Estudo teórico da interação do íon óxido de urânio (UO22+) em matrizes de biopolímeros

Abstract

Uranium (U) is the main raw material for nuclear energy, which has been an alternative to renewable energy sources. In nature, its most stable form, which is highly soluble, is hexavalent uranium U(VI). Its presence in deep repositories created for the disposal of radioactive waste or nuclear reprocessing and processing means that this species is present in aqueous solutions, which can cause damage to the environment and human health, making its removal necessary. As a result, adsorption is considered an efficient technique for removing uranium from water resources, mainly due to the expected ease of adsorption in bioadsorbents such as cellulose, hemicellulose, and lignin compounds. Thus, the objective of this work is to study the mechanisms of removal by adsorption of uranium dioxide (UO22+) from the aqueous medium using cellulose (CE), hemicellulose (Hm1 and Hm2), and lignin (GS) matrices through computational simulations. The adsorbate-adsorbent systems were optimized, and it was observed that among the matrices, UO22+ presented the highest interaction energy with the CE matrix due to its hydroxyl groups, followed by Hm1, Hm2, and finally GS, which presented weaker interactions. All interactions evaluated were exothermic (ΔH < 0) and almost all were spontaneous (ΔrG < 0), with the exception of Hm1-UO22+(1) and GS-UO22+(1). For the topological parameters obtained by Quantum Theory of Atoms in Molecules (QTAIM), all types of interactions were characterized as non-covalent, in which the interactions of uranium with the oxygen atoms of the matrices were partially covalent, and those of the oxygen atoms of UO22+ with the hydrogen atoms of the electrostatic matrices. These trends were also visualized in the Non-Covalent Interactions (NCI) analyses, through isosurface graphs, since, in summary, the U-Oadsorbent interactions presented a bluish color indicating strong interaction, and the Oadsorbate-Hadsorbent interactions presented a greenish color indicating van der Waals forces. Thus, it was concluded that unmodified cellulose, hemicellulose and lignin are good adsorbent matrices for removing UO22+from water resources. The theoretical studies on the adsorption mechanisms of cellulose, lignin, and hemicellulose matrices shown in this work, such as the simulation of electronic structures, can provide insights into the interaction mechanisms and enhance our understanding of UO22+∙∙∙biopolymer interactions during environmental remediation processes.