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

Cr(VI) can cause great harm to human beings and the environment and often exists in the form of HCrO₄̅ in aqueous environments. The adsorption characteristics of HCrO₄̅ on nitrogen-doped and iron-nickel-modified carbon substrates were systematically investigated using first principles. The properties of electron transfer and orbital hybridization of the substrates and HCrO₄̅ during the adsorption process were analyzed by electron deformation density and density of states. The electrons were donated by the metal atoms and gained by the oxygen atoms involved in the adsorption of HCrO₄^-. The binding energies of the substrates and metal atoms were larger than the cohesive energies of the metal atoms, indicating excellent structural stability. Both mono- and bimetallic modifications of the carbon materials by Fe/Ni were favorable for the adsorption of HCrO₄^-. The increased number of doped nitrogen atoms could promote the adsorption. Among them, (Fe,Ni)/N-C possesses the optimal adsorption of HCrO₄^-, with an adsorption energy of -4.64 eV. This is mainly attributed to the fact that the Fe-Ni bimetallic atoms simultaneously participate in the electron transfer and orbital hybridization, providing a new perspective for the adsorption of Cr(VI) on bimetallic-modified substrates.