Preparation Of Underwater Superhydrophilic/Superoleophobic PVDF-based Membrane And Its Oil-water Separation Performance

Membrane separation technology is widely used in the treatment of oily wastewater because of its excellent characteristics such as low energy consumption,small footprint and easy operation.However,existing separation membranes are susceptible to oil droplet contamination during use and are not suitable for complex separation environments.In this study,polyvinylidene fluoride（PVDF）membranes were prepared by phase conversion method and hydrophilically modified by surface modification method to prepare antifouling superhydrophilic-submerged superoleophobic PANI/Ag/PVDF membranes and T-PVDF membranes that can be used in complex environments.The specific modification methods are as follows:（1）Superhydrophilic-submerged superoleophobic PANI/Ag/PVDF membranes were prepared from aniline（ANI）and silver nitrate（Ag NO₃）and PVDF powder.The prepared PANI/Ag/PVDF membranes possess good oil-water separation performance,anti-fouling performance,chemical stability and catalytic degradation performance.Under gravity conditions,for toluene-water emulsion,chloroform-water emulsion,petroleum ether-water emulsion,and hexane-water emulsion,the separation flux of PANI/Ag/PVDF membrane can reach more than 400 L/m²/h,and the separation efficiency reaches more than 99%.In the cyclic separation test,the separation performance of the separation membranes did not decay significantly and showed good cyclic stability.After 12 h immersion in HCl solution at p H=1,3.5 wt.%Na Cl solution,and Na OH solution at p H=13,the PANI/Ag/PVDF membrane still had submerged super-oilophobicity and the separation performance did not decay significantly.In addition,the prepared separation membranes had good catalytic degradation performance for methylene blue and methyl orange dyes,which could be completely degraded within 10 min.（2）T-PVDF superhydrophilic-submerged superhydrophobic oil-water separation membranes were prepared by using the self-polymerization reaction of tea polyphenols in tea leaves under weak alkaline conditions as raw materials and modifying the PVDF membrane hydrophilically.The prepared T-PVDF separation membranes possess good oil-water separation performance,anti-fouling property and chemical stability.Under gravity conditions,the separation flux of T-PVDF membranes for petroleum ether-water emulsion,kerosene-water emulsion,cyclohexane-water emulsion and dichloromethane-water emulsion can reach more than 250 L/m²/h,and the separation efficiency reaches more than 99%.The separation performance of the T-PVDF membrane did not deteriorate significantly in 11 cycles of the cyclohexane-water emulsion separation test.After soaking in HCl solution at p H=1,3.5 wt.%Na Cl solution,and Na OH solution at p H=13 for 24 h,the T-PVDF membrane still maintained the underwater superoleophobicity and the separation performance did not decay significantly.The BT-PVDF membrane was prepared by black tea,and the separation flux reached more than 140 L/m²/h,and the separation efficiency reached more than 99%,indicating the good oil-water separation performance,which indicates that the strategy adopted in this experiment has certain universality.