Filtration And Dye Adsorption Properties Of PVDF Membranes Modified By MOFs

The pollution caused by industrial wastewater with the characteristics of complicated component and low degradability is of great concern in recent years.At present,membrane separation technology and adsorption method are effective methods for the removal of pollutants from wastewater.Polyvinylidene fluoride?PVDF?membrane is a kind of polymer membrane material with excellent performance.It is widely used in the field of membrane separation.But the hydrophilicity of PVDF is poor,it needs to be modified.Compared with conventional pulverescent adsorbents,membrane adsorbent has the advantages of simple operation and easy to reuse.In this paper,PVDF/ZIF-67 and PVDF/ZIF-8 composite membranes were fabricated via phase inversion method with two kinds of metal organic framework?MOFs?ZIF-67 and ZIF-8 as additive.The synthetic ZIF-67 and ZIF-8 were characterized by XRD.The surface morphology and thermal stability of the samples were characterized by scanning electron microscopy and thermogravimetric analysis.The filtration and adsorption properties of PVDF/ZIF-67 and PVDF/ZIF-8 composite membranes were tested.The main research contents are as follows:?1?The effect of mass fraction of ZIF-67 on the filtration performance of PVDF membrane was investigated.The experimental results showed that when the mass fraction of ZIF-67 is 0.2wt%,the effect of modification is the best.Compared with PVDF pure membrane,the hydrophilicity of the membrane surface was improved obviously.The water flux reached the maximum value with 151.7L·m^-2·h^-1 which is nearly 2 times of the water flux of PVDF pure membrane.The rejection was 70%,increased by 6.7%compared with PVDF pure membrane.The flux recovery ratio reached the maximum value with 94.3%,increased by 8.8%compared with PVDF pure membrane.In the cycle measurement,only the first cycle suffered irreversible pollution,and the flux recovery ratio of the third cycle reached as high as99%.The antifouling performance was improved.?2?The effect of mass fraction of ZIF-8 on the filtration performance of PVDF membrane was investigated.The experimental results showed that when the mass fraction of ZIF-8 is 0.2wt%,the effect of modification is the best.Compared with PVDF pure membrane,the hydrophilicity of the membrane surface was improved obviously.The water flux reached the maximum value with 143.6L·m^-2·h^-1 which is nearly 1.9 times of the water flux of PVDF pure membrane.The rejection was 71.8%,increased by 7.9%compared with PVDF pure membrane.The flux recovery ratio reached the maximum value with 95.2%,increased by 9.7%compared with PVDF pure membrane.In the cycle measurement,only the first cycle suffered irreversible pollution,and the flux recovery ratios of the second and the third cycle were above 95%.The antifouling performance was improved.?3?The adsorption of methyl orange on PVDF/ZIF-67 membrane was investigated.The experimental results showed that the optimal dosage of PVDF/ZIF-67 membrane is 30 mg.At 303K,the maximum adsorption capacity of methyl orange on PVDF/ZIF-67 membrane is 47.42mg·g^-1,and the adsorption process reached equilibrium at 90min.The Langmuir isotherm model is more suitable to describe the adsorption behavior.The adsorption kinetics is in accordance with the quasi-secondary kinetic model.The intraparticle diffusion also had significant effect on the adsorption.Thermodynamic parameters illustrated that the adsorption process was spontaneous and exothermic.After 6 adsorption-desorption,PVDF/ZIF-67membrane still maintained high adsorption capacity for methyl orange.?4?The adsorption of Congo Red on PVDF/ZIF-8 membrane was investigated.The experimental results showed that the optimal dosage of PVDF/ZIF-8 membrane is 30 mg.At 303K,the maximum adsorption capacity of Congo Red on PVDF/ZIF-8 membrane is 34.80mg·g^-1,and the adsorption process reached equilibrium at 90min.The Langmuir isotherm model is more suitable to describe the adsorption behavior.The adsorption kinetics is consistent with the quasi-secondary kinetic model.The intraparticle diffusion also had significant effect on the adsorption.Thermodynamic parameters illustrated that the adsorption process was spontaneous and exothermic.After7 adsorption-desorption,PVDF/ZIF-8 membrane still maintained high adsorption capacity for methyl orange.