Cuervo Montserrat R, Asedegbega-Nieto Esther, Díaz Eva, Vega Aurelio, Ordóñez Salvador, Castillejos-López Eva, Rodríguez-Ramos Inmaculada
Department of Chemical Engineering and Environmental Technology, University of Oviedo, Julián Clavería s/n, 33006 Oviedo, Spain.
J Chromatogr A. 2008 Apr 25;1188(2):264-73. doi: 10.1016/j.chroma.2008.02.061. Epub 2008 Mar 5.
The effect of the chemical activation, using HNO3, of a commercial carbon nanofiber (CNF) on its surface chemistry and adsorption properties is studied in this work. The adsorption of different alkanes (linear and cyclic), aromatic compounds and chlorohydrocarbons on both the parent and the oxidized CNF were compared. Temperature-programmed desorption results, in agreement with X-ray photoelectron spectroscopy experiments, reveal the existence of oxygen groups on the surface of the treated CNF. Capacity of adsorption was derived from the adsorption isotherms, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined from chromatographic retention data. Both the capacity and the strength of adsorption decrease after the oxidant treatment of the carbon nanofibers, although in the case of chlorinated compounds the specific component of the surface energy shows an important increase. For n-alkanes and cyclic compounds, it was demonstrated that the presence of oxygen surface groups does not affect their interaction, the morphology of the surface being the key parameter. The oxidation of the nanofiber leads to steric limitations of the adsorption. In the adsorption of aromatic compounds, these limitations are compensated by the nucleophilic interactions between the aromatic ring and surface oxygenated groups, leading to similar performances of both materials. The absence of nucleophilic groups in the chlorinated compounds hinders their adsorption on the activated nanofibers.
本工作研究了使用硝酸对商用碳纳米纤维（CNF）进行化学活化对其表面化学性质和吸附性能的影响。比较了不同烷烃（直链和环状）、芳香族化合物和氯代烃在原始CNF和氧化后的CNF上的吸附情况。程序升温脱附结果与X射线光电子能谱实验结果一致，表明处理后的CNF表面存在氧基团。吸附容量由吸附等温线得出，而热力学性质（吸附焓、表面自由能特征）则由色谱保留数据确定。碳纳米纤维经氧化剂处理后，吸附容量和吸附强度均降低，不过对于氯代化合物，表面能的特定组分有显著增加。对于正构烷烃和环状化合物，已证明表面氧基团的存在不影响它们之间的相互作用，表面形态才是关键参数。纳米纤维的氧化导致吸附的空间位阻。在芳香族化合物的吸附中，这些位阻通过芳香环与表面含氧基团之间的亲核相互作用得到补偿，使得两种材料的性能相似。氯代化合物中不存在亲核基团，这阻碍了它们在活化纳米纤维上的吸附。
