Photoelectrocatalytic Degradation Of Nitrogen Pollutants And Antibiotics In Water Using TiO₂ Nanotube Arrays Electrode

Recently,the industry of aquaculture has been developing rapidly and tends to be intensive.The aquaculture wastewater has a high concentration of total ammonia nitrogen,nitrite and nitrate due to fish excretion and the decomposition of residual feed and even low concentration of ammonia and nitrite can do harm to fish.In addition,a considerable part of antibiotics is remained in water after they are used for prevention and treatment of fish diseases,which poses a threat to humans as well as the environment.Photocatalytic technology using semiconductors has attracted great interest due to its outstanding performance on removal of hazardous substances from the wastewater.The thesis focuses on the degradation performance of nitrite and antibiotics of chloramphenicol and norfloxacin in aquaculture wastewater using TiO2 nanotube arrays electrode,and then on the graphene modification of TiO2 nanotube arrays to improve the utilization rate of light.The experiments are as follows:The Y-branched TiO2 nanotube arrays(Y-TiO2NTs)and conventional TiO2 nano tube arrays(TiO2NTs)are fabricated by a three-step anodic oxidation and one-step anodic oxidation respectively.Field emission scanning electron microscopy(FESEM),and X-ray diffraction(XRD)are used to characterize the morphology and crystal form of the samples.The results indicate that the as-prepared Y-branched TiO2 nano tube arrays grow up-side down and perpendicularly on the surface of Ti substrate and in high order.The inner diameters of these nanotubes are about 50 um and the wall thicknesses are around 10 nm.The samples are anatase phase.The inner diameters of the conventional TiO2 nanotubes at anneal temperature of 450℃ are about 60 nm and the wall thicknesses are around 10 nm The samples are also anatase phase.The photoelectrocatalytic(PEC)performances of Y-branched and conventional TiO2 nanotube arrays electrodes are compared through the photoelectrochemical degradation of nitrite in simulated aquaculture wastewater.The factors influencing the degradation of nitrite by PEC process such as bias potential,initial pH,initial nitrite concentration,Cl-concentration,the UV light power and the existence of ammonia are investigated.The reaction mechanism using Y-branched TiO2 nanotube arrays is also studied,and a comparison is made about the PEC degradation efficiency of nitrite using Y-branched TiO2 nano tube arrays electrode to that of using TiO2 film in the literatures.The experimental results show that the nitrite removal rate using Y-branched TiO2 nanotube arrays electrode is 1.5-fold of that using conventional nanotube arrays electrode.The PEC degradation efficiency is enhanced when increasing bias potential and UV light power,adding Cl-to the solutions and in acid solutio.In acid condition,the existence of ammonia has little influence in nitrite degradation,and when there is Cl-in solutions,active chlorine is responsible for nitrite degradation.The PEC degradation performance of Y-branched TiO2 nanotube arrays electrode is estimated using chloramphenicol(CAP)and norfloxacin(NOR)as antibiotics contaminants in simulated aquaculture wastewater.The factors such as initial pH,initial antibiotics concentration and the existence of inorganic ions are studied.The results demonstrate that acid solution benefits the degradation of CAP,while alkaline condition is good for the degradation ofNOR.Low levels of NH4+ and NO3-seems to have little effect on the degradation of CAP and NOR,and a relatively high Cl-level accelerates the degradation of NORFinally,the rGO/Y-TO2 nanotube arrays(rGO/Y-TiO2NTs)electrodes are fabricated by one-step cyclic voltammetric electrodeposition.Field emission scanning electron microscopy(FESEM),X-ray energy dispersive spectrum(EDS),X-ray diffraction(XRD),UV-Vis diffuse reflection spectrum(UV-Vis DRS)and Raman spectrum are used to characterize the morphology,element composition and crystal form and so on of the samples.A slight red shift of the absorption edge accompanied by increased light absorption intensities is observed for the rGO/Y-TiO2NTs compared with the bare Y-TiO2NTs.Photocurrent responses are investigated under 1.0 V bias potential using rGO/Y-TiO2NTs electrodes prepared under different cyclic voltammetric cycle numbers,and the performance of PEC oxidation of ammonia is also studied.The results indicate that the PEC efficiency of ammonia using rGO/Y-TiO2NTs electrode reach 95.9%in 30 min when the electrodeposition cycle number is 30,which is 1.3 time higher than that of the pristine Y-TiO2NTs electrodes.