The Preparation Of Plant Polyphenols Magnetic Composites And Adsorption Of Heavy Metals

As a natural polyphenolic material,plant polyphenols(PP)are abundant in nature,ubiquitous and inexpensive.PP exhibit a specific affinity towards numerous metal ions and can form stable complexes.However,plant polyphenols are water soluble.In order to remove aqueous heavy metals,PP require immobilization or modification processes before being used.In this study,the traditional way of plant polyphenols used was changed and PP were combined with Fe3O4 to prepare Fe3O4/PP and Fe3O4/SiO2/PP.It can not only effectively adsorb heavy metals,but also achieve rapid separation under an external magnetic field which overcome the difficulty in separating immobilized PP adsorbents after removing heavy metals from aqueous solution.Fe3O4/PP was synthesized by physical coating method,and characterized by FE-SEM,VSM,TGA and XRD.The surface morphology of Fe3O4/PP was observed and the magnetic properties,thermal stability and crystal structure were analyzed.To investigate the adsorption properties of Cu(Ⅱ),Cd(Ⅱ)and Pb(Ⅱ)on Fe3O4/PP,the effect of some factors,such as pH,contact time,initial metal ion concentration,adsorbent dosage,agitating speed and coexisting ions were studied.The adsorption eapacity of Cu(Ⅱ),Cd(Ⅱ)and Pb(Ⅱ)increased gradually with the increase of pH.The results of adsorbent dosage showed that the coating of PP could improve the adsorption properties of magnetic material.The adsorption kinetics of Cu(Ⅱ),Cd(Ⅱ)and Pb(Ⅱ)followed a pseudo second-order model indicating that the adsorption was controlled by chemieal proeesses and the reaction reached equilibrium around 2 h.The adsorption isotherm fitted well with the Langmuir model.Thermodynamic studies demonstrated that the adsorption process of Cu(Ⅱ),Cd(Ⅱ)and Pb(Ⅱ)were spontaneous and endothermic processes with an increase of entropy,The results of FT-IR and XPS showed that electrostatic interaction and complexation may be involved in the adsorption of Cd(Ⅱ)on Fe3O4/PP.The complexation of hydroxyl functional groups ofPP with Cd(Ⅱ)is the main mechanism.The Cd(Ⅱ)adsorbed on Fe3O4 could not be completely desorbed,but Cd(Ⅱ)reacted with PP could be desorbed and re-adsorbed.Fe3O4/SiO2/PP was synthesized by orthogonal experiment.The prepared material was characterized by FE-SEM,VSM,TGA and XRD.The surface morphology of Fe3O4/SiO2/PP was observed and the magnetic properties,thermal stability and crystal structure were analyzed.To investigate the adsorption properties of Cd(Ⅱ)on Fe3O4/SiO2/PP,the effect of some factors,such as pH,contact time,initial metal ion concentration,adsorbent dosage,agitating speed and coexisting ions were studied.The adsorption capacity of Cd(Ⅱ)increased gradually with the increase of pH.The results of adsorbent dosage showed that the coating of S1O2 and PP significantly improved the removal of Cd(Ⅱ)by magnetic material.The adsorption kinetics of Cd(Ⅱ)onto Fe3O4/SiO2/PP followed a pseudo second-order model indicating that the adsorption was controlled by chemical processes and the reaction reached equilibrium around 2 h.The adsorption isotherm fitted well with the Langmuir model.Thermodynamic studies demonstrated that the adsorption process of Cd(Ⅱ)was spontaneous and endothermic processes with an increase of entropy.The results of FT-IR and XPS showed that electrostatic interaction and complexation may be involved in the adsorption of Cd(II)on Fe3O4/SiO2/PP.The complexation of hydroxyl functional groups of PP with Cd(Ⅱ)is the main mechanism.The Cd(Ⅱ)adsorbed on Fe3O4 and Fe3O4/SiO2 could not be completely desorbed,but Cd(Ⅱ)reacted with PP could be desorbed and re-adsorbed.