Design And Preparation Of Super-wetting Oil/water Separation Membrane Based On Polyphenol-metal Coordination

With the rapid development of the global economy,great quantities of oily wastewater are constantly generated,which causes severe threats to the environment and human health.The effective treatment of oily wastewater is an urgent issue for various related industries.Compared with the traditional oily wastewater treatment technology,membrane separation technology arouses more attention and shows their priority in the field of oily wastewater treatment with the high-efficiency and eco-friendly features.However,membrane fouling has become a bottleneck problem that limits the further development of membrane technology.Inspired by the super-wetting phenomenon in nature,researchers have prepared a variety of super-wetting materials and provided new ideas for the design and preparation of anti-fouling membrane materials.Based on polyphenol-metal coordination and the multi-functionality of polyphenols,high-flux and super-wetting oil/water separation membranes were designed and fabricated in this paper,providing new methods for the design of various functional membranes.The main research contents and results were summarized as follows:Based on the surface coating modification strategy,the PVDF/Fe-TA/PEI membrane was prepared via in situ assembling Fe-TA/PEI coating on the surface and inside of PVDF micropore membrane.On the one hand,catechol-rich tannic acid（TA）was coordinated with iron ions(Fe³⁺)to form metal-polyphenol network（MPN）coating;on the other hand,polyethyleneimine（PEI）was electrostatic assembled with TA to form TA/PEI nano-aggregates.Under alkaline environment,TA and PEI could cross-link into TA/PEI nano-particles and the binding force between TA and Fe³⁺could be further enhanced.Through the synergistic effect of polyphenol-metal chemistry coordination assembly and polyphenol-cationic polyelectrolyte electrostatic assembly,the modified PVDF/Fe-TA/PEI micropore membrane had superhydrophilicity-underwater superoleophobicity and excellent oil-in-water emulsion separation performance.At a low pressure of 0.05 MPa,the emulsion permeation flux of the membrane reached 3397 Lm^-2h^-1（4 times compared with the original PVDF membrane）,and the rejection rate was higher than 99%.What’s more,the prepared PVDF/Fe-TA/PEI membrane also showed excellent anti-fouling performance and cycle stability.The flux recovery ratio reached 93.3%,and the total flux decline ratio was42.1%（the irreversible flux decline ratio was about 6.7%）.In addition,the flux recovery ratio of PVDF/Fe-TA/PEI membranes remained at a high level（higher than 86%）after multiple separation cycles.Based on the in situ mineralization modification strategy,CNT@CS/TA-Fe OOH nanohybrid membranes were prepared via polyphenol-metal manipulated Fe OOH nanorods（NRs）mineralization.Firstly,CNT@CS/TA membranes were prepared by vacuum-assisted co-assembly of chitosan（CS）and TA co-modified carbon nanotubes（CNTs）.Subsequently,Fe³⁺ion chelating formed polyphenol-metal(CS/TA-Fe³⁺)complex primers on CNT@CS/TA membranes to obtain CNT@CS/TA-Fe³⁺membranes.Afterwards,with CS/TA-Fe³⁺complex primers providing nucleation and binding sites,Fe OOH NRs were in situ mineralized and uniformly embedded within CNT assembled network of the as-prepared CNT@CS/TA-Fe OOH nanohybrid membranes.CNT-polymer co-assembly and polyphenol-metal manipulated in-situ mineralization could integrate the high permeability of CNT membranes and the hydrophilicity and photo-degradation activity of Fe OOH NRs.The prepared CNT@CS/TA-Fe OOH nanohybrid membranes had superhydrophilicity-underwater superoleophobicity,excellent oil-in-water emulsion separation performance and anti-fouling performance.When separating different oil-in-water emulsions,the permeation flux of the CNT@CS/TA-Fe OOH nanohybrid membrane reached 2000 Lm^-2h^-1,the rejection ratio was higher than 99%,and the flux recovery ratio was as high as 97%.