Study On Photocatalytic Degradation Of Oxytetracycline By Titanium Dioxide/graphene And Titanium Dioxide/phosphorene Composites And Biotoxicity Of Degradation Process

Oxytetracycline(OTC)is one of tetracycline antibiotics which are widely used in medical and animal husbandry.It is difficult to naturally degrade oxytetracycline in the environment.In addition,oxytetracycline could also cause bioconcentration in the envirornment and pose a significant threat to human health.For decades,TiO2 photocatalysis technology has been specifically developed to deal with non-biodegradate antibiotics in the water environment.However,TiO2 is difficult to recycle and easy to agglomerate due to its small size.Therefore,composite materials doped or loaded with TiO2 have been extensively studied.Among composite materials,graphene and phosphoenene owned high specific surface area and high-speed electron mobility,could lead with diffierent percent of TiO2 to increase its photocatalytic performance.In this thesis,graphene/TiO2(GN-TiO2)and Phosphoenene/TiO2(PN-TiO2)were prepared by hydrothermal method and solid dispersion method respectively.The photocatalytic materials were used for photocatalytic degradation of oxytetracycline in aqueous solution.The characteristics of the composite photocatalytic materials were analyzed through inspections of of transmission electron microscopy(TEM),scanning electron microscopy(SEM),ultraviolet-visible absorption spectroscopy(UV-VIS),X-ray diffraction(XRD)and so on.The catalytic performance of the composite photocatalytic materials under different pH,temperature,catalyst dosage,pollutant concentration and scavenger was investigated.Moreover,the possible reaction mechanism were also proposed.The reusability was also tested for the composite GN-Ti02 still exhibiting promising catalytic efficiency.In addition,transient dynamics of the biotoxicity change of the photocatalytic degradation of oxytetracycline was evaluated by using Caenorhabditis elegans as.organism.The main conclusions could be showed as follows:(1)GN-TiO2 and PN-TiO2 composites were successfully prepared by hydrothermal method and solid state dispersion method.The results showed that the structure of graphene,TiO2 and phosphoenene remained intact.TiO2 particles are loaded on graphene and phosphoenenene respectively.The absorbance of titanium dioxide at full wavelength was apparently increased by graphene and phosphoenene.(2)GN-TiO2 are using as photocatalyst for photodegradation of oxytetracycline.For feasibility resting,10%GN-TiO2 was used as the photocatalyst,and the light source was a UV light source with a wavelength of 254 nm and 8 W.The initial pH of the solution was 5.5,the catalytic material was supplemented at 0.1 g L-1,and the temperature was 25 0C.After 180 min of photocatalytic degradation,the maximum degradation rate was 98%.The photodegradation of oxytetracycline was carried out by using a PN-TiO2 composite as a photocatalyst.For feasibility resting,1%PN-TiO2 was used as the model photocatalyst,and the light source was a UV light source with a wavelength at 254 nm and 8 W.The initial pH of the solution was 8.5,the catalytic material was augmented at 0.1 g L-1,and the temperature was 35 ?.After 180min photocatalytic degradation reaction,the almost promising degradation rate could be achieved at 98%;(3)GN-TiO2 and PN-TiO2 composites were prepared by hydrothermal method and solid state dispersion method,respectively.The degradation rate could reach the maximum,when the loading ratio of graphene and phosphoenene was 10%and 1%,respectively.The findings showed that at the loading ratio of graphene and phosphoenene is 10%and 1%,the photocatalytic reaction rate could reach 0.131 mg L-lmin-1 and 0.22 mg L-1 min-1,respectively;(4)To investigate photocatalytic characterization,EDTA,isopropanol,benzoquinone and other free radical scavengers were amended to the reaction solution to determine the degradation effect of different scavengers on OTC.The results indicated that when GN-TiO2 was used as the photocatalyst,H+ scavenger(EDTA)expressed the greatest influence upon photodegradation efficiency,indicating that H+were the main active groups in the photocatalytic process.Moreover,when PN-TiO2 was used as photocatalyst,superoxide radical scavenger(benzoquinone)exhibited the greatest suggesting on photodegradation efficiency,indicating that superoxide radical was the main active group in the photocatalytic process;(5)The GN-TiO2 composite material could at least be reused for 5 times.Although the degradation rate of oxytetracycline was slightly decreased,the degradation effect still remain satisfactorily(the degradation efficiency was 90%).The results showed that the GN-TiO2 composite photocatalytic material owned high stability;(6)Assessment of the change in biotoxicity of the photocatalytic degradation process using C.elegans.The results show that using GN-TiO2 composite as a photocatalyst to degrade oxytetracycline could produces two higher toxic by-products which affect the hatching rate and larval survival rate respectively.However,the water sample after 180 minutes degradation exhibited insignificant effect upon C.elegans;.(7)Apprently,PN-TiO2 composites should higher reaction rates than GN-TiO2 composites.However,GN-TiO2 composites have much better photocatalytic capabilities and lower preparation cost than PN-TiO2 composites.These owned more practical potential for treatment of antibiotic-bearing waste water.