Preparation Of Piezoelectric Polyvinylidene Fluoride Separation Membrane And Study On Its Membrane Fouling Control Strateg

Membrane fouling is an important challenge in the application of Polyvinylidene fluoride(PVDF)membrane in drinking water treatment.Membrane fouling can be alleviated through the electrified membrane fouling control strategy by the effect of electrostatic repulsion and micro electric field on membrane surface.However,its application is limited by the high energy consumption of external power supply and the strict requirements on the conductivity of the membrane material.PVDF can harvest the environment pressure and convert it into surface potential.Such direct piezoelectric property has potential to solve above problems.On the one hand,the post poling process is important to the fabrication of piezoelectric PVDF membrane,which will have an adverse effect on the membrane pore structure.On the other hand,the influence of the direct piezoelectric response on membrane fouling is rarely reported.Therefore,in order to promote the quality and efficiency of the application in drinking water treatment for membrane technology,how to construct a PVDF membrane with both piezoelectric property and filtration performance,and how to control the membrane fouling through the direct piezoelectric effect both have certain theoretical significance and practical application value.Firstly,the PVDF/Barium titanate(BTO)blending UF membrane was fabricated and the effect of BTO additive on membrane piezoelectric performance,crystal structure,surface characteristic,filtration and antifouling performance were systematically investigated.For the membrane with 0.1 wt%BTO loading,its piezoelectric output was reached as high as-3.99 V at 0.15 MPa,and the membrane was dominated by the polar polymorphs(90.19%),exhibiting enhanced surface charge(-53 mV),wettability(43°)and selectivity.Moreover,in Bovine serum albumin(BSA)fouling experiments,the fouling resistance of PVDF/BTO membrane did not increased obviously when the trans-membrane pressure(TMP)was rised from 0.07 to 0.15 MPa.This observation demonstrated the responsiveness of piezoelectric PVDF/BTO UF membrane on pressure-driven filtration process,and the improved antifouling performance could attribute to the intensified electro-static repulsion between membrane and foulant.Secondly,a membrane fabrication method of weak-field in-situ poling coupled ion dipole interaction was constructed to activate the intrinsic piezoelectric property of PVDF membrane,and its inherence mechanism was investigated in combination with material characterization.For the membrane fabricated under the poling strength as60×10~4 V/m,its piezoelectric output was reached as high as-9.93 V at 0.15 MPa.The transformation of piezoelectric crystal form was mainly affected by ion dipole interaction,and the spatial orientation of crystallites was mainly controlled by in-situ poling.The PVDF membrane had both piezoelectric activity and stable filtration performance(the pure water flux was 341.5 LMH·10 psi and the BSA rejection was93.9%)through this synergistic effect.Finally,the membrane fouling behavior and the in-situ potential on membrane surface were investigated to analyze the influence of direct piezoelectric effect on membrane fouling.The barrier between membrane and foulant was enhanced by electrostatic repulsion due to the direct piezoelectric effect.And the high potential on membrane surface allowed the cake layer to form faster and play a pre-filtering effect to further alleviate membrane fouling.With the increase of TMP,membrane surface potential was improved by the dynamic characteristics of the direct piezoelectric response,thereby the membrane fouling mitigation mechanism was enhanced.Moreover,compared with hydrophilic commercial membrane,the performance was more stable for piezoelectric PVDF membrane.