Fabrication And Separation Performances Of Efficient MOF-based Membrane Materials

In the process of transportation and utilization for petroleum and natural gas,water pollution caused by oil leakages and the corrosion of pipelines caused by acidic impurity carbon dioxide are likely to be encountered,respectively.Membrane separation technology with their superiorities of high separation efficiency,operation simplicity,low energy consumption and environmental-friendness have been widely used in separation of oil/water and CO₂/CH₄.Among various new materials,metal-organic framework materials（MOFs）have attracted much attention in the field of oil/water separation membrane and carbon dioxide separation membrane due to their advantages including diverse structures,adjustable wettability,unsaturated metal sites and easy modification.In this work,based on the characteristics of MOFs,certain key problems existing or ignored in the process of oil/water separation and carbon dioxide separation were resolved.The synthesized functional membranes are capable of separating oil/water and CO₂/CH₄ efficiently.In order to clean up spilled oil quickly,a superhydrophilic multi-scale MOF mesh membrane with ultrahigh throughput was prepared.By controlling the growth process of crystals with liquid phase epitaxial technique,a uniform Cu BTC seed layer was prepared.Then,micro-scale Cu BTC mesh membrane was prepared on this basis.Multi-scale Cu BTC mesh membrane with rough structures was finally obtained by fabricating nano-sized humps on the surface of micro-sized Cu BTC crystals.The synthesized mesh memabrane exhibited excellent superhydrophilicity and underwater superhydrophobicity,and separated various oil/water mixtures with a separation efficiency of more than 99%.In addition,the stabilities and anti-fouling behavior were investigated.Most importantly,the membrane achieved an extremely high flux(148.3L·m^-2·s^-1)and a satisfactory oil intrusion pressure（2.2 k Pa）,demonstrating its application potential for quick oil-spill cleanup.In order to overcome the problem that the superhydrophobicity of membranes are vulnerable to the harsh environment,a self-repairing superhydrophobic MOF mesh membrane was prepared.Firstly,dense cross-linked ZIF-7 membrane with the rough surface was prepared,and then modified with coordinated polysiloxane elastomer（CPE）.The obtained CPE-ZIF-7 mesh membrane showed excellent superhydrophobicity and could separate various oil-in-water emulsions with separation efficiencies of above 99.9%.Also,the stability of the membrane was investigated by cyclic testing,high temperature treatment,ultrasonic treatment and solvent corrosion.The self-repairing ability and working mechanism of the CPE-ZIF-7 mesh membrane was mainly demonstrated by continuous mechanical abrasion and O₂ plasma etching.The membrane exhibited remarkably fast self-repairing ability upon damage in less than10 min without any externally imposed input of matter/energy,which would play an important role in the process of waste oil treatment under harsh conditions.In order to solve the problem that the open metal sites of some MOF are vulnerable to the attack of water molecules in natural gas,glycine was introduced for shielding.Taking Cu BTC as an example,glycine was introduced to prepare Gly@Cu BTC to improve its moisture stability and CO₂ adsorption capacity simultaneously.After blending with Poly（ether-b-amide）（Pebax 1657）,the Pebax/Gly@Cu BTC mixed matrix membrane（MMM）was prepared.The synthesized MMM possessed improved interface compatibilitities and mechanical strengths.Moreover,CO₂/CH₄ separation performance of the MMMs were studied at different filler loadings and feeding pressures.At humidified state,the permeability and selectivity of the MMM were significantly improved to 934 Barrer and 34,respectively,surpassing Robeson Upper Bound in 2008.Most importantly,the MMM revealed good long-term stability at humidified state,which would be very promising to play an important role in practical CO₂ separation applications.In order to overcome the trade-off effect between selectivity and permeability,the synergistic effect of diffusion and solution mechanisms was adopted.First,ultra-thin Co BDC nanosheets were directly synthesized by surfactant-assisted method,and their lamellar morphology was characterized.Then,the ternary MMMs were fabricated by blending polyethylene glycol（PEG）and Co BDC nanosheets with Pebax,and the physicochemical properties of the MMM were characterized.The MMM was applied to the separation of CO₂/CH₄,and the effects of the incorporation amount of Co BDC nanosheets and PEG on the separation performance of the MMM were investigated.Through the synergistic effect of diffusion and dissolution mechanisms,the CO₂permeability and CO₂/CH₄ selectivity of the MMM were increased by 19.9%and112.67%respectively,which was obviously superior to most of the MMMs incorporated with MOF nanosheets reported in the literature.