Adsorption of perfluorooctanoic acid on humic acid from black soil
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(R2＞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.△H0=30.81 kJ/mol,168.72 J/(mol·K),△G0 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.
environmentalologyblack soil humic acidperfluorooctanoic acidadsorptionFourier Transform Infrared Spectroscopy(FT-IR)Nuclear Magnetic Resonance(NMR)
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