The Construction And Performances Of Three-dimensional Titanium Dioxide Arrays As Functional Materials

Environmental pollution and energy crisis are two urgent problems in various fields.Titanium dioxide（Ti O₂）has the advantages of abundant element reserves,low cost,non-toxicity,good biocompatibility,and good stability.It has potential applications in photocatalytic degradation of pollutants and energy storage.The three-dimensional（3D）array structure has the advantages of high specific surface area,abundant diffusion channels,good contact with the substrate,and convenient recycling,but its controllable manufacturing is still difficult.It is of great significance to develop reasonable design of high-performance titanium dioxide three-dimensional arrays for solving the problems of environmental pollution and energy shortage.In order to solve the problem of environmental pollution,single-crystal-like anatase Ti O₂hierarchical nanowire arrays were prepared.By the"convertible-precursor-induced growing"method,the uniaxial lattice constant of anatase Ti O₂ was modulated without changing the composition,morphology,phase structure and surface state of the materials.Unlike conventional substrate-manipulating methods,this method relies on a precursor-induced oriented growth and the lattice mismatch in the liquid deposition process to modulate the lattice parameters,and the employed precursor can be converted into the final materials（i.e.,anatase Ti O₂）,which can eliminate the effects of additional imported parameters of composition and phase brought by the conventional substrate methods.Experimental study and density functional theory（DFT）calculations show that the elongation of lattice parameter a leads to the shift-up of the conduction band bottom of anatase Ti O₂ and can thus accelerate the reduction reactions of O₂.The elongation of the lattice parameter a and the unique single-crystal-like 3D array structure make the Ti O₂hierarchical nanowire arrays highly active for photocatalytic activity of photocatalytic degradation of toluene in the air and the photocatalytic reduction of Cr⁶⁺ions in water.The turnover frequency（TOF）of toluene degradation is 3.8 times and 2.1 times,respectively,that of normal Ti O₂ arrays and commercial P25 powder under ultraviolet irradiation.In addition,the arrays show good stability in cycling test.Renewable energy sources such as solar energy and wind power are intermittent,and their practical applications require efficient energy storage devices.To solve the energy problems,F-modified polycrystalline Ti O₂ hierarchical nanowire arrays were prepared by liquid deposition method,as the anodes for supercapacitors.The backbone of the 3D array is Ti O₂ nanowires,and the branches are nanoporous Ti O₂ mesocrystal particles containing F.According to DFT calculations,F modification can greatly reduce the diffusion energy barrier of Li⁺ions on the anatase Ti O₂ surface（0.39 e V vs 1.46 e V）.The porous structure of the sample and the decrease of the diffusion barrier of Li⁺ions on the surface lead to the increase of its pseudocapacitance.Compared with the reported Ti O₂ electrode materials for supercapacitor,the F-containing Ti O₂ hierarchical nanowire arrays show high area specific capacitance,fast charge-discharge capability and long cycle life.It has an area capacitance of 41.14 m F·cm^-2 at the current density of 1 m A·cm^-2;the mass specific capacitance of F-containing Ti O₂ nanoparticles is about 7 times that of F-free Ti O₂ nanoparticles.After 2000cycles,the retention of the capacitance is 158%,exhibiting good cycling stability.This study provides a new idea for the adjustment of material lattice parameters and an effective way to reduce the energy barrier of alkali metal ion on the surface of materials.It can provide an effective strategy to improve the performances of materials for photocatalyticly environmental purification and energy storage.The fabricated materials may have potential applications.