%0 Journal Article
%T Ab Initio Studies on Hematite Surface and the Adsorption of Phosphate
%A Swati Chaudhury
%A Chandrika Varadachari
%A Kunal Ghosh
%J Journal of Theoretical Chemistry
%D 2014
%R 10.1155/2014/312921
%X This investigation explores the ab initio DFT method for understanding surface structure of hematite and the nature and energetics of phosphate adsorption. Using the full potential linearized plane wave method (FP-LAPW), we derived the structure and energies of various magnetic forms of hematite. The antiferromagnetic (AFM) form was observed to be the most stable. Hematite surfaces with Fe-termination, O-termination, or OH-termination were studied. The OH-terminated surface was the most stable. Stability of hematite surfaces follows the order OH-termination > Fe-termination > O-termination. Thus, surface reaction with hematite would occur with the OH at the surface and not with Fe atoms. The structure of phosphate adsorbed on hematite was derived. Bonding is through the H atom of the OH at the surface. An alternative mechanism of phosphate adsorption on hematite has been derived. Adsorption energy is high and suggests chemisorption rather than physisorption of phosphate on hematite. 1. Introduction Hematite is ubiquitous in all soils but is predominant in soils of the tropical and subtropical regions. Due to large surface area and high reactivity, hematite influences several physical and chemical properties. Modelling the reactivity of hematite surfaces is, therefore, based on its bulk crystal structure and particularly on the surface arrangement of atoms. Hematite, -Fe2O3, belongs to the space group 167 R-3c with either two or six formula units in the primitive rhombohedral and in the conventional hexagonal unit cells, respectively. Hexagonal close-packed layers of O atoms are present, with Fe atoms filling 2/3rd of the octahedral holes, which are all in a high-spin d5 electronic configuration [1]. The stable phase is antiferromagnetic (AFM) below the Neel temperature, at 955£¿K [2]. Catti et al. [3] studied the electronic, magnetic, and structural properties of hematite by periodic unrestricted Hartree-Fock method and showed that the band gap is of p-d rather than d-d type, confirming the charge-transfer-insulator nature of hematite. Rollmann et al. [2] studied hematite by using density functional theory (DFT) and the generalized gradient approximation (GGA) and observed that the ground state is antiferromagnetic. Analysis of the density of states confirms the strong hybridization between Fe 3d and O 2p states. Spin-density functional theory was used for the calculation of slab geometry in the surface study of hematite [4]. They observed that, depending on the ambient oxygen partial pressure, either the iron terminated surface or the oxygen terminated
%U http://www.hindawi.com/journals/jtc/2014/312921/