| Membrane distillation(MD)is a separation technology that combines traditional distillation methods with membrane separation technology.It has great application prospects in seawater desalination,salt solution concentration crystallization,and pure water preparation processes.However,the potential membrane fouling problem will reduce the flux and efficiency of membrane distillation.The pollution of organic pollutants to the membrane is one of the important factors that hinder the application of membrane distillation technology in actual production.Metal organic frameworks(MOFs)are composed of inorganic metal centers and bridged organic ligands connected to each other through self-assembly to form a porous material with a periodic network structure.CuBTC,as a type of MOFs,has good hydrophilicity The oleophobic performance,attaching it to the membrane surface,is expected to resist organic contamination and achieve continuous and stable operation of the membrane distillation process..In this paper,hydrothermal method was used to synthesize hydrophilic CuBTC metalorganic framework crystals.Polyvinyl alcohol(PVA)was used as a binder.The CuBTC crystals with different contents(0.2,0.4,0.6 and 0.8 g)were attached by suction filtration.On the polyvinylidene fluoride(PVDF)membrane,PVA was cross-linked with glutaraldehyde(GA)to prepare a CuBTC / PVDF composite membrane with a hydrophilic surface layer and a hydrophobic bottom layer.The crystallinity purity,specific surface area,surface morphology of CuBTC crystals,as well as the hydrophobicity,pore size,porosity,surface roughness,surface characteristics,and structural morphology of the composite membrane were characterized.The results show that CuBTC crystals have higher crystallinity and purity,larger specific surface area,and specific morphological characteristics;as the content of CuBTC increases,the pore size and porosity of the composite membrane will gradually decrease,and the surface roughness will Gradually increase.When the content of CuBTC is 0.6 g,the composite membrane exhibits good hydrophilic and oleophobic properties.The contact angle of water in air is 28.1 °,and the contact angle of underwater oil is 151.3 °,and CuBTC crystals are evenly and firmly attached to the composite Membrane surface.Using 35 g / L sodium chloride solution as the feed liquid,direct contact membrane distillation desalination experiments were carried out on the original membrane and the composite membrane.The CuBTC / PVDF composite membrane has a desalination effect similar to that of the PVDF original membrane,with a salt rejection rate of up to 99.99%.In the 48-hour desalination experiment,the flux has remained stable and can be used for long-term DCMD desalination experiments.In order to investigate the anti-organic pollution performance of the CuBTC / PVDF composite membrane,three organic pollutants,crude oil,humic acid and sodium alginate,were selected as the research objects.Take oily high salt solution(crude oil content was 1 g/ L,sodium chloride content was 35 g / L),humic acid high salt solution(humic acid content was 50 mg / L,sodium chloride content was 35 g / L,calcium chloride content was 2.22 g /L),sodium alginate high salt solution(sodium alginate content was 1 g / L,sodium chloride content was 35 g / L,calcium chloride content was 2.22 g / L)was used as feed liquid,direct contact membrane distillation experiment was conducted,and the anti-fouling performance of the original membrane and the composite membrane was compared.The results show that the original membrane is continuously polluted by organic substances,which leads to a continuous decline in flux;and under the same conditions,the composite membrane shows good anti-pollution performance for three organic substances,and the flux remains in a stable state.It can be used for industrial application selection and reference for direct contact membrane distillation process to treat organic wastewater. |
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