Performance And Mechanism Of Titanium Dioxide Nanowire Catalytic Ceramic Membrane For Tetracycline Wastewater Treatment

Antibiotics are widely used in human life because of their highly efficient sterilization against pathogenic bacteria.The discharge of antibiotic wastewater would negatively affect the growth of aquatic organisms and induce the formation of more harmful drug-resistant bacteria.The threat to human health has attracted extensive attention.Developing advanced antibiotic wastewater treatment technology is of great research importance and practical significance.Despite the advantages of high separation efficiency,environmental friendliness,and sustainability,membrane separation technology still suffers from key challenging issues such as membrane fouling,insufficient contaminant removal and water flux.To address these issues,herein,we designed a novel TiO₂ nanowire catalytic ceramic membrane with three-layer structure.Enhancement of water permeability and fouling resistance can be achieved for the membranes with increased porosity,exhibiting much higher permeate flux than conventional pressure driven membranes.Photocatalytic separation performance was systematically studied under different operating conditions.Moreover,the degradation path mechanism and toxicity of intermediate products during photocatalysis were investigated.The main research content and conclusions are shown as follows:（1）Preparation and characterization of transition metal ion doped TiO2 nanowires.The nanowires doped with different transition metal ions（Fe,Co,Ni）were synthesized via hydrothermal method.All the nanowires showed a pure anatase phase.The absence of characteristic diffraction peaks of doped metal oxides indicates that the minor doping of Fe,Co,Ni did not affect the crystalline phase structure.The XPS results showed that Fe element partially exists in the form of Fe₂O₃,while Co and Ni elements exist mainly in the form of Co TiO₃ and Ni TiO₃.The Ti peak shifted toward the high-energy region after doping.Both TiO₂nanowires and commercial TiO₂ showed strong absorbance in the UV region ranging from 200to 380 nm,but almost no absorption in the visible region.The absorption edges of the doped nanowires all show significant red shift,indicating that the light absorption ability was enhanced by doping.The degradation rate order for tetracycline:Ni doped TiO₂ nanowire>Fe doped TiO₂ nanowire>Co doped TiO₂ nanowire>TiO₂ nanowire>TiO₂ nanopowder.Especially,the Ni doped nanowires could degrade 88.8%tetracycline within 90 min.（2）Fabrication and water treatment performance of ceramic membranes catalyzed by titanium dioxide nanowires.A hydrophilic ceramic based TiO₂ nanowire membrane was constructed by respectively using porous mullite,TiO₂ nanoparticles and Ni-TiO₂ nanowire as substrate,interlayer and functional separation layer.The nanowire membranes with a novel three-layered structure exhibited a special network surface structure with 64.5%porosity and5.4μm layer thickness.The SEM results showed that they had a hollow fiber tubular structure with high aspect ratio and uniform dimension.Their morphology was not affected by doping.The performance was evaluated by using tetracycline solution as simulated antibiotic wastewater.Compared with conventional TiO₂ particle membrane,the nanowire membrane showed a higher adsorption capacity under dark condition,and that removal efficiency could be significantly improved up to 90%under simulated sunlight.The stable water permeance was high as 1253 L·m^-2·h^-1·bar^-1 with mitigated membrane fouling.Compared with other catalytic membranes and pressure driven membranes,the nanowire membrane has significant advantages in removal efficiency,especially water permeance.（3）Path mechanism and toxicity assessment of tetracycline degradation by photocatalytic membrane.The radicals generated during photocatalysis were captured and identified,indicating that the radicals were·O₂^-and·OH.The active radicals that played a dominant role in reactions were confirmed to be·O₂-by radical catching experiments.3-D EEM results indicate that during photocatalytic process an intermediate product with a fluorescent group was produced（i.e.,humic acid like organics）.The degradation pathway mechanism is proposed by the LCMS results combined with DFT calculations,indicating that tetracyclines undewent oxidative ring opening,then degraded into small molecules of carboxylic acids,and amides（such as propionamides and acetamides）,and ultimately into H₂O、CO₃^2-、NO₃^-and NH₄⁺.The toxicity evaluation results indicate that the toxicityt was significantly lowered,which can be ascribed to the higher LC50 value of small molecule intermediate products after deep oxidation.Under simulated sunlight,the nanowire catalytic ceramic membranes designed in this work show the rapid treatment ability and high-efficiency application potential for tetracycline wastewater,which can be considered as a green and environmentally friendly water treatment technology.This work hopefully provides new research ideas and scientific references for water treatment applications of next-generation ceramic membranes.