Performance and mechanisms of Cr(VI) removal by nano-MnO2 with different lattices

Currently, Cr(VI) pollution of water poses a major threat worldwide. In this study, alpha-MnO2 and ,B-MnO2 with different lattices were prepared to remove Cr(VI) from an aqueous solution. alpha-MnO2 could remove up to 92% of Cr(VI), which was higher than that of ,B-MnO2. According to the Brunauer, Emmett and Teller and X-ray photoelectron spectrometry results, large pores, large surface area, and abundant func-tional groups of alpha-MnO2 were observed, which contributed to the high removal rate of Cr(VI). The Cr(VI) reduction occurred with nano-MnO2, which was confirmed by the results of electrochemistry, density functional theory calculations, and X-ray absorption fine structure. alpha-MnO2 contained large amounts of Mn(II) and Mn(III), which were oxidized through the reduction of Cr(VI), the formation of stable metal salts, and surface complexation. After the Cr(VI) treatment, the bond lengths of the Mn-O and Mn-Mn shells were shortened, and the peak intensity was reduced, which indicated a change in the valence state of the Mn ion. In conclusion, the mechanism of Cr(VI) removal by nano-MnO2 involves a combination of reduction, complexation, and electrostatic adsorption. Our results were helpful for understanding the process of Cr(VI) removal by nano-MnO2.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

In this study, alpha-MnO2 and beta-MnO2 were prepared to remove Cr(VI) from water. It was found that alpha-MnO2 exhibited a higher removal rate of 92% compared to beta-MnO2. The presence of large pores, high surface area, and abundant functional groups in alpha-MnO2 contributed to its superior performance in removing Cr(VI). The findings of this study provide valuable insights into the mechanism of Cr(VI) removal by nano-MnO2.