Exfoliation And Compound Of Layered Mg/Al LDHs And MnO₂ And Their Adsorption Performance

In recent year,2D nanomaterials has became research focus in the field of nanomaterials for their excellent performance in sensors,photocatalysis,capacitor,and adsorption etc.Now,nuclear energy has playing an increasingly important role in human life.Adsorption is recognized as a new,efficient and economical method for separation and enrichment of uranium.Adsorption has good prospects.In the process of adsorption,2D nanosheets has more exposure interface and adsorption sites compared to bulk materials.In this paper,three kinds of effective solution exfoliation Methods has proposed.Used thosethreemethods,wepreparedLDHsandMnO₂nanosheetsuccessfully.SEM,TEM,XRD and other testing means,has used to confirm the morphology and formation mechanism of product.Compositing with Fe₃O₄,a series of magnetic materials,such as Fe₃O₄@E-LDHs and Fe₃O₄@E-MnO₂ has prepared.The introduction of Fe₃O₄ magnetic particles makes the fast and efficient recovery of adsorbent.The uranium adsorption properties by as-prepared products are investigated.Mg/Al LDHs ultrathin nanosheetswere successfully prepared byMg/Al-CO₃^2-LDHs as precursor,NH₄NO₃ as plate expander,formamide as agent.E-LDHs ultrathin nanosheets colloidal substance was completely transparent,with obvious Tyndall effect,the diamete of E-LDHs about hundreds of nanometer and the thickness is about 8.7 nm.We prepared E-LDHs film for methyl orange（MO）adsorption.The results show that LDHs layered structure maintaind well after the adsorption.In the interlayer,MO^-ion in parallel to the LDHs plate.With Fe₃O₄ magnetic material as substrate,Fe₃O₄@E-LDHs composite material was successful prepared.Fe₃O₄@E-LDHssize is about 1²μm,with uneven surface and severalFe₃O₄sphericalparticlescloselybondedtogetherby LDHs.Fe₃O₄@E-LDHs composite has good magnetic response,saturation magnetization is23.5 emu/g.Study found that Fe₃O₄@E-LDHs composite has good uranium adsorption properties.When Co=121.1 mg/L,Fe₃O₄@E-LDHs is 0.01 g,adsorption timeis 2h,adsorption temperature is 25℃and pH=5,the uranium adsorption capacity reached224.6mg/g.Kinetic studies showed that Fe₃O₄@E-LDHsadsorption of uranyl is homogeneous monolayer adsorption.Thermodynamics research shows that Fe₃O₄@E-LDHs on adsorption of uranium in different temperature are all showed:（35）G⁰<0,（35）H⁰>0,indicating that the adsorption is the endothermic process,adsorption reaction occur spontaneously.Suggesting that raise the temperature promote adsorption reaction.Using K-MnO₂ as precursor,with the protonation exchanging and solution exfoliation steps,E-Birnessite nanosheets were prepared.Addition K-MnO₂ to（NH₄）₂S₂O₈ solution can occur following changes:（001）peak changed from 12.967°to 12.300°,suggesting interlayer spacing increased from 0.6823 nm to 0.7198 nm,and the transformation of K-MnO₂ structure to the H-MnO₂ happened.With H-MnO₂ as precursor,TMAOH as solvent,E-MnO₂ ultrathin nanosheets can be prepared successfully,the nanosheet thickness is about 5.2nm,about 7 MnO₂ layers.At the same time,the nano film has spontaneousstacking,crimpcharacteristics.StudiesshownH-Birnessite（001）and（002）peaks gradually shift to lower angles,（001）peaks were appeared in10.959°,9.480°and 7.351°,corresponding to layer spacing 0.8074 nm,0.9330 nm and1.2027 nm.Compared to K-MnO₂,H-MnO₂layer spacing of 0.7198 nm increased a lot,and layered structure from crystal structure change into a non crystal structure.With Fe₃O₄ magnetic material as substrate,Fe₃O₄@E-MnO₂ composite material was successful prepared,Fe₃O₄@E-MnO₂ size is about sevralμm,dozens of Fe₃O₄ spherical particles closely bonded together by MnO₂.Those composite has good magnetic response,the saturation magnetization is 41.6 emu/g.Studies found that Fe₃O₄@MnO₂composite has good adsorption properties for uranium.When Fe₃O₄@MnO₂ is 0.01g,adsorption time is 6 h,C₀=688.9 mg/g,T=45°C,the adsorption capacity reached1325.8mg/g.Kinetic studies showed that Fe₃O₄@E-MnO₂ adsorption of uranyl ion in water is more in line with the pseudo-second-order kinetics with R²=0.9903.The Langmuir isothermal adsorption equation can describe the adsorption behavior of Fe₃O₄@E-MnO₂.So,adsorption is homogeneous monolayer adsorption.H₂O₂as solvent,usingpropertyof H₂O₂exfoliatedLDHslayered materialsintoultrathinnanosheets.AlargenumberofO₂generationwhen H₂O₂ decomposition and create a super high pressure environment.For violent movement of molecularoxygen,theLDHslayeredmaterialsexfoliatedintoultrathin nanosheets,realizating the LDHs layer prepation in one step.Changing H₂O₂ concentration to 0 wt%,10 wt%,20 wt%and 30 wt%,results show that with the increase of H₂O₂concentration,crystallization degree of LDHs decreased and the interlayer spacing increased.At the same time,the LDHs product is becoming more and more transparent,whenhydrogen peroxide content reached 30wt%,the product is translucent gelatinous material.the product is ultrathin nanosheets,with size of 50¹00nm,thickness is 1.4 nm（two LDHs layers）.LDHs prepared by the method of strip products with high thermal stability.