Research On Degradation Of Tetracycline Hydrochloride In Simulated Animal Husbandry Wastewater Based On Titanium Dioxide Photocatalytic Technology

Modern science and technology have promoted the rapid development of animal husbandry in ethnic areas.And the rapid development of livestock farming has made the important contributions for the social and economic development in ethnic areas.However,antibiotics,especially tetracycline hydrochloride(TH),are extensively used in livestock farming to treat common diseases and provent some diseases of domestic animals.Most of TH is excreted into the water and soil by domestic animals due to poor absorption.Thus the extensive ulitization of TH in livestock farming has caused serious damage to the ecological environment in ethnic areas due to its stable chemical structure.Therefore,the removal of TH from wastewater has attracted considerable attention in recent years.The traditional methods for removal of TH from wastewater include physical adsorption,biological degradation,and so on.However,these methods usually suffer from low removal efficiency.Photocatalysis of semiconductor is condideraded as one of the most promosing methods for the removal of TH due to its high photodegradation efficiency.Furthermore,photocatalysis of semiconductor can convert organic pollutants into H2O and CO2 without introducing extra pollutants.Semiconductor can be excited to generate electrons and holes under irradiation of light with photon energy larger than band energy.And photogenerated electrons and holes can conduct redox reaction with the antibiotics adsorbed on the semiconductor surface,leading to the dagradation of antibiotics.Titanium dioxide(TiO2)is considered as one of important photocatalysts due to several advantages such as the appropriate band structure for photocatalytic reaction,cheapness,nontoxicity and dexcellent stability.However,TiO2 usually only can absob violet light energy due to its larger band gap and suffers from high recombination rate of photoproduced charge carriers,leading to low quantum efficiency and thus limiting its practical application in the field of organic pollutants in wastewater treatment.The aim of this thesis is to obtain TiO2-based photocatalysts with excellent photocatalytic activity,achieving efficient degradation of TH in simulated livestock wastewater.Because the heterojunction photocatalysts constructed by coupling TiO2 with different materials exhibit different photocatalytic performances,nickel oxyhydroxide(Ni(OH)2),cuprous oxide(Cu2O),zinc ferrate(ZnFe2O4)and tungsten Au-acid bismuth(Bi2WO6)were selected to combine with TiO2 to construct a TiO2-based heterojunction structure with energy band structure matching,respectively.Through photocatalytic performance studies,we screened excellent photocatalysts to achieve efficient degradation of tetracycline hydrochloride in water.The thesis mainly includes the following contents:(1)As an important transition metal hydroxide,modification of Ni(OH)2 to TiO2 can form p-n heterojunction,which facilitates the effective transfer and separation of photogenerated cariers.Photocatalyst of TiO2-Ni(OH)2 nanorod arrays were constructed by growing Ni(OH)2 nanosheets on TiO2 nanorod arrays through a facile chemical method.The photocatalytic activity of the heterojunction photocatalysts was evaluated by photocatalytic degradation of TH in simulated livestock wastewater.The effect of concentration and pH value of TH on the photocatalytic performance of the photocatalysts was studied.With simulated sunlight irradiation for 90 min,the photodegradation rate of TH over heterojunction photocatalyst is 78.1%,which is 1.7 times that of pure TiO2 nanorod arrays.The heterojunction photocatalyst displays the best photocatalytic ability for the degradation of TH with concentration of 10 mg/L and pH vale of 6.8.In addition,the recyclable experiments for the degradation of TH(10 mg/L,pH 6.8)show that the heterogeneous photocatalyst exhibits an excellent photostability.The results desmonate that the photocatalytic degradation of the fourth cycle is 92%that of the first cycle.According to the investigation of the TiO2-Ni(OH)2 heterojunction structure,the significantly enhanced photocatalytic activity of TiO2-Ni(OH)2 heterojunction nanorod array photocatalyst is attributed to the efficient separation and a low recombination rate of photogenerated electron-hole pairs,which is achieved by the p-n heterojunction built at the interfaces of TiO2 and Ni(OH)2 in the heterojunction photocatalyst.(2)As an important transition metal oxide,modification of Cu2O to TiO2 not only can form p-n heterojunction that is beneficial to the effective transfer and separation of photogenerated carriers,but also can effectively extend the light response to the visible region.A facile chemical bath deposition(CBD)method was employed to grow Cu2O nanoparticles on TiO2 nanorod arrays to fabricate TiO2-Cu2O heterojunction nanorod arrays.TiO2-Cu2O heterojunction nanorod arrays with different loading Cu2O nanoparticles were fabricated through controlling CBD cycling times.The photocatalytic activity of the heterojunction photocatalysts was evaluated by photocatalytic degradation of TH in wastewater.The effect of concentration and pH value of TH on the photocatalytic performance of the photocatalysts was studied.The results show that the dagradation rate for TH of photocatlyst prepared by optimizing Cu2O nanoparticle amounts is 1.7 times that of pure TiO2 nanorod arrays.And the degradation rate of heterojunction photocatalyst for TH with concentration of 10 mg/L and pH value of 6.8 is up to 83.3%.In addition,the recyclable experiments for the photodegradation of TH demonstrate that the heterojunction nanorod array photocatalyst displays a good photostability.According to the band structure of the heterojunction,both Type ? band alignment and p-n heterojunction established in TiO2-Cu2O heterojunction photocatalyst are favorable for the effective transfer and separation of photogenerated electrons and holes,suppressing the recombination rate of photogenerated electron-hole pairs and improving the photocatalytic performance.(3)As an important metal oxide with two transition metal elements,modification of ZnFe2O4 to TiO2 not only can form heterojunction that is beneficial to the effective transfer and separation of photogenerated carriers,but also can effectively extend the light response to the visible region.The TiO2-ZnFe2O4 heterojunction nanorod array photocatalyst was prepared by growing ZnFe2O4 nanoparticles on TiO2 nanorod arrays through a simple solvothermal method.The photocatalyticdegradation for TH demonstrates that the degradation rate of TH over photocatalyt is 83.4%,which is 1.8 times that of pure TiO2 nanorod arrays.When the concentration and pH value of TH solution is 5 mg/L and 6.8,the photodegradation rate of TH over the photocatalyst is the highest(86.9%).The recyclable experiments show that the heterojunction photocatalyst demonstrates a good photostability.Based on the study of the TiO2-ZnFe2O4 heterojunction structure,the Type ? band alignment in the photocatalyst promotes effective transfer and separation of photogenerated electrons and holes and suppresses recombination rate of photogenerated electron-hole pairs,leading to significantly enhanced photocatalytic performance of TiO2-ZnFe2O4 heterojunction nanorod arrays.(4)Modification of noble metal nanoparticles and nanorow-band-gap semiconductor to TiO2 heterojunction photocatalyst with surface plasmon resonance(SPR)effect and Type ? band alignment not only can extend the light response region,facilitates transfer and separation of photoproduced charge carriers,but also improves the light harvesting ability and provides hot electrons injection to significantly enhance photocatalytic performance.Bi2WO6 nano flowers were grown on the surface of TiO2 nanorod arrays to fabricate TiO2-Bi2WO6 heterojunction nanorod arrays by a solvothermal method.Then the ternary TiO2-Bi2WO6-Au heterojunction nanorod arrays were constructed by growing Au nanoparticles on the surface of TiO2-Bi2WO6 nanorod arrays through a simple chemical reduction in solution.The photocatalytic degradation for TH demonstrates that the degradation rate of TH over photocatalyt is 92.2%,which is 2 times that of pure TiO2 nanorod arrays.When the concentration and pH value of TH solution is 10 mg/L and 6.8,the ternary heterojunction photocatalyst exhibits the best photocatalytic dearadation performance for TH.In addition,the photodegradation rate of TH over the ternary heterojunction photocatalyst is still up to 85.8%after four cycles,demonstrating an outstanding photostability.The significantly improved photocatalytic performance of TiO2-Bi2WO6-Au heterojunction nanorod array photocatalyst is attributed to the efficient separation and a low recombination rate of photogenerated electrons and holes,which is achieved by synergistic action of Type ? band alignment and surface plasmon resonance effect integrated in the heterojunction photocatalyst.