Performance Of Arsenic And Antimony Removal By ZIF-8 And Its Complex And Structural Stability On ZIF-8

Zeolitic imidazolate frameworks(ZIFs)are a subclass of MOFs by construction of metal ions(Zn and Co cations)with imidazolate-type links,exhibiting a Rho topology which is well known for zeolites.Among them,ZIF-8 is a most compelling example as a result of its remarkable hydrolytic stability,which formed by zinc and 2-methylimidazole(Hmim)with Sod-type porous structure.We investigates ZIF-8 removal rates of arsenite[As(III)],arsenate[As(V)],and antimonite[Sb(V)],which result that the higher of aqueoue solution is,the lower of removal rates are.The suitable pH is around 9.0.The maximum adsorption density is determined to be 2.02 mmol/g,1.42 mmol/g,0.93 mmol/g for As(III),As(V),and Sb(V)at pH 8.6.In the As(?)-Sb(V)and As(V)-Sb(V)coexisting systems,As(?)and As(V)inhibits Sb(V)removal rates in the pH range from 8.0 to 9.8.The substitution of As(?)and As(V)by Sb(V)occurs at lower pH of below 8.8.The stability of zeolitic imidazolate framework-8 was investigated in 7 common anions aqueous solutions.The results showed that Cl",SO42-,NO3-PO43-and CO32-cause insignificant change in the structure of ZIF-8 which can be confirmed by SEM images,XRD patterns and dissolution of Zn and Hmim.Nevertheless ZIF-8 phase is damaged by the presence of HCO3-for that ZIF-8 can attract HCO3-due to itself carried positive charge in HCO3-solution,and the dissolution of Zn and Hmim underwent a process of a giant ascent at the first stage and then a fall to a stable value meaning recrystallization of a new material.Furthermore the morphology of ZIF-8 changes a lot in the HPO42-solution and the XRD peaks declined with increasing the HPO42-concentration,although there is no new XRD phases appeared,which be caused by adsorption of phosphate by ZIF-8 because that HPO42-can be attracted by ZIF-8 carried positive charge in HPO42-solution.ZIF-8 is endowed with high water-stability when immersed in HCO3-or HPO42-solutions with excessive Hmim.In the paper,we have successfully synthesized(?-MnO2@ZIF-8 nanowires by a rapid and easy method.The P-MnO2@ZIF-8 can be a desired adsorption to achieve oxidation and adsorptive removal of As(III).Furthermore,the results of adsorption show that ?-MnO2@ZIF-8 has a higher adsorption capacity than ZIF-8 bulks.And the ZIF-8 on P-MnO2@ZIF-8 is more easeier dispersed than ZIF-8 particles.The P-MnO2@ZIF-8 nano wires exhibited an excellent settleability by gravity alone,which solved the problem that nanoparticles ZIF-8 is difficult to separate from aqueous solution.