Preparation And Application Of New Functional Materials Based On Antibiotic Degradation In Livestock Wastewater

Inner Mongolia,Qinghai,Xinjiang,Tibet and other minority concentrated region have the world's vast grassland and livestock resources,which depended on animal husbandry for their livelihood and are an important livestock production,processing,and export base.In recent years,animal husbandry gradually transform from family ranch to intensive pasture.However,with the expansion of the scale of animal husbandry,ecological and environmental problems have emerged,especially in livestock wastewater.Large scale farm wastewater discharge is large and concentrated.The nature of wastewater is similar,mostly in the residual veterinary antibiotics and pathogens.The ecological and environmental conditions of minority concentrated region are very fragile and the capacity is low.Therefore,with the rapid development of animal husbandry,it is the guarantee of water ecological environment to properly treated wastewater discharged from animal husbandry.Due to its non-toxicity,low cost,high stability and excellent oxidation capability,titanium dioxide?TiO₂?has long been regarded as one of the most promising photocatalysts and commonly applied to the area of environmental pollution control.Photocatalytic processes involving Ti02-based semiconductor particles have hence been proved to be advantageous in the photodegradation of organic pollutants.However,with the wide band gap?3.2 eV?,TiO₂ is only sensitive to the UV light which only accounts for a little portion?3-5%?of solar light in comparison to the visible region?-45%?.Moreover,the rapid electron-hole recombination often leads to low quantum efficiency and weak photosensitivity.Therefore,the development of Ti02-based photocatalysts with high quantum efficiency and an enhanced visible-light-harvesting property remains a great challenge and attracts intensive interest.In this paper,some efforts including elements doping and coupling with other narrow band gap semiconductors?g-C3N4 or C?have therefore been paid to alter the intrinsic band structure of Ti02 in order to extend its light absorption into visible region and high quantum efficiency.These materials were applied to the removal and degradation of antibiotics in the livestock wastewater.In the dissertation,the research work and results are as following:1.?1?Titanium dioxide?M-N-Ti02?,which was codoped with N and 9 different metal ions?including La?Ce?Pr?Nd?Sm?Gd?Er?Yb?Lu?was synthesized by standard sol-gel methods and characterized by X-ray diffraction?XRD?,field-emission scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,Brunauer-Emmett-Teller method?BET?,and ultraviolet-visible absorption spectroscopy?UV-vis?.The photocatalytic activities of codoped TiO₂ samples were investigated under visible-light irradiation,where Gd-N and La-N co-doped TiO₂ showed significantly enhanced visible-light photocatalytic activity.?2?Visible-light-active Gd-N-codoped porous TiO₂?Gd-N-TiO₂?photocatalysts were fabricated by an evaporation-induced self-assembly route using surfactants as structure-directed agents.As-prepared samples were characterized.The results indicated that synergistic reaction occurred when codoping with Gd3+ and N,which enhanced the light absorption properties of TiO₂.Irregular worm-like particles with wide interparticle spaces were clearly observed by TEM.The average particle size of Gd-N-TiO₂ decreased to⁸ nm because co-doping inhibited the particles growth significantly.Thus,the specific surface area of Gd-N-TiO₂?198.7 m2·g-1?was higher than that of Degussa P25 TiO₂?50 m2·g-1?.Gd-N-TiO₂ exhibited a high photocatalytic activity toward pollutants degradation under UV-vis or visible-light irradiation.2.Bio-hierarchical TiO₂-based porous structures?denoted as morph-Ti02?with N and La codoping?denoted as N-La-morph-TiO₂?are successfully synthesized via a facile one-pot reaction by using butterfly wings as bio-template and surfactant as co-template.Due to the novel dual-template strategy,the well-aligned 3D bio-hierarchical porous structures in combination with N-La codoping not only modify the band structure of TiO₂ to make it more responsive to visible light,but also increase the surface area and lead TiO₂ to have enhanced photocatalytic activity under UV and/or visible light.The optimized N-La-morph-Ti02 nanostructures present a narrow pore size distribution with an average pore diameter of 8.7 nm and a high specific surface area?196 m2 g-1?,which is nearly four times that of P25 Ti02.3.?1?Composite materials,made of graphitic carbon nitride/gadolinium and nitrogen co-doped titanium dioxide?g-C3N4/Gd-N-TiO₂?,have been successfully prepared by a simple and reproducible in-situ synthetic method.Specific surface area,pore size,particle morphology,crystalline structure,energy band gap,and chemical bonding mode of the materials have been characterised by spectroscopic and electron microscopic means.The composites exhibit significant photocatalytic activity,higher than either g-C3N4 or Gd-N-TiO₂.Our experimental results indicate that nanoscale heterojunctions are formed in the composites,and these junctions have played a key role in the separation and transportation of photo generated electrons and holes,and hence the effective promotion of the photocatalytic.?2?TiO₂-carbon composites?C@N-TiO₂?were prepared by a sol-gel method in a simple and green synthetic pathway.Compared with TiO₂,C@N-TiO₂ displays superior pollutant-adsorption ability and photocatalytic activity under visible light.4.The semiconductor photocatalyst Gd-N-TiO₂,N-La-morph-TiO₂,g-C3N4/Gd-N-TiO₂ and C@N-Ti02 were used to degraded antibiotics in livestock wastewater.Various factors in the process of degradation were investigated,such as pH value,catalyst dosage,initial concentration,and ions.An increasing order of Gd-N-TiO₂<N-La-morph-TiO₂<g-C3N4/Gd-N-TiO₂<C@N-TiO₂ in terms of photocatalytic degradation of antibiotics was observed.