Fabrication And Performance Of The Evolved MOFs Modified Hydrophobic Material

Superhydrophobic materials show a huge advantage due to waterproof,anti-fouling,self-cleaning,and reduced fluid viscosity in oil/water separation.However,there are still some drawbacks that need to be overcome such as the complex manufacturing process and secondary environmental pollution caused by being discarded after use.Therefore,it is very necessary to choose a biodegradable molecule to construct superhydrophobic materials.Poly（lactic acid）（PLA）is one of the most promising biodegradability materials.The separation efficiency of using PLA directly as an oil/water separation membrane is very low,so it is necessary to hydrophobically modify the PLA to improve the efficiency of its oil/water separation.Combining nanoparticles with polymer has been considered as an effective method for the construction of oil/water separation materials,which can significantly improve separation efficiency and flux.Nano metal-organic frameworks（MOFs）have gained widespread interests due to their high specific surface area,porosity and unique pore structure.In this work,we use PLA non-woven fabric(PLA_NWF)as the base material,and MOFs are grown and modified on the surface.Through the morphology control and micro-nano structure design of MOFs,the whole system is endowed with superhydrophobicity and shows a good oil-water separation effect.The details are as follows:（1）The influence of solvent effect and molar ratio of reactants on the crystal morphology and size of MOFs was studied,and the optimal synthesis conditions for ZIF-8 and ZIF-L（Co）were determined.According to the experimental results,when the methanol is a solvent,ZIF-8 crystals can be synthesized with a low molar ratio(Zn²⁺:2-MIM=1:8),and the crystal particle size is about 250～40 nm;when water is the solvent,ZIF-8 crystals can be synthesized under high molar ratio(Zn²⁺:2-MIM=1:70),and the crystal particle size is about 2μm.In the study of the phase transition between ZIF-67 dimensions,we found that by adjusting different solvent volume ratios（methanol:water=1:0,1:2,1:3,1:4,1:5,0:1）and different reactant molar ratios(Co²⁺:2-MIM=1:2,1:4,1:8 and 1:16),Co-ZIF with different crystal numbers and morphologies can be obtained.It can be seen that the solvent effect and reactant molar matching are critical to the formation and evolution of the MOFs crystals.（2）A superhydrophobic surface based on the hierarchical structure of MOFs was designed and constructed on PLA_NWF.First,grow micron-sized ZIF-L（Co）vertically on the surface of PLA_NWF,and then load nano-scale ZIF-8 onto ZIF-L（Co）by a simple spraying method,thereby giving the material a micro/nano multi-level rough structure.These micro/nano structures form many cavities,which can be used to capture and lock the air,and form an air layer on the surface of the PLA_NWF,which not only realizes the super-hydrophobic modification of the material,but also gives the material low surface adhesion,making it self-cleaning.（3）Designed a novel method to evaluate the wetting performance of the material surface using the wetting envelope curve.By drawing the wetting envelope curve,a large number of contact angle testing procedures can be avoided,and the wetting of a known liquid on a solid surface can be directly evaluated.In addition,by immersing the material in water for a long time,the reversible wettability switch of the ZIF-8/ZIF-L（Co）/PLA_NWF surface was realized.This wettability conversion will undoubtedly broaden the application fields of superhydrophobic materials,and provide new research ideas for oil/water separation and industrial wastewater purification.（4）Studied the preparation methods of bimetal MOFs and Janus materials.Based on the research of ZIF-8 and ZIF-67,MOFs with two metal sources,Fe-Ni MOF and Zn-Ni MOF,were prepared respectively;based on the preparation of superhydrophobic materials,one-sided hydrophobic and the other side porous Janus membranes（JMs）were prepared.MOFs have many chemically active sites,making it possible to further functionalize the material.This work provides a design idea for the preparation of multifunctional JM.In addition,in the preparation process of bimetal MOFs,the foamed nickel（NF）substrate can be treated with alkali and directly used as another metal source to prepare bimetal MOFs.Compared with the traditional preparation method that requires two metal salts to be added to the precursor solution,the method used in this experiment is more conducive to the simple,rapid and cheap preparation of bimetal MOFs.It brings new research prospects for the functional application of MOFs,not only in the field of oil/water separation,but also in the application of other superhydrophobic materials.