Preparation Of Amino Polymeric Magnetic Adsorbents And Their Removal Of Cr(Ⅵ) From Contaminated Water

As a common heavy metal pollutant in wastewater of industry,Cr（Ⅵ）has a serious impact on the ecological environment and even human safety.To efficiently remove Cr（Ⅵ）from water bodies,a core structure of Fe₃O₄@ZIF-8 was constructed by coating a metal-organic skeleton ZIF-8 on the surface of magnetic material Fe₃O₄,and amino functionalization was further carried out on this basis.Consequently,two amino functionalized magnetic adsorbents,Fe₃O₄@PmPD（Z）and Fe₃O₄@ZIF-8@PmAP,were synthesized by polymerization of m-Phenylenediamine and 3-Aminophenol as monomers,respectively.Besides,the adsorption performance and removal mechanism of Cr（Ⅵ）by Fe₃O₄@PmPD（Z）and Fe₃O₄@ZIF-8@PmAP were investigated.The conclusions are as follows.（1）According to the results of TEM,XRD,and BET,as well as other morphological and structural characterization,the superparamagnetic core-shell materials Fe₃O₄@PmPD（Z）was successfully synthesized by polymerizing with m-Phenylenediamine.Static adsorption experiments showed that the adsorption of Cr（Ⅵ）by Fe₃O₄@PmPD（Z）increased with the decrease of pH,and the optimum pH was 2.The adsorption capacities of Fe₃O₄@PmPD（Z）for Cr（Ⅵ）reached 309.59,335.57,and 371.75 mg g^-1at temperatures of 298K,308K,and 318K,respectively.After the first round of the adsorption-desorption cycle,the recycled adsorption capacity of adsorbent Fe₃O₄@PmPD（Z）is only 78.00%of the original.In addition,the presence of interfering ions reduced the adsorption capacity of Fe₃O₄@PmPD（Z）for Cr（Ⅵ）,with the greatest effect of SO₄^2-.The adsorption process is best fitted by the pseudo-second-order kinetic model,and the results of thermodynamic model show that it is a spontaneous and endothermic chemisorption reaction.The mechanism study showed that the adsorption of Cr（Ⅵ）by Fe₃O₄@PmPD（Z）includes two parts,one is the electrostatic adsorption of-N=⁺and HCr O₄^-;the other is the redox reaction between Cr（Ⅵ）and-NH-to generate Cr（III）first,and then adsorbed and removed by the chelation of-N=with Cr（III）.（2）The magnetic adsorbent Fe₃O₄@ZIF-8@PmAP was also successfully synthesized using raw material 3-Aminophenol as the polymeric monomer.Similarly,the adsorption effect of Fe₃O₄@ZIF-8@PmAP for Cr（Ⅵ）was closely related to pH,and the optimum pH value was 2.In addition,the adsorption capacity of Fe₃O₄@ZIF-8@PmAP for Cr（Ⅵ）increased with the increase of reaction temperature and initial concentration of pollutants.Specifically,the adsorption capacities of Fe₃O₄@ZIF-8@PmAP for Cr（Ⅵ）at 298K,308K,and 318K were 373.32,456.80,and506.05 mg g^-1,respectively,which were similar to the results of 406.50,485.44,and526.32 mg g^-1fitted by Langmuir model.The adsorption process is best fitted by the pseudo-second-order kinetic model,and the results of thermodynamic model show that it is a spontaneous and endothermic chemisorption reaction.Besides,the characterization results of material before and after the adsorption of Cr（Ⅵ）indicated that in addition to the similar adsorption mechanism to Fe₃O₄@PmPD（Z）.The oxidation of hydroxyl groups of poly（m-aminophenol）on the surface of Fe₃O₄@ZIF-8@PmAP to carboxyl groups provides more adsorption sites.Hence,the adsorption performance of Fe₃O₄@ZIF-8@PmAP is significantly improved and its adsorption capacity is 19.42%higher than that of Fe₃O₄@PmPD（Z）.