Goto Tatsuru, Amano Yoshimasa, Machida Motoi, Imazeki Fumio
Graduate School of Engineering, Chiba University.
Chem Pharm Bull (Tokyo). 2015;63(9):726-30. doi: 10.1248/cpb.c15-00039.
In this study, introduction of acidic functional groups onto a carbon surface and their removal were carried out through two oxidation methods and outgassing to investigate the adsorption mechanism of aromatic compounds which have different polarity (benzene and nitrobenzene). Adsorption experiments for these aromatics in aqueous solution and n-hexane solution were conducted in order to obtain the adsorption isotherms for commercial activated carbon (BAC) as a starting material, its two types of oxidized BAC samples (OXs), and their outgassed samples at 900 °C (OGs). Adsorption and desorption kinetics of nitrobenzene for the BAC, OXs and OGs in aqueous solution were also examined. The results showed that the adsorption of benzene molecules was significantly hindered by abundant acidic functional groups in aqueous solution, whereas the adsorbed amount of nitrobenzene on OXs gradually increased as the solution concentration increased, indicating that nitrobenzene can adsorb favourably on a hydrophilic surface due to its high dipole moment, in contrast to benzene. In n-hexane solution, it was difficult for benzene to adsorb on any sample owing to the high affinity between benzene and n-hexane solvent. On the other hand, adsorbed amounts of nitrobenzene on OXs were larger than those of OGs in n-hexane solution, implying that nitrobenzene can adsorb two adsorption sites, graphene layers and surface acidic functional groups. The observed adsorption and desorption rate constants of nitrobenzene on the OXs were lower than those on the BAC due to disturbance of diffusion by the acidic functional groups.
在本研究中，通过两种氧化方法将酸性官能团引入到碳表面并将其去除，同时进行脱气处理，以研究具有不同极性的芳香族化合物（苯和硝基苯）的吸附机理。为了获得以商业活性炭（BAC）为原料、其两种氧化后的BAC样品（OXs）以及它们在900℃脱气后的样品（OGs）对这些芳香族化合物在水溶液和正己烷溶液中的吸附等温线，进行了吸附实验。还考察了BAC、OXs和OGs在水溶液中对硝基苯的吸附和解吸动力学。结果表明，水溶液中大量的酸性官能团显著阻碍了苯分子的吸附，而随着溶液浓度的增加，硝基苯在OXs上的吸附量逐渐增加，这表明与苯相比，硝基苯由于其高偶极矩能够在亲水性表面上良好吸附。在正己烷溶液中，由于苯与正己烷溶剂之间的高亲和力，苯难以吸附在任何样品上。另一方面，在正己烷溶液中，硝基苯在OXs上的吸附量大于在OGs上的吸附量，这意味着硝基苯可以吸附在两个吸附位点上，即石墨烯层和表面酸性官能团。由于酸性官能团对扩散的干扰，观察到硝基苯在OXs上的吸附和解吸速率常数低于在BAC上的速率常数。
