School of Urban and Environmental Sciences, Key Laboratory of the Ministry of Education for Earth Surface Processes, Peking University, Beijing 100871, China.
Analysis and Test Center, Guangdong University of Technology, Guangzhou 510006, China.
Sci Total Environ. 2020 Jun 1;719:137389. doi: 10.1016/j.scitotenv.2020.137389. Epub 2020 Feb 19.
Doping heteroatoms in carbon nanotubes can substantially enhance the electronic polarizability of the carbon surface and thus may facilitate adsorptive interactions of organic contaminants. Here, the adsorption isotherms of three polar/ionizable emerging organic contaminants, bisphenol A, tylosin, and tetracycline from aqueous solutions to synthesized heteroatom nitrogen-doped multiwall carbon nanotubes (N-MCNT) were compared with those to commercial non-doped multiwall carbon nanotubes (MCNT) at pH ~ 6. N-MCNT exhibited much stronger adsorption (3-4 folds higher sorption distribution coefficients, K) towards the three adsorbates than MCNT. The hydroxyl group-substituted bisphenol A molecule is rich in π-electrons and thus interacts with the polarized π-electron-depleted N-heterocyclic aromatic ring on N-MCNT via π-π electron-donor-acceptor (EDA) interaction, whereas the protonated amino group and enone groups in the tylosin molecule are deficient in electrons and interact with the neighboring π-electron-rich aromatic ring on N-MCNT via cation-π and π-π EDA interactions, respectively. The tetracycline molecule contains both electron-rich moiety (phenol ring) and electron-depleted moieties (protonated amino group and enone groups), which interact with the corresponding π-electron-acceptor/donor sites on N-MCNT. The proposed adsorption mechanisms were tested by the effects of ionic strength (NaCl or CaCl), co-present Cu ion, and changing pH on adsorption, and further by the adsorption behavior of a model organic cation (tetraethylamine). These results indicate that enhanced adsorption of emerging organic contaminants to carbon nanotubes can be achieved by doping with heterocyclic nitrogen atoms to facilitate specific EDA interactions. Capsule: Nitrogen-doped multiwall carbon nanotubes exhibit enhanced adsorptive removal of bisphenol A, tylosin, and tetracycline from aqueous solutions.
掺杂杂原子可以显著增强碳表面的电子极化率，从而可能促进有机污染物的吸附相互作用。在此，在 pH 值约为 6 时，将三种极性/可离子化的新兴有机污染物（双酚 A、泰乐菌素和四环素）从水溶液中吸附到合成的杂氮掺杂多壁碳纳米管（N-MCNT）上的吸附等温线与商业非掺杂多壁碳纳米管（MCNT）上的吸附等温线进行了比较。N-MCNT 对三种吸附物的吸附作用要强得多（吸附分布系数 K 高 3-4 倍）。羟基取代的双酚 A 分子富含π电子，因此通过π-π 电子给体-受体（EDA）相互作用与 N-MCNT 上的极化π电子耗尽的 N-杂环芳环相互作用，而泰乐菌素分子中的质子化氨基和烯酮基团电子不足，通过阳离子-π 和 π-π EDA 相互作用分别与 N-MCNT 上相邻的富π电子芳环相互作用。四环素分子同时含有富电子部分（苯酚环）和缺电子部分（质子化氨基和烯酮基团），与 N-MCNT 上的相应π-电子受体/供体位点相互作用。通过测定离子强度（NaCl 或 CaCl）、共存 Cu 离子和改变 pH 值对吸附的影响，以及通过模型有机阳离子（四乙胺）的吸附行为，对吸附机制进行了验证。这些结果表明，通过掺杂杂环氮原子可以增强碳纳米管对新兴有机污染物的吸附，从而促进特定的 EDA 相互作用。
