The Study On Degradation Of Ciprofloxacin In Water By Zinc Oxide Composite Photocatalytic Materials

Ciprofloxacin（CIP）is widely used to treat various infections and infectious diseases due to its broadspectrum antibacterial activity.However,CIP has been constantly detected in a wide range of aquatic ecosystems in recent years,posing a serious risk to public health and even ecological balance as a result of its inherent chemical toxicity and drug resistance,making it difficult to remove CIP completely by conventional water treatment processes.Consequently,there is an urgent need to develop an efficient,green and energy-saving purification technology to achieve effective removal of CIP.Semiconductor photocatalytic technology driven by sunlight or visible light has attracted extensive attention because of its advantages of strong redox property,high degradation efficiency,thorough pollutant purification and low secondary pollution.Zinc oxide（ZnO）,as an inorganic semiconductor material,has large exciton binding energy and fast electron transfer capability,meanwhile,its large specific surface area,low preparation cost and good physicochemical and photonic stability make it considered as a promising photocatalytic material for applications.However,some inherent defects such as high carrier complexation rate,narrow spectral response range,difficulty in separation and recovery,and susceptibility to photocorrosion have hindered its further utilization.Hence,in this thesis,two ZnO composite photocatalysts with high photocatalytic activity and easy recovery were constructed to address the above problems.The photocatalytic performance and reaction mechanism of the composites were investigated through a series of characterization methods and experiments on the degradation of CIP under different impact factors.And on this basis,a simulated device for the removal of CIP in flowing water was designed,which provided a reference for the processing of organic pollutants in actual wastewater.The major research contents and conclusions are as follows:（1）Ag₂O quantum dots/ZnO nanoparticles/platelet Bi OI（AZI）photocatalyst was synthesized using a low temperature chemical bath and deposition method.The introduction of Ag₂O and Bi OI effectively extended the photoresponse range of ZnO to the visible region and improved the charge separation efficiency.The composite photocatalyst with 40%Ag₂O mass ratio（40%-AZI）achieved a high CIP removal rate of 98.11%within 6 min of LED visible light irradiation.The presence of common anions(Cl^-,SO4^2-and NO3^-)and humic acids in the water existed some degree of inhibition of the catalytic degradation reactions.The results of free radical burst experiments and electron paramagnetic resonance spectroscopy tests verified that the main active species participated in degradating CIP were h⁺,·O2^-and e^-.Four reuse experiments and characterisation of used photocatalyst further demonstrated the excellent stability of AZI.（2）A direct Z-type heterojunction,consisting of ZnO nanorod and Ag₂O nanoparticle,was immobilized on nickel foam（Ni F）by a combination of hydrothermal and deposition methods to successfully construct a 3D mesh immobilized photocatalytic material,named AZN.A series of photoelectrochemical tests showed that the charge separation efficiency of AZN was significantly improved,which was attributed to the synergistic effect of direct Z-type heterojunction,the matched energy band structure and the 3D porous structure.Light could be reflected multiple times in the porous structure of the photocatalyst,thus increasing the utilization of light.The photocatalytic activity of AZN was investigated by the degradation of ciprofloxacin（CIP）and rhodamine B（Rh B）under simulated solar irradiation,with a degradation rate of 98.84%for CIP and 99.26%for Rh B within 12 min of light exposure.At the same time,the surface wettability of the AZN composite was significantly improved,increasing the contact frequency between the photocatalyst and the pollutant molecules.·O2^-and photogenerated h⁺active species generated in the AZN/simulated sunlight system were involved in the degradation of pollutants,which was confirmed by radical trapping experiments and electron paramagnetic resonance spectroscopy.The energy band structure of the composite was inferred from the Mott-Schottky curve test,and the Z-type charge transfer pathway and photocatalytic mechanism in the AZN/simulated sunlight system were then proposed.（3）The durability and practical application potential of AZN were evaluated through recycling experiments,generalization experiments and energy consumption comparisons.After four reuse experiments,AZN still maintained a high Rh B removal rate（98.62%）and very little Ag⁺and Zn²⁺leaching during each cycle of degradation,indicating that AZN had outstanding physicochemical stability.AZN showed rapid and efficient removal of different types of antibiotics（tetracycline,sulfadiazine and ciprofloxacin）,indicating its high universal applicability.Comparing the energy consumption of the AZN/simulated sunlight system with other reported photocatalytic systems for the treatment of Rh B,the former had a competitive energy saving advantage.Sequential batch experiments in a home-made simulated flowing water device showed the complete removal of CIP and 93.85%removal of Rh B after 4 stages of treatment,further verifying the feasibility of AZN for practical applications.