Department of Molecular Engineering, Graduate School of Engineering , Kyoto University , Kyotodaigaku Katsura, Nishikyo-ku, Kyoto 615-8510 , Japan.
Element Strategy Initiative for Catalysts and Batteries (ESICB) , Kyoto University , 1-30 Goryo-Ohara , Nishikyo-ku, Kyoto 615-8245 , Japan.
ACS Appl Mater Interfaces. 2019 Oct 16;11(41):37875-37884. doi: 10.1021/acsami.9b14671. Epub 2019 Oct 4.
SrKNaTaO, which belongs to the Na-substituted SrKTaO series of compounds with a tetragonal tungsten bronze structure, was fabricated using a flux mixture of KCl and NaCl (KCl/NaCl molar ratio = 55:45). It exhibited higher CO formation rate (94.6 μmol h), better selectivity for CO evolution (85.5%), and better stability of the photocatalytic activity than those of bare SrKTaO and other Na-substituted SrKTaO samples synthesized from flux mixtures with different KCl/NaCl ratios. X-ray photoelectron spectroscopic studies revealed that the surface atomic Sr/Ta ratio of SrKNaTaO was larger than that of SrKTaO. To clarify the factor responsible for the improvement in the photocatalytic activity facilitated by Na substitution, as well as to elucidate the reaction mechanism, the surface species were characterized by in situ Fourier transform infrared spectroscopy. It was observed that the bicarbonate species (HCO) adsorbed on the active Sr sites of SrKNaTaO was reduced to CO via the formate species during photoirradiation. The plot of the CO formation rate vs. the surface atomic Sr/Ta ratio for tetragonal tungsten bronze-type Sr-K-Ta-O complex oxides had the summit, indicating that Sr atoms on the surface enhance the photocatalytic activity, while an excessive amount of Sr on the surface leads to the decrease in the photocatalytic activity. Hence, it can be concluded that while the presence of Sr on the surface has a determining effect on the adsorption of CO and eventually on the photocatalytic activity, excess Sr on the surface that exists as SrCO or SrTaO suppresses the photocatalytic activity. Thus, SrKNaTaO showed higher CO formation rate than SrKTaO did.
SrKNaTaO 属于四方钨青铜结构的 Na 取代 SrKTaO 系列化合物，是通过 KCl 和 NaCl（KCl/NaCl 摩尔比=55:45）的助熔混合物制备的。与裸 SrKTaO 和其他通过不同 KCl/NaCl 比例的助熔混合物合成的 Na 取代 SrKTaO 样品相比，它表现出更高的 CO 生成速率（94.6 μmol h）、更高的 CO 演化选择性（85.5%）和更好的光催化活性稳定性。X 射线光电子能谱研究表明，SrKNaTaO 的表面原子 Sr/Ta 比大于 SrKTaO。为了阐明 Na 取代促进光催化活性提高的因素，并阐明反应机制，通过原位傅里叶变换红外光谱对表面物种进行了表征。观察到，在光照射下，吸附在 SrKNaTaO 活性 Sr 位上的碳酸氢盐物种（HCO）通过甲酸盐物种还原为 CO。在四方钨青铜型 Sr-K-Ta-O 复合氧化物中，CO 生成速率与表面原子 Sr/Ta 比的关系图有一个峰值，表明表面上的 Sr 原子增强了光催化活性，而表面上过多的 Sr 则导致光催化活性降低。因此，可以得出结论，虽然表面上 Sr 的存在对 CO 的吸附并最终对光催化活性有决定性影响，但表面上过量的 Sr 以 SrCO 或 SrTaO 的形式存在会抑制光催化活性。因此，SrKNaTaO 比 SrKTaO 具有更高的 CO 生成速率。
