Effect of coexisting trivalent aluminum on the adsorption of hexavalent chromium on sp 2 carbon

The analysis of the influence of coexisting ion impurities on the adsorption behavior of Cr 6+ 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 Al 3+ affects the adsorption behavior of Cr 6+ on sp 2 carbon structure -containing defects, as evidenced by density functional theory calculations. After conducting electronic environment analyses based on isolated Al 3+ -Cr 2 O 7 2- coordination and its adsorption models, the Al 3+ ion acts as an electron relay station that srapidly transfer the electrons of the 2p orbital of the ortho -carbon atoms to Cr 2 O 7 2- owing to the saturation of its own p orbital. These findings lead to two conclusions: (i) the facilitated reduction of Cr 6+ and its positive charge neutralized by approximately 0.16 Coulomp, and (ii) the increased adsorption energy of Cr 2 O 7 2- by 3.0 % and 14.6 % on the unelectron-neutralized and electronneutralized (002) plane of sp 2 C -containing defects, respectively, owing to the presence of Al 3+ . This is attributed to the decreased in 0.089 Hartree Gap value resulting from the energy change of the molecular orbital after Al 3+ stable coordination with Cr 2 O 7 2- . 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 Al 3+ bridge.