镍掺杂TiO2纳米管的制备及光催化性能研究

通过前驱体水热法成功制备出不同镍掺杂比例的二氧化钛纳米管粉体,利用场发射扫描电镜(FESEM)、X射线衍射仪(XRD)、X射线光电子能谱(XPS)、紫外可见吸收光谱(UV-Vis)等对其进行检测表征。制备出的镍掺杂二氧化钛纳米管具备相对分离和独立的管状形貌,管径约10 nm,其对应的EDS谱图中出现了镍的特征峰。经500℃热处理后样品呈锐钛矿和晶红石的混晶结构。XPS检测表明掺杂样品中镍主要以Ni²⁺形式存在。样品的紫外可见吸收光谱表明镍掺杂样品的光吸收发生红移且镍掺杂明显提升了样品的光吸收能力。光催化测试表明适宜的镍掺杂能够有效降低二氧化钛光生电子和空穴的复合率,从而提升了纳米管样品对亚甲基蓝的降解率。其中2%镍掺杂纳米管对亚甲基蓝显示出最高的2 h降解率,达到95.7%,而过量的镍掺杂则会对其催化性能产生抑制作用。

Preparation and Photocatalytic Properties of Ni Doped TiO Nanotube

At present,element doping has been proved to be an effective means to solve the shortcomings of TiO₂ photocatalytic materials such as narrow light response range and low quantum efficiency,and to optimize and improve the catalytic performance of TiO₂.Element doping introduces various transition metal or non-metal electronic active bodies into the TiO₂ crystal lattice to reduce the forbidden band width,thereby improving the photocatalytic efficiency of TiO₂ and shifting the maximum excitation wavelength to the near ultraviolet or visible light region.Therefore,the research on suitable doping elements and the doping optimization mechanism have become the current research hotspot.Among all the transition metals,Ni element has become the focus of this article as a potential doping element due to its abundant reserves,environmental friendliness,and low price.Titanium dioxide nanotube powder with different Ni doping ratios were successfully prepared by the precursor hydrothermal method and characterized by field emission scanning electron microscope(FESEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),ultraviolet and visible spectrophotometry(UV-Vis).The photocatalytic performance of the sample was characterized by catalytic degradation of methylene blue under ultraviolet light and simulated sunlight.FESEM and TEM results showed that the diameter of the undoped TiO₂ nanotubes was about 10 nm,and the tubes were relatively independent and entangled with each other.The appropriate amount of nickel doping would not affect the structure and size of the nanotubes.Energy dispersive X-ray spectrum(EDX)analysis showed that Ni doping in TiO₂ nanotubes was achieved during the preparation process,and the Ni content slightly lower than the doping ratio was mainly due to the loss of nickel during the preparation process.XRD analysis showed that nanotube samples were transformed into a mixed crystal structure of anatase and rutile after heat treatment.Since the proportion of Ni in the doped sample was low,the characteristic peak corresponding to Ni was not detected.The characteristic peaks of C 1 s,Ti 2 p,O 1 s,and Ni 2 p were detected in the XPS spectrum.The characteristic peaks of Ni 2 p at 855.37 and 872.87 eV were corresponding to the Ni 2 p_3/2 and Ni 2 p_1/2 peaks of Ni²⁺ in NiO,respectively,which indicated that the nickel element mainly existed in the form of NiO.The characteristic peaks at 861.45 and 879.51 eV corresponded to the Ni 2p_3/2 and Ni 2p_1/2 peaks of Ni³⁺ with a small amount of Ni2O3 produced during the preparation process.The ultraviolet-visible absorption spectrum showed that as the nickel doping ratio increases,the absorption intensity of nanotube powder sample in the visible light region gradually increased,and the sample with 4% nickel doping reached the strongest.The absorption of the sample had a significant red shift with the increase of the doping ratio,which was mainly because Ni doping into the TiO₂ lattice,generating a new energy level on the TiO₂ valence band,thereby reducing the band gap of the sample.Therefore,nickel doping was beneficial to improve the absorption performance of the TiO₂ nanotube sample in the visible light region.Experiments on the catalytic degradation of methylene blue by different nanotube samples under simulated sunlight and ultraviolet light showed that the catalytic efficiency of the samples under ultraviolet light was significantly higher than that under simulated sunlight.Under simulated sunlight and ultraviolet light,the degradation rate of each sample to methylene blue gradually increased with the increase of the Ni doping ratio.However,when the Ni doping amount reached 4%,the catalytic efficiency decreased to a certain extent.The possible mechanism of the modification effect of nickel doping in TiO₂ nanotubes was as follows:Since the conduction band position of NiO(2.1 eV)was lower than that of TiO₂(3.05 eV),the conduction band electrons on TiO₂ would transition to the conduction band of NiO which has lower energy.This reduced the recombination rate of electrons and holes in TiO₂,and ultimately improved the catalytic performance of TO2.However,when the nickel doping ratio was further increased,the catalytic performance of the composite sample would decrease.The main reasons for this phenomenon included:On the one hand,when the Ni doping ratio of the system increased,the relative content of TiO₂ would become smaller.The catalytic effect of the system was weakened;secondly,excessive nickel doping would become the recombination center of electrons and holes to increase the probability of photogenerated electron-hole recombination,thereby inhibiting the catalytic effect of the system.The nickel-doped titanium dioxide nanotube powder was prepared by the precursor hydrothermal method.The diameter of the nanotube was about 10 nm,and it had a mixed crystal structure of anatase and rutile after heat treatment.Nickel doping enhanced the light absorption capacity of TiO₂ nanotubes and made its light absorption redshift.A proper amount of nickel doping was beneficial to inhibit the recombination of photo-generated electrons and holes,thereby enhancing the catalytic activity of the material.The 2% Ni doped nanotube showed the highest 2 h degradation rate for methylene blue,which was 95.7%,while excessive Ni doping would have inhibitory effect on its catalytic performance.