Fabrication Of TiO₂-Based Photocatalytic Nanocomposite Membranes For Visible Light Degradation Of Tetracycline In Water

Photocatalytic composite membranes technology is a new photocatalytic composite membranes system formed by the combination of photocatalytic technology and membrane technology.It can not only degrade pollutants efficiently,but also quickly separate and recycle powder catalyst and reduce membrane fouling.It is expected to achieve a green and efficient"win-win"strategy for managing water pollution.In this paper,the TiO₂ based catalyst materials were modified by means of Au doping,pDA sensitization,heterojunction BiOBr-TiO₂construction and introduction of NCQDs.The above-mentioned modified TiO₂ photocatalysts were combined with the PVDF powder or biomimetic pDA modified PVDF membrane to synthesize the TiO₂-based photocatalytic nanocomposite membranes materials by blending phase conversion process and vacuum filtration method.A variety of characterization methods,such as scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffractometer?XRD?attenuation,total reflection Fourier transform infrared spectroscopy?FTIR?,X-ray photoelectron spectroscopy?XPS?,water contact angle measuring instrument?WCA?and UV-vis diffuse reflectance spectrometer?UV-vis DRS?,were used to test and analyze the microscopic morphology,structural composition,wettability and optical properties of the as-synthesized catalyst nanoparticles and composite membranes.Through different performance tests,the antifouling performance and regeneration stability of the composite membrane were studied.The TiO₂-based photocatalytic nanocomposite membranes were used for the study of photocatalytic degradation of tetracycline in water under visible light.The main research contents are as follows:?1?The Au-TiO₂ photocatalysts were synthesized by the sodium citrate reduction method,the sol-gel method and the high-temperature hydrothermal method.The Au-TiO₂ nanocomposite and PVDF powder were mixed into casting solutions by physical blending.And the mixed Au-TiO₂/PVDF photocatalytic nanocomposite membranes with visible light response were prepared by phase conversion process.Various characterization methods,such as SEM,TEM,FTIR,XRD,XPS,WCA and UV-vis DRS,etc.,were used to systematically characterize the micromorphology,structural composition,wettability and optical properties of different samples.The UV-vis DRS results showed that nano-Au doping improved the utilization of visible light.The antifouling performance of different membranes was investigated using BSA adsorption experiments,and the results showed that 0.3-Au-TiO₂/PVDF composite membranes had antifouling performance.By analyzing the regeneration stability experiments,it was found that the 0.3-Au-TiO₂/PVDF composite membranes exhibited good regeneration stability and easy separation and recovery features.The photocatalytic degradation of different membranes under visible light was investigated with tetracycline.The results showed that the photocatalytic degradation rate of 0.3-Au-TiO₂/PVDF nanocomposite membranes reached 75%within 120 min.Moreover,the first-order kinetic linear fitting showed that the k value of 0.3-Au-TiO₂/PVDF composite membranes was 0.01212 min^-1,which was 2.7 times of 0.1-Au-TiO₂/PVDF composite membranes and 2.0 times of 0.5-Au-TiO₂/PVDF composite membranes.Therefore,photocatalytic activity of 0.3-Au-TiO₂/PVDF composite composite membranes is obviously improved.?2?The PVDF membranes were selected as the substrate,a pDA/PVDF secondary reaction platform was then obtained by the biomimetic self-polymerization modification procedure of dopamine hydrochloride?DA-HCl?.The prepared Au-TiO₂ nanoparticles were vacuum-filtered onto pDA/PVDF composite membranes to prepare the supported Au-TiO₂/pDA/PVDF photocatalytic nanocomposite membranes with visible light response.The morphology and structure of different sample materials were systematically analyzed by means of SEM,TEM,FTIR,XRD and XPS.The UV-vis DRS results showed that both the the surface plasmon?SPR?resonance effect of Au nanoparticles and the visible light absorption of pDA increased the utilization rate of visible light.The BSA adsorption experiment was used to compare the antifouling performance of different membranes.The results showed that the Au-TiO₂/pDA/PVDF composite membranes had better antifouling performance.By analyzing the regeneration stability experiments,it was found that the Au-TiO₂/pDA/PVDF composite membranes exhibited good regeneration stability and easy separation recovery performance.The photocatalytic degradation and kinetic of different membranes under visible light was investigated in detail with tetracycline as the target pollutant.The results showed that the photocatalytic degradation rate of Au-Ti O₂/pDA/PVDF composite membranes reached 92%within 120 min.Compared with Au-TiO₂ powder and TiO₂/pDA/PVDF composite membranes,the degradation rate of Au-TiO₂/pDA/PVDF composite membranes was increased by 26%and51%,respectively.Moreover,the pseudo first order kinetic apparent rate constant k value of the Au-TiO₂/pDA/PVDF composite membranes was 0.02130 min^-1,which was 1.8 times of the Au-TiO₂ powder and 2.5 times of the TiO₂/pDA/PVDF composite membranes.The main reasons of the photocatalytic activity enhancement of the Au-TiO₂/pDA/PVDF composite composite membranes are the SPR effect of Au and photosensitizing effect of pDA on TiO₂.?3?Porous TiO₂ nanorods were synthesized by H₂SO₄ etching method,combined with the synthesis technology of BiOBr-TiO₂ heterojunction and NCQDs to synthesise the ternary NCQDs-BiOBr-TiO₂ photocatalyst materials with visible light response.The prepared mixed NCQDs-BiOBr-TiO₂nanocompositewasmixedwithPVDFpowdertoprepare NCQDs-BiOBr-TiO₂/PVDF photocatalytic nanocomposite membranes by phase conversion method.The micromorphology and structural composition of different powder catalysts and photocatalytic nanocomposite membranes were studied by means of various characterization methods.UV-vis DRS results indicated that the formation of BiOBr-Ti O₂ heterojunction and the introduction of NCQDs extended the visible light absorption range of photocatalytic materials.The BSA adsorption performances of different composite membranes were investigated,and the results showed that 0.5-NCQDs-BiOBr-TiO₂/PVDF composite membranes had strong antifouling properties.Moreover,it was found that the 0.5-NCQDs-BiOBr-TiO₂/PVDF composite membranes exhibited high regeneration stability and easy separation recovery performance.The visible light degradation performance and kinetic behavior of different membranes was investigated in detail with tetracycline as the target pollutant.The results showed that the TC degradation rate of 0.5-NCQDs-BiOBr-Ti O₂/PVDF composite membranes reached 77%in 120 min.Moreover,the pseudo first order kinetic apparent rate constant k value of the 0.5-NCQDs-BiOBr-TiO₂/PVDF composite membranes was 0.01342 min^-1,which was 3.7times of the 0.1-NCQDs-BiOBr-TiO₂/PVDF photocatalytic composite membranes,2.5 times of the 0.3-NCQDs-BiOBr-TiO₂/PVDF photocatalytic composite membranes,and 2.2 times that of the 0.5-BiOBr-TiO₂/PVDF photocatalytic composite membranes.