Study On The Properties Of Regenerative LDH/Carbon Composites To Remove Heavy Metals From Water

In recent years,the water pollution caused by heavy metals has become more and more serious as it is easy to accumulate,difficult to degrade,and toxic.Based on the advantages of low cost,high efficiency and simple operation,adsorption method has attracted wide attention to remove heavy metals from water.The key to the adsorption is to find adsorbent with low cost,easy separation and excellent adsorption performance.Humic acid?HA?is the main precursor of disinfection by-product of drinking water,which seriously affects the efficiency of water pollution treatment.Likewise,graphene oxide?GO?has been shown to cause inflammatory cell infiltration,granuloma formation and even pulmonary edema,and to be difficult to degrade into non-toxic small molecules or harmless products.In this dissertation,two kinds of carbon/layered double oxides were successfully obtained from spent magnetic layered double hydroxides?Mag-LDH?via regeneration technology.Heavy metal ions?Cu?II?,Pb?II?and Cd?II??in wastewater were eliminated by the as-synthesizde materials using batch sorption experiments.And the results are as follows:?1?Mag-LDH was applied for humic acid removal,which prepared via a solvothermal method.After reaction,the spent adsorbent was recovered and calcined in muffle roaster,and yielded the magnetic MgAl-layered double oxide/carbon?Mag-LDO/C?.The obtained Mag-LDO/C was characterized by XRD?X-ray diffraction?,EL?elemental analyzer?,TEM?transmission electron microscopy?,SEM?scanning electron microscopy?,EDS?energy dispersive spectroscopy?,XPS?X-ray photoelectron spectroscopy?,and specific surface area determination.The results indicated Mag-LDO/C was the carbonaceous composite with abundant functional groups and large specific surface area.To study the sorption performance of Mag-LDO/C for Cd?II?,Pb?II?,and Cu?II?,the batch equilibrium experiments were carried out.The obtained data were fitted by the adsorption kinetic and isotherm models.The results suggested that the kinetic data were well followed with the pseudo-second-order equation and the equilibrium isothermal data fitted the Langmuir isotherm model well.Moreover,the potential application of Mag-LDO/C was further explored through the recycling and simulated wastewater experiments.Finally,the mechanisms of heavy metals adsorption on Mag-LDO/C were also investigated using various characterization methods,such as zeta potential,XRD,and XPS.The results indicated Cu?II?,Pb?II?,and Cd?II?ions may be removed by Mag-LDO/C via bonding with surface function groups,precipitation of hydroxide or carbonate of heavy metals,and electrostatic attraction with negatively charged surface of Mag-LDO/C.?2?Mag-LDH and Mag-LDO were prepared by the solvothermal method and two-step method.The results of XRD,FTIR,and TEM indicated that that Fe₃O₄ particles were successfully loaded on the surface of the materials.The batch adsorption experiments showed that Mag-LDH and Mag-LDO efficiently removed GO from water.The adsorption mechanism was the electrostatic interaction and surface complexation.In order to recover and reuse the spent adsorbents,Mag-LDH after GO adsorption was collected in the presence of external magnetic field.Using the calcination method as in the previous chapter,we prepared magnetic graphene oxide/layered double oxide?Mag-LDH/GO?from waste Mag-LDH after adsorption of GO.And then,Mag-LDO/GO was performed with XRD,XPS,TEM,SEM with EDS techniques,surface area determination,and also with VSM?vibrating sample magnetometer?.The characterization results suggested that unlike the structure of Mag-LDO/C,the carbon in Mag-LDO/GO was present in GO flake.Through the adsorption performance tests of Cu?II?and Cd?II?,the adsorption capacity of Mag-LDO/GO had been greatly improved,as compared to Mag-LDH/GO.Moreover,it is applicable to a wide range of pH,has a short adsorption time,and can achieve rapid solid-liquid separation in the presence of external magnetic field.The above results proved that Mag-LDO/GO exhibited great potential practical application value.In addition,the interaction mechanisms involved the formation of metallic hydroxides and metallic carbon oxides,memory effect of calcined LDH,as well as surface complexation.