Electronic and magnetic properties of the adsorption of As harmful species on zero-valent Fe surfaces, clusters and nanoparticules

ALFONSO TOBÓN, LESLIE L.; FUENTE, SILVIA; BRANDA, MARÍA M.

APPLIED SURFACE SCIENCE

ELSEVIER SCIENCE BV

Año: 2019 vol. 465 p. 715 - 723

0169-4332

A systematic theoretical study of the adsorption of H 3 AsO 3 and H 3 AsO 4 acids on Fe nanoparticles was carried out using the Density Functional Theory (DFT). Different sizes of zero-valent iron particles and also the two most stable surfaces of Fe, (1 1 1) and (1 1 0), were studied by characterizing the type of interaction present between the substrates and the adsorbates. Arsenic acid (H 3 AsO 4 ) is spontaneously reduced in both extended surfaces of iron, producing arsenious acid and oxidizing the metal surface. Arsenious acid (H 3 AsO 3 ) completely decomposes into (AsOH)(OH)(OH) fragments on the smallest particles, Fe 32 and Fe 59 , but also on the (1 1 1) surface. However, on greater particles (NP 80 and NP 113 ) and on the (1 1 0) surface, H 3 AsO 3 retains its initial free configuration and is joined to the surface through both atoms, As and O. Large dispersion components of the adsorption energy were observed when the acids interact with the substrates without decomposition. From a Bader analysis of the atomic charges, important charge transfers were found. Both the As and the interacting Fe atom are slightly reduced on the (1 1 0) surface and NP 80 . However, the four nearest neighboring irons are oxidized because of the interaction with H 3 AsO 3 . In the case of the Fe 32 cluster, where this acid is totally broken, all the interacting Fe atoms are oxidized. A significant decrease of the magnetic moment was found for the Fe atom that interacts with H 3 AsO 3 . This fact was confirmed with the diminution of the spin up population and the increase of the spin down population observed in the PDOS of d states after the acid was bond to the iron substrates. Besides, important changes in the PDOS have point out the central role of the iron d orbitals on the reactivity of the surface and nanoparticles, but also an important participation of the p ones in the case of the cluster Fe 32 .