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Effects of Ta2O5 Surface Modification by NH3 on the Electronic Structure of a Ru-Complex/N–Ta2O5 Hybrid Photocatalyst for Selective CO2 Reduction
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2018-01-19 00:00:00 , DOI: 10.1021/acs.jpcc.7b09670
Soichi Shirai 1 , Shunsuke Sato 1 , Tomiko M. Suzuki 1 , Ryosuke Jinnouchi 1 , Nobuko Ohba 1 , Ryoji Asahi 1 , Takeshi Morikawa 1
Affiliation  

This work examined a Ru-complex/N–Ta2O5 (N–Ta2O5: nitrogen-doped Ta2O5) hybrid photocatalyst for CO2 reduction. In this material, electrons are transferred from the N–Ta2O5 to the Ru-complex in response to visible light irradiation, after which CO2 reduction occurs on the complex. N-doping is believed to produce an upward shift in the conduction band minimum (CBM) of the Ta2O5, thus allowing more efficient electron transfer, although the associated mechanism has not yet been fully understood. In the present study, the effects of NH3 adsorption (the most likely surface modification following nitrification) were examined using a combined experimental and theoretical approach. X-ray photoelectron spectroscopy data suggest that NH3 molecules are adsorbed on the N–Ta2O5 surface, and it is also evident that the photocatalytic activity of the Ru-complex/N–Ta2O5 is decreased by the removal of this adsorbed NH3. Calculations show that both the occupied and unoccupied orbital levels of Ta16O40(NH3)x clusters (x = 4, 8, 12, or 16) are shifted upward as x is increased. Theoretical analyses of Ru-complex/cluster hybrids demonstrate that the gap between the lowest unoccupied molecular orbital of the Ta16O40 moiety and the unoccupied orbitals of the Ru-complex in Ru-complex/Ta16O40(NH3)12 is much smaller than that in Ru-complex/Ta16O40. The highest occupied molecular orbital of [Ru-complex/Ta16O40] is evidently localized on the Ta16O40 moiety, whereas that of [Ru-complex/Ta16O40(NH3)12] is spread over both the Ta16O40 and Ru-complex. These results indicate that the NH3 adsorption associated with N-doping can result in an upward shift of the CBM of Ta2O5. Additional calculations for Ta16O40–y(NH)y (y = 2, 4, 6, 8, or 10) suggest that the substitution of NH groups for oxygen atoms on the Ta2O5 surface may be responsible for the red shift in the adsorption band edge of the oxide but makes only a minor contribution to the upward shift of the CBM.

中文翻译:

NH 3对Ta 2 O 5表面改性对Ru-Complex / N-Ta 2 O 5杂化光催化剂选择性还原CO 2的电子结构的影响

这项工作研究了Ru-络合物/ N-Ta 2 O 5(N-Ta 2 O 5:掺杂氮的Ta 2 O 5)杂化光催化剂以减少CO 2。在这种材料中,电子响应于可见光辐照而从N–Ta 2 O 5转移到Ru-络合物,然后在络合物上发生CO 2还原。据信,N掺杂会在Ta 2 O 5的最小导带(CBM)中产生上移,尽管相关的机理还没有被完全理解,但是因此允许更有效的电子转移。在本研究中,使用组合的实验和理论方法研究了NH 3吸附的影响(硝化后最可能的表面改性)。X射线光电子能谱数据表明,NH 3分子被吸附在N–Ta 2 O 5表面上,而且很明显,Ru-络合物/ N–Ta 2 O 5的光催化活性会由于去除N而降低。该吸附的NH 3。计算表明,Ta 16 O 40的占据和未占据轨道能级(NH 3x簇(x = 4、8、12或16)随着x的增加而向上移动。Ru-络合物/团簇杂化体的理论分析表明,Ta-络合物/ Ta 16 O 40(NH 312中Ta 16 O 40部分的最低未占据分子轨道与Ru-络合物的未占据轨道之间的间隙为比Ru-络合物/ Ta 16 O 40小得多。[Ru-络合物/ Ta 16 O 40 ] -的最高占据分子轨道显然位于Ta 16上O 40部分,而[Ru-络合物/ Ta 16 O 40(NH 312 ] -的部分分布在Ta 16 O 40和Ru-络合物上。这些结果表明,与N掺杂相关的NH 3吸附可以导致Ta 2 O 5的CBM向上移动。对Ta 16 O 40– y(NH)y的其他计算(y = 2、4、6、8或10)表明,Ta 2 O 5上的NH基团取代了氧原子。 表面可能是氧化物吸附带边缘的红移的原因,但对CBM的向上移位仅贡献很小。
更新日期:2018-01-19
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