Effect of coexisting trivalent aluminum on the adsorption of hexavalent chromium on sp2 carbon

Abstract

The analysis of the influence of coexisting ion impurities on the adsorption behavior of Cr6+ on activated carbon at microscopic interfaces should be highlighted. Based on the research background on the adsorption treatment for waste solutions of chromic anhydride, this study reveals that coexisting Al3+ affects the adsorption behavior of Cr6+ on sp2 carbon structure-containing defects, as evidenced by density functional theory calculations. After conducting electronic environment analyses based on isolated Al3+–Cr2O72− coordination and its adsorption models, the Al3+ ion acts as an electron relay station that srapidly transfer the electrons of the 2p orbital of the ortho-carbon atoms to Cr2O72− owing to the saturation of its own p orbital. These findings lead to two conclusions: (i) the facilitated reduction of Cr6+ and its positive charge neutralized by approximately 0.16 Coulomp, and (ii) the increased adsorption energy of Cr2O72− by 3.0 % and 14.6 % on the unelectron-neutralized and electron-neutralized (002) plane of sp2 C-containing defects, respectively, owing to the presence of Al3+. This is attributed to the decreased in 0.089 Hartree Gap value resulting from the energy change of the molecular orbital after Al3+ stable coordination with Cr2O72−. Therefore, the reduced energy barrier facilitates the electron transfer from the 2p orbital of the edge carbon atom to the O–Al–O bridge via the Al3+ bridge.