalent chromium [Cr(VI)]. This approach involves the direct carbonization of EDTA dipotassium salt at different temperatures under a N₂ atmosphere without any activators. The influence of adsorbent dosages, pH, temperature, initial concentration of Cr(VI) ions, and competing ions on the adsorption behavior of Cr(VI) was systematically examined. The findings reveal that the optimal conditions for adsorption are a pH of 2 and an adsorbent dosage of 1.0 g L⁻¹. Furthermore, Cr(VI) rapid adsorption onto N-doped porous carbon follows Freundlich isotherm and pseudo-second-order kinetic models. Notably, adsorbent KNC-700 exhibits an exceptional specific surface area of 2124.6 m² g⁻¹ and a well-defined pore structure. It shows maximum adsorption capacity for Cr(VI) of 270.3 mg g⁻¹ at 328 K with an equilibrium time of 20 min. Further mechanistic investigations suggest that efficient uptake of Cr(VI) primarily occurs through physico chemical adsorption involving electrostatic interactions and reduction reactions. This study provides novel insights into the preparation of porous carbon materials and their potential applications in addressing Cr(VI) pollution.