Fabrication And Separation Properties Of Mo(?)/W(?) Anion-Imprinted Ceramic Membrane

Molybdenum and tungsten,as relative rare elements in the earth crust and its resources are rather limited,but widely used in many aspects because of its excellent physical and chemical properties.On the one hand,it is necessary to develop the recovery of ruthenium secondary resources,due to it always exists as the associated mineral.On the other hand,because of the development of global industrialization,which can cause the increase of molybdate and tungstate level in water solution,and can lead to an environmental problem as well as do harm to human health.Therefore,it is an urgent task of environmental governance,and significantly important to develop new technologies and materials for the removal of Mo and W from waste and ground waters.Herein,we fabricated a novel surface ion-imprinted ceramic membrane by combining the membrane-based separation technique with ion-imprinting technology,to remove molybdate and tungstate anions from aqueous solutions selectively.The ion-imprinted membrane not only possesses the high selectivity of polymer,but also take advantages of the high temperature and corrosionresistance of inorganic membranes.In this work,we used an alu-mina ceramic membrane as the supporting material,and deposited with Si O2 active layer by situ hydrolysis deposition method.Subsequently,modified by ?-methacryloxy propyl trimethoxyl silane(MPS).Then,by using Mo(?)anion as template,1-vinylimidazole(?)as a complexing monomer and 1,6-dibromohexane as a cross-linker.Combining the advantages of membrane separation technology and surface ion imprinting technology.A Mo(?)anion surface-imprinted ceramic membrane(?P-PVI/CM)was prepared.The obtained samples were characterized by Fourier infrared spectroscopy(FT-IR),scanning electron microscopy(SEM),and thermogravimetric analyzer(TGA).The selective properties of ?P-PVI/CM for Mo(?)anions wereexamined by static adsorption and dynamic separation experiments in the presence of W(?)anions.In the process of graft-polymerization,the effects of monomer concentration,temperature,initiator amount and reaction time on the grafting degree of PVI were investigated in detail.Further,the effect of p H value on adsorption performance of ?P-PVI/CM was investigated.Results indicate that ?P-PVI/CM shows excelent adsorption capacity in the p H range 2-4.The adsorption behavior of ?P-PVI/CM toward Mo(?)were studied through adsorption kinetics and thermodynamics.The kinetics curve meets pseudo-second-order model.The adsorption isotherm can be described by Langmuir isotherm model.Also,?P-PEI/CM shows higher selectivity for Mo(?)in the presence of W(?)anions,and the selectivity coefficient is 7.48 for Mo(?)to W(?).A dynamic adsorption experiment was done by using a membrane apparatus.Results indicated that,?P-PVI/CM also shows good selectivity for separation of Mo(?)and W(?).The saturated adsorption times of W(?)and Mo(?)anions are 24 and 47 min,corresponding to the saturated adsorption amounts of 0.163 mmol/100 g for W(?)and 0.672 mmol/100 g for Mo(?),respectively.After nine adsorption-desorption cycles,the adsorption capacity of ?P-PVI/CM towards Mo(?)still reaches 92% of the initial capacity.The ?P-PVI/CM has good regeneration and recycling performance.A surface anion-imprinted ceramic membrane(?P-PEI/CM)was also facilely fabricated in this work,to remove tungstate anions(W(?))from aqueous solutions selectively.In this strategy,Cu SO4/H2O2 was used as a trigger.Polyethyleneimine(PEI)with Dopamine(DA)was co-deposited on the surface of ceramic membrane by one-step method,and because of the existence of the trigger,the deposition time was largely decreased.Then,W(?)anion was employed as a template to imprint in the PEI/PDA by using glutaraldehyde(GA)as a cross-linker,and then W(?)ions were eluted,obtaining the ?P-PEI/CM with many imprinted cavities for W(?).FT-IR,XPS,TGA and SEM were used to study the membrane performance.The binding behavior of ?P-PEI/CM towards W(?)anions was investigated in details.Results indicate that,binding capacities of W(?)onto ?P-PEI/CM and non-imprinted membrane(NIP-PEI/CM)are 139.4 and 47.9 mg/100 g at p H=2.0,respectively.The results of static adsorption indicates that the homogeneous binding sites are proved by Langmuir isotherm,and the kinetic data are fitted to both pseudo-first and second-order rat model.The binding equilibrium is achieved within 3 min,showing an ultra-fast kinetic process.Impacted by the process of imprinting,there are lots of imprinted cavities in the polymer matrixes,which could effectively match with the shape and size of the W(?)anions.?P-PEI/CM shows higher selectivity for W(?)in the presence of Mo(?)and Cr(?)ions,and selectivity coefficients for W(?)/Mo(?)and W(?)/Cr(?)are 15.47 and 19.74,respectively.During dynamic membrane filtration,?P-PEI/CM is effective and selective for removal of W(?),the saturation times of W(?),Mo(?)and Cr(?)are 360,60 and 50 s,corresponding to the saturation binding capacities of 136.14 mg/100 g for W(?),22.86 mg/100 g for Mo(?)and 19.05 mg/100 g for Cr(?),respectively.After three cycles,the rejection ratio of W(?)declines only 3.87%,and it has a good reusability.Finally,binding mechanism was further studied by X-ray photoelectron spectroscopy analysis.The protonated amine groups within PEI participate the uptake of W(?)anions by the electrostatic interactions.