Visible Light-responsive ZnFe₂O₄/C/TiO₂ And Fe₂O_{3/SrTiO3/TiO2 Catalyst And Its Application In Photodegradation Of Antibiotic Wastewater}

Since the antibiotics were discovered,they have played a crucial role in protecting human health and promoting the development of livestock and poultry breeding industry.However,with the increasing growth of the pharmaceutical industry,the species of antibiotics gradually become diversified and their large-scale-application is continuously expanded.Accordingly,the resultant wastewater containing antibiotics has the features of difficult decomposition,poor biodegradability,easy residue and induction of resistance genes,which is constantly destroying the natural environment and considered to be a tough problem in wastewater treatment.At present,the industrial treatment methods of antibiotics-contained wastewater mainly include the ultrasonic synergistic oxidation,electrochemical oxidation removal,adsorption,photocatalytic oxidation and advanced oxidation,etc.Among the reported various approaches,the photocatalytic technology is regarded to be competitive with high oxidation efficiency,long service life,mild reaction conditions,as well as low energy consumption.In terms of the photocatalytic oxidation technique for antibiotics-contained wastewater,the investigation and development of efficient photocatalyst are deemed to be the keypoints of this technology.Tetracycline having broad-spectrum antibacterial activity is one of the most common used among various antibiotic drugs,and thus the photocatalytic degradation of tetracycline is selected as the probe reaction in present study.This work is originated from specific technical points in how to make full use of sunlight,and mainly focuses on the design of photocatalysts with high response to visible light.Two kinds of the ZnFe₂O₄/C/TiO₂ hollow sphere photocatalyst and Fe₂O₃/SrTiO₃/TiO₂ nanostructured photocatalyst were developed,and the related assembly process was systematically elucidated.The X-ray diffraction(XRD)analysis,Scanning electron microscopy(SEM),transmission electron microscopy(TEM),uv-vis diffuse reflectance spectroscopy(DRS),X-ray photoelectron spectroscopy(XPS),Raman spectroscopy,specific surface area and pore structure analysis(BET),transient photocurrent response(I-T),electrochemical impedance spectroscopy(EIS)as well as other advanced testing techniques were utilize to characterize the photocatalyst structures and explore theit assembly process.Meanwhile,the electron paramagnetic resonance spectrum(EPR),photoluminescence spectroscopy(PL)were performed to investigate the reaction mechanisms of photocatalytic degradation of tetracycline,and detect the interfacial phenomena during catalyst assembly,and thereby the scientific working principles of catalyst assembly were revealed.Herein,this study is expected to supplement the important basic dataset for the research on photocatalysis,and provide key technologies for photodegradation of tetracycline-contained wastewater.The main conclusions have been drawn as follows.1.The ZnFe₂O₄/C/TiO₂ hollow sphere photocatalyst was synthesized by a template method.The experimental results demonstated that the carbon layer was distributed at the interface between of ZnFe₂O₄ and TiO₂ crystals.It should be noted that the introduction of carbon layer can enhance the electrical conductivity of the contact interface between ZnFe₂O₄ and TiO₂,improve the electrical conductivity of the contact interface,promote the charge transfer effectively,improve the separation efficiency of photogenerated electrons and holes,and thus the activity of the photocatalyst can be obviously increased.This novel method can be applied to obtain an enhancement in the activity and stability of photocatalyst by adjusting the interfacial energy band of carbon and guiding the transfer of photocarriers.Under the irradiation of visible light,the degradation rate of tetracycline reached 99%in ZnFe₂O₄/C/TiO₂ catalyzed reaction for 90 minutes.The degradation process was in accordance with the quasi-first-order kinetic equation,and the degradation rate constant was determined as 0.0132 min^-1.The generation of the superoxide radicals and hydroxyl radicals with strong oxidation activity were detected during the photocatalytic reaction process.2.The Fe₂O₃/SrTiO₃/TiO₂ photocatalyst was synthesized by hydrothermal method and layer by layer assembly process.The study showed that within the nanostructured of Fe₂O₃/SrTiO₃/TiO₂ were identified,the crystal phase structures of Fe₂O₃,SrTiO₃ and TiO₂ are observed respectively,and the close contact with strong bonding force between various crystal phases was responsible for the construction of appropriate heterojunction,leading to significant improvement in the photocatalytic performance.The degradation rate of tetracycline on Fe₂O₃/SrTiO₃/TiO₂ catalysts was87%after 120 minutes of photocatalytic reaction.After 10 cycles,the photocatalytic activity of tetracycline were still maintained good stability.The photocatalytic reaction process was observed by both active species capture experiment and EPR analysis.It was found that superoxide radicals and hydroxyl radicals with strong oxidation activity were generated during the photocatalytic reaction process,the rapid degradation of tetracycline can be realized through the strong oxidation effects of superoxide radicals and hydroxyl radicals.