Construction Of Yeast Carbon Based Magnetic Composite Photocatalyst And Study On The Behavior And Mechanism Of Photodegradation Of Antibiotics Residue

Environmental pollution issue has become an important factor that restricts the development of modern human society.The problem about antibiotic residues in water seriously affects the balance of ecological environment and human health.Therefore,it is urgent to remove pollutants from water and improve water environment.Photocatalytic technology has many advantages,such as simple operation,high efficiency,and environmental protection,etc.,which has wide application prospects in the treatment of water pollutants.The key of photocatalytic technology is to design and prepare high efficiency photocatalyst.In many widely research of semiconductors,TiO₂,BiVO₄ and Co₃O₄ photocatalytic materials have potential applications in environmental purification due to their advantages of stable physical and chemical properties,non-toxic and harmless.However,the photocatalytic activity of the semiconductor is limited by the single photocatalyst due to the poor dispersion and smaller surface area.Yeast is considered as the ideal material for carbon source because of their high carbon content,wide sources and environmental protection.Yeast carbon has a pore structure inside and good adsorption performance,which is excellent catalyst carrier.Constructing composite materials with semiconductor photocatalysts can effectively solve the problems of poor dispersibility and small specific surface area of a single catalyst,thereby enhancing photocatalytic activity.Due to the lack of effective separation technology,the powder composites are often difficult to recover and reuse,thus restricting their practical application.Therefore,the introduction of magnetic semiconductor materials into the photocatalytic material system can give its excellent magnetic separation function and improve the recovery and reuse efficiency.In this paper,a yeast carbon-based magnetic composite photocatalyst was successfully constructed by using yeast as carbon source,then applied to degradation of antibiotic residues from water environment.A variety of characterization test methods were used to investigate the structural characteristics,physical and chemical properties of the prepared yeast carbon-based magnetic composite photocatalyst.Meanwhile,through the study of the degradation of antibiotic residues,the structure-activity relationship and photocatalytic degradation mechanism of the yeast carbon based magnetic composite photocatalyst were clarified.The main work of this thesis is as follows:1.Preparation of yeast carbon/titanium-based magnetic composite photocatalyst and study on photocatalytic performance?1?The Fe₃O₄@TiO₂-C magnetic composite photocatalyst was synthesized by hydrothermal method,sol gel method and high temperature calcination by using yeast as carbon source.The Fe₃O₄@TiO₂-C composite photocatalyst of crystal structure,sample morphology,light absorption capacity,magnetic properties and free radical species were analyzed by XRD,SEM,EDS,TEM,HRTEM,UV-vis DRS,FT-IR,XPS,Raman,VSM,ESR and other characterization methods.The effects of as-prepared samples on the degradation of antibiotic were investigated under different temperature conditions.When the reaction temperature was 300 ^oC,Fe₃O₄@TiO₂-C-300 had the optimum degradation activity,and the degradation rate has reached 82.6%.The photocatalytic reaction mechanism study showed that yeast carbon could effectively promote the separation efficiency of photogenerated carriers and further increase the photocatalytic activity.?2?Fe₃O₄@mTiO₂/C magnetic composite photocatalyst was prepared by solvent thermal method,hydrolysis method and high temperature calcination method by using yeast as a carbon source.The microstructure and physicochemical properties of as-synthesized samples were systematically studied by a variety of characterization tests.The experimental results of photodegradation showed that the Fe₃O₄@mTiO₂/C exhibited the superlative degradation effect compared with the mTiO₂,Fe₃O₄@mTiO₂and mTiO₂/C.The degradation rate of TC was 64%under visible light within 60minutes.Meanwhile,the effects of double sensitization of Fe₃O₄ and yeast carbon on photodegradation of antibiotics in water were investigated.Through free radical capture experiment and ESR test,the main active species in photocatalytic degradation were h⁺,·O₂^-and·OH.2.Preparation of yeast carbon/bismuth-based magnetic composite photocatalyst and study on photocatalytic performance?1?Firstly,Fe₃O₄ nanoparticles and dumbbell-shaped BiVO₄ were synthesized by hydrothermal method.Then,the Fe₃O₄/C magnetic composites were synthesized by using yeast as carbon source.Finally,the Fe₃O₄/C composites were assembled with dumbbell-shaped BiVO₄ to construct Fe₃O₄/C/BiVO₄ magnetic composite photocatalyst.The various physical and chemical characteristics of the samples were systematically analyzed by different characterization test methods.The effects of Fe₃O₄/C/BiVO₄magnetic composite photocatalytic materials on the degradation of TC efficiency were investigated by adjusting amounts of Fe₃O₄/C.When the content of Fe₃O₄/C was 5%,Fe₃O₄/C/BiVO₄ showed the best photocatalytic activity,and the degradation rate was 83%under visible light within 60 min.Moreover,the photocatalytic degradation of TC over Fe₃O₄/C/BiVO₄ showed that the main active species during the photocatalytic degradation process were h⁺,·O₂^-and·OH.?2?Using yeast as the carbon source,Co₃O₄/BiVO₄ p-n junction composites were successfully loaded on the surface of the yeast charcoal with block morphology by one-step method to prepare Co₃O₄/BiVO₄/C magnetic composite photocatalysts.The physicochemical properties of the as-synthesized Co₃O₄/BiVO₄/C samples?such as morphology,photoresponsivity,magnetic properties,active species composition,and electrochemical properties,etc.?were analyzed by a series of characterization tests.The effects of different Co²⁺/BiVO₄ molar ratios on the TC performance were investigated.When Co²⁺/BiVO₄ mole ratio was 0.05,the photocatalytic activity of Co₃O₄/BiVO₄/C-5was the highest under visible light,and the degradation rate reached 83%within 120min.The constructing composites relationship of valence band and conduction band position of Co₃O₄ and BiVO₄ semiconductors were studied in detail.The photocatalytic degradation of TC by Co₃O₄/BiVO₄/C showed that the yeast carbon modified p-n junction system could effectively promote the electron migration rate and increase the photocatalytic activity.3.Preparation of yeast carbon/cobalt-based magnetic composite photocatalyst and study on photocatalytic performance?1?Using yeast as the carbon source,Fe₃O₄@C/Co₃O₄ magnetic composite photocatalyst was successfully synthesized by hydrothermal method,self-assembly method and high-temperature calcination method.The physicochemical properties of the prepared Fe₃O₄@C/Co₃O₄ magnetic composite photocatalyst?such as morphology structure,photoresponsivity,magnetic properties and electrochemical performance,etc.?were analyzed through a series of characterization tests.The effect of different carbon content on the activity of catalyst was investigated.When the carbon content was 0.3 g,Fe₃O₄@C/Co₃O₄-0.3 showed the best photocatalytic activity under visible light,and the degradation rate of TC was 80%.In addition,the valence band and conduction band position of the Co₃O₄ semiconductor are calculated through the UV-vis DRS and valence band spectrum characterization tests.The results showed that the electrons on the conduction band of Co₃O₄ could react with O₂ to produce·O₂^-.The photocatalytic mechanism of photodegradation of TC by Fe₃O₄@C/Co₃O₄ showed that the main active species in photocatalytic degradation process were h⁺,·O₂^-and·OH.?2?A yeast carbon-modified g-C₃N₄/Co₃O₄ Z-scheme heterojunction magnetic composite?g-C₃N₄/Co₃O₄/C?was successfully prepared by hydrothermal synthesis and self-assembly method using yeast as carbon source.The physicochemical properties of samples were analyzed by a series of characterization methods,such as XRD,SEM,TEM,HRTEM,EDS,UV-vis DRS,XPS,VSM,ESR,photocurrent,impedance and so on.The activity of the catalyst for degrading antibiotics was investigated.The results of photocatalytic experiments showed that compared with g-C₃N₄ and Co₃O₄,the g-C₃N₄/Co₃O₄/C Z-scheme heterojunction system exhibited the best photocatalytic activity,and the degradation rate was 79%under visible light within 120 min.It demonstrated that yeast carbon modified Z-scheme heterojunction system can promote the separation efficiency of carriers and thus increase the photocatalytic activity.The positions of the valence band and the conduction band of the g-C₃N₄ semiconductor and the Co₃O₄ semiconductor were calculated in detail,and the results showed that the two semiconductor photocatalysts can be constructed into Z-scheme heterojunction system.The results of free-radical trapping experiment and ESR test showed that the main active species in photocatalytic degradation process were·O₂^-,·OH and h⁺.