Surface Wettability Manipulation Of Zeolite Membranes And Coatings For Enhanced Separation Of Liquid Mixtures

Zeolite membranes and coatings serve in an impressive range of applications due to their unique tunnel structure and excellent stabilities.Effective manipulation of surface wettability of zeolite membranes and coatings is of great significance for improving their application performances.By improving surface free energy and regulating surface microstructure,simple and versatile modification methods were proposed to optimize the surface wettability of beta-and MFI-type zeolite membranes and coatings.The modified zeolite membranes were applied to the separation of alcohol/water and organics/organics mixtures,and the synthesized superwettable zeolite coatings were used to separate various oil/water mixtures.Mussel-inspired chemistry was employed to functionalize the surface of zeolite Al-beta membranes.On one hand,the surface hydrophilic modification of the zeolite Al-beta membrane was achieved via co-deposition of polydopamine and polyethyleneimine.With respect to 95 wt%n-butanol/water solution,the modified zeolite Al-beta membrane exhibited a separation factor of 420.7,which was approximately 21.6-fold over that of the unmodified zeolite Al-beta membrane.The flux of modified zeolite Al-beta membrane increased from 1.42kg m^-2h^-1 to 1.67kgm^-2h^-1.On the other hand,the step-by-step deposition of polydopamine and octadecylamine was used to functionalize the zeolite Al-beta membrane with hydrophobicity.The pervaporation performance of surface hydrophobic modified zeolite Al-beta membrane was measured for 5 wt%n-butanol/water solution.The separation factor of zeolite Al-beta membrane after hydrophobic modification increased to 100.7,which was 76.5 times higher than the unmodified one,whereas the flux only decreased by ca.19.5%.This facile and controllable modification method is capable of obtaining significantly enhanced separation selectivity and the lowest permeability loss after modification.On the basis of polyelectrolyte complexes（PECs）,the vacuum-wipping deposition strategy was proposed to achieve defects-healing and surface functionalization of zeolite Al-beta membranes simultaneously.The spherical PEC nanoparticles could be deposited preferentially in the non-zeolitic channels under vacuum suction,and the wiping process could form an ultrathin and uniform PEC modification layer on the surface of the zeolite Al-beta membrane.The modified zeolite Al-beta membrane was applied to the separation of Me OH/MTBE mixture with a notably increased separation factor of 489.8（by a factor of ca.243.9）,while the flux decreased from 9.38 kgm^-2h^-1to 4.07 kgm^-2h^-1.Compared with other available zeolite membranes in the literature,the modified zeolite Al-beta membrane exhibited the highest permeation flux and satisfactory separation selectivity.This simple approach can be directly applied to various zeolite membranes,and gives promise for large-scale application of zeolite membranes.The superhydrophobic pure-silica zeolite beta coating was fabricated on the stainless steel mesh via secondary growth for the first time.The polydopamine modified seeding method was proposed to form uniform seed layers on the surface of stainless steel meshes with high coverage degree.After the seeded growth,the rough hierarchical structure on the outer surface of stainless steel mesh-supported pure-silica zeolite beta coatings together with intrinsic hydrophobicity of pure-silcia zeolite beta gave both superhydrophobicity and superoleophilicity.It was demonstrated that the stainless steel mesh-supported pure-silica zeolite beta coating exhibited excellent separation performances for various oil/water mixtures.In addition,its durability and stability were checked systematically when exposed to rigorous operation conditions,and the strong adhesion of the pure-silica zeolite beta coating on the substrate was tested.The cost-effective and environmentally-friendly method was developed to prepare the superhydrophobic and self-cleaning zeolite W-MFI coating on the stainless steel mesh in the dilute alkaline solution.The incorporation of W species into the zeolite framework would vanish the surface silanol groups on zeolite W-MFI coatings,leading to an upside down turning in wettability in contrast to zeolite Si-MFI coatings.In the oil/water separation,the synthesized stainless steel mesh-supported zeolite W-MFI coating presented excellent separation performances and good durability and stability.Compared with the state-of-the-art superhydrophobic stainless steel mesh-supported materials reported in the literature,this robust stainless steel mesh-supported zeolite W-MFI coating possessed the highest flux and superior durability,together with satisfactory separation efficiency.It is believed that our finding would be easily applied to produce other superhydrophobic zeolite materials,which will extend the application area of zeolite coatings.