Theoretical Study on the Adsorption of Hexavalent\nChromium by Metal-Modified and Nitrogen-Doped Carbon Materials

Cr(VI)\ncan cause great harm to human beings and the environment\nand often exists in the form of HCrO<sub>4</sub>̅ in aqueous\nenvironments. The adsorption characteristics of HCrO<sub>4</sub>̅\non nitrogen-doped and iron–nickel-modified carbon substrates\nwere systematically investigated using first principles. The properties\nof electron transfer and orbital hybridization of the substrates and\nHCrO<sub>4</sub>̅ during the adsorption process were analyzed\nby electron deformation density and density of states. The electrons\nwere donated by the metal atoms and gained by the oxygen atoms involved\nin the adsorption of HCrO<sub>4</sub><sup>–</sup>. The binding\nenergies of the substrates and metal atoms were larger than the cohesive\nenergies of the metal atoms, indicating excellent structural stability.\nBoth mono- and bimetallic modifications of the carbon materials by\nFe/Ni were favorable for the adsorption of HCrO<sub>4</sub><sup>–</sup>. The increased number of doped nitrogen atoms could promote the\nadsorption. Among them, (Fe,Ni)/N–C possesses the optimal adsorption\nof HCrO<sub>4</sub><sup>–</sup>, with an adsorption energy\nof −4.64 eV. This is mainly attributed to the fact that the\nFe–Ni bimetallic atoms simultaneously participate in the electron\ntransfer and orbital hybridization, providing a new perspective for\nthe adsorption of Cr(VI) on bimetallic-modified substrates.