Preparation Of Ti³⁺ Self-doped TiO₂ And Improve The Photocatalytic Properties For Hydrogen Evolution By Surface Plasm On Resonance

As one of the earliest studied n-type semiconductor photocatalysts, TiO₂ has been widely used in environmental purification, self-cleaning, H₂ production, photosynthesis, CO₂ reduction, organic synthesis, solar cells, etc. However, because of large band gap of TiO₂ photocatalysts, which can only use of ultraviolet light region and exhibit low conversion rate, the photocatalytic activities up to now is still low. In this paper, we combine Ti³⁺ doped and surface plasmon resonance effect of metal to improve catalytic activity of TiO₂. We report a simple hydrothermal method and chemical reduction method to successfully prepare TiO₂ with visible light absorption, Au/TiO₂ and Ag/AgI/TiO₂ nanoparticles. In this article, the morphology, size, composition, crystal structure and optical absorption of the sample were characterized by SEM, TEM, EDS, XRD, XPS, DRS analysis, and the photocatalytic activities of the prepared catalysts were tested by photocatalytic hydrogen evolution from water splitting.First of all, anatase phase TiO₂ photocatalytic materials were synthesized by one-step hydrothermal method using different alcohol as solvent, which consists of many small and uniform nanoparticles with an average diameter of about 5-10 nm. Experimental results show that TiO₂ photocatalytic materials synthesized using ethylene glycol as solvent have the highest photocatalytic activities for water splitting. For the further discussion, we found that the synthesized TiO₂ is single crystal semiconductor, and the morphology of TiO₂ is slightly truncated bipyramidal. DRS shows that the preparedTiO₂ has a strong absorption in the visible region. Secondly, in order to improve the photocatalytic activities of TiO₂ nanoparticles, metal Au was loaded on the surface of TiO₂ nanoparticles by photochemical reduction method. SEM analysis show that Au nanoparticles were uniformly dispersed on the surface of TiO₂ nanoparticles by this method, which is consistent with the XRD analysis, and the DRS analysis results show that the Au/TiO₂ have strong absorption peak at 520 nm. This is mainly caused by the surface plasmon resonance of Au nanoparticle. Meanwhile, the effects of loading Au and the amount of Au on the photocatalytic water splitting for hydrogen production were studied. When the amount of Au loading is 3%, the hydrogen production rate is the highest, the production rate is 155.37 μmol/g/h. The result shows that the photocatalytic activity of the TiO₂ is remarkably enhanced by loading Au, and the optimal Au loading is 3 %. In addition, we also discussed the reaction mechanism of TiO₂ photocatalytic water splitting.Finally, Ti³⁺ self-doped Ag/AgI/TiO₂ plasmon photocatalytic were successfully prepared by one-step hydrothermal method in different concentrations of AgI. XRD analysis results indicate that the samples contained anatase TiO₂, metal Ag and AgI. XPS analysis results show that Ti mainly exists in the form of Ti⁴⁺ in the samples, and contains a small amount of surface Ti³⁺. The SEM images display that the prepared samples were all small particles. Due to the surface plasmon resonance effect of Ag nanoparticles, Ag/AgI/TiO₂ has strong absorption peak in visible light region. Then the photocatalytic performances of Ag/AgI/TiO₂ were studied by photocatalytic hydrogen evolution from water, and the photocatalytic properties of Ag/AgI/TiO₂ with different concentrations of AgI preparation, the results showed that the concentration of AgI is 0.5M, photocatalytic activity of Ag/Ag I/TiO₂ is the highest, and hydrogen production rate of Ag/AgI/TiO₂ reached 571 μmol/g/h. Because of synergistic effect involving surface plasmon resonance（SPR） of Ag nanoparticles and Ti³⁺ self-doped, Ag/AgI/TiO₂ can enhance photocatalytic activity for hydrogen production under visible light illumination.In addition, on the basis of 0.5M AgI, the proportion of Ag and I was changed. The experimental results show that with the decreasing of proportion of Ag and I, the content of metallic Ag and AgI in the sample were obviously changed. The absorbtion of sample is also gradually lower under visible region. When the ratio of Ag and I is 1:1, the photocatalytic water splitting for hydrogen production is the highest.