Preparation Of On-Demand/Self-Cleaning Special Wettability Functional Membrane And Study On Oil/Water Separation Performance

A large number of oily wastewater produced from oil leakage,daily life and industrial production has posed a huge threat to environment and human health.Therefore,the effective treatment of oily wastewater is of great significance for the protection of ecological environment and the promotion of social and economic development.In recent years,the superwetting membrane materials have shown a great advantage in the application of efficient selective oil/water separation.However,most of the superwetting membrane materials still have some shortcomings,such as poor durable antifouling,poor applicability,single separation system and so on.Therefore,the main development direction of oil/water separation membrane in the future is to develop robust antifouling separation membrane and on-demand oil/water separation membrane.In this paper,on-demand/self-cleaning special wettability functional membrane materials were prepared by constructing micro/nano hierarchical structures and regulating surface energy,coupling advanced oxidation technology and membrane technology.By adjusting the experimental parameters,the structure and performance of the membranes were optimized to achieve high-efficiency,long-term antifouling of the membrane and on-demand oil/water separation.This paper is devoted to the research and development of novel special wettable membrane materials,mainly focusing on the surface wettability,antifouling and separation performance of the membrane,as follows:1.Preparation of needle-like hierarchical carbon cloth@Ni-Co LDHs composite membrane and study on oil/water mixture separation performance（1）In order to achieve on-demand oil/water mixture separation,the needle-like hierarchical Ni-Co LDHs coated carbon cloth（CC@LDH）was constructed by in-situ hydrothermal growth method.Then,the surface energy of CC@LDH was adjusted by alternately impregnation in stearic acid ethanol solution and THF to realize the reversible switching between superhydrophilicity/underwater superoleophobicity and superhydrophobicity.The effects of hydrothermal time on needle-like hierarchical structures and wettability were studied.The on-demand oil/water mixture separation performance of CC@LDH was evaluated.The oil/water separation mechanism was clarified through the fluid-based gating and liquid-infusion-interface mechanism.The experimental results showed that CC@LDH displayed high separation efficiency（>98.5%）and high flux(15903-32916 L m^-2 h^-1)for light oil and heavy oil,and showed excellent environment,mechanical durability and stable regeneration performance.（2）In order to further enhance the antifouling property of the membrane,based on needle-like hierarchical CC@LDH,the CC@LDH/Ag composite membranes were prepared by deposition of Ag with plasma resonance effect on the CC@LDH surface.The effects of Ag deposition on self-cleaning and wettability of CC@LDH/Ag were studied,and the oil/water mixture separation performance of CC@LDH/Ag was evaluated.The experimental results showed that CC@LDH/Ag is superhydrophilic/underwater superoleophobic,and showed high separation efficiency（>98.6%）and high flux(6551-22050 L m^-2 h^-1)for different kinds of oil/water mixtures.The CC@LDH/Ag also showed excellent environmental and mechanical durability.Good light-induced self-cleaning ability enabled CC@LDH/Ag to be separated at least 30 times,and still maintained high separation performance.2.Preparation of photo-Fenton self-cleaning PVDF composite membrane and study on oil/water emulsion separation performance（1）In order to endow the membrane with excellent self-cleaning property,NM88B with photo-Fenton catalysis was introduced into PVDF membrane matrix,and PVDF/NM88B membrane was prepared by one-step simple non-solvent induced phase conversion method.The effects of NM88B blending amount on the structure,pore characteristics and wettability of PVDF/NM88B membrane were studied.The oil/water emulsion separation performance of PVDF/NM88B membrane was evaluated,and the photo-Fenton self-cleaning mechanism was analyzed.The experimental results showed that the PVDF/NM88B membrane exhibited excellent separation performance（>99.4%）and high flux(340-1970 L m^-2 h^-1 bar^-1)for different oil/water emulsions.The PVDF/NM88B membrane with good hydrophilicity and high photo-Fenton activity exhibited good antifouling performance,flux recovery ratio of almost 100%,and good mechanical properties and reproducibility.This work provides a new idea for the application of Fe-based MOFs in wastewater treatment and potential application.（2）In order to overcome the embedding problem of active sites in blending,firstly,the tannic acid（TA）-Fe（III）complex was assembled on the PVDF membrane surface,and then superhydrophilic/underwater superoleophobic PVDF/TA/β-FeOOH membrane was prepared by surface in-situ mineralization ofβ-FeOOH.The effects of the mineralized solution concentration（FeCl₃·6H₂O）on the structure and wettability of PVDF/TA/β-FeOOH membrane were studied.The oil/water emulsion separation performance of PVDF/TA/β-FeOOH membrane was evaluated,and the photo-Fenton self-cleaning mechanism was analyzed.The experimental results showed that the membrane exhibited high separation efficiency（>99.1%）and high flux(1426.8-2106.2 L m^-2 h^-1 bar^-1)for a series of oil/water emulsions.PVDF/TA/β-FeOOH membrane showed rapid（within 10 min）and good flux recovery ratio（>98%）due to the excellent photo-Fenton activity ofβ-FeOOH.This study highlights a new direction in the development of photo-Fenton self-cleaning membrane with fast and robust flux recovery for efficient oil/water emulsion separation.3.Preparation of special wettable cellulose@polydopamine based composite membrane and study on on-demand oil/water emulsion separation performance（1）In order to achieve on-demand oil/water emulsion separation,polydopamine（PDA）was coated on the regenerated cellulose membrane（RC）surface to build a bionic secondary reaction platform,and then the RC@PDA/ZIF-8 membrane was prepared by coordination-driven in situ self-assembly ZIF-8.The introduction of PDA enhanced the dispersion and stability of ZIF-8 nanoparticles on the membrane surface.RC@PDA/ZIF-8 membrane was prewetted by water or oil without additional external stimulation,which can realize the switch between underwater superoleophobicity and underoil（super）hydrophobicity.The effects of precursor concentration on the structure and wettability of RC@PDA/ZIF-8 membrane were studied.The on-demand oil/water emulsion separation performance of RC@PDA/ZIF-8 membrane was evaluated,and the switching mechanism of membrane surface wettability was elucidated.The experimental results showed that the membrane exhibited excellent separation efficiency（>99%）,good flux for various oil-in-water and water-in-oil emulsions,and good reproducibility,indicated that MOFs-based membranes have potential application in oil/water separation.（2）In order to develop an easy preparation,green and sustainable Janus membrane for on-demand oil/water emulsion separation,the heirarchical structures of PDA layer/particle was constructed by high temperature dopamine self-polymerization with the sustainable RC as the base membrane realizing superhydrophilic/underwater superoleophobic modification in one step.Then,the hydrophobic modified attapulgite（SOATP）was sprayed on the bottom surface of RC@PDA membrane by a simple spray method,and the RC@PDA/SOATP Janus membrane with superhydrophilic top surface and superhydrophobic bottom surface was successfully prepared.The Janus membrane exhibited excellent separation efficiency（>99%）and good flux for for various oil-in-water and water-in-oil emulsions,and showed good renewability and excellent environmental and mechanical durability.The simple and versatile PDA coating and spraying method as well as the green and sustainable raw materials make the Janus membrane have a broad application prospect in the field of oil/water separation.