金红石TiO2纳米团簇与铀酰相互作用的相对论密度泛函理论计算

采用全电子相对论密度泛函理论方法探索金红石型Ti O_2纳米团簇与铀酰的相互作用。考察金红石团簇模型(包括层数和表面积大小)变化对吸附铀形成复合物结构、吸附作用能等性质的影响,确定2层、表面积为1.1 nm×0.6 nm、包括63个原子的纳米团簇(标记为2L-Ti15)能够合理描述金红石纳米粒子性质的同时,还能节约计算资源。对2L-Ti15-[(UO_2)(H_2O)_3]~(2+)复合物计算表明,纳米团簇和铀酰存在共价键作用;优化得到U-O_(surf)键长0.233~0.238 nm,这一距离在已发现铀酰基配合物U-O距离范围内。在气相条件下,纳米团簇对铀酰吸附反应为放热过程(-3.02 e V);考虑溶剂介质环境的影响,反应则需要吸收少许能量(0.16e V)。U-O_(surf)键的能量分解发现,纳米团簇和铀酰的化学键作用为轨道相互作用主导的(占94%),它的静电吸引略大于Pauli排斥。基于电子密度的QTAIM(quantum theory of atoms in molecule)分析揭示,U-O_(surf)作用是介于离子和共价之间的配位键,其强度高于复合物中的U-OH_2键作用,但比U=O键弱。波函数分析表明,来自纳米团簇的O(2p)贡献HOMO轨道,并混有σ(U=O)成键性质,而LUMO轨道则为Ti(3d)修饰的U(5f)性质,复合物HOMO-LUMO带隙为2.40 e V,相对吸附前的纳米团簇半导体粒子的3.35 e V变窄。从吸收光谱角度而言,复合物体系可能在可见光区域具有更强的捕光性能。

Relativistic DFT Calculations of Interaction between Rutile TiO2 Nanoparticle Clusters and Uranyl Species

The interaction between rutile TiO₂ nanoparticle clusters (NPCs) and aquouranyl species have been examined using a relativistic functional theory (DFT). Effects of NPCs with various layers (1~4) and different surface areas on structural parameters of uranium adsorption complexes as well as adsorption interaction energies were investigated. It is found that the two-layered (2L) NPC (labeled as 2L-Ti15) with a surface area of 1.1 nm×0.6 nm and containing 63 atoms can reasonably stand for experimentally real TiO₂ nanocrystallite. Moreover, the model is able to save computational resources. Calculations reveal a covalent bonding interaction in the 2L-Ti15-[(UO₂)(H₂O)₃]²⁺ complex. The direct evidences include that the bond lengths of U-O_surf were optimized to be 0.233~0.238 nm, which fall well within the range of U-O distances of reported uranyl complexes. The process that the NPC adsorbs aquouranyl species is exothermic in the gas phase, releasing energy of -3.02 eV; the consideration of environment media of solution results in a slightly uphill process, requiring 0.16 eV energy. The energetic decomposition indicates that U-O_surf bonds are dominated by orbital interactions, accounting for 94%; other factors show a little effect, although electrostatic attraction is a little larger than Pauli repulsion. Electron density-based QTAIM (quantum theory of atoms in molecule) analyses unravel that the U-O_surf interaction is a dative bond per se, whose strength is stronger than that of U-OH₂, but much weaker than that of U=O_yl. Inspection of wavefunction demonstrates that HOMO is contributed by O(2p) of NPC TiO₂ mixed with a small amount of σ(U=O) bonding character, while LUMO is U(5f)-based character modified by Ti(3d). The HOMO-LUMO gap was calculated to be 2.40 eV, which much narrower than the one of NPC semiconductor (3.35 eV). From a point of view of absorption spectra, the complex system would present a visible light-harvesting capability.