ZnCl2、KOH和HNO3改性MWCNT对苯酚的吸附行为研究

通过扫描电子显微镜、X射线衍射仪、N₂吸附分析仪及Boehm滴定法获得ZnCl₂、KOH和HNO₃化学处理对高纯多壁碳纳米管的结构和表面含氧官能团的影响，通过批处理实验考察吸附条件（吸附时间、初始浓度、温度）对处理前后的碳纳米管吸附苯酚行为的影响，并采用准一级、准二级、Evolich动力学模型和热力学方程拟合其吸附数据，分析其动力学行为、热力学行为和吸附机理。结果表明，虽然ZnCl₂、KOH和HNO₃化学处理法均未对碳纳米管BET比表面积产生显著影响，但会影响其表面化学性质（即，对于ZnCl₂和KOH化学处理降低表面羧基、内酯基含量和增大碱性官能团量，而对于HNO₃化学处理可以增大表面羧基、内酯基含量，而碱性官能团略有增加）；改性处理影响碳纳米管去除苯酚效率：由于ZnCl₂和KOH改性处理降低碳纳米管表面羧基量，故其提高了苯酚去除率，而HNO₃处理则略减小碳纳米管的苯酚去除率，可能是由于碳纳米管结构和表面化学性质共同影响所致；碳纳米管的苯酚去除率均随苯酚溶液初始浓度的增大而减小；高温不利于吸附；热力学研究发现碳纳米管吸附苯酚过程是自发的和放热的，属于物理吸附；动力学研究表明，吸附过程符合准二级动力学方程。通过ZnCl₂和KOH化学处理，可以显著提高碳纳米管对苯酚的吸附性能。

Adsorptive behaviors of phenol in water by MWCNT modified by ZnCl2, KOH and HNO3

The texture and surface chemistry of carbon nanotubes before and after chemical treatment using ZnCl₂, KOH and HNO₃ were determined by scanning electronic microscope, X-ray diffraction, N₂ adsorption, and Boehm titration; and the effect of adsorptive conditions (contact time, initial concentration and temperature) on phenol removal and the thermodynamic and kinetic behavior and adsorption mechanism were investigated by tests and data fitting with three kinetic models (pseudo-first order, pseudo-second order and the Elovich kinetic equations) as well as thermodynamic equation. The results show that the treatment by HNO₃, ZnCl₂ or KOH less changes the BET surface area of carbon nanotubes, but obviously changes the surface chemical property. Specifically, the treatment by HNO₃ obviously enhances surface acidic groups and slightly increases basic groups, whereas the treatment by ZnCl₂ or KOH greatly decreases surface carboxyl groups and lactonic groups but obviously increases surface basic groups, which affects the phenol removal by carbon nanotubes. It is found that the phenol removal by carbon nanotubes treated with ZnCl₂ or KOH increases due to a decrease in surface carboxyl groups of carbon nanotubes, but HNO₃ treatment slightly reduces the phenol removal possibly because the adsorption is influenced by both structure and surface chemical property. Moreover, the adsorption of phenol by carbon nanotubes is spontaneous, exothermic and physically controlled, and the adsorption process of phenol by carbon nanotubes complies with the pseudo-second order equation.