Elaboração e estudo estrutural de compostos "tipo-hidrotalcita" com ânion interlamelar fosfato

Abstract

The term “anionic clays” is used to designate layered double hydroxides (LDH) containing anionic species in the interlayer. The hydrotalcite (HTC) is one of the most famous compounds of this group. These materials possess brucite-like layers and a great amount of anions can occupy the interlayer region. Nowadays the LDHs are utilized in several research fields, which one of them is fertilizer release with the transportation of anionic macronutrients such as H2PO4-, HPO42-, NO3- , SO42- and even cations like Na+. Despite the various applications, the information about the interlayer region of these materials are still scarce in the literature due to the difficulty of its characterization. For instance, the structures of the hydrotalcites containing phosphate and sodium are not yet fully determined. Therefore, a theoretical- experimental work is proposed with the objective of performing an deep study of the interlayer region of a HTC Mg-Al with a molar fraction of 0.33, starting from two models: one model with phosphate and sodium intercalated and another containing only phosphate. The dehydration was also studied for both models. Thereby, a theoretical-experimental work is proposed for a detailed investigation about the interlayer of a Mg-Al LDH containing phosphate. Ab initio calculations based on Density Functional Theory (DFT) with periodic boundary conditions has been presenting sound results with respect to the prediction of crystallographic and electronic data of these materials. In an experimental point of view, the syntheses were performed and characterized by X-ray diffraction by polycrystals and solid state nuclear magnetic resonance for the 27Al and 31P nuclei and the synthetic route that provided the best responses was the reconstruction using ultrasound methodology. The structural data of the hydrotalcite obtained experimentally was used to verify the validity of the theoretical model, aiming to obtain a hydrotalcite without sodium intercalated in the interlayer region. The results showed a good agreement with the X-ray patterns by experimental polycrystals. The projected state density (PDOS) as well as the local density difference were evaluated for the two models and their respective dehydrations.