Adsorption Of Typical Perfluorinated Compounds By Modified Nylon-6

Perfluorooctanoic acid?PFOA?and perfluorooctane sulfonic acid?PFOS?are typical perfluorinated compounds widely existing in water,atmosphere and soil.PFOA and PFOS have biological toxicity and good stability.It is difficult to degrade them by traditional methods.However,adsorption can remove them from water quickly,and the removal effect is good.It was systematically studied the adsorption behaviors of PFOA and PFOS in simulated wastewater by nylon-6,and analyzed the adsorption mechanism in this paper.Furthermore,nylon-6 was modified by hexadecyltrimethylammonium bromide and Fe³⁺.And the adsorption behavior of 1%CTMAB-nylon and 5%Fe-nylon on PFOA was investigated.In order to further explore the effect of Fe³⁺on adsorption of PFOA,the comparison experiment of 5%Fe-nylon adsorption of PFOA and nylon-6adsorption of PFOA when Fe³⁺coexisted with PFOA was conducted.On the basis of this,the removal rule and adsorption mechanism of PFOA in water by modified nylon-6 were studied by infrared and other characterization methods.The specific conclusions are as follows:The results showed that nylon-6 has strong adsorption capacity for PFOA and PFOS.The adsorption kinetics results showed that nylon-6 can quickly remove PFOA and PFOS from water and reach adsorption equilibrium within 120 minutes.When the equilibrium was reached,the adsorption capacities of PFOA and PFOS were 17.07mg/g and 18.17 mg/g,respectively.The adsorption isotherms showed that the adsorption of PFOA and PFOS by nylon-6 was consistent with Langmuir model.It was also found that the adsorption amount of PFOA and PFOS on nylon-6 decreased with the increase of pH value and first increased and then decreased with the increase of temperature.In the case of metal ions coexisting,the adsorption amount of PFOA on nylon-6 decreased with the increase of K⁺,Na⁺and Mg²⁺concentrations.While the adsorption amount of PFOS on nylon-6 increased with the increase of K⁺,Na⁺and Mg²⁺concentrations.Moreover,the adsorption capacity of PFOA/PFOS adsorbed on the desorbed nylon-6 was basically unchanged,and the results showed that nylon-6could be reused.The adsorption kinetics results showed that 1%CTMAB-nylon and 5%Fe-nylon adsorbed PFOA rapidly,and the adsorption equilibrium time was 100 min.The adsorption capacity at equilibrium was 23.09 mg/g and 100.66 mg/g,respectively.The adsorption isotherms showed that the adsorption of PFOA by 1%CTMAB-nylon and5%Fe-nylon was consistent with both the Langmuir model and the Freundlich model.The effect of modifier dosage on the adsorption behavior of modified nylon-6 showed that the amount of modifier is not as much as possible.The effects of other conditions on the adsorption of PFOA by 1%CTMAB-nylon and 5%Fe-nylon were also studied.The results showed that the adsorption capacity of 1%CTMAB-nylon on PFOA decreased gradually with the increase of pH,increased first and then decreased with the increase of K⁺,Na⁺and Mg²⁺concentration and temperature,while the adsorption capacity of 5%Fe-nylon on PFOA increased first and then remained unchanged with the increase of pH,and decreased gradually with the increase of K⁺,Na⁺,Mg²⁺concentration,and the cyclic experiments show that 1%CTMAB-nylon can be reused.Further comparisons of the experimental results show that when Fe³⁺coexisted with PFOA,the adsorption performance of PFOA by nylon-6 was greatly improved.And the adsorption capacity of PFOA decreases with the increase of pH,but decreases slightly with the increase of temperature,which is different from that of 5%Fe-nylon.However,the trend with the changes of K⁺,Na⁺and Mg²⁺concentration is consistent with the adsorption of PFOA on 5%Fe-nylon.This study provides experimental and theoretical basis for advanced treatment of wastewater containing typical perfluorochemicals.