Study On Functionalized TiO₂ Nanotube Arrays:Design,Synthesis And Applications

In recent years,extensive research efforts have been devoted to the development of photocatalytic materials for eliminating organic pollutants.Semiconductor photocatalysis is one of the advanced physicochemical processes.Among various oxide semiconductor photocatalysts,TiO₂ has received immense attention.However,TiO₂ responds only in the UV region due to the wide bandgap which hinders its practical applications.On the other hand,TiO₂ material is not benefit for transferring the photogenerated electrons and holes due to the low conductivity,resulting in the high photogenerated electrons and holes recombination rate and reduced photoconversion efficiency.To handle these problems,many efforts have been devoted to extend the spectral response of TiO₂ to the visible spectrum and improve the photoconversion efficiency,such as metal complex sensitization,doping transitional metal and coupling with a small band gap semiconductor and so on.TiO₂ nanotube arrays prepared by anodization own the excellent properties because of the uniform structure,high orientation,chemical stability and unique optical and chemical properties.Since the discorvery in 2001,TiO₂ nanotube arrays have attracted great interests.It has been reported that TiO₂ nanotube arrays has great applications in photoelectrical and photocatalytic fields.In this work,to improve the harvesting of visible light,enhance the photoelectrical property and photocatalytical efficiency as goals,we carry out the basic research on the composited TiO₂ nanotube arrays which applying in the removal of organic pollutants.Specific contents are as follows:?1?A green and facile process was developed to fabricate ultra-fine p-type Cu2O single crystal nanowires modified TiO₂ nanotube arrays by pulse electrodepositon technique and electro-anodization technique.The Cu2O nanowires with a diameter of less than 5 nm were assembled on the top surface of n-type TiO₂ nanotube arrays,constructing a novel p-n junction heterostructure.Compared to the unmodified TiO₂ nanotube arrays,the resulting composited material owned larger specific surface area.X-ray diffractometer?XRD?and high resolution transmission electron microscopy?HRTEM?were employed to demonstrate that the resulting Cu2O was single crystalline.The composite Cu2O/TiO₂ nanotube arrays exhibited significantly enhanced response to the visible light,resulting from Cu2O with a narrow-band gap.Furthermore,enhanced efficiency in separating photogenerated hole-electron pairs was achieved due to the potential difference generated on the p-n interface.A possible mechanism was proposed to explain the formation of crystal Cu2O nanowires.?2?CuSe/TiO₂ nanotube arrays has been successfully synthesized using a photo-assisted chemical bath deposition method with the TiO₂ nanotube arrays pre-loaded with Cu2O nanowires.The pre-synthesized Cu2O nanowires served as copper precursor and nucleation centers for the crystal growth,resulting in the rapid formation of 3D rosalike CuSe crystals at low temperature.This novel material held the advantages of both p-n junction and micro/nanocomposite structure,thus facilitating the transfer of the electrons and inhibiting the recombination of the photogenerated hole-electron pairs.The photoelectrochemistry measurements exhibited the photoconversion efficiency of composited CuSe/TiO₂ nanotube arrays was 10 times than the unmodified Ti02 nanotube arrays.The influence factors on the forming 3D rosalike architecture CuSe were investigated,incoulding time,temperature,irradiation and stiring.In addition,this novel material exhibited remarkablely photocatalytic performance in the degradation of anthracene-9-carboxylic acid?ACA?.?3?It is well recognized that the surface properties,morphologies and the sizes of the particles heavily influence the performance of heterostructure photocatalysts.Larger particles are more prone to serve as electron-hole recombination centers than smaller nanoparticles.This work,the property of composited In2S3/TiO₂ nanotube arrays prepared by CV deposition,potentiostatic deposition and pulse deposition were investigated.The results showed that the pulse prepared In2S3/TiO₂ yield a highest and stable photocurrent response,consequently exhibiting a superior photocatalytic activity in the degradation of p-Nitrophenol?PNP?.This may be attributed to the homogeneous,ultra-fine morphology of In2S3 nanoparticles and thus the enhanced charge separation efficiency.Furthermore,trapping tests showed that both radicals and holes were the main active species in the photocatalytic degradation of PNP.?4?The Cu-nZVI bimetallic nanoparticls were deposited on TiO₂ nanotube arrays by a convenient and green pulse electrodeposition method.Homogeneous nanoparticles were deposited both on the surface and inset of TiO₂ nanotube arrays.The diffuse reflectance spectroscopy UV-vis spectra exhibited Cu-nZVI/Ti02 composited material has the highest absorption in both UV and visible region,indicating the best ability of harvesting solar light.The photocurrent density on the Cu-nZVI/TiO₂ nanotube arrays was increased to 0.24 mA/cm²,which was 2.67 times than that of unmodified TiO₂ nanotube arrays?0.09 mA/cm²?.The electron-hole recombination rate was greatly reduced on the composite material,which was confirmed by the PL test.?5?The photocatalytic degradation of PNP was investigated by different samples,including TiO₂ nanotube arrays,Cu/TiO₂ nanotube arrays,Fe/TiO₂ nanotube arrays and Cu-nZVI/TiO₂ nanotube arrays.The result indicated that the Cu-nZVI/TiO₂ nanotube arrays exhibiting the highest photocatalytic efficiency of PNP.The degradation efficiency of initial concentration of 10 mg/L PNP reached 90.12%by using Cu-nZVI/TiO₂ nanotube arrays within 150 min,while the removal efficiency was only 51.58%by using the unmodified TiO₂ nanotubes.Furthermore,we carried out the study on testing the specific reactive species during the photocatalytic process both in TiO₂ system and Cu-nZVI/TiO₂ system,a proposed mechanism was given.