碳纳米管吸附腐植酸的动力学_热力学及机理研究

第26卷 第2期

无 机 材 料 学 报 Vol. 26

No. 2 2011年2月

Journal of Inorganic Materials Feb. , 2011 收稿日期: 2010-05-06; 收到修改稿日期: 2010-09-05

基金项目: 国家自然科学基金(20976016); 湖南省自然科学基金(09JJ6067)

National Nature Science Foundation of China (20976019); Nature Science Foundation of Hunan Province (09JJ6067)

作者简介: 朱志平(1963−), 男, 硕士, 教授. E-mail: zzp8389@163.com

通讯联系人: 黄可龙, 教授. E-mail: huangkelong@163.com 文章编号: 1000-324X(2011)02-0170-05 DOI: 10.3724/SP.J.1077.2011.00170

碳纳米管吸附腐植酸的动力学、热力学及机理研究

朱志平1,2, 黄可龙1, 周 艺2

(1. 中南大学 化学与化工学院, 长沙410086; 2. 长沙理工大学 化学与生物工程学院, 长沙410114)

摘 要: 针对天然水中腐植酸(HA)类溶解性有机物去除问题, 采用多壁碳纳米管为吸附剂, 在不同的pH 值、吸附剂量、初始HA 浓度下进行吸附动力学实验, 用准二级速率方程拟合了动力学数据, 其线性相关度在0.99以上, 拟合得到的平衡吸附量为27mg/g, 与实验结果(25.5 mg/g)基本一致. 在25~50℃下进行了碳纳米管吸附腐植酸的等温吸附实验, 以Langmuir 模型拟合的平衡吸附量为29.7mg/g, 与实验结果相近. 用Clapeyron-Clausius 与Gibbs- Helmholtz 方程计算的自由能(ΔG )、焓(ΔH )、熵(ΔS )皆为负值, 说明碳纳米管对腐植酸的吸附为放热熵减过程. 碳纳米管的表面、管间隙、管内腔及管束之间形成的束聚孔为其有效吸附点位, 腐植酸与碳纳米管间的π−π作用也是吸附的主要原因之一.

关 键 词: 碳纳米管; 腐植酸; 吸附; 动力学; 热力学

中图分类号: TQ174 文献标识码: A Study on Kinetics, Thermodynamics and Mechanism for Carbon Nanotubes

Adsorbing Humic Acid

ZHU Zhi-PING 1,2, HUANG Ke-Long 1, ZHOU Yi 2

(1. College of Chemistry and Chemical Engineering, Central South University, Changsha 410082, China; 2. College of Chemi-cal and Biological Engineering, Changsha University of Science & Technology, Changsha 410114, China)

Abstract: The dissolved organic carbon in natural water was mainly from soluble humic acid(HA) which had much harms in industrial and drinkable water. As a new adsorbent, the multi-walled carbon nanotubes (MCNTs) were used to remove HA at different pH value, different MCNTs dosages and different HA initial concentration, a series of experiments including batch adsorption, adsorption isotherm were carried. The adsorption kinetics data was fitted with pseudo-second-order rate model, their linear correlations was above 0.99, and equilibrium adsorption capacity obtained from fitting curve was 27mg/g, consistent with the experimental results (25.5mg/g). The adsorption isotherm test was carried at 25℃−50℃, the equilibrium adsorption capacity was 29.7mg/g by Langmuir model, which was similar to the experiment results. The free energy (ΔG ), enthalpy(ΔH ) and entropy (ΔS ) were obtanined with Clapeyron-Clausius and Gibbs-Helmholtz equation in the adsorption isotherm, which all were negative, indicated that HA adsorbed by MCNT was an exothermic process of entropy reduction. MCNT’s outer surfaces, layer interspace, inner cavity and aggregated pores became efficient adsorption space for HA. The π−π interactions between HA and MCNT played an important role in the adsorption process.

Key words: multi-walled carbon nanotubes (MCNT); humic acid (HA); adsorption; kinetics; thermodynamics

腐植酸(HA)是一种广泛地存在于天然水体中

的高分子聚合物, 一般为深色的、酸性的胶体类有

机物. 腐植酸占据了天然水体40%∼50%的溶解性

有机碳源(在高色度的地表水中可达90%以上). 天

然水体中的腐植酸分子量分布范围一般在103~105之间, 粒径3~10nm, 如河流HA 的平均分子量为1500到5000[1], 而土壤HA 的分子量分布上限为50 k 到500 k [2], 含碳、氢、氧和氮, 有时也含硫.

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