| Phthalates acid esters(PAEs)and polycyclic aromatic hydrocarbons(PAHs)are both typical organic pollutants ubiquitous in the environment,which are frequently exchanged between different environmental media,and are subjected to enrichment and delivery through the food chain,ultimately posing a serious threat to human health and safety.The adverse effects of two kinds of substances in the aquatic environment have attracted wide attention,and adsorption by sediment and aquatic plants were considered as effective way to remove these organic pollutants from the aquatic environment to achieve the purpose of water purification.On one hand,as an important reservoir for water pollutants,the adsorption kinetics and mechanism of different PAEs as well as the influence of low-molecular-weight organic acids and soil particulate matter and organic carbon content on the adsorption process of PAEs in mangrove sediments are not systematic.One the other hand,Eichhornia crassipes as a natural non-toxic,reproductive,abundant,low-cost and degradable adsorption material,has a huge potential for water purification application.However,little attention has been focused on adsorption process and removal efficiency of PAHs and alkylated PAHs by Eichhornia crassipes.Therefore,the main research work conducted in this work are shown as follows:(1)In this study,diethyl phthalate(DEP),dimethyl phthalate(DMP)and dibutyl phthalate(DBP)were selected as the representative substances to study the adsorption kinetics of the three PAEs in mangrove sediments collected from three different locations,namely Yunxiao mangrove wetland(YX),Jiulongjiang Estuary mangrove wetland(JL)in Fujian province(China),and Zhanjiang Estuary mangrove wetland(ZJ)in Guangzhou province(China).Additionally,the effects of citric acid on the adsorption process and related mechanism were also determined.The results show that,in the fast adsorption phase,PAEs diffuses rapidly in the boundary layer on the outer surface of the sediment by the way of liquid film diffusion,and the slow adsorption phase is dominated by pore diffusion or intracellular diffusion,finally reaching the adsorption equilibrium.Whether citric acid is present or not,the adsorption kinetic can be well described by the pseudo-second-order model,which indicates that the chemisorption of PAEs in mangrove sediments is realized through the electron sharing or exchange of equivalent electron forces between the surface active groups of the sediments and PAEs,revealing the characteristics of its heterogeneous chemisorption.Secondly,there are chemical differences between the adsorption isotherms and the dominant mechanism of adsorption strength of the three PAEs.The qe of the three PAEs changes significantly with the sequence of DBP> DEP> DMP(P < 0.05),indicating that the adsorption concentration is proportional to the hydrophobicity of PAEs.Mangrove sediments from different sources of PAEs adsorption ability is also different,three kinds of sediment samples of DMP and DEP adsorption capacity size order for JL > YX > ZJ,and the order of DBP as YX > JL > ZJ,because organic pollutants adsorption ability largely depends on the soil or sediment organic matter in which the surface polarity of POM index;For DMP and DEP,the R~2 value of the Freundlich model(0.97-0.99)was higher than that of the Henry model(0.93-0.97)and the Langmuir model(0.88-0.92),indicating that the Freundlich model was more suitable than the other two models to describe the adsorption isotherms of DMP and DEP in mangrove sediments,indicating that the adsorption of DMP and DEP in mangrove sediments was affected by multi-layer adsorption on heterogeneous surfaces.However,for DBP,the R~2 value of the Freundlich model(0.98-1.00)was higher than that of the Henry model(0.93-0.97)and the Langmuir model(0.87-0.91),indicating that hydrophobic distribution plays a leading role in the adsorption process of DBP.Citric acid mainly promotes the adsorption of DBP by enhancing the hydrophobic distribution,while for DMP and DEP,it increases the adsorption sites on the sediment surface and enhances the polarity indexon the sediment surface.Therefore,low-molecular-weight organic acids play an important role in affecting PAEs migration in mangrove sediments.(2)The adsorption behavior of anthracene(Ant)and 1-Methylpyrene(1-MP)by root powder derived from Eichhornia crassipes was determined using fluorescence spectrophotometry.The experimental results showed that,within a certain concentration range,the fluorescence intensity had a good linear relationship with the concentration of Ant and 1-MP,with the correlation coefficients(R~2)up to 0.9808 and 0.9939,respectively.With the increase of Eichhornia crassipes root powder,the obsorption capacity increased significantly,which could be explained by the fact that solid phase would provide more adsorption sites,leading to more PAHs captures,thus the removal efficienc increases.In a certain range,there is a good linear relationship between the adsorption amount of Ant and 1-MP by the adsorption substrate and the initial concentration of the two PAHs.That is to say,the higher the initial concentration of pollutants was,the more the adsorption of Eichhornia crassipes root powder to PAHs was.The fitting results of adsorption isotherms showed that the highest correlation coefficients(R~2)of Ant and 1-MP were 0.989 and 0.987 fitted by Henry model,respectively.It shows that partition dominated the main mechanism of adsorption.In addition,the maximum equilibrium adsorption capacity of Eichhornia crassipes root powder to Ant and 1-MP were up to 342.39 ug g-1and 21.84 ug g-1 respectively,which indicated that PAHs could be effectively absorbed by Eichhornia crassipes root powder.For the adsorption kinetics,the R~2 fitted by the pseudo-second-order model was 0.967(Ant)and 0.994(1-MP),respectively,which were higher than that fitted by the pseudo-first-order model,suggesting that the adsorption of parent PAHs and alkylated PAHs by Eichhornia crassipes root powder was dominated by chemical heterogeneous adsorption. |
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