Synthesis, Modification And Photocatalytic Performance Of One Dimensional Titanium Based Nanomaterials

Titanium dioxide and titanate one dimensional nanomaterials have attracted considerable attention for their large specific surface area and unique photoelectric properties. However, they do not show better photocatalytic activities than commercial P25 TiO₂. On the basis of the band theory of semiconductor, one dimensional titanium based nanomaterials has the potential to be modified for wide range of spectral response and better photocatalytic activity. In this paper, plenty of experiments have been performed in the field of synthesis, modification and photocatalytic performance of one dimensional titanium based nanomaterials.A simple and cost effective hydrothermal method was used for synthesizing one dimensional titanium based nanomaterials. The as-synthesized nanotubes/nanorods were characterized by X-ray diffraction, transmission electron microscopy and UV-vis diffuse reflectance spectroscopy. Protonated titanate nanotubes and sodium titanate nanotubes can be synthesized with and without hydrogen ions treatment. The absorption curves of TNT(H) show obvious red shift relative to that of TNT(Na). Then energy bandgap of nanotubes is estimated by Kubelka-Munk theory and hypothesis of indirect gap semiconductor. The effect of heat treatment on the phase and microstructure of one dimensional titanium based nanomaterials has been discussed. The results showed that anatase TiO₂ nanotubes can be obtained after heat treatment at 400°C for 90 min and anatase TiO₂ nanorods can be obtained after heat treatment at 400°C for 180 min.The microstructure of nanotubes was characterized by SEM, HRTEM and SAED. The agglomeration of nanotubes can be found before ultrasonic dispersion. The nanotubes are interlaced with each other to form a porous particle with diameter of 2 - 3μm. After ultrasonic dispersion, particles are dispersed into 100 -500 nm single nanotubes and parts of nanotubes are broken due to excessive ultrasonic energy. From the high resolution images, layered microstructure can be obviously observed in sodium titanate nanotubes. Based on FFT calculation, the interplanar spacing is estimated to be ca. 0.35 nm and the interlayer spacing is estimated to be ca. 0.69 nm. The wall of a nanotube contains 3– 5 layers.The adsorption studies of methylene blue and methyl orange were performed in the dark. Based on Zeta potential measurement, it is reasonable to believe that electrostatic interaction is dominant force to drive adsorption of dye molecules onto the surfaces of H2Ti3O7 and TiO₂ nanotubes. The IR spectroscopic study further reveals that methylene blue molecules interact with surface of nanotubes through chemical adsorption. The results showed that the photocatalytic activities on methylene blue follow the decreasing order TiO₂ nanotubes > TiO₂ nanorods > H2Ti3O7 nanotubes and the photocatalytic activities on methyl orange follow the decreasing order TiO₂ nanorods > TiO₂ nanotubes > H2Ti3O7 nanotubes.Photochemical reaction study demonstrates that adsorption of dyes on TiO₂ plays an important role in the catalytic photodegradation process. The adsorption of dye molecules in photochemical reaction might increase the probability of direct hole oxidation and thus promotes the photodegradation of the dye on TiO₂ nanocatalysts. For enhancing photocatalytic activity, the ion-exchange method was used to modify one dimensional titanium based nanomaterials. Lead titanate and cobalt titanate nanotubes can be synthesized via a two-step method. The DRS analysis of the samples reveals that the exchanged lead ions effectively narrow the bandgap of the nanotubes. The bandgap of lead ion-exchanged TNT and TNA are 3.30 eV and 3.12 eV, lower than that of its precursor TNT(Na). After cobalt ions modification, the absorption edge of nanotubes extends to 480 nm.The results of methyl orange degradation curves demonstrated that the sample with Ti:Co = 1:1 showes the best photocatatlytic acvitity.A two-steps synthesis of hydrothermal treatment and electrostatic surface doping technique is proposed for the preparation of TiO₂ nanorods in the anatase form doped with rare earth ions La³⁺, Ce³⁺, Pr³⁺, Sm³⁺, Eu³⁺, Tb³⁺ and Er³⁺. Their physical and morphology properties have been investigated by using Raman spectroscopy, transmission electron microscopy, and UV-vis absorption spectroscopy. Furthermore, photodegradation of dye using these novel materials as photocatalysts were investigated in this study. Degradations of methyl orange take place very fast with photocatalysts. It is obvious that La³⁺, Sm³⁺, Eu³⁺ and Er³⁺ doped TiO₂ catalysts show higher reactivity than pure TiO₂ nanorods and P25 TiO₂. And total mineralization of the dye can be reached. Ce³⁺, Pr³⁺ and Tb³⁺ doped samples exhibit the lower photocatalytic activities. The effect of temperature of heat treatment was studied. The results showed that the photocatalytic activities on methyl orange follow the decreasing order 600°C > 400°C > 200°C.The one dimensional titanium based nanomaterials were used for photocatalysis of biomacromolecule lignin and organic explosive TNB. Lignin in aqueous solution shows trace degradation under UV light. With photocatalysts assistance, the photocatalytic activities are enhanced. The chemical changes in the lignin after different photodegradated periods were analyzed through the application of UV-visible spectroscopy and IR spectroscopy. The results demonstrated that different RE ions doped photocatalysts show the different degraded route of lignin. A small quantity of TNB can be adsorbed onto the surface of TiO₂ nanorods in the dark. After 4 hours UV irradiation, the TNB in aqueous solution can be degraded totally and the products are aromatic compound.