Electronic Structure Regulation Of Metal-defected Titanium Dioxide For Photocatalytic Applications

Photocatalytic technology has become a research hotspot in the field of energy and environment.The preparation of efficient photocatalysts has become a bottleneck problem in improving photocatalytic efficiency.Photogenerated electrons and holes are mainly active species for photocatalytic reaction.Generally,the photogenerated electrons have two inherent characteristics of charge and spin.The charge properties of electrons in photocatalyst have been deeply demonstrated,but the spin states of electrons are seldom concerned.In addition to the conservation of energy,electrons also follow the conservation of angular momentum during the transition process.Therefore,the spin state of electrons will affect the photocatalytic process.In this article,the spin state of titanium dioxide,the typical photocatalyst,is regulated,and the influence of electronic spin properties on the photocatalytic process is deeply explored.First,titanium vacancies are introduced by density functional theory calculations to design spin-polarized states.It is found that titanium dioxide with different titanium vacancies has different spin-polarized electronic structures.Layered glycerin titanium was prepared by solvothermal method and then calcined to obtain anatase titanium dioxide containing different concerntrations of titanium vacancies.What’s more,we discussed the growth mechanism of titanium vacancies.The existence of titanium defects was strongly verified by the characterizations of XANES,EXAFS and so on,and the concentrations of titanium vacancies on surface and in bulk were quantitatively calculated by XPS and chemical titration methods respectively.Finally,it is proved that the titanium dioxide with the series of titanium defects has different spin states and spin-polarized states.In addition,the photocatalytic activity of titanium dioxide with different spin states were tested by photocatalytic degradation and photocatalytic hydrogen production.It is found that the activity of photocatalytic hydrogen evolution of TiO₂-10（with 6.4%Ti vacancies）with a total spatial spin polarization of-100%and the widest distribution in real space shows a 20 times higher than normal titanium dioxide.What’s more,the activity of photocatalytic phenol degradation is 8.6 times higher than normal titanium dioxide.Finally,we confirmed that spin-dependent effect through photocatalytic degradation under magnetic field.For TiO₂-10（with 6.4%Ti vacancies）,we found that the degradation rate of rhodamine B under 8000Oe magnetic field is 54%higher than that without magnetic field.Combined with theoretical calculation and experimental results,we gave the mechanism of spin states effects on the photocatalysis from the aspects of light excitation,charge transfer and surface reactions.After that,we constructed a p-n heterojunction of TiO₂/g-C₃N₄,which not only extended the light absorption range to the visible light,but also further promoted the separation of photo-generated charges.The photocatalytic activities of CNT-40 for hydrogen production,degradation of MO and phenol under visible light are the best among similar samples,5.7 times,3.6 times and 1.6 times that of g-C₃N₄,respectively.Those ideas open our mind to construct new efficient photocatalysts.