Fang Mengyuan, Zhao Tianhui, Zhao Xiaoli, Tang Zhi, Liu Shasha, Wang Junyu, Niu Lin, Wu Fengchang
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
College of Geoexploration Science and Technology, Jilin University, Changchun 130026, China.
Nanomaterials (Basel). 2022 May 7;12(9):1592. doi: 10.3390/nano12091592.
The adsorption and suspension behaviors of carbon nanotubes (CNTs) in the water environment determine the geochemical cycle and ecological risk of CNTs and the compounds attached to them. In this study, CNTs were selected as the research object, and the effect of tube diameters and functional groups (multiwall CNTs (MWNTs) and hydroxylated MWNTs (HMWNTs)) on the adsorption and suspension behaviors of the CNTs in the presence of humic acid (HA) was systematically analyzed. The results indicate that HA adsorption decreased with the increase in the solution pH, and the adsorption amount and rate were negatively correlated with the tube diameter of the CNTs. The surface hydroxylation of the CNTs prevented the adsorption of HA, and the maximum adsorption amounts on the MWNTs and HMWNTs were 195.95 and 74.74 mg g, respectively. HA had an important effect on the suspension of the CNTs, especially for the surface hydroxylation, and the suspension of the CNTs increased with the increase in the tube diameter. The characteristics of the CNTs prior to and after adsorbing HA were characterized by transmission electron microscopy, fluorescence spectroscopy, Fourier-transform infrared spectroscopy and Raman spectroscopy. The results indicate that surface hydroxylation of the CNTs increased the adsorption of aromatic compounds, and that the CNTs with a smaller diameter and a larger specific surface area had a disordered carbon accumulation microstructure and many defects, where the adsorption of part of the HA would cover the defects on the CNTs' surface. Density functional theory (DFT) calculations demonstrated that HA was more easily adsorbed on the CNTs without surface hydroxylation. This investigation is helpful in providing a theoretical basis for the scientific management of the production and application of CNTs, and the scientific assessment of their geochemical cycle and ecological risk.
碳纳米管（CNTs）在水环境中的吸附和悬浮行为决定了碳纳米管及其附着化合物的地球化学循环和生态风险。本研究选取碳纳米管作为研究对象，系统分析了管径和官能团（多壁碳纳米管（MWNTs）和羟基化多壁碳纳米管（HMWNTs））对腐殖酸（HA）存在下碳纳米管吸附和悬浮行为的影响。结果表明，HA吸附量随溶液pH值升高而降低，吸附量和吸附速率与碳纳米管的管径呈负相关。碳纳米管的表面羟基化抑制了HA的吸附，MWNTs和HMWNTs上的最大吸附量分别为195.95和74.74 mg/g。HA对碳纳米管的悬浮有重要影响，尤其是对表面羟基化的影响，碳纳米管的悬浮量随管径增大而增加。采用透射电子显微镜、荧光光谱、傅里叶变换红外光谱和拉曼光谱对吸附HA前后碳纳米管的特性进行了表征。结果表明，碳纳米管的表面羟基化增加了芳香族化合物的吸附，直径较小、比表面积较大的碳纳米管具有无序的碳堆积微观结构和许多缺陷，部分HA的吸附会覆盖碳纳米管表面的缺陷。密度泛函理论（DFT）计算表明，HA更容易吸附在无表面羟基化的碳纳米管上。本研究有助于为碳纳米管生产和应用的科学管理以及地球化学循环和生态风险的科学评估提供理论依据。
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