Preparation and Photocatalytic Properties of Ni Doped TiO2 Nanotube
Tian Ang Shi Xiaoguo Tan Haocun Li Bingxuan Ma Jiawei Yang He
School of Metallurgy,Northeastern University
Abstract：
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 p3/2 and Ni 2 p1/2 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 2p3/2 and Ni 2p1/2 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.
