Preparation And Photoelectrochemical Performance Research Of Visible Light-Responsive TiO₂-Based Nanotube Arrays

Environmental and energy issues are the two major problems facing human survival and development today.Semiconductor photoelectric catalytic technology is regarded as one of the most effective ways to solve these problems.TiO₂ nanotube arrays(TNTs)can directly use sunlight to oxidize and remove pollutants,and electrocatalyze water to generate hydrogen.It is the most potential semiconductor photoelectric one of the catalysts.However,TNTs has a wide band gap(Eg=3.0?3.2 eV),which can only be partially excited by ultraviolet light(3?5%)of sunlight,and the photo-generated electron-hole pairs are easily recombined during the migration process.These defects greatly limit the application of TNTs in the environment and energy fields.In addition,TNTs needs to undergo high-temperature calcination(?400?)to be transformed into a specific crystal form to show certain photoelectrochemical performance,which undoubtedly puts huge pressure on the environmental and cost.We from the perspective of production cost and energy saving and environmental protection,this article explores the Fe³⁺ion doping and MoS₂ compound modification of TNTs through different methods to realize the low-temperature,simple and rapid preparation of TiO₂-based nanotubes array catalysts with excellent comprehensive performance of photochemistry and electrochemistry.The main findings are as follows:(1)The MoS₂/TNTs composite material was prepared by electrochemical cyclic voltammetric deposition,and the preparation process conditions were optimized by the response surface test design,which improved the traditional hydrothermal method for high reaction temperature,long heating time and MoS₂ agglomeration High degree of defects.The experimental results show that the prepared material has a stronger visible light response,a smaller band gap and a highly ordered tubular array structure;when the number of deposition turns is 20,the scanning rate is 51.00 mV/s,it is in the visible light The degradation rate of methyl orange(MO)solution is 82.98%,which is 48.82%higher than pure TNTs;its hydrogen evolution overpotential at current density of-10 mA cm-2 is-183.14 mV,which is 336.96 mV lower than TNTs,And the material still shows good photoelectrochemical performance after repeated use.(2)Using amorphous TNTs as the base material,through the method of water-assisted low-temperature crystallization,Fe³⁺ embedded doped TNTs is prepared under normal pressure,medium and low temperature(?80?)conditions.The effect of Fe(NO3)3 solution concentration,reaction time and reaction temperature on the photocatalytic performance of the material was mainly investigated,and the preparation process conditions were optimized by the design of response surface experiments.The results showed that the introduction of Fe³⁺ did not destroy the tubular array structure,and Fe³⁺ successfully entered the TiO₂ lattice.The band gap width of TNTs was shortened from 3.21 eV to 2.46 eV,and the light response range was extended to the visible light region.When the Fe(NO3)3 solution concentration is 0.30 mol/L,the reaction temperature is 75?,and the reaction time is 8.42 h,the degradation rate of Fe-TNTs to MO solution is 95.96%,which is 61.81%higher than that before doping.After the second cycle of use,it still has good visible light catalytic activity.In terms of electrocatalytic hydrogen evolution performance,the hydrogen evolution overpotential of the material prepared with 0.2 mol/L Fe(NO3)3 solution concentration is-383.56 mV,which is 136.70 mV lower than before doping.(3)The MoS₂/Fe-TNTs ternary composite material is prepared by water-assisted low-temperature crystallization method and electrochemical cyclic voltammetric deposition method with low consumption and environmental protection.The analysis results of SEM,XRD and UV-Vis showed that the introduced MoS₂ nanoparticles formed abundant exposed active sites on the surface of Fe-TNTs without destroying the original crystal structure.The absorption sideband of the material was obviously red shifted.The band gap width is shortened to 2.13 eV,and the light response range is extended to the visible light region.Its degradation rate of MO solution under visible light is 76.33%,which is 42.17%higher than pure TNTs.The hydrogen evolution overpotential is-228.27 mV,which is 291.99 mV lower than pure TNTs.The prepared material has certain photocatalytic degradation activity of pollutants and relatively excellent electrocatalytic hydrogen evolution performance.The improvement of hydrogen evolution performance may be due to the formation of abundant reactive sites on the surface of the material by MoS₂.On the other hand,it may be due to the electron transfer mode of TiO₂? Fe³⁺ ?MoS₂ which improves the electron transfer efficiency of the material.However,in the narrow energy band gap of MoS₂/Fe-TNTs,a part of Fe³⁺ will also become the recombination center of photogenerated electron-hole pairs,which will reduce the photocatalytic performance.