Adsorption and desorption of Cu2＋ on paddy soil aggregates pretreated with different levels of phosphate

Interactions between anions and cations are important for understanding the behaviors of chemical pollutants and their potential risks in the environment.Here we prepared soil aggregates of a yellow paddy soil from the Taihu Lake region,and investigated the effects of phosphate（P） pretreatment on adsorption-desorption of Cu2＋ of soil aggregates,free iron oxyhydrates-removed soil aggregates,goethite,and kaolinite with batch adsorption method.The results showed that Cu2＋ adsorption was reduced on the aggregates pretreated with low concentrations of P,and promoted with high concentrations of P,showing a V-shaped change.Compared with the untreated aggregates,the adsorption capacity of Cu2＋ was reduced when P application rates were lower than 260,220,130 and110 mg/kg for coarse,clay,silt and fine sand fractions,respectively.On the contrary,the adsorption capacity of Cu2＋ was higher on P-pretreated soil aggregates than on the control ones when P application rates were greater than those values.However,the desorption of Cu2＋ was enhanced at low levels of P,but suppressed at high levels of P,displaying an inverted V-shaped change over P adsorption.The Cu2＋ adsorption by the aggregate particles with and without P pretreatments was well described by the Freundlich equation.Similar results were obtained on P-pretreated goethite.However,such P effects on Cu2＋adsorption-desorption were not observed on kaolinite and free iron oxyhydrates-removed soil aggregates.The present results indicate that goethite is one of the main soil substances responsible for the P-induced promotion and inhibition of Cu2＋ adsorption.

Complex interplay between formation routes and natural organic matter modification controls capabilities of C_(60)nanoparticles(nC_(60)) to accumulate organic contaminants

Accumulation of organic contaminants on fullerene nanoparticles（nC（60）） may significantly affect the risks of C（60） in the environment.The objective of this study was to further understand how the interplay of nC（60） formation routes and humic acid modification affects contaminant adsorption of nC（60）.Specifically,adsorption of 1,2,4,5-tetrachlorobenzene（a model nonionic,hydrophobic organic contaminant） on nC（60） was greatly affected by nC（60）formation route- the formation route significantly affected the aggregation properties of nC（60）,thus affecting the available surface area and the extent of adsorption via the pore-filling mechanism.Depending on whether nC（60） was formed via the ＂top-down＂ route（i.e.,sonicating C（60） powder in aqueous solution） or ＂bottom-up＂ route（i.e.,phase transfer from an organic solvent） and the type of solvent involved（toluene versus tetrahydrofuran）,modification of nC（60） with Suwannee River humic acid（SRHA） could either enhance or inhibit the adsorption affinity of nC（60）.The net effect depended on the specific way in which SRHA interacted with C（60） monomers and/or C（60） aggregates of different sizes and morphology,which determined the relative importance of enhanced adsorption from SRHA modification via preventing C（60） aggregation and inhibited adsorption through blocking available adsorption sites.The findings further demonstrate the complex mechanisms controlling interactions between nC（60） and organic contaminants,and may have significant implications for the life-cycle analysis and risk assessment of C（60）.