| In recent years,parabens,a kind of commonly used preservatives in medical and food,can cause harm to ecological environment and human body,which have become emerging organic pollutants in the environment.Among various methods for removing aqueous parabens,the adsorption technology has attracted much attention because it is simple,safe and environmentally-friendly.The development of efficient adsorbent is a hot spot.In this paper,a novel NH2-MIL-101（Fe）/Fe3O4/GO（MMGO）composites were designed and synthesized,based on the high adsorption selectivity of metal-organic framework material NH2-MIL-101（Fe）,magnetic properties of Fe3O4 and high structural stability and great adsorption performance of graphene oxide（GO）,which could be quickly separated from water and had stable structure.Methyl paraben（MP）,ethyl paraben（EP）,propyl paraben（PP）,3,5-dichlorophenol methyl paraben（DMP）and 3,5-dichlorophenol ethyl paraben（DEP）were studied as adsorbates.The effect of each component of MMGO on the adsorption capacity of parabens was studied.The differences and similarities of parabens adsorption on NH2-MIL-101（Fe）with high（MMGO-H）and low（MMGO-L）ratio were researched in detail.The effect of component ratio on the adsorption kinetics,thermodynamics and driving forces were revealed.The results are helpful to further understand the adsorption behavior and mechanism of parabens on MMGO,and provide experimental data and theoretical basis of the design and selection of specific adsorption materials for pollutants.The main contents and conclusions are as follow:（1）Eleven kinds of magnetic MMGO with NH2-MIL-101（Fe）loading capacities ranging from 0 to 512 g/g were synthesized.The results of adsorption experiments showed that the total adsorption capacity and the adsorption selectivity of the adsorbent for DMP and DEP were increased with appropriate loading of NH2-MIL-101（Fe）.The total adsorption capacity reached 53.01 mg/g on MMGO with Fe3O4 load was 0.021 g/g and the NH2-MIL-101（Fe）load was 8 g/g.The correlation analysis of load of Fe3O4 and NH2-MIL-101（Fe）and the adsorption capacities of parabens found that,the adsorption capacity of MP increased when NH2-MIL-101（Fe）load increased（the ratio of NH2-MIL-101（Fe）increased）（|Rs|=0.559,p<0.1）,while the adsorption capacities of EP,PP,DMP and DEP decreased（|Rs|>0.648,p<0.05）.The effect of Fe3O4 on the adsorption capacities of parabens was low（|Rs|<0.529,p>0.1）.（2）MMGO-H and MMGO-L were characterized by TEM,N2adsorption-desorption,TG-DTA,XRD,XPS and FTIR.The characterization results showed that MMGO-H and MMGO-L were mesoporous materials（4.5-50.6 and 1.1-12.9 nm）,with high crystallinity（67.39%and 72.01%）,large specific surface area（120.35 and 211.12 cm2）and strong magnetic properties（2.3 and 3 emu/g）.MMGO-L had smaller pore size,higher crystallinity,larger specific surface area and strong magnetism than MMGO-H.The structure and element content of MMGO-L after adsorption of parabens changed less than MMGO-H,so the stability was stronger.（3）The research on the adsorption mechanisms of parabens on MMGO-H and MMGO-L.The experimental results showed that the order of adsorption capacity followed:DEP,DMP>MP>EP and DEP,DMP>PP>EP>MP,respectively.The decrease of NH2-MIL-101（Fe）load would reduce the adsorption sites of MP and reduce the adsorption capacity of MP.The adsorption capacity increased when initial concentration of parabens increasing.The adsorption capacities decreased with rising the temperature on both MMGO-H and MMGO-L,while the adsorption capacities of DMP and DEP decreased only on MMGO-H.With the elevating the ratio of GO,the influence of increasing temperature on improving hydrophobic forces would be enhanced,and the adsorption capacities of DMP and DEP increased.Compared to MMGO-H（6.0-11.0）,MMGO-L（4.0-11.0）maintained a higher adsorption capacity in a wider p H range.The total adsorption capacity of MMGO-H and MMGO-L reached the maximum at p H=8.0（36.26 mg/g）and 6.0（39.50 mg/g）,respectively.The adsorption interaction was the hydrophobic force.The adsorption of MP on MMGO-H and MMGO-L accorded with Langmuir model,and the adsorption of DMP and DEP accorded with Freundlich model.The adsorption of parabens on both MMGO-H and MMGO-L conformed to the pseudo-second-order model,controlled by internal diffusion and liquid film diffusion.Thermodynamic results showed that the adsorption process of paraben ester was spontaneous physical adsorption process.Multivariate adsorption results indicated that the adsorption capacity of MP（5.32 mg/g,6.09 mg/g）was greatly affected by DMP and DEP while the adsorption capacity of EP（1.79 mg/g）was greatly affected by DMP.The strong competitive adsorption among PP,DMP and DEP was found.Column adsorption results showed that under the conditions of packing height of 0.8 cm,initial concentration of 5 mg/L,temperature of25°C and flow rate of 1.13 m L/min,the removal efficiency of parabens on MMGO-L was 6-27%higher than that on MMGO-H. |
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