The Research Of Silver-loading,Photoelectric And Antibacterial Properties Of TiO₂ Nanotube Arrays

Titania nanotube arrays are well-organized tubular titania,the tops of the tubes are open,the bottoms of the tubes are closed.At present,the main method of fabrication is anodic oxidation.Recent studies have indicated that titania nanotube arrays have improved properties compared to any other form of titania for application in photo-catalysis,photo-voltaics and medicine,which has more significance of research.In this work,using scanning electron microscopy,X-ray diffraction,Raman spectrometer,UV visible spectrophotometer,gas phase chromatograph and electrochemical workstation equipments,we examine the self-organization process of titania nanotube arrays,the photo-electrics properties and electrochemical impedance spectrum of the two length of titania nanotube arrays,the photoelectric properties and electrochemical impedance spectrum of the ordered titania nanotube arrays,their photoelectric conversion performance of the loaded titania nanotube arrays,photocatalysis properties,biological activity and antibacterial properties.The main results are as follows:（1）The work indicated that the current experienced three stages of the decay-state,rising-state and steady-state corresponds to the forming of titania film,the solubility and split of the titania film and the dynamic balance between the formation and dissolution of titania near the bottom.Under the electric field,the competition between the formation and dissolution of titania near the bottom bottom caused the sawtooth-shapedcurrent-time curve.This work still indicated that when the other conditions are settled,the length of titania nanotube arrays can be controlled by regulating the anodic oxidation time.When the PH value of water quality electrolyte is in the range of 3-5,themorphology of obtained TNAs is regular.The evolution of TNAs hole maybe due to the swelling stress.（2）The work indicated that:the reasons which caused the short TNAs have better Photo sensitive characteristic,improved Photoelectron transfer capability than the long one could be as follows:（1）In the process of heat treatment and subsequent cooling,the damage of interface between titanium sheet and the short TNAs is relatively small,and the resistance of photo electron transfer via interface is small;（2）The anodic oxidation time of fabricating short TNAs is relatively short,the particle size is small,so there is enough space to transfer the crystal structure when heat treatment,which makes the acquired TNAs has anatase and rutile two crystal structure.The mix-crystal structure TNAs has wider range of optical response frequency.Another conclusion can be obtained that fabrication of high quality titanium matrix TNAs may be restricted and influenced by two factors.One is the length of TNAs,however,unilaterally pursuing the length and ignoring the damage of interface between titanium matrix and the TNAs layer,still cannot guarantee excellent photoelectric property;the other one is the crystal structure of TNAs,the mix-crystal structure of anatase and rutile is conducive to the expands TNAs optical response frequency range,enhance its photovoltaic performance.（3）Research shows that photo-deposition can achieve the loading Ag in TNA,which is based on the basic principles of silver nitrate decomposition into silver under visible light,use the hollow tube array structure of TNAs to achieve composition of titania and silver.Using the Ag-loaded by photo-deposition method,heat treatment process can control the TNAs crystal structure,and turn it into anatase which has photoelectric properties.This method can not only change the ways of the photo-electron transfer,improve the photo-electrical properties of the TNAs,but also makes the TNAs antibacterial,effectively restrain the increase of bacteria.（4）Research shows that after soaking with appropriate concentration silver nitrate solution and proper heat treatment,the decomposition of silver nitrate and the crystal structure transformation of titania are synchronous,which effectively improve the photo-catalysis properties of the TNAs,the concentration of silver nitrate impact the morphology structure and catalysis properties of titania-Ag composite catalyzer.Higher concentration of silver nitrate solution compact the TNAs surface,and caused the worse photo-catalysis properties.when the silver nitrate concentration is 0.1⁰.5 mol·L^-1,the surface is loose and porous,the photo-catalysis properties is relatively better,the hydrogen-generation rate is 2.14μmol·cm₂^-1·h^-1,which is 4 times of the TNAs.the advance of catalysis properties is due to both the loading of silver reduced the compound rate of photo-generated electron-hole pairs and Ag nano particle has special surface plasma effect,by enhancing the intensity of regional electromagnetic field,generate plasma resonance region,increase the resonant electron energy,strengthen the photon absorption efficiency,and expands TNAs optical response frequency range.（5）This work indicated that the thermally-driven loaded method can effectively improve the photo-catalysis properties of TNAs,yet fabricate titania-Ag composite coating which is biological activity and antibacterial on the titanium alloy surface.This method is based on the basic principles of silver nitrate decomposition into silver when being heated,the TNA is firstly immersed in the saturated AgNO₃ solution,then be heat treated at 500℃or 600℃,the silver nitrate decomposition and the titania crystal structure transformation occured synchronously.Biological activity of the composite coating was formed because the titanium dioxide can induce the formation of apatite in the simulated body fluid,while the anti-bacterial property was formed because the silver can make the protein of bacterial cells coagulate,damage the activity of bacterial cell synthetase,influence the synthesis of bacterial DNA,deprive the multiplication capacity of bacterial cell and then extinct bacteria.（6）The work on thermally-driven Ag-loading mechanism shows that the core mechanism of this method is silver nitrate thermal decomposition in tubes of the TNAs and titania crystal structure transition occured synchronously.The needed heat treated temperature only require over 300℃.The achievement of the phase transition of titania at low temperature is due to the Ag⁺particle is bigger,hard to enter into the titania lattice,and forming a solid solution,so through the heat treated process,the Ag⁺particle can spread,transfer only on the surface of the TNAs,When the Ag⁺was deoxidized,in order to balance the charge,the TNAs surface will produce oxygen hole,the concentration of negative ion hole on the TNAs surface increases,which will promote the rearrangement of Ti⁴⁺and O^2-and the recombination of titania lattice,promote the generation of rutile titania.The achievement of silver nitrate decomposition at low temperature may be because of nanometer size effect.The titania-Ag composite coating prepared by this method is interlacing（heat treatment at high temperature）,or silver stays in nanotubes（heat treatment at low temperature）,which ensure the durability of the antibacterial.The technology is simple,mild condition,low cost,easy to spread and application.