摘要
Fe_(3)O_(4)-based materials are widely used for magnetic separation from wastewater.However,they often suffer from Fe-leaching behavior under acidic conditions,decreasing their ac-tivity and limiting sustainable practical applications.In this study,covalent organic frame-works(COFs)were used as the shell to protect the Fe_(3)O_(4) core,and the Fe_(3)O_(4)@COF core-shell composites were synthesized for As(Ⅲ)removal from acid wastewater.The imine-linked COFs can in situ grow on the surface of the Fe_(3)O_(4) core layer by layer with[COFs/Fe_(3)O_(4)]mol ratio of up to 2∶1.The Fe-leaching behavior was weakened over a wide pH range of 1-13.Moreover,such composites keep their magnetic characteristic,making them favorable for nanomaterial separation.As(Ⅲ)batch adsorption experiments results indicated that,when COFs are used as the shell for the Fe_(3)O_(4) core,a balance between As(Ⅲ)removal efficiencies and the thickness of the COF shell exists.Higher As(Ⅲ)removal efficiencies are obtained when the[COFs/Fe_(3)O_(4)]mol ratios were<1.5∶1,but thicker COF shells were not beneficial for As(Ⅲ)removal.Such composites also exhibited better As(Ⅲ)removal performances in the pH range of 1-7.Over a wide pH range,the zeta potential of Fe_(3)O_(4)@COF core-shell compos-ites becomes more positive,which benefits the capture of negative arsenic ions.In addition,thinner surface COFs were favorable for mass transfer and facilitating the reaction of Fe and As elements.Our study highlights the promise of using COFs in nanomaterial surface protection and achieving As(Ⅲ)depth removal under acidic conditions.
基金
This work was partly supported by the National Key R&D Program of China(No.2017YFC0210500)
the National Natural Science Foundation of China(Nos.21806105,and No.52070129)
This study was also supported by the Startup Fund for Youngman Research at SJTU(No.19×100040083).
