Study On The Preparation Of Functionalized Magnetic Attapulgite And Its Application In Wastewater Treatment

In recent years,with the fast development of industry in China,water pollution is more and more serious,especially the dye pollution and heavy metal pollution,which has great harm to river water source,aquatic organisms and the health of human.Therefore,the development of efficient,low energy consumption,environment-friendly and renewable new materials for dye and heavy metal wastewater treatment has become an important issue to be solved.In this work,attapulgite was used as raw material to develop a low-cost,green,efficient and stable environment-friendly adsorbent.Functional magnetic attapulgite adsorbents ATP-Fe₃O₄-PEI and ATP-Fe₃O₄-APTES were prepared by grafting magnetic Fe₃O₄nanoparticles onto the surface of purified attapulgite（ATP）and then modifying with polyethyleneimine（PEI）and 3-aminopropyl triethoxy silane（APTES）,respectively.Taking the Congo red and Pb²⁺as the representative pollutants of dye and heavy metal ions to study the adsorption properties of the functional magnetic attapulgite composites.The main achievements are as follows:（1）The composition and structure of the ATP-Fe₃O₄-PEI and ATP-Fe₃O₄-APTES adsorbent were characterized by using X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）,specific surface area（BET）,Zeta potential measurement,analysis of magnetic properties（VSM）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The results showed that the crystal structure of attapulgite was not damaged after grafting with the magnetic Fe₃O₄nanoparticles and PEI/APTES modification.The specific surface area of the modified attapulgite decreases,which may be due to the fact that partial ATP channels were filled by the attachment of magnetic Fe₃O₄nanoparticles and the modification of PEI/APTES.Zeta potential analysis showed that the ATP-Fe₃O₄-PEI material was positively charged in neutral to acidic environment,which is conducive to the adsorption of negatively charged dye molecules.（2）Functional magnetic attapulgite adsorbents ATP-Fe₃O₄-PEI was used to treat the Congo red wastewater.The effects of solution p H,initial concentration of Congo red,adsorption time and temperature on the adsorption of ATP-Fe₃O₄-PEI for Congo red were studied.The results showed that the increase of Congo red solution concentration,decrease of p H value and increase of adsorption time are conducive to the adsorption of Congo red.When the concentration of Congo red solution is3000mg·L^-1,p H=3 and adsorption time 1h,the adsorption capacity of ATP-Fe₃O₄-PEI for Congo red is as high as 5623.23mg·g^-1,which is the largest adsorption capacity of known mineral materials for dyes.The adsorption kinetics and isotherm of Congo red on ATP-Fe₃O₄-PEI were studied.It was found that the adsorption process conformed to the pseudo second order kinetic model and Freundlich model,indicating that the adsorption of Congo red on ATP-Fe₃O₄-PEI was a multi-layer physical adsorption.The driving force for adsorbing was mainly from the electrostatic attraction and hydrogen bond between the material and Congo red,as well as the electrostatic attraction andπ-πinteraction between Congo red molecules.These results indicate that ATP-Fe₃O₄-PEI is an adsorbent with excellent adsorption performance for dye molecules,and it is expected to be applied in dye wastewater treatment.（3）The adsorption behavior of functional magnetic attapulgite adsorbents ATP-Fe₃O₄-APTES for heavy metal ions of Pb²⁺was studied.The effects of solution p H,adsorption time,initial Pb²⁺concentration and adsorption temperature on the adsorption efficiency of Pb²⁺were investigated.The results showed that the increase of Pb²⁺concentration,p H value,temperature and adsorption time will contribute to the increase of the adsorption capacity for Pb²⁺.When the concentration of Pb²⁺is100mg·L^-1,p H=5,temperature 30℃and adsorption time 6h,the ATP-Fe₃O₄-APTES composite has the best adsorption efficiency for Pb²⁺with adsorption capacity about129.32mg·g^-1.The study of adsorption kinetics and isotherm shows that the adsorption process accords with the pseudo second order kinetic model and Langmuir model,indicating that the adsorption is monolayer chemical adsorption.The thermodynamics of adsorption shows that the adsorption is a spontaneous endothermic process.The driving force for adsorbing mainly comes from the coordination between Pb²⁺and-NH₂on the material surface.These results show that the prepared functional ATP-Fe₃O₄-APTES composite has excellent adsorption performance for heavy metal ions,and has potential application value in heavy metal ion wastewater treatment.（4）ATP-Fe₃O₄-PEI and ATP-Fe₃O₄-APTES have different adsorption performance for the dyes and heavy metal ions.ATP-Fe₃O₄-PEI has lager adsorption capacity for Congo red,while ATP-Fe₃O₄-APTES has better adsorption efficiency for Pb²⁺,which is related to the surface feature of the amino groups on the two materials and the molecular/atomic property of the adsorbates.The primary,secondary and tertiary amino groups on the surface of PEI are in a disordered state,which may not be conducive to the adsorption of Pb²⁺,but the adsorption for Congo red macromolecules with a large number of-NH₂,-N=N-,and-SO₃^-groups are probably not affected,and exhibit better adsorption performance through electrostatic attraction and hydrogen bonding.The adsorption of Pb²⁺on ATP-Fe₃O₄-APTES is mainly carried out by the coordination of Pb²⁺with-NH₂groups.The compact and ordered-NH₂groups on the APTES surface is more conducive to the adsorption of Pb²⁺,so the ATP-Fe₃O₄-APTES composite has better adsorption performance for Pb²⁺.