Sorption Mechanism of Tributyltin to Black Carbon in Seawater System

Abstract

Two BC(black carbon) samples,BC700 and BC400,were prepared from China fir wood by pyrolytic charring at 700 and 400 ℃,respectively.The sorption behavior and mechanisms of tributyltin(TBT) on the two BC samples were evaluated as a function of seawater pH and salinity.The results indicated that BC700 had a higher specific surface area but lower content of organic matter than BC400.TBT sorption on BC700 was primarily a physical adsorption process while hydrophobic partitioning also significantly contributed to TBT sorption on BC400.Increasing salinity from 5 to 35 g/kg facilitated TBT sorption by 1.03—2.12 times as an overall result of the enhancing effective concentration of TBT because of 'salting-out' and the reducing role of electrostatic interaction because of BC surface charge neutralization.Environmental pH had a significant influence to TBT forms in the solution.It was found that TBT existed in both cationic(TBT+) and uncharged species at pH=4.00 and 6.25 but mostly in uncharged species(TBT) at pH=8.00.TBT sorption reached maximum at pH=6.25,as compared to pH=4.00 and 8.00,due presumably to multiple mechanisms involving electrostatic interaction,physical adsorption and hydrophobic partitioning between TBT and BC.In addition,XPS spectra showed that the binding energy of Sn3d5/2 peak shifted higher with decreasing pH,confirming the TBT-BC electrostatic interaction.Therefore,sorption of TBT on the BC700 was mainly physical adsorption and electrostatic interaction while hydrophobic partitioning also significantly contributed to TBT sorption on BC400.