Preparation And Dye Separation Property Of Self-cleaning Membrane Based On Metal-organic Frameworks

Membrane-based separations have emerged as a promising alternative to traditional separation processes?adsorption,distillation,etc.?due to their high separation efficiency,low energy consumption,and eco-friendliness.At present,membrane separation technology has been widely used in chemical,energy,food,medical treatment,environmental protection and other aspects.However,despite impressive advances of membrane technologies,membrane fouling severely impairs the separation performance and lifespan,remaining a challenging task to be addressed.In this paper,the metal-organic frameworks?MOFs?with photocatalytic features were introduced to polymeric membranes.The regulation of MOF concentrations is to optimize the separation and permeation performance and allow the modified membranes to possess self-cleaning and antibacterial properties,with the aim of effectively mitigating the issue of membrane surface fouling.The main research contents of this paper are as follows:?1?Preparation of self-cleaning membranes based on MIL-125?Ti?The MIL-125?Ti?/PVDF membrane with self-cleaning and dye separation merits was constructed through a wet phase inversion method.Interestingly,MIL-125?Ti?was commonly utilized for photocatalytic degradation of organic matters under UV light,but the self-cleaning membranes containing MIL-125?Ti?were able to effectively degrade the foulant Rh B under natural light.This is due to the sensitization of MIL-125?Ti?caused by the adsorption of Rh B dye molecules on MIL-125?Ti?during the rejection process,where they could promote electron transfer to produce hole?e^-?and superoxide free radicals??O^–₂?.When the membrane with10%MIL-125?Ti?,self-cleaning membranes exhibit water permeance(64.3 L m^-2 h^-1bar^-1)and remarkably high dye retention?Rh B,99.7%?.Furthermore,due to superb photocatalytic degradation of the foulants,the flux of the treated membranes can almost be recovered to the initial state even after three cycles.More importantly,the self-cleaning membranes exhibit an ultra-high bacteriostatic rate of nearly 100%.?2?Preparation of self-cleaning membrane based on CuTz-1In order to overcome the limitation of photocatalytic conditions and improve the photocatalytic efficiency,the CuTz-1 selected in this study has the unprecedented Cu5tz6 cluster as secondary building units?SBU?,has the thermal and chemical?alkaline and acidic?stability,and can degrade the dyes under the natural light.In order to prevent the infiltration of CuTz-1 and to improve the membrane properties,GO nanoparticles?GO?were introduced during the membrane preparation process.In specific,a certain amount of GO and different amounts of CuTz-1 were mixed in the polyvinyl alcohol?PVA,0.2 w/v%?solution,filtered on the surface of the HPAN support layer,and then crosslinked with glutaraldehyde?GA,0.4 w/v%?solution.The effect of CuTz-1 contents on self-cleaning properties of the modified membrane was studied systematically.Compared with the membrane without CuTz-1,the self-cleaning membrane had higher water flux and dye rejection.When the membrane with 0.5 mg CuTz-1,self-cleaning membranes exhibit water permeance of 40.2 L m^-2h^-1 bar^-1,the rejections of Congo red,Methyl blue,Active black 5 and Direct red 23were 98.8%,94.9%,92.7%and 98.2%,respectively,and low rejections for salts?Na Cl 0.3%,Mg Cl₂ 2.1%,Na₂SO₄ 26.4%,Mg SO₄ 6.7%?.Furthermore,due to superb photocatalytic degradation of the foulants,the flux of the treated membranes can almost be recovered to the initial state even after three cycles.More importantly,the self-cleaning membrane has an ultra-high bacteriostatic rate of nearly 100%.In this work,CuTz-1 self-cleaning membrane has excellent separation performance,self-cleaning and antibacterial properties,and has a broad application prospect in the treatment of dye wastewater.