| The removal of heavy metal ions and recovery of precious metal ions from wastewater is an important issue for green and sustainable development.Adsorption method is widely used for the removal and recovery of heavy and precious metal ions from wastewater due to its high efficiency,low cost and simple operation.Magnetic Fe3O4 nanoparticle displays the advantages of high specific surface area,easy separation and no-secondary pollution.Thus,it has been widely applicated in the field of adsorption and separation of metal ions.In order to realize the efficient adsorption and separation of typical highly toxic heavy metal ions of Hg(Ⅱ)and Pb(Ⅱ)and precious metal ion of Au(Ⅲ),a series of nano-magnetic metal ion adsorbents were prepared by functionalizing silica coated Fe3O4(Fe3O4@SiO2)with nitrogen,oxygen and sulfur functional groups.The adsorption property and mechanism of the adsorbents for target metal ions were systematically studied.The relationship between the functional group structure and the adsorption performance was obtained.The research can provide theoretical basis and technical support for the preparation of novel efficient adsorption and separation materials.The main research contents are as follows:1.For the adsorption and separation of Hg(Ⅱ),a series of nano-magnetic Hg(Ⅱ)adsorbents(Fe3O4@SiO2-EDA,Fe3O4@SiO2-TEPA,Fe3O4@SiO2-AP,Fe3O4@SiO2UEA)were prepared by using Fe3O4@SiO2 as matrix.The epoxy groups were introduced by the reaction with 3-glycidoxypropyltrimethoxysilane(GPTS)first,and then functionalized with ethylenediamine,tetraethylenepentamine,aminopyridine and urea,respectively.The adsorption property of the as-prepared adsorbents for Hg(Ⅱ)was systematically studied by considering the effects of solution pH,time,temperature,Hg(Ⅱ)concentration,ion strength,coexisting ions,etc.The results show that the optimum pH of the four adsorbents for Hg(Ⅱ)was 6.Adsorption kinetic indicates the adsorption equilibrium of Fe3O4@SiO2-ED A,Fe3O4@SiO2-TEPA,Fe3O4@SiO2-AP and Fe3O4@SiO2-UEA for Hg(Ⅱ)can be achieved at 120,100,150 and 150 min,respectively.The adsorption kinetic process can be well fitted by pseudo-second-order kinetic model with film diffusion process as the rate-controlling step.Adsorption isotherm demonstrates the adsorption capacity of the as-prepared adsorbents for Hg(Ⅱ)increased with the increase of Hg(Ⅱ)concentration and temperature.The adsorption process is accorded with Langmuir model and is a spontaneous,endothermic,and entropy-increased chemical adsorption process.The adsorbents can selectively adsorb Hg(Ⅱ)with nearly 100%selectivity with the existence of Cd(Ⅱ),Fe(Ⅲ),Cu(Ⅱ)or Mn(Ⅱ).Adsorption mechanism indicates the interaction between ethylenediamine group and Hg(Ⅱ)is super than other functional groups.The adsorption capacity of the per-unit functional group(mmol)of ethylenediamine for Hg(Ⅱ)is 2.07 mmol,while those for tetraethylenepentamine,urea and aminopyridine are 0.80,0.26,and 0.16 mmol,respectively.2.For the adsorption and separation of Au(Ⅲ),a series of nano-magnetic Au(Ⅲ)adsorbents(Fe3O4@SiO2-EAL,Fe3O4@SiO2-TCA,Fe3O4@SiO2-LC,Fe3O4@SiO2TEA)were prepared by functionalizing Fe3O4@SiO2 with 1,2-ethanedithiol,mercaptoacetic acid,L-cysteine and thiourea using GPTS as the bridging group.The adsorption performance of the as-prepared adsorbents for Au(Ⅲ)was systematically studied.The results show that the optimal adsorption pH of the four adsorbents for Au(Ⅲ)was 2.5.Adsorption kinetics indicate the adsorption equilibrium for Au(Ⅲ)can be achieved at 180,120,100 and 150 min,respectively.The adsorption kinetic process can be well fitted by pseudo-second-order kinetic model and controlled by film diffusion process.Adsorption isotherms prove the adsorption capacity of the as-prepared adsorbents for Au(Ⅲ)increased with the increase of temperature and concentration.The maximum adsorption capacities of the four adsorbents for Au(Ⅲ)are 0.74,0.61,9.77,and 0.47 mmol·g-1,respectively.The adsorption process for Au(Ⅲ)can be fitted by Langmuir model and is a spontaneous,endothermic and entropy-increased chemical adsorption process.The adsorbents exhibit high adsorption selectivity for Au(Ⅲ)with the coexisting of Cu(Ⅱ),Mn(Ⅱ),Co(Ⅱ),Cd(Ⅱ),Cr(Ⅲ),Ni(Ⅱ)or Fe(Ⅲ).Adsorption mechanism shows that the adsorption capacity of 1,2-ethanedithiol group for Au(Ⅲ)is the highest one.The adsorption amount of per-unit functional group(mmol)of 1,2ethanedithiol for Au(Ⅲ)is 1.45 mmol,while those for thiourea,mercaptoacetic acid and L-cysteine are 0.71 mmol,0.57 mmol,and 0.40 mmol,respectively.3.For the adsorption and separation of Pb(Ⅱ),novel bridging groups were first prepared by the reaction of GPTS with diethylenetriamine,aminomethylpyridine,arginine,and thiourea.And then they were employed to functionalized Fe3O4@SiO2 to synthesize nano-magnetic Pb(Ⅱ)adsorbents(Fe3O4@SiO2-DETA,Fe3O4@SiO2-AMP,Fe3O4@SiO2-ARG,Fe3O4@SiO2-TSC).The adsorption performance and mechanism for Pb(Ⅱ)was systematically studied.The results show that the optimal pH of the four adsorbents for Pb(Ⅱ)is 6.Adsorption kinetics indicates the adsorption equilibrium can be reached at 240,300,180 and 150 min,respectively.The adsorption process was fitted by pseudo-second-order model with film diffusion as the rate-controlling step.Adsorption isotherm indicates that the adsorption capacity of the four adsorbents for Pb(Ⅱ)increased with the raising of temperature and Pb(Ⅱ)concentration.The adsorption isotherm process can be fitted by Langmuir model.The maximum adsorption capacity of Fe3O4@SiO2DETA,Fe3O4@SiO2-AMP,Fe3O4@SiO2-ARG and Fe3O4@SiO2-TSC for Pb(Ⅱ)are 0.93,0.54,0.66 and 0.99 mmol-g-1,respectively.The as-prepared adsorbents exhibit high adsorption selectivity for Pb(Ⅱ)in the presence of Ni(Ⅱ),Cu(Ⅱ),Fe(ⅡI),Cd(Ⅱ),Mn(Ⅱ)or Co(Ⅱ).Adsorption mechanism shows that the binding ability of diethylenetriamine group for Pb(Ⅱ)is superior than other functional groups.The adsorption capacity of the per-unit functional group of diethylenetriamine group for Pb(Ⅱ)is 1.11 mmol,which are 2.02,7.4,and 1.54 times to that of thiourea,aminomethylpyridine and arginine,respectively. |
