DFT Studies Of Chemisorptions Of Zn(II), As(V) And PFOS On Metal Oxide Surface

Chemisorptions of some kinds of typical contaminations Zn(II), As(V) and PFOS on metal oxide surface were calculated with Density Functional Theory (DFT) method. The surface systems that mentioned in this study include Zn(II) /γ-MnOOH, As(V) / anatase, Zn(II) / anatase, As(V)-Zn(II) / Anatase co-sorption system, PFOS /α-FeOOH and PFOS / anatase system. Various studies were carried out to describe the microscopic characters of systems above from aspects of geometric structure, electronic structure, thermodynamics, etc. The main investigative results are as follows:(1) In the study of Zn(II)/γ-MnOOH system, the thermochemistry analysis indicated that the stability order of adsorption species is DC > SE-B > SE-A > DE for hydrated species, DC > SE-A > SE-B > DE for hydrolysis species, all of them accord with the 3rd law of Pauling. And the adsorption and hydrolysis are always showing an inter-antagonistic relationship in this system. Natural population analysis indicated the electronic transfer from cluster model to Zn-O unit, this conclusion can explain the stabilization of adsorption species combine with electronic donor-acceptor and frontier molecular orbital analysis.(2) In the study of As(V)/TiO₂ and Zn(II)/TiO₂ systems, the natural bond orbital analysis indicate that some obvious difference of the adsorption bonding mechanism is exist between As(V) and Zn(II) species on TiO2 surface. For As(V), it tend to form stable As-Oσbond with O atom of TiO2 surface, but Zn(II) always link with surface in a incompact way by electronic exchange between its LP/RY and surface. This difference result in a series of difference with two system: vibrational spectra, charge distribution and the component of frontier orbital, etc.(3) In the As(V)-Zn(II)/TiO₂ co-sorption system, the bonded degree of adsorbate with adsorbent is lower than it in single adsorption system. But thermochemical data imply that presence of Zn(II) has promote the thermodynamics tendency of As(V) adsorption, vice versa, and As(V) would tend to form double corner mode in surface with the coexistence of Zn(II). The influence of As(V) in frontier molecular orbital distribution is stronger than Zn(II), and single edge mode is stronger than double corner mode, and the reactivity of Zn(II) was weakened while As(V) exist in the co-sorption system.(4) In the study of PFOS/anatase and PFOS/α-FeOOH systems, PFOS tend to adsorb on surface erectly with sulfonic unit and the change degree of atoms and bonds in the sulfonic unit is more obvious. The bond order of S-O is decrease and C-S and C-F bond is increase during adsorption, and the stabilization order of adsorbed species is Fe system > Ti system, SC > SE2 > SE1 > DC. Charge is transfers from PFOS to metal oxide surface during adsorption. NBO analysis indicated that there are some intense electronic offer effects from other natural bond orbital to S-C and S-Oσ* orbital in adsorbed PFOS, this effect is helpful to the stabilization of adsorbed PFOS.