Fabrication And Separation Properties Of Pt(Ⅳ) Ion-Imprinted Blending Membrane

Platinum is a precious metal that is lesser availability in nature and is increasing demand in various fields.Hence,it is important to develop high-efficiency technologies for separating and recovering platinum ions in aqueous solution.Ion-imprinted membranes（ⅡMs）have received much attention due to their high selectivity for target ions.In this paper,platinum（Ⅳ）ion-imprinted membranes（Pt（Ⅳ）-ⅡMs）were prepared based on amphiphilic block copolymers and graphene derivatives,respectively,and their separation properties were studied.The main contents are as follow:First,An amphiphilic block copolymer poly（methyl methacrylate）-b-poly（4-vinylpyridine）（PMMA-b-P4VP）was synthesized via the reversible addition fragmentation chain transfer polymerization,and characterized by hydrogen nuclear magnetic resonance（¹H NMR）,Fourier transform infrared（FTIR）and gel permeation chromatography（GPC）.Subsequently,poly（vinylidene fluoride）（PVDF）blend membranes were prepared using PMMA-b-P4VP as a blending additive.Effects of the following factors on performance of blend membranes were systematically examined:P4VP content of PMMA-b-P4VP,solvent type,and PMMA-b-P4VP/PVDF ratio.Further,platinum（Ⅳ）ion-imprinted membrane（Pt（Ⅳ）-ⅡM）was fabricated by blending polymer-Pt（Ⅳ）complexes with PVDF.Scanning electron microscope（SEM）,attenuated total reflection Fourier transform infrared（ATR-FTIR）,contact angle,water flux and adsorption capacity were employed to characterize all membranes.Results indicated that the membrane,which was prepared using the copolymer with high P4VP content（PP3）as a functional polymer,N,N-dimethylacetamide as a solvent and PMMA-b-P4VP/PVDF ratio of30 wt%,exhibited an intriguing morphology and much higher performance.Pt（Ⅳ）-ⅡM showed higher adsorption and selectivity for Pt（Ⅳ）（selectivity coefficients of 27.66 and 77.16 for Pt（Ⅳ）/Cu（Ⅱ）and Pt（Ⅳ）/Ni（Ⅱ）,respectively）compared with a non-imprinted membrane（NIM）.During membrane filtration,Pt（Ⅳ）-ⅡM was effective and selective for separation of Pt（Ⅳ）in the presence of Cu（Ⅱ）and Ni（Ⅱ）ions.Also,Pt（Ⅳ）-ⅡM was chemical stable,and had a good regeneration performance.Second,graphene oxide（GO）was synthesized via a pressurized oxidation.The GO was then functionalized with 3-amino propyl triethoxy silane（APTS）to obtain functionalized graphene oxide（GO-NH₂）,and characterized by X-ray diffraction（XRD）,FTIR and energy dispersive spectroscopy（EDS）.Further,Pt（Ⅳ）-ⅡM was fabricated by blending polymer-Pt（Ⅳ）complexes with PVDF.SEM,pure water contact angle and water flux were employed to characterize pure PVDF membrane,GO/PVDF blended membrane,GO-NH₂/PVDF blended membrane and Pt（Ⅳ）-ⅡM,and the adsorption properties of Pt（Ⅳ）-ⅡM and NIM were investigated.Results indicated that GO-NH₂ had good dispersibility in the membrane matrix compared with GO.GO and GO-NH₂ can significantly improve the hydrophilicity and water flux of the blend membrane.The adsorption behavior of Pt（Ⅳ）-ⅡM for Pt（Ⅳ）was significantly affected by pH value.The experimental results of static adsorption indicated that the adsorption capacities of Pt（Ⅳ）-ⅡM for Pt（Ⅳ）were 19.49 mg/g at pH 0.5.Pt（Ⅳ）-ⅡM had higher ability to adsorb Pt（Ⅳ）than NIM,and the adsorption process was fitted well with the Langmuir isotherm and the pseudo-second-order kinetic model.Pt（Ⅳ）-ⅡM had higher adsorption capacity and selectivity for Pt（Ⅳ）relative to Cu（Ⅱ）and Ni（Ⅱ）.During membrane filtration,the breakthrough occurs for Pt（Ⅳ）at the permeate volume of about 20 mL.Pt（Ⅳ）-ⅡM had a 18.7%loss of initial adsorption capacity after five adsorption-desorption cycles.Third,the GO was grafted with 3-methacryloxy propyl trimethoxyl silane（MPS）to obtain modified graphene oxide（GO-MPS）.The functionalized graphene oxide（GO-P4VP）was synthesized via radical polymerization of GO-MPS and 4-vinylpyridine（4VP）,and characterized by XRD,FTIR and EDS.Subsequently,Pt（Ⅳ）-ⅡM was fabricated by blending polymer-Pt（Ⅳ）complexes with PVDF.SEM,pure water contact angle and water flux were employed to characterize pure PVDF membrane,GO/PVDF blended membrane,GO-P4VP/PVDF blended membrane and Pt（Ⅳ）-ⅡM,and the adsorption properties of Pt（Ⅳ）-ⅡM and NIM were investigated.Results indicated that GO-P4VP had good dispersibility in the membrane matrix compared with GO.Nanosheets can significantly improve the hydrophilicity and water flux of the blend membrane.The adsorption behavior of Pt（Ⅳ）-ⅡM for Pt（Ⅳ）was significantly affected by pH value.The experimental results of static adsorption indicated that the adsorption capacities of Pt（Ⅳ）-ⅡM for Pt（Ⅳ）were 58.62 mg/g at pH 0.5.Pt（Ⅳ）-ⅡM had higher ability to adsorb Pt（Ⅳ）than NIM,and the adsorption process was fitted well with the Langmuir isotherm and the pseudo-second-order kinetic model.Pt（Ⅳ）-ⅡM had higher adsorption capacity and selectivity for Pt（Ⅳ）relative to Cu（Ⅱ）and Ni（Ⅱ）.During membrane filtration,the breakthrough occurs for Pt（Ⅳ）at the permeate volume of about 50 mL.Pt（Ⅳ）-ⅡM had a high reusability and only 6.6%loss of initial adsorption capacity after five adsorption/desorption cycles.