Preparation Of Photocatalytic Nanofiltration Membrane Based On Porphyrin Organic Framework

The massive discharge of high-salt printing and dyeing wastewater seriously pollutes the environment and endangers human health.Membrane separation technology has become one of the most promising technologies for the treatment of printing and dyeing wastewater and the purification of industrial products because of its high separation efficiency,low energy consumption and environmental friendliness.However,during the long-term operation of the membrane,organic matter,soluble inorganic matter,suspended particles and microorganisms are trapped on the membrane surface or in the membrane hole,resulting in membrane contamination,which reduces the membrane separation performance and shortens the service life.How to effectively solve the problem of membrane fouling is still a great challenge facing the current membrane technology.Reasonable material design and controllable membrane preparation process are the keys to improve the membrane separation performance and anti-fouling ability.The interfacial polymerization method is simple and controllable,which can be used to obtain anti-fouling membrane with high separation performance by introducing nano-fillers or using modified monomers.Melamine is a low-toxic,heat-resistant,and highly polar aqueous monomer.The polyamide layer prepared by it is loose and resistant to oxidation.The porphyrin-based organic framework has great potential in the preparation of high-throughput photocatalytic membranes due to its easy control and high photocatalytic efficiency.In this paper,porphyrin-based organic framework with photocatalytic performance was introduced into the polyamide membrane of melamine to regulate and optimize the permeable separation of the membrane.So that the modified membrane can not only efficiently separate dyes and salts,but also have good photocatalytic degradation ability,aiming to effectively solve the problem of membrane pollution.(1)Photocatalytic membrane based on porphyrin-based Zn-TCPPIn this study,melamine was selected as the aqueous phase monomer for interfacial polymerization.It was pumped and filtered with Zn-TCPP nanosheets to PS membrane surface,and then interfacial polymerization with tribenzoyl chloride was performed to prepare the porous nanofiltration membrane with high performance and anti-pollution.Taking the retention and catalytic degradation of organic dyes as the research objects,the effects of different addition amounts of Zn-TCPP nanosheets on the interfacial polymerization process were explored.Melamine/triphenylchloride thin layer composite(TFC)membrane has a similar structure of braided polyamide layer,water permeance up to 30.1 L m^-2h^-1bar^-1,and has good dye retention effect(?97.0%).It was found that the permeance of thin layer nanomaterial composite(TFN)membranes was improved with the addition of Zn-TCPP nanosheets.The permeance of TFN-2 membrane was increased to 63.2 L m^-2h^-1bar^-1,twice that of TFC membrane,and the rejection of Na Cl,Na₂SO₄were all less than 10%.In addition,the TFN-2 membrane can completely degrade the dye under visible light within 15 min,and the permeance can be restored to the original state after treatment.The recovery rate of membrane permeance is more than 99%after three cycles of degradation.The morphology of the membrane surface was characterized by SEM,XPS,FTIR,etc.The results show that with the addition of Zn-TCPP to the polyamide layer,the woven-like structure is obvious,and the thickness of the separation layer of all TFN membranes is thinner than that of TFC membranes.(2)Photocatalytic membrane based on porphyrin-based COF-366In this study,COF-366/PES mixed matrix membrane(MMM)with excellent comprehensive properties was successfully prepared by using COF-366 as nano-additive and polyethersulfone(PS)as polymer matrix material,combining phase transformation with interfacial polymerization process.Specifically,the concentration of melamine in the polymer matrix was adjusted by changing the immersion time of the water bath during the liquid phase transformation of COF-366/PES casting membrane,thus affecting the interfacial polymerization process,and forming a high-throughput anti-pollution porous nanofiltration membrane.The optimum membrane M4 has a permeance of 70.0 L m^-2h^-1bar^-1,and the rejection of Na₂SO₄is less than 10.0%,which can realize the efficient separation of dye and salt.The M4 membrane can completely degrade the methyl blue(MB)on the membrane within 15 minutes under visible light and restore the permeance to achieve three cycles.The surface morphology of the membrane was characterized by SEM,XPS,FTIR,etc.The results showed that all mixed matrix membranes showed the characteristic peaks of the polyamide layer on the surface,and the cross section showed finger-like holes and thin skin structure.The addition of COF-366 not only increases the permeation channel of the membrane,but also provides the membrane with photocatalytic degradation of pollutants.