Preparation Of TiO₂/PVDF Composite Membrane And Study On Its Oil-water Separation Performance

With the increase of oil spill accidents in the exploitation of petroleum resources and the continuous increase in the discharge of oily wastewater from industrial production,the global ecosystem and human health are being threatened by water pollution.Membrane separation technology has received widespread attention as a high-efficiency and low-consumption separation technology in water treatment.This aspect has received widespread attention from people.Polyvinylidene fluoride（PVDF）membrane has good mechanical properties and stable chemical properties,but due to its own unique hydrophobicity,it is easy to be contaminated by contaminants during the membrane separation process,causing the membrane pores to be blocked.Hydrophilic modification of PVDF membrane to improve the anti-fouling performance of the membrane has become a research trend.In this paper,PVDF membranes are prepared by vapor-induced phase separation technology,and then TiO₂ nanoparticles are grafted onto the surface of PVDF membranes for hydrophilic modification through intermediates.The details are as follows:（1）PVDF membranes are prepared by vapor-induced phase separation technology.In the previous study,it was found that the content of additives in the membrane casting solution and the exposure time in the environment during vapor-induced phase separation have great impact on the membrane.In this paper,the influence of the content of additive PVP（K60）in the casting liquid and the exposure time in vapor-induced phase separation on the structure and permeability of PVDF membranes were studied.The results showed that as the content of PVP（K60）in the casting solution increased,the number of surface pores on the surface of the prepared PVDF membrane gradually increased,and the surface pore size first increased and then decreased.The porosity of the PVDF membrane appeared first.Changes after increase and decrease.When the content of PVP（K60）in the casting liquid is 2 wt%,the PVDF membrane shows the best permeability.In the process of vapor-induced phase separation membrane production,when the exposure time increases from 0 min to 10 min,the cross-sectional structure of the membrane changes from finger-like pores to sponge pores.When the exposure time is 5 min,the permeability of the prepared membrane reaches the best pure water flux of 806.98 L·m^-2·h^-1·bar^-1,and all membranes show more than 99%oil-water separation performance.（2）The citric acid（or succinic acid）modified TiO₂/PVDF composite membrane is prepared by grafting citric acid or succinic acid on the hydroxylated PVDF membrane,and then grafting different concentrations of TiO₂ on the surface of the membrane.Characterization and penetration performance research.As the concentration of the TiO₂ solution increases,the number of TiO₂ particles grafted on the surface of the citric acid modified TiO₂/PVDF composite membrane also shows an increasing trend.The flux first increases and then decreases.When the TiO₂ solution concentration is 0.3 wt%,The citric acid modified TiO₂/PVDF composite membrane has the best pure water flux of 1185.47 L·m^-2·h^-1·bar^-1.As the concentration of the TiO₂ solution increases,the number of TiO₂ particles grafted onto the surface of the succinic acid modified TiO₂/PVDF composite membrane also shows an increasing trend.When the concentration of the TiO₂ solution is 0.5 wt%,the membrane reaches its best performance.The contact angle of the acid-modified TiO₂/PVDF composite membrane is 63.2±2.1°,the pure water flux is 1073.03 L·m^-2·h^-1·bar^-1,and all the membranes maintain an oil-water separation efficiency of more than 99%.（3）Oil-water separation performance and anti-pollution performance of the citric acid（or succinic acid）modified TiO₂/PVDF composite membrane were studied to compare the difference between citric acid and succinic acid grafting TiO2 on the surface of the PVDF membrane.The citric acid（or succinic acid）modified TiO₂ The amount can reach 138.38 L·m^-2·h^-1·bar^-1.The citric acid（or succinic acid）modified TiO₂/PVDF composite membrane did not change significantly in the oil-water separation efficiency during multiple oil-water separation cycles.The flux recovery rate of PVDF membrane prepared by TiO₂ grafted modification with succinic acid reached80.89%after the fourth cycle,while the flux recovery rate of PVDF membrane prepared by graft modification of TiO₂ citric acid was 74.26%.The PVDF membrane prepared by graft modification of TiO₂ with succinic acid showed better anti-pollution performance.