Activated carbon was prepared from the seeds of aguaje palm (Mauritia flexuosa L.f.) by a chemical activation with phosphoric acid. This activated carbon was used for adsorbing metal ions: Pb(II), Cd(II), and Cr(III). To understand the mechanism of adsorption of these heavy metals (Cr, Cd, and Pb), the activated carbon surface was oxidized with nitric acid (1 M) increasing the oxygenated surface groups showing an increasing in their adsorption capacities of these metals. The oxidized activated carbon slightly increased the maximum adsorption capacity to 5–7%. The order of adsorption for unoxidized and oxidized activated carbons was Pb> Cd> Cr. This experimental information was corroborated by molecular modeling program Hyperchem 8 based adsorption mainly on two factors: the electron density and orbitals—highest occupied molecular orbital and lowest unoccupied molecular orbital.Activated carbons were characterized by adsorption/desorption of N2, obtaining an increase of microporous surface area for oxidized activated carbon. An increase of surface acidity and a reduction of isoelectric points were observed in oxidized activated carbon. According to these results, the adsorption of metal ions is favored in contact with an oxidized activated carbon, which has more amount of phenolic and carboxylic functional groups. Similarly, decreasing the isoelectric point indicates that the surface has a higher negative charge. The surface information was corroborated by Hyperchem, which indicates that the surface of the oxidized activated carbon has a higher electron density, indicating a larger amount of electrons on its surface, which means the surface of oxidized activated carbon charges negatively and thereby attracts metal ions.

中文翻译：

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使用计算化学软件研究金属离子与活性炭表面的相互作用

活性炭是由 aguaje palm (Mauritia flexuosa Lf) 的种子通过磷酸化学活化制备的。这种活性炭用于吸附金属离子：Pb(II)、Cd(II) 和 Cr(III)。为了了解这些重金属（Cr、Cd 和 Pb）的吸附机制，活性炭表面用硝酸 (1 M) 氧化，增加了氧化表面基团，表明它们对这些金属的吸附能力增加。氧化活性炭将最大吸附容量略微增加至 5-7%。未氧化和氧化活性炭的吸附顺序为Pb> Cd> Cr。这一实验信息得到了分子建模程序 Hyperchem 8 基于吸附的证实，主要基于两个因素：电子密度和轨道——最高占据分子轨道和最低未占据分子轨道。活性炭的特点是吸附/解吸N2，增加氧化活性炭的微孔表面积。在氧化活性炭中观察到表面酸度增加和等电点降低。根据这些结果，金属离子的吸附有利于与氧化活性炭接触，后者具有更多的酚类和羧基官能团。类似地，降低等电点表明表面具有更高的负电荷。Hyperchem 证实了表面信息，这表明氧化活性炭的表面具有更高的电子密度，