Study On The Effect Of Aluminum Doping On The Photocatalytic Performance Of Nano-TiO₂ With Oxygen Deficiency

Semiconductor photocatalytic technology is a green technology used to solve environmental pollution problems.As a semiconductor material,TiO₂ has the characteristics of non-toxic,strong oxidation capacity and good biocompatibility.It is an preferred choice for environmental applications such as sewage treatment,air purification,clean hydrogen energy production,solar cells and so on.However,there are still some typical problems that limit the application in the field of photocatalysis.For example,TiO₂ has a wide band gap（3.2 e V）,which make it only respond to the UV-light and can’t utilize visible light.The high recombination rate of photo-generated electron-hole pairs reduces the quantum efficiency of photocatalytic process.To address the above issues,a series of nano-TiO₂ photocatalyst with oxygen deficiency caused by aluminum doping were prepared in this research to expand the range of the light adsorption of TiO₂ and improve its quantum efficiency.The specific contents are as follows:（1）A series of nano-TiO₂ photocatalyst with oxygen deficiency caused by aluminum doping has been successfully synthesized by sol-gel method with aluminum nitrate and tetrabutyl titanate as precursors.The visible light photocatalytic activity of the catalysts were evaluated through the reaction of phenol photodegradation and the hydrogen production by photocatalytic water splitting.The results showed that the sample has the best photocatalytic activity when the molar ratio of Al/Ti was 1:10 and calcination temperature was 400°C.The results showed that some Al³⁺is doped into the TiO₂ crystal lattice to replace Ti⁴⁺and others aggregates on the surface of the TiO₂ in the form of amorphous Al₂O₃.Al doping leads to the formation of a large number of oxygen vacancy defects,and the appropriate concentration of oxygen vacancy serve as the capture center of photogenerated carriers to inhibit the recombination of photo-generated electron-hole pairs.In addition,the residual carbon species on the surface can serve as photosensitizers and interact with impurity energy level induced by oxygen vacancy to enhance the light absorption range.The synergistic effects can significantly enhance the visible-light photocatalytic activities of TiO₂ with oxygen deficiency caused by aluminum doping.（2）In order to further investigate the effect of amorphous Al₂O₃ on the photocatalytic properties of TiO₂,nano-TiO₂ was prepared by precipitation method with titanium oxide sulfate as precursors,and then Al modified TiO₂with oxygen deficiency was synthesized by impregnation and calcination method.The results show that Al exists on the surface of TiO₂in the form of amorphous Al₂O₃,and the amorphous Al₂O₃ is connected to TiO₂ through the Al-O-Ti bond at the interface.Al modification increases the content of oxygen vacancies on the surface of TiO₂.The surface oxygen vacancies can introduce impurity energy level to enhance the light absorption range and capture photogenerated electrons to inhibits the recombination of charge carriers.What’s moer,it can react with H₂O,O₂ and other molecules adsorbed on the surface of TiO₂ to generate reactive oxygen species for improving the photocatalytic performance.At the same time,the photogenerated electrons generated on TiO₂ surface can be transferred to the defect level of amorphous Al₂O₃,which promotes the separation of photo-generated electron-hole pairs.The synergistic effects of the amorphous Al₂O₃and oxygen vacancy significantly enhanced the photocatalytic degradation activity of TiO₂ for methyl orange.