Structural Regulation And Performance Enhancement Of Antifouling Oil-water Separation Membrane Based On Nanomaterials

With the progress of industrialization,the shortage and pollution of water resources have become a serious problem facing the whole world.Membrane technology has been widely used in the treatment of industrial wastewater,oily wastewater and domestic wastewater due to its advantages of low energy consumption,high single-stage separation efficiency,flexible and simple process,low environmental pollution and strong versatility.Membrane technology has made considerable progress in the past decades,however,membrane fouling has become a bottleneck restricting the further development of membrane technology.Therefore,how to effectively control and reduce membrane fouling becomes the key in the field of membrane separation.The preparation of high-performance antifouling membrane is considered to be the main way to solve the membrane fouling problem.In recent years,the synthesis of nanomaterials and their research in surface and interface engineering have provided new ideas for the design and preparation of antifouling membrane materials.In this paper,the research progress of nanomaterials in antifouling membranes preparation and structure regulation was systematically reviewed,and the synthesis and assembly methods of nanomaterial were further innovated.Based on the two mechanisms of bulk structure regulation and surface structure regulation,antifouling membrane materials were prepared to enhance the antifouling performance,separation performance,mechanical properties of membranes.Based on the idea of bulk structure regulation for membrane performance enhancement,the in-situ biomimetic mineralization hybridization method was used to prepare PVDF/DA/TiO₂ hybrid membranes.Dopamine（DA）,an amino acid-containing small molecule,was employed as the mineralization inducer and favor the hydrolysis and polycondensation of Ti-BLADH into DA/TiO₂ HNPs in the membrane casting solution.PVDF/DA/TiO₂ hybrid membranes were thus obtained via non-solvent induced phase separation of the casting solution.The in-situ DA/TiO₂ HNPs endowed the prepared PVDF/DA/TiO₂ hybrid membranes better surface hydrophilicity,high surface energy,underwater superoleophobicity,more pore structure and better mechanical properties.The results showed that the water flux of PVDF/DA/TiO₂ 12%hybrid membrane was as high as 171.8 L/（m²h）（four times that of the original PVDF/DA membrane）,and the flux recovery rate was higher than 95%when the 1g/L oil-in-water emulsion was used as the feed liquid.Based on the idea of bulk structure regulation for membrane performance enhancement,the TA/PEI@TiO₂ organic-inorganic hybrid nanoparticles（TPTi HHNs）were firstly synthesized and introduced into the PVDF matrix to prepare PVDF/TPTi hybrid membranes.The TPTi HHNs were synthesized by combining the chemical features of catechol-rich tannic acid and the biomimetic mineralization chemistry of titanium dioxide.The PVDF/TPTi hybrid membranes were thus obtained by phase inversion method.TPTi HHNs imparted higher porosity,graded roughness,better hydrophilicity and underwater superoleophobicity to PVDF/TPTi HHNs hybrid membranes.The PVDF/TPTi hybrid membranes exhibit enhanced antifouling properties after loading TPTi HHNs.When used for separating 1 g/L oil-in-water emulsion,the flux recovery rate could reach to 92%.Even with a higher concentration（10 g/L）of oil-in-water emulsion for three cycles,the PVDF/TPTi 10%membrane still maintained high flux and 85%flux recovery.Based on the surface structure regulation for membrane performance enhancement,the metal-polyphenol hybrid layer（TAT）assembled from catechol-rich tannic acid（TA）and Ti⁴⁺on the surface and pore surface of PVDF microfiltration membrane was utilized to realize membrane surface functionalization.Subsequently,the TAT coating could manipulate the in-situ growth of ZIF-8 nanocrystals on the membrane surface to create the micro/nano structures.Finally,the hydrophilicity of the membrane surface was further enhanced by further TAT reassembly to prepare PVDF/TAT/ZIF-8/TAT membrane.The synergistic effect of the hydrophilic chemical composition and the micro/nano structure endowed the PVDF/TAT/ZIF-8/TAT membrane superhydrophilicity,underwater superoleophobicity and excellent oil-in-water emulsion separation performance.At a pressure of 0.05 MPa,PVDF/TAT/ZIF-8/TAT membrane showed the water permeation flux of 6649.4 L/（m²h）（55.4%relative to the original PVDF membrane）,and the rejection rate of four oil-in-water emulsions（pump oil,hexadecane,soybean oil,motor oil）were higher than 99.9%.In addition,the modified membrane has good antifouling ability and stability,that is,using 5 g/L pump oil for 5 cycles of continuous testing,the water permeation flux of PVDF/TAT/ZIF-8membrane was as high as 5500.0 L/（m²h）.