Study On Electrospun Titanium Dioxide Nanofiber Modified By Rare Earth Doping And Its Photocatalytic Performance

Titanium dioxide(Ti O₂)photocatalyst has been widely used in handling the environmental pollution due to its advantages of non-toxicity,low cost and strong oxidation and reduction.But common Ti O₂ nanoparticles are easy to aggregate and difficult to recycle.The one-dimensional Ti O₂ nanofibers prepared by electrospinning technology can solve the above problems well.In addition,in order to improve the catalytic performance of Ti O₂,scholars have extensively explored its modification methods.Among them,the modification mode of doping with rare earth shows excellent effect in restraining the recombination of photogenerated carriers and broadening the light absorption range,which is one of the most effective modification ways at present.In this paper,the theoretical analysis of anatase Ti O₂doped with rare earth elements(La,Sm,Gd)was carried out,and then the Ti O₂ hybrid nanofibers doped with rare earth elements were prepared by electrspinning.In the meantime,the mechanism of improving the catalytic efficiency was explored by combining theory and experiment.On this basis,ZIF-8 was supported on the surface of La@Ti O₂ hybrid nanofiber membrane by in-situ growth method to form heterojunction structure,which further improved the catalytic performance of Ti O₂ hybrid nanofiber membrane and provided a new idea to achieve the efficient catalysis of Ti O₂.Firstly,this paper utilizes CASTEP module in Materials Studio to calculate and discuss the structure about the crystal and band of the La,Sm or Gd doped Ti O₂.The results show that when Ti O₂ is doped with La,the introduced D impurity state is distributed in the valence band and hybridized with O 2p state.When Ti O₂ is doped with Sm or Gd,the introduced 4f impurity state produces impurity levels in the band gap.The changes make the band gap of La(Eg=1.882e V),Sm(Eg=0.457 e V)and Gd(Eg=0.380 e V)doped Ti O2 smaller than that of pure Ti O2(Eg=2.149 e V),and the change rule of the band gap is consistent with the analysis of UV-vis absorption spectrum in the experiment.Subsequently,we combined the electrospinning and the sol-gel method to prepare pure Ti O₂ nanofiber membranes and the Ti O₂ hybrid nanofiber membranes,which was doped with La,Sm or Gd respectively.The XRD results show that at the calcination temperature of 800?,the pure Ti O₂ nanofiber film has a mixed crystal structure,while the Ti O₂ hybrid nanofibers all maintain the anatase phase,and La@Ti O₂(d=21.076 nm),Sm@Ti O₂(d=22.488 nm)and Gd@Ti O₂(d=26.570 nm)have a smaller grain sizes than Ti O2 nanofiber membranes(d=A:31.568/R:36.094 nm),which proves that the doping of rare earth can suppress the transformation of anatase Ti O₂ and inhibit the growth of the crystal grains of Ti O₂.At the same time,comparing the photocatalytic effects of each sample,it can be seen that the La@Ti O₂hybrid nanofiber has the best catalytic efficiency,and its degradation rate of rhodamine B reaches 98.05%after irradiated by ultraviolet for 60 minutes.In addition,since the doping amount of rare earth has a great influence on the photocatalytic performance of Ti O₂,the doping amount of La is designed to be 0.1,0.3,0.5,0.8,1.0 and 1.2 mol%.The photocatalytic results show that the optimal doping amount of La is 1.0 mol%,and the reaction rate k of the hybrid nanofiber membrane is the largest at this time,which is 0.07046 min^-1.Finally,by using the in-situ growth method and adjusting the concentration of zinc nitrate in the reaction solution,ZIF-8-La@Ti O₂ hybrid nanofiber membranes with different loadings of ZIF-8 were prepared,which uses La@Ti O₂ hybrid nanofiber membrane as the base material.According to TGA analysis,when the molar ratio of 2-methylimidazole and zinc nitrate is 2:1,4:1,8:1,and 16:1,the loading capacity of ZIF-8 in ZIF-8-La@Ti O₂ hybrid nanofiber membrane is 9.74,5.58,2.67,1.54%,respectively.In addition,it can be seen from the photocatalytic degradation results that the degradation rate of Z4-La@Ti O₂ hybrid nanofiber membrane for rhodamine B is 99.11%after irradiated by ultraviolet for 30 minutes.Besides,its reaction rate(k=0.1628 min-1)is the biggest among the samples,which shows that has the best photocatalytic effect.