Immobilization of gaseous As2O3 on γ-Fe2O3 (001) surface by forming monodentate and bidentate complexes: Insight from DFT study

Abstract

Coal combustion is one primary anthropogenic emission source of atmospheric arsenic. Ferromagnetic γ-Fe2O3 has been regarded as an effective and promising immobilization sorbent for As2O3(g) in flue gas with good magnetic properties. The reported mechanism explorations about gaseous arsenic capture in flue gas by density functional theory (DFT) are mainly based on forming one chemical bond between arsenic and sorbent. Recent studies demonstrated that multidentate arsenic complexes could be formed with iron oxides in solution. However, the possible formation pathway of multidentate complexes between gaseous As2O3 and γ-Fe2O3 was not been reported yet. This is the first study to investigate the thermodynamics and quantum mechanics of bidentate complexes between As2O3(g) and γ-Fe2O3 (001) by DFT. Three kinds of arsenic bidentate complexes were discovered at γ-Fe2O3 (001) surface, including “2 O to 2 Feoct”, “2 O to Fetet & Feoct,” and “As & O to 2 Feoct,” which were named as configuration A, B and C, respectively. Configuration B, “2 O to Fetet & Feoct”, showed the lowest adsorption energy (Eads) among the three kinds of bidentate complexes. The Mulliken population analysis further confirmed the electron transfer between the atoms of newly formed chemical bonds in bidentate configurations. In addition, the projected density of states (PDOS) analysis exhibiting resonance peaks also showed the formation of hybrid orbitals. The criteria for the determination of bidentate complexes were also proposed. The results evidence a convincing conclusion that monodentate and bidentate complexes with stable chemical bonds can be formed when As2O3(g) is immobilized by γ-Fe2O3 (001).