Effect Of Ag, N Doping On TiO₂ Nanotube Electrode Photocatalytic Degradation Organic Dye Solution

The technics of preparion TiO₂ nanotube by anodizing and photocatalytic performance under UV-light of TiO₂ nanotube have been studied in detail in this dissertation.Modification of TiO₂ nanotube by doping Ag,N and influence on its photocatalytic property under both UV-light and visible light were also discussed.The influence of preparation parameters including oxidation voltage,the composition of electrolyte,pH value,oxidation time and annealing temperature on stmction,morphology of TiO₂ nanotube were systematically evaluated.The samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM) and specific area were measured by BET test instrument.The results show:oxidation voltage is the most important factor to control the appearance and sizes of TiO₂ nanotube,at voltage of 20V,array of TiO₂ nanotube with well ordered morphology can be produced.In different electrolyte,the pH value is different,so relationship between length of nanotube and time is not the same.In electrolyte of HF,after 20min,the length of nanotube is not grow as reaction continue and only reaches to 500nm.In electrolyte of HF+NH₄H₂PO₄ and NaF+Na₂SO₄,it needs 15h and 4-6h respectively to reach 2.2μm.TiO₂ nanotube prepared by anodizing is amorphous phase,after annealed at 250℃,anatase phase appears,the anatase phase is the predominant phase at 500℃annealing,and further heating of 600℃,the mixed crystal with the rutile phase is the predominant phase can be get.By study photo-degradation behavior of acid red G under UV-light with the prepared TiO₂ nanotube electrode in different experiment condition,shows that the best prepare condition for the growth of TiO₂ nanotube is:in electrolyte of 0.5(wt) %NaF +1mol/L Na₂SO₄,at 20V,reaction time is 6h,then annealed in air at 500℃for lh.The applied bias TiO₂ nanotube prepared by this process is 0.45V(vs.SCE). After 5 h of UV irradiation(pH=3,using TiO₂ nanotube electrode),the degradation rate of acid red G about 20×10^-6mol/L was 92.4%. Basing on these work,in electrolyte of AgNO₃,Ag nanoparticles were deposited photocatalytically on the TiO₂ nanotube surface,for the first time.The samples were characterized by XRD,SEM and X-ray Photoelectron Spectroscopy(XPS).The results show:Ag particles(from 10nm-100nm) are deposited on TiO₂ nanotube surface un-uniformly,exist as Ag⁰,and Ag particles show good chemical stability.The photo-degradation rate of mathylene bule solution increases as content of Ag loaded on nanotube surface increases,if content greater then the most optimum content,photo-degradation rate will decrease.Experiment shows that the optimum content of Ag is about 1.15(wt)%.The Ag loaded nanotubes have much higher photo-degradation rate than un-loaded nanotubes,increases about 22.98%,After 3 h of UV irradiation of mathylene bule 10×10^-6mol/L,the degradation rate of chemical oxygen demand(COD) is about 95%.Nitrogen-doped TiO₂ nanotube array was fabricated by anodizing followed imme -rsed into liquid ammonia and anneal process.XPS result indicates that the nitrogen atoms were doped into lattice of TiO₂ nanotubes.The UV-ViS spectra shows that the photo-absorption of N-doped TiO₂ nanotube is enhanced in the visible light region. The bias was applied to improve photocatalytic property of N-doped TiO₂ nanotube under visible light for the first time.Using N-doped TiO₂ nanotube(Nitrogen content is 0.53(wt)%) as anode,after 16h of irradiation under visible light,the degradation rate of mathylene bule about 10×10^-6mol/L is 55.3%with 0.45V(vs.SC E) bias.Ag nanoparticles were deposited photocatalyticaUy on the N-doped TiO₂ nano -tube surface,modification of TiO₂ nanotube by Ag,N co-dope was made for the first time.Results show Ag/TiO_2-xN_x nanotube not only can improve photodegradation performance under UV-light,but also has photodegradation performance under visible light.After 16h of irradiation under visible light,the photoeleccatalytic degradation rate of mathylene bule(10×10^-6mol/L) and acid red G(20×10^-6mol/L) is 63.5%and 25.2%respectively with 0.45V(vs.SC E) bias.The result shows Ag/TiO_2-xN_x nanotube made in this dissertation is applicable for organic solution universally.