DFT study of the removal of nitrates from water using metal oxide catalysts

DOMANCICH, N.; MEIER L. A.; SCHVVAL A. B.; MORGADE C. I. N.; ROSSI-FERNÁNDEZ, A. C.; FUENTE, S. A

Buenos Aires

Congreso; WCCE11 - 11th WORLD CONGRESS OF CHEMICAL ENGINEERING; 2023

Asociación Argentina de Ingenieron Químicos

The use of catalytic technologies for the purification of water contaminated with high levels of nitrates is of great interest in our country, where the contamination of fresh water with these ions is no longer an isolated or uncommon event. This occurs due to the confluence of various factors, for example, the increased use of fertilizers and pesticides, and contamination with chemical waste of household and industrial origin, among others. According to the Argentine Food Code, the nitrate limit established in drinking water is 45 mg/L. The most vulnerable population are babies under 6 months since high concentrations of this ion can cause cyanosis due to the formation of methemoglobin in the blood. Likewise, it has been shown that catalysts based on metal oxides are highly efficient for the removal of ions from water, whose presence affects human health [1]. For the aforementioned reasons, we began with the theoretical study, at the atomic level, of the adsorption of nitrates on metal oxides, in order to design an efficient and low-cost catalyst for their removal from water for human consumption. The calculations were carried out within the DFT formalism, using the commercial package VASP [2], with a base of plane waves and periodic conditions. The most stable surfaces of each oxide were modeled, being: TiO2 (in its rutile (110) and anatase (101) phases), Fe2O3 (0001) and MgO (100). In the first instance, the adsorption of the NaNO3 molecule on the aforementioned oxides was studied. The geometries were optimized and the adsorption energies were calculated, resulting in the most favorable anatase TiO2, with an adsorption energy of -4.51 eV, followed by rutile TiO2 (Eads = -2.65 eV), Fe2O3 (Eads = -2.42 eV) and finally MgO (Eads = -2.33 eV). Atomic charges were calculated using the Bader model, density of total states (DOS) and bond order (BO) which gives an idea of the stability of the chemical bond. The BO were calculated according to the DDEC06 analysis, demonstrating that in all cases the adsorption is non dissociative. Analyzing the atomic charges, it can be concluded that in systems where adsorption is more favored, a charge transfer from the surface to the molecule is observed, leaving it with a net charge of 0.16e when it interacts with the anatase TiO2 surface. Currently, the effect of pH on adsorption is being analyzed in all the systems studied. References 1. L.A. Meier, A.B. Schvval, S.B. Ulacco, A.S. Lorenzetti, E. Vidal, C. Domini, C.I.N. Morgade (2022). Study of phase-pure TiO2 for the removal of fluorides in water. Materials Today Communications 31(103389), 1-9. 2. G. Kresse, J. Furthmüller; Comput. Mater. Sci. 6 (1996) 15-20.