Study On The Characteristics And Mechanism Of Photoelectrocatalytic Degradation Of Tetracycline In Water By PEDOT Modified PVDF Membrane

Polyvinylidene fluoride（PVDF）membrane is a widely used water treatment membrane separation material.It has the advantages of good chemical stability and high mechanical strength.It also has problems like weak hydrophilicity and serious membrane fouling.In order to further break through the limitations of PVDF membranes in applications,the surface modification of PVDF membranes to give them new functions has attracted more and more attention.The combination of modified membrane materials and other water treatment technologies further ensures the treatment efficiency and the anti-pollution performance of membrane materials.Therefore,this study proposes to use a visible light-responsive conductive polymer,poly 3,4-ethylenedioxythiophene（PEDOT）,to modify the surface of PVDF membrane to prepare a photoelectrocatalytic separation membrane.The performance of the membrane materials before and after modification was investigated in detail.By coupling with the photoelectrocatalytic process,the degradation effect of tetracycline under the synergistic effect of photocatalysis,electrocatalysis and membrane separation was systematically studied,and the degradation path and mechanism of tetracycline were deeply explored.The specific research contents are as follows:1)Preparation of PEDOT modified PVDF membrane.The PVDF membrane obtained by phase transformation method was used as the substrate,and the oxidant Fe Cl₃·6H₂O was precoated on the substrate membrane by an innovative mechanical arm automatic printing method.Under the constant temperature of 80℃in 4 hours,PEDOT polymerization was realized by chemical vapor deposition（CVD）reaction with EDOT as the monomer to complete the membrane surface modification.Scanning electron microscope（SEM）and atomic force microscope（AFM）were used to characterize the surface morphology of the membrane.The surface hydrophilicity of the membrane was tested using a contact angle measuring instrument.The electro-optical properties of the membrane were characterized using an electrochemical workstation and a multimeter.The spectral characteristic test of the membrane involved infrared spectrum,ultraviolet-visible spectrum and Raman spectrum.Through characterization,it was found that the photoelectric activity of the modified membrane was the best when 10%mass concentration oxidant was printed with four layers,the photocurrent intensity was 3.78×e^-4A.Therefore,it was determined that the optimal printing number of oxidants in the preparation process was four layers.2)The effects of light and voltage on tetracycline removal were investigated in a photoelectrocatalytic membrane separation system.Six conditions of dark reaction,photolysis,photocatalysis,1.5V and 3.0V photoelectrocatalysis,and 3V electrocatalysis were set,respectively.The test results after 2 hours of reaction showed that the effect of removing tetracycline hydrochloride during the separation of the photocatalytic membrane after the application of voltage was good.The removal rate of tetracycline hydrochloride is up to 71%under visible light catalytic conditions assisted by 3.0V external voltage,which is 1.6 and 7.9 times that of photocatalysis and photolysis,respectively.The removal rate of tetracycline hydrochloride can also be stabilized at about75%after running for 12 hours at a hydraulic residence time of 4 hours,which indicates that the modified photoelectrocatalytic separation membrane has good long-term stability.The presence of typical organic pollutants such as bovine serum albumin（BSA）,sodium humate（SH）and sodium alginate（SA）can interfere with the degradation of tetracycline hydrochloride.,among which the interference effects of BSA and SH+SA+BSA mixture were greater than that of SH and SA alone,resulting in a reduction of 17%and 34%of the removal rate,respectively.3)According to the free radical capture experiment,the three oxidation active species that play a major role in the photocatalytic coupling reaction of the modified membrane are SO₄^-·、·OH、¹O₂,respectively.The removal mechanism is as follows:under the action of visible light irradiation and applied voltage,·OH、¹O₂ and SO₄^-generated in the reaction system take advantage of their strong oxidation ability to capture electrons on tetracycline hydrochloride,so that the electron transfer of tetracycline hydrochloride occurs in the structure and gradually transforms from large molecules to small molecules.