The effect of single rare earth atom (Y) adsorption on the photocatalytic activity of anatase TiO2 thin film was studied by the first-principles calculation based on density functional theory (DFT). Due to the charge transfer of yttrium atom to anatase TiO2 (101) surface, the work function of the adsorbed surface is significantly smaller than that of the pure surface, indicating that the surface activity is enhanced. The 3d orbital of titanium atom appears as an impurity energy level at the bottom of the conduction band, becoming a shallow energy level and enhancing the optical absorption rate by narrowing the band gap. When the single yttrium atom is adsorbed, the potential energy of the surface Ti atom is close to the vacuum level, which significantly promotes electron transfer and thus hydrogen production. In the excited TiO2 photocatalyst, the photoinduced electrons can be transferred to the target species via the surface titanium atom, meaning that the electron-hole pair can be effectively separated to improve the photocatalytic activity. In addition, due to the adsorption of yttrium atom, the upward shift of the conduction band edge will improve the reduction ability of anatase TiO2. The results of this study provide a new idea for improving the photocatalytic performance of single metal atom adsorption.
Keywords:Single-Atom Adsorption, Anatase Thin Film (101) Surface, Active Site, Impurity Level, Optical Absorption, Photocatalytic Activity
式中 E TiO 2 与 E TiO 2 : Y 表示稀土原子被吸附前后TiO2体系的总能量;EY表示稀土原子基态能量。式(1)表示稀土原子吸附前后系统的能量差。当E△值为负值时,对应放热吸附,即负值的绝对值越大,吸附体系就越稳定。当E△值为正数值时,吸附体系不能稳定存在。如表2所示,吸附能远小于零,说明吸附结构是非常稳定。
Average bond length of four Ti-O bonds (two Ti6c-O2c and two Ti5c-O2c), average bond length value of Y-O2c bond, adsorption energy, average Hirshfeld Charge of four Ti ions (two Ti6cand two Ti5c), surface work function (experimental value 7.20 eV) and average charge Population of Ti-O bon
其中,Ptotal为整个吸附体系的电荷密度, P TiO 2 和PY分别表示锐钛矿TiO2表面和单个Y的电荷密度。图2显示了由单原子Y吸附在锐钛矿TiO2 (101)表面上引起的电荷密度差。可知电荷从被吸附的单原子Y转移到锐钛矿TiO2 (101)表面,说明Y原子被稳定地吸附于锐钛矿TiO2 (101)表面。大量的电子积聚在界面区域,Ti离子上都有电子集中,说明由Y向表面输入的电子可以被转移到Ti离子上去,使表面钛原子还原。这刚好与Ti离子Hirshfeld电荷值的变小符合,Ti离子Hirshfeld电荷值越小,表面向Ti离子上转移的电子越多。电荷密度差和Hirshfeld电荷值可知使用U (U = 2.5 eV)参数来而激活的Ti离子能蒱获更多的电子。此外,从Ti-O键的平均电荷布局得知Ti-O键强度变弱,因为平均电荷布局越小,键的共价键性越弱。说明因为Ti离子获得电荷引起它和O离子之间产生排斥力,导致Ti-O键强度变弱,所以相应的键长变大,同时把O3c离子往上推(如图1(b)所示)。正因为以上的原因吸附结构表面的凹凸不平程度和还原性变强,有利于污染物与表面的有效接触,容易进行化学反应来达到分解污染物的目的。
伊力哈尔•艾散,甫尔开提•夏尔丁,买买提热夏提•买买提,王 青. 稀土单原子钇(Y)吸附对锐钛矿TiO2薄膜光催化活性的影响Influence of Rare Earth Single-Atom Yttrium (Y) Adsorption on the Photocatalytic Activity of TiO2 Thin Film[J]. 材料科学, 2021, 11(11): 1155-1164. https://doi.org/10.12677/MS.2021.1111134
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