二氧化锰改性碳纳米管对四环素和泰乐菌素的吸附

Adsorption of Tetracycline and Tylosin on MnO_2 Coated Carbon Nanotubes

采用氧化还原法制备二氧化锰负载碳纳米管(Mn O2/MWNT),通过批次吸附实验研究其对所选四环素和泰乐菌素的吸附行为及其影响因素。研究结果表明:与未处理的碳纳米管相比,二氧化锰负载后显著提高了碳纳米管对四环素和泰乐菌素的吸附,约提高了5~8倍;两种抗生素在Mn O2/MWNT上的强吸附机制可解释为π-π电子交互作用、阳离子-π键作用和路易斯酸碱对作用;随着p H升高,四环素和泰乐菌素在Mn O2/MWNT上的吸附显著降低,两种抗生素所含官能团的去质子化作用,以及Mn O2/MWNT表面含氧官能团的解离,导致Mn O2/MWNT与两种抗生素之间的吸附作用减弱。可溶性腐植酸降低了泰乐菌素在Mn O2/MWNT上的吸附,而对四环素影响很小,主要原因是大分子腐植酸不能有效地与四环素竞争Mn O2/MWNT孔道内部的吸附位点。

Carbon nanotubes have strong adsorption affinities to organic pollutants in water due to their large and hydrophobic surface areas.However, carbon nanotubes are easy to flocculate. Here we studied the adsorption behaviors of two typical pharmaceutical antibiotics(tetracycline and tylosin)on multi-walled carbon nanotubes coated with manganese dioxide(Mn O2/MWNT). Mn O2/MWNT showed extraordinarily high adsorption affinity to both antibiotics. Adsorption of tetracycline and tylosin by Mn O2/MWNT enhanced 5 ~8 times, compared to MWNT alone. This enhanced adsorption of tetracycline and tylosin by Mn O2/MWNT was due to strong interactions(π-π electron-donor-acceptor interactions, cation-π bonding and Lewis acid-base interaction)with the graphene surface of Mn O2/MWNT. Similar p H-dependent adsorption was observed in tetracycline and tylosin. When p H was increased from 3 to 11, adsorption coefficient decreased significantly. Increasing p H facilitated deprotonation of charged amino group and protonated enol groups, hence weakening the cation-π bonding, π-π EDA interaction and Lewis acid-base interaction between antibiotics and Mn O2/MWNT. The presence of humic acids prominently suppressed tylosin adsorption on Mn O2/MWNT, but only slightly affected tetracycline adsorption on Mn O2/MWNT. This was because relatively large humic acid could not effectively compete adsorption sites with relatively small tetracycline on Mn O2/MWNT.