Construction And Separation Performance Of Composite Nanofiltration Membrane Based On Zr-MOFs Nanomaterials

Highly efficient and economical membrane separation technology is playing an important crucial role in industrial wastewater treatment,water purification and desalination.The printing and dye wastewater is remarkable in dye wastewater treatment.It is difficult to clean the dyes wastewater.The dye molecules are potential carcinogens due to the complex structures of aromatic compounds.Furthermore,in order to improve the absorption capacity between dyes and fabric,the inorganic salts are added to the dyeing process.Therefore,the principal purpose of this paper is to research the treatment of the dye wastewater and removal of high concentration salt in the wastewater.Membrane technology currently has two major challenges:membrane fouling and trade-off effect between the selectivity and permeability of membrane.In order to overcome these challenges,this study mainly focused on modifying the structure and performance of composite nanofiltration membrane.The Zr-based metal-organic frameworks(Zr-MOFs)were selected as fillers to fabricate effective separation layers on the porous polyacrylonitrile membrane(HPAN).These series of membranes show good performances in dye/salt separation,salt rejection,photodegradation and antibacterial.Firstly,in order to overcome the agglomeration phenomenon of MOFs materials in polymer,MOFs nanoparticles were modified by in-situ growth method.UiO-66-NH2 MOFs have great potential for water treatment attributing to high chemical and thermal stability,and the hydrophilic-NH2 functional group in the skeleton.However,UIO66-NH2 is prone to agglomeration in polymers,which limits its development in composite nanofiltration membranes.Polyvinylpyrrolidone(PVP)assisted.in-situ growth method was utilized to synthesize Zr-MOFs(PVP-UiO-66-NH2),which has well dispersibility in water,negatively charged,high surface area and uniform shape.The PVP-UiO-66-NH2 was incorporated into polyvinyl alcohol(PVA)aqueous solution and drop-coated on the surface of HPAN supporting layer.The resultant membranes prove hydrophilicity and their potential in filtration properties.The optimized membrane(PVP-UiO-66-NH2 content of 0.3 wt%)has a water permeability of 13.1 LMH bar-1,remarkable rejection(>99.8%)for four dyes(Congo red,Methyl blue,reactive Black 5 and Direct red 23),low rejection of monovalent salts(5.2%,6.0%for NaCl and MgCl2)and moderate rejection for bivalent salts(10.2%,22.3%for MgSO4 and Na2SO4).These membranes also demonstrated an excellent stability in continuing operation for 50 hours.Overall,the resultant membranes show an exciting prospect in dyes purification and the separation of dye/salt mixture.Secondly,in order to improve the permeability of the membrane and overcome the trade-off effect,the size of MOFs nanoparticles was reduced to increase the surface area,which increased the contact area and reduced the non-selective defects between the polymer and MOFs.Furthermore,constructing water transport channels with different dimensions is an effective method.Therefore,3D MOFs were grown in situ on 2D lamellas to restrict their growth,and enhance the activity of their active sites,which construct multiple dimensional water transport channels.2D graphene lamellar materials were selected as the research object.PVP-UiO-66-NH2 nanoparticles were grown in situ on the porous graphene sheet to enhance the activity of their active sites.The loose nanofiltration membranes were prepared by pressure filtration method.When the content of UPG is 0.075wt%,the permeability of TFN-UPG-3 membrane is 19.8 LMH bar-1,and the rejection of dye is more than 99.8%.The bacteriostatic rate of the membranes was enhanced with the increase of the amount of UPG.Therefore the membranes with higher UPG content exhibited a sufficient antibacterial activity(91.5%).Compared with the PM membrane,the permeability of TFN-UPG-3 membrane increases significantly.In addition,Zr-porphyrin MOFs with photocatalytic activity were synthesized by changing the organic ligands of Zr-MOFs.And Zr-porphyrin MOFs were considered to be ideal material for preparing wastewater treatment membranes due to their stability in aqueous solution.Zr-porphyrin MOFs,with good chemical stability and superior photocatalytic degradation ability,may be promising nanofillers for synthesis of self-cleaning thin-film nanocomposite(TFN)membranes.In this paper,hydrophilic Zr-porphyrin MOFs were embedded in the polyamide active layer to develop self-cleaning membranes.The optimum membranes exhibit a superior water permeability of 27.6 LMH bar-1(three times higher than the pristine TFC membrane)while maintaining a high dyes rejection(>99.9%)for four dyes(Congo red,Direct red 23,Reactive Black 5 and Methylene blue)and an outstanding photocatalytic degradation self-cleaning ability(the recovery of water permeability exceeds 97%after 4 cycles).Overall,this study may offer a new inspiration for designing and tuning MOFs based self-cleaning membranes with excellent dyes removal ability.Finally,in order to enhance the salts rejection and antibacterial properties of the membranes,Zr-porphyrin MOFs were grown in situ on the porous graphene sheets structure,and the structures of composite nanoparticles were adjusted.Zr-porphyrin MOFs nanoparticles were in situ grown on porous graphene sheets to synthesize hybrid nanoparticles(Zr-porphyrin@PG),which were used to fabricate multifunctional composite nanofiltration membranes by interfacial polymerization.When the content of Zr-porphyrin@PG2 was 0.01wt%,the permeability of membrane was 29.2 LMH bar-1,and rejection of four dyes was greater than 99.9%,that of Na2SO4 and NaCl were 97%and 18%.In addition,the membranes also have excellent photocatalytic degradation of dyes and antibacterial activities.Therefore,the versatility of membranes was endowed,mainly in the aspects of dye purification,salt rejection,dye photodegradation and antibacterial.