Activation or passivation: Influence of halogen dopant (F, Cl, Br) on photothermal activity of Mn2O3 in degrading toluene

Abstract

Mn2O3 is an exceptional earth-abundant mineral that has been extensively applied in catalytic oxidation because of the strong redox couples like Mn3+/Mn2+ and Mn4+/Mn3+ exposed on Mn2O3 surface. Herein, the catalytic activity of Mn2O3 in photothermal degradation of toluene was regulated by halogens including F-, Cl-, and Br-. As the electronegativity ordered in F (3.98) > O (3.44) > Cl (3.16) > Br (2.96), F- doped Mn2O3 overperforms Cl- doped and Br- doped Mn2O3 in decomposing toluene. DFT theoretical calculation illustrates that F- attracts the shared electrons from Mn to itself, the deviated charge center stretches the adjacent Mn-O bonds and boosts the generation of abundant oxygen vacancies, helping to strengthen the catalytic activity of Mn2O3. Conversely, Mn-O bonds are shortened by Cl- and Br- that have lower electronegativity than O. The multiple electrons circling Cl- and Br- push Mn towards O and squeeze Mn-O bonds, resulting in the formation of passivated Mn2O3. In conjunction with Mn redox couples and oxygen vacancies, 99% of 400 ppm toluene can be eliminated by F- doped Mn2O3, corresponding mineralization rate is high up to 95.8%.