State Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100, China.
Langmuir. 2012 Jul 17;28(28):10415-24. doi: 10.1021/la301679h. Epub 2012 Jun 29.
An understanding of the interaction between Zn(2)GeO(4) and the CO(2) molecule is vital for developing its role in the photocatalytic reduction of CO(2). In this study, we present the structure and energetics of CO(2) adsorbed onto the stoichiometric perfectly and the oxygen vacancy defect of Zn(2)GeO(4) (010) and (001) surfaces using density functional theory slab calculations. The major finding is that the surface structure of the Zn(2)GeO(4) is important for CO(2) adsorption and activation, i.e., the interaction of CO(2) with Zn(2)GeO(4) surfaces is structure-dependent. The ability of CO(2) adsorption on (001) is higher than that of CO(2) adsorption on (010). For the (010) surface, the active sites O(2c)···Ge(3c) and Ge(3c)-O(3c) interact with the CO(2) molecule leading to a bidentate carbonate species. The presence of Ge(3c)-O(2c)···Ge(3c) bonds on the (001) surface strengthens the interaction of CO(2) with the (001) surface, and results in a bridged carbonate-like species. Furthermore, a comparison of the calculated adsorption energies of CO(2) adsorption on perfect and defective Zn(2)GeO(4) (010) and (001) surfaces shows that CO(2) has the strongest adsorption near a surface oxygen vacancy site, with an adsorption energy -1.05 to -2.17 eV, stronger than adsorption of CO(2) on perfect Zn(2)GeO(4) surfaces (E(ads) = -0.91 to -1.12 eV) or adsorption of CO(2) on a surface oxygen defect site (E(ads) = -0.24 to -0.95 eV). Additionally, for the defective Zn(2)GeO(4) surfaces, the oxygen vacancies are the active sites. CO(2) that adsorbs directly at the Vo site can be dissociated into CO and O and the Vo defect can be healed by the oxygen atom released during the dissociation process. On further analysis of the dissociative adsorption mechanism of CO(2) on the surface oxygen defect site, we concluded that dissociative adsorption of CO(2) favors the stepwise dissociation mechanism and the dissociation process can be described as CO(2) + Vo → CO(2)(δ-)/Vo → CO(adsorbed) + O(surface). This result has an important implication for understanding the photoreduction of CO(2) by using Zn(2)GeO(4) nanoribbons.
理解 Zn(2)GeO(4) 与 CO(2) 分子之间的相互作用对于开发其在 CO(2) 光催化还原中的作用至关重要。在这项研究中，我们使用密度泛函理论平板计算，研究了 CO(2) 在化学计量的完美和氧空位缺陷的 Zn(2)GeO(4) (010) 和 (001) 表面上的吸附结构和能量。主要发现是 Zn(2)GeO(4) 的表面结构对 CO(2) 的吸附和活化很重要，即 CO(2)与 Zn(2)GeO(4) 表面的相互作用是结构依赖性的。(001) 表面上 CO(2) 的吸附能力高于 (010) 表面上 CO(2) 的吸附能力。对于 (010) 表面，活性位点 O(2c)···Ge(3c) 和 Ge(3c)-O(3c) 与 CO(2) 分子相互作用，导致双齿碳酸盐物种。(001) 表面上 Ge(3c)-O(2c)···Ge(3c) 键的存在增强了 CO(2)与 (001) 表面的相互作用，导致桥连碳酸盐样物质。此外，比较完美和有缺陷的 Zn(2)GeO(4) (010) 和 (001) 表面上 CO(2) 吸附的计算吸附能表明，CO(2)在表面氧空位附近具有最强的吸附，吸附能为-1.05 至-2.17 eV，比在完美 Zn(2)GeO(4) 表面上吸附 CO(2)更强（E(ads) = -0.91 至-1.12 eV）或在表面氧缺陷位置吸附 CO(2)更强（E(ads) = -0.24 至-0.95 eV）。此外，对于有缺陷的 Zn(2)GeO(4) 表面，氧空位是活性位点。直接在 Vo 位点吸附的 CO(2)可以离解成 CO 和 O，并且 Vo 缺陷可以通过离解过程中释放的氧原子来修复。进一步分析表面氧缺陷位上 CO(2)的离解吸附机制，我们得出结论，CO(2)的离解吸附有利于逐步离解机制，离解过程可以描述为 CO(2) + Vo → CO(2)(δ-)/Vo → CO(adsorbed) + O(surface)。这一结果对于理解使用 Zn(2)GeO(4) 纳米带进行 CO(2)光还原具有重要意义。
