Preparation Of The Novel Composite Photocatalyst And Its Applications In Pollutant Degradation In Water

With the continuous progress of science and technology and the growing population,the production and use of drugs have gradually increased,increasing their accumulation in water and soil seriously.Pharmacutical pollutants,especially antibiotic pollutants,have become the primary pollution source in the current water environment,and the rapid and efficient removal of them has become a hot spot in the current water environment research.Compared with physical adsorption,chemical oxidation and other traditional methods,photocatalytic technology uses sunlight to provide sustainable energy to achieve the removal of pollutants in water,which has the advantages of green environmental protection and sustainability.In this study,the aim was to achieve the efficient degradation of tetracycline and the removal of Staphylococcus aureus（S.aureus）.Emodin,a natural product of traditional chinese medicine,was used as a photosensitizer,and its unique largeπconjugated anthraquinone structure was used to achieve the efficient utilization of UV-visible light.A new type of multifunctional composite photocatalyst Emodin/HAp was prepared by using hydroxyapatite（HAp）,which has high thermal stability and can be recycled,as the carrier material under mild condition.Through the migration of photogenerated electrons and holes between emodin and HAp,the composite photocatalyst showed high photocatalytic activities.Within 15 min of irradiation,the photodegradation rate of tetracycline was 99%,and it had complete photoinactivation effect on S.aureus.Therefore,this study provided a new way for the design and preparation of novel multifunctional photocatalysts using widely available natural products to realize the environmental remediation.The main research contents are as follows:（1）Preparation and characterization of Emodin/HAp photocatalystsIn order to improve the photocatalytic activity,stability and recoverability of emodin which was used as a photosensitizer,a series of complex photocatalysts Emodin/HAp-x were prepared under mild conditions through the interaction between emodin and HAp with large specific surface area and good stability.X-ray diffraction,fourier transform infrared spectroscopy,fluorescent inverted microscope,field-emission scanning electron microscope and transmission electron microscopy were used to study the crystal surface characteristics,functional group structure,fluorescence characteristics,surface morphology and confirmed the successful synthesis of the composite photocatalyst.The chemical element composition and surface state were determined by X-ray photoelectron spectroscopy,Brunauer-Emmett-Teller method and other methods.Emodin,HAp and Emodin/HAp-x were characterized by UV–vis diffuse reflection absorption spectra,band structure analysis,photophysical and electrochemical properties,and their optical absorption capacities,electron-hole transfer capacities and photochemical properties were also studied.It was confirmed that the composite photocatalyst has the potential of antibiotic degradation and bacteriostasis in visible light.（2）Application of Emodin/HAp photocatalysts in tetracycline degradationTetracycline,which is difficult to be degraded and easy to develop drug resistance in water environment,was selected as the model antibiotic,and the photodegradation abilities of Emodin/HAp-x composite photocatalyst prepared above were evaluated.By optimizing the degradation system,including the actual loading of emodin,the initial p H of tetracycline solution,the initial concentration of tetracycline solution and the amount of compound photocatalyst,the optimal degradation conditions were determined.Using 32 W CFL as light source,the degradation efficiency of tetracycline was up to 99%after irradiation for 15 min.When the degradation system was amplified to 500 m L,the degradation rate of 40 mg·L^-1tetracycline by Emodin/HAp-4 was 95.7%.The results of three cycles of photocatalyst degradation,the characterization of the composite photocatalyst after three cycles and the amount of Emodin residue in the solution were studied.It was confirmed that the composite photocatalyst Emodin/HAp had good stability and recyclability.The degradation route and mechanism of tetracycline were also studied.The intermediates in the degradation process were captured by high performance liquid chromatography-mass spectrometry and the degradation path of tetracycline was predicted.The roles of oxygen negative ion radical（·O₂^-）and hole（h⁺）in the photocatalytic degradation of tetracycline were confirmed by capture experiments and electron spin-resonance spectroscopy experiments,and the electron and hole migration in the composite photocatalyst was speculated.（3）Application of Emodin/HAp photocatalysts in bacteriostasisIn view of the high efficiency of Emodin/HAp-4 in the degradation of tetracycline,Emodin/HAp-4 was applied to the removal of common food-borne pathogen S.aureus in water.The bacteriostatic effects of emodin,HAp and Emodin/HAp-4 under dark and light conditions were studied,respectively.The efficacy of Emodin/HAp-4 against S.aureus in dark conditions was similar to that of emodin,and the survival rate of S.aureus was 50.1%after incubation for30 min,indicating that Emodin/HAp-4 retained the bacteriostatic activity of emodin.The Emodin/HAp-4 composite photocatalyst showed excellent photocatalytic antibacterial activity under light condition,and S.aureus was completely removed after 30 min of irradiation.The inhibition mechanism of Emodin/HAp composite photocatalyst was speculated.It showed endogenous antibacterial activity under dark condition,and photocatalytic activity under light condition.It destroyed bacterial cell membrane and inactivated bacterial DNA and protein by producing reactive oxygen species and reacted with cell membrane,thus killed bacteria.