黑土腐殖酸对全氟辛酸的吸附特征研究

Adsorption of perfluorooctanoic acid on humic acid from black soil

研究全氟辛酸(Perfluorooctanoic Acid, PFOA)在黑土腐殖酸(Humic Acid, HA)中的吸附特征,有助于更好地理解和管理这种新兴污染物对人类健康和生态系统的潜在危险。研究以PFOA作为目标污染物,探讨其在黑土腐殖酸中的吸附动力学和等温吸附特征,并通过傅里叶变换红外光谱(Fourier Transform Infrared Spectroscopy, FT-IR)和核磁共振碳谱(13C Nuclear Magnetic Resonance, NMR)揭示其分子作用机理。研究结果显示:黑土腐殖酸对PFOA的吸附过程可分为3个阶段:开始为快速吸附阶段,且吸附量占总吸附量的78.8%,之后为慢速吸附阶段,直至48 h后达到吸附平衡。吸附动力学采用拉格朗日准一级动力学、准二级动力学和颗粒扩散模型对数据进行拟合,结果显示拉格朗日准二级动力学模型拟合较好(R^(2)> 0.998);吸附等温线用Henry、Freundlich和Langmuir模型对试验数据进行拟合,结果显示Freundlich和Langmuir模型拟合效果较好;吸附量随温度升高而升高,当温度为298.15 K时,其值为1.717 mg/g。此外,ΔH^(0)=30.81 kJ/mol,ΔS^(0)=168.72 J/(mol·K),ΔG^(0)在-19.49~-16.11 kJ/mol,表明腐殖酸对PFOA的吸附属于易自发过程,吸附自由能的减少是腐殖酸吸附PFOA的主要驱动力,吸附过程中的驱动力主要是氢键。通过对比吸附前后FT-IR和NMR图谱可知,腐殖酸对PFOA的吸附过程中存在离子交换和氢键作用,PFOA与腐殖酸的主要结合位点为芳香碳和脂肪碳,且PFOA会与HA发生原位化学反应并产生羧酸类物质。

A study of the adsorption characteristics of Perfluorooctanoic Acid(PFOA)in black soil Humic Acid(HA)will be helpful to better understand and manage the potential risks of it,as an emerging pollutant to human health and ecosystems.In this paper,PFOA was used as the target pollutant to study its adsorption kinetics and isothermal adsorption characteristics in black soil humic acid,and its molecular mechanism was revealed by Fourier transform infrared spectroscopy and 13 C Nuclear Magnetic Resonance(NMR).The results show that the adsorption process of PFOA by black soil humic acid can be divided into three stages.The first stage is the rapid adsorption stage,the adsorption amount of which accounted for 78.8%of the total adsorption amount.Then,the slow adsorption stage lasted until the adsorption equilibrium reached after 48 h.The adsorption kinetics was fitted by Lagrangian pseudo-first-order kinetics,pseudo-second-order kinetics,and particle diffusion model.The results show that the Lagrangian pseudo-second-order kinetic model fitted well(R^(2)>0.998).To compare the fitting of different adsorption models,Henry,Freundlich,and Langmuir models were used to fit the experimental data,and the results showed that Freundlich and Langmuir models had better effects.The adsorption capacity increases with rising temperature.When the temperature is 298.15 K,the value is 1.717 mg/g.ΔH^(0)=30.81 kJ/mol,168.72 J/(mol·K),ΔG^(0) in-19.49~-16.11 kJ/mol,indicating that the adsorption of PFOA by humic acid is easy to be spontaneous.The decrease in adsorption-free energy is the main driving force for the adsorption of PFOA by humic acid.The hydrogen bond force is the main role of the adsorption process;By comparing FT-IR and NMR before and after adsorption,it can be concluded that ion exchange and hydrogen bonding occur in the adsorption process of PFOA by humic acid.The main binding sites of PFOA and humic acid are aromatic carbon and aliphatic carbon,and PFOA undergoes an in-situ chemical reaction with HA to produce carboxylic acids.