Research On The Photoelectrocatalytic Degradation Of Organic Pollutants And Simultaneous Hydrogen Generation By TiO₂Nanotubes

With the rapid development of industrial and urbanization, environmental problems and energy crisis have been becoming increasingly serious. Because hydrogen energy possesses the characteristic with clear, high energy density, better heat conduction, it will become a main direction of energy for people in the near future. Photocatalyst was used as the photoanode to degrade organic pollutants and simultaneously produce hydrogen using solar energy as a drive, and combine optical energy and electrical energy, realize the conversion of optical energy and electrical energy into chemical energy(hydrogen energy), which not only solve serious environment pollution problems, but also provide an effective method to relieve energy cnsis.As the key of photocatalytic technology, developing the photocatalytic materials with high photoconversion efficiency is the key study direction. Titania nanotube arrays (TNT) were fabricated by anodization method, and they were also modified to improve their photoelectrocatalytic performance. The main factors affecting preparation of TNT on its structural features and photoelectrocatalytic activity were investigated.Effecting factors of TNT for the photoelectrocatalytic hydrogen generation performance, its modification and application in photoelectrocatalytic degradation of organic pollutants degradation and simultaneous hydrogen generation were also studied, and its mechanism of photoelectrocatalytic degradation organic pollutants and simultaneous hydrogen generation for TNT were preliminarily investigated, and provided a technical support to develop a high efficiency titania nanotube arrays and its multiplex photocatalyst. The main study results were listed as following:Firstly, under the same conditions of anodization time, the tube length, pore size, aspect ratio, roughness factor, growth rate of TNT increased and the wall thickness decreased with the increase of anodization voltages (20V,30V,45V,60V). Under the same conditions of anodization voltages, the tube length, aspect ratio, roughness factor of TNT increased, and the wall thickness and pore size did not change with the increase of anodization time (3h,4h,5h,6h). In a word, anodization voltages decided the structural features of TNT, especially, it decisively affected the aspect ratio of TNT. TNT fabricated at60V for6h has an optimum aspect ratio, when the aspect ratio was178, TNT exhibited the maximum capacity for the photoelectrocatalytic degradation and simultaneous hydrogen generation. TNT that was annealed at450℃showed the mixture of anatase and rutile, and its XPS test indicated that TNT contained C, N, and successfully the in-situ modification of C, N. The aspect ratio of TNT has a decisive effect on its performance for the photoelectrocatalytic degradation and hydrogen generation. When TNT with the aspect ratio of178showed the maximum degradation kinetic constant of2.26x10-3min-1and the maximum photocurrent density of48×10-3mA/cm2. TNT showed the maximum photocurrent density of0.05mA/cm2under the bias potential of0.45V.Secondly, TNT fabricated by two-step anodization demonstrated the higher aspect and thin wall thickness, which were104.83and16.36nm. TNT fabricated by two-step anodization showed higher photoelectrocatalytic activity than those prepared by one-step anodization, their photocurrent density and photo-hydrogen conversion efficiency were0.2mA/cm2and0.4mA/cm2,0.14%and0.36%. When ethylene glycol was used as organic electron donor, the photocurrent density of TNT fabricated by two-step anodization and one-step anodization were0.026mA/cm2and0.022mA/cm2.Thirdly, TNT fabricated by anodization at20V,30V,45V for1h was used to dope ZnFe2O4nanoparticles using electrochemical deposition, and the results indicated that TNT prepared by anodization at45V for1h showed the maximum photo-hydrogen cinversion efficiency of0.18%.Fourthly, TNT fabricated by anodization at45V for5h was utilized to prepare Pt/TiO2electrode using dipping-pulling method, the results indicate that the uniform dispersion of platinum successfully broadens the absorption spectrum of TiO2nanotube arrays to visible light region and the photocurrent density of Pt/TNT is18times that of TNT. The degradation of methyl orange on Pt/TNT conforms to pseudo first-order kinetics and the reaction rate constant is about3times that of TNT. The photo-hydrogen conversion efficiency of Pt/TiO2photoelectrode is2.1times that of TNT, it also demonstrates the highest mechanical and chemical stability.Fifth, Using three-electrode system,0.1mol/L KOH, Na2SO4, Na2CO3solution were used as supporting electrolyte solution under the condition of bias potential of0.45V, TNT shows the highest photocurrent density in KOH solution. Na2SO4solution of0.1mol/L was used as supporting electrolyte solution under the condition of bias potential of0.45V, pH was2,6.8,10, TNT exhibits the maximum photocurrent density when pH of Na2SO4solution is6.8. Under the conditions of ethylene glycol of0mol/L,0.1mol/L,0.25mol/L,0.5mol/L, the photocurrent density increases with the increase of concentration of ethylene glycol. At the presence of ethylene glycol and oxalic acid, TNT in the electrolyte of ethylene glycol shows the higher photocurrent density than oxalic acid without the bias potential. And TNT in the electrolyte of oxalic acid demonstrates the higher photocurrent with the increase of the bias potential from0V to0.9V.