Design Of Magnetic Micro/Nanostructured Composites And Their Application In Heavy Metal Decontamination

The progress of human society has brought serious ecological damage and environmental pollution,which causes serious threats and injuries to human health.Heavy metals are the most common class of environmental pollutants in the environment and often coexist with organic matter in polluted wastewater,which makes the removal of heavy metal ions more challenging.It is important to develop efficient adsorbent materials.In this paper,three kinds of highly efficient adsorbable materials,namely GO/Fe₃O₄,Fe₃O₄/PDA/LDH（denoted as MPL）and NZVI/rGOs composites,were synthesized by coprecipitation method,hydrothermal method and low temperature H2/Ar plasma technique and used for the removal of heavy metal ions from wastewater.These three materials combined the high adsorption properties of graphene/dopamine/LDH and the magnetic separation properties of magnetic iron oxide/zero valent iron nanoparticles,demonstrating excellent removal and recycling properties for heavy metal ions.At the same time,we also studied the effects of solution environment,such as solution pH,background electrolyte ionic strength,contact time,amount of adsorbent and system temperature on the removal of heavy metal ions by these three materials.In addition,we also studied the effects of coexistence of organic compounds,such as natural organic macromolecules FA,MO and CR dyes,on the removal of heavy metal ions by the three adsorbent materials.Moreover,we used XPS,XRD,FTIR and other methods to study the adsorption mechanism of heavy metal ions on by these three materials.These research results are of great significance to the design and development of new adsorbent materials and the practical application of adsorbent materials in the environment.The main research findings are listed as follows:1)GO/Fe₃O₄ composites were synthesized and characterized by SEM,TEM and XPS.The removal of Cu（Ⅱ）and a natural organic macromolecule（fulvic acid（FA））by GO/Fe₃O₄ was investigated.The mutual effects of FA/Cu（Ⅱ）on Cu（Ⅱ）and FA sorption onto GO/Fe₃O₄,as well as the effect of pH,ionic strength,FA/Cu（Ⅱ）concentrations,and the addition sequences of FA/Cu（Ⅱ）were examined.The results indicated that Cu（Ⅱ）sorption on GO/Fe₃O₄ were strongly dependent on pH and independent of ionic strength,indicating that the sorption was mainly dominated by inner-sphere surface complexation rather than outer-sphere surface complexation or ion exchange.The presence of FA leads to a strong increase in Cu（II）sorption at low pH and a decrease at high pH,whereas the presence of Cu（II）led to an increase in FA sorption.The adsorbed FA contributes to the modification of sorbent surface properties and partial complexation of Cu（II）with FA adsorbed.Different effects of FA/Cu（II）concentrations and addition sequences on Cu（II）and FA sorption were observed,indicating the difference in sorption mechanisms.After GO/Fe₃O₄ adsorbed FA,the adsorption capacity for Cu（II）was enhanced at pH 5.3;the adsorption capacity for FA was also enhanced after Cu（II）sorption on GO/Fe₃O₄.These results are important for estimating and optimizing the removal of metal ions and organic substances by the GO/Fe₃O₄ composites.2)We reported a novel magnetic polydopamine（PDA）-LDH（MPL）bifunctional material,which is fabricated by an easy and green approach for the simultaneous removal of potentially toxic metals and anionic dyes.In this assembly,both PDA and LDH are expected to capture these pollutants.In a mono-component system,the removal behaviors showed heterogeneous removal capacities of 75.01,624.89 and 584.56 mg/g for Cu（Ⅱ）,methyl orange（MO）and Congo red（CR）,respectively.Interestingly,the presence of CR and MO enchanced the removal of Cu（II）significantly in the Cu（Ⅱ）-dye binary system.However,the presence of Cu（II）had no significant effect on dyes.Based on the characterization results including XRD analysis,FTIR spectroscopy,XPS and elemental mapping,the removal of Cu（II）was mainly controlled by bonding with surface functional groups（hydroxyl,catechol,imine and amine groups）,coupled with the isomorphic substitution and surface precipitation.In summary,such green and facile synthesis method,efficient removal performance and superior reusability suggest that the MPL assemblies have practical application potential for integrative and efficient treatment of coexisting toxic pollutants.3)The nanoscale zero-valent iron（NZVI）particles supported on reduced graphene oxides（denoted as NZVI/rGOs）from spent GO-bound Fe ions was proposed by using a H2/Ar plasma reduction method to improve the reactivity and stability of NZVI.The NZVI/rGOs exhibited excellent water treatment performance with an excellent removal capacity of 187.16 and 396.37 mg/g for Cr and Pb,respectively.Moreover,the NZVI/rGOs could be regenerated by plasma treatment and maintained high removal ability after four cycles.XPS analysis results implied that the removal mechanisms could be attributed to adsorption/precipitation,reduction or both.Such multiple removal mechanisms by the NZVI/rGOs were attributed to the reduction ability of the NZVI particles and the role of dispersing and stabilizing abilities of the rGOs.The results indicated that the NZVI/rGOs prepared a H2/Ar plasma reduction method may be an effective composite for heavy metal ion removal.In conclusion,herein we have prepard three kinds of magnetic nanocomposites for the removal of heavy metal ions from aqueous solutions,which showed excellent removal performance and recycling ability.These results are important guide the development and design of highly efficient adsorbent materials.