碳纳米管吸附腐植酸的动力学、热力学及机理研究

Study on Kinetics,Thermodynamics and Mechanism for Carbon Nanotubes Adsorbing Humic Acid

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.

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.