碳纳米管对不同分区溶解有机物的吸附研究

Adsorption of dissolved organic matters categorized by different EEMs regions in aqueous phase by carbon nanotubes

选用单壁碳纳米管、多壁碳纳米管两种吸附剂,对广州市3种地表水体(城市径流、农田径流、森林径流)中不同分区溶解性有机物(DOM)进行吸附研究,并以腐殖酸溶液作为标准对照组。以UV254、荧光激发-发射矩阵光谱、溶解性有机碳质量浓度作为吸附效果的评价指标。结果表明,在UV254上,单壁碳纳米管比多壁碳纳米管平均多吸附11%的DOM。3种地表水样中均无Ⅰ区荧光峰,而有明显的Ⅱ、Ⅲ、Ⅳ区荧光峰。水样中II区、III区、IV区、Ⅴ区荧光峰的位置分别为Ex230/Em345、Ex245/Em445、Ex275/Em320、Ex335/Em380,误差在40 nm内。多壁碳纳米管吸附溶解性有机物的动力学模式符合准二级动力学方程,决定系数高达0.994 7。Langmuir方程相对于Freundlich方程更适合描述MWNT-1030对DOM的吸附过程。

This paper is aimed to study the influence of carbon nanotubes（CNTs） on dissolved organic matters（DOM） as well as their adsorption mechanism.Single-walled carbon nanotubes（SWNT） and multi-walled carbon nanotubes（MWNT-1030） were employed as adsorbents to adsorb dissolved organic matters（DOMs） which are categorized by different regions from three types of surface waters which representing urban runoff,agricultural drainage and forest stream in the city of Guangzhou.The adsorption on humic acid on CNT was also examined as reference.Characteristic changes of DOMs in the experiments were assessed by measuring the UV254 absorbance,fluorescence excitation-emission matrix spectroscopy（EEMs） and concentration of dissolved organic carbon（DOC）.The experimental results showed that SWNT reduces extra 11% of UV254 when compared to MWNT-1030.The average values of UV254 reduced to 47% and 56%,respectively when SWNT and MWNT-1030 were applied to the three types of surface water.Region I fluorescent peak was absent in the observation but clear fluorescent characteristic peaks for region II,III and IV which having position at Ex230/Em345,Ex245/Em445 and Ex275/Em320,respectively could be observed with error within the 40 nm.Nevertheless,only forest stream sample has been detected to have region I（Ex350/Em400） fluorescent peak,which was different position（Ex265/Em465） from the standard humic acid.Adsorption of DOMs on MWNT-1030 could be well described with pseudo-second order kinetic equation with the R2 of 0.979.The calculated adsorption capacity（11.02 mg/g,5.17 mg/g） obtained from the pseudo-second order kinetic equation was closed to the experimental adsorption capacity（11.55 mg/g,5.25 mg/g）.The adsorption capacity of MWNT-1030 towards DOMs increased with the increases of initial concentration and temperature.Langmuir equation was found to be more suitable in describing the adsorption process of DOMs on MWNT1030（R2 = 0.991） rather than Freundlich equation.