Changes in the solid-state properties of bismuth iron oxide during the photocatalytic reformation of formic acid
Changes in the solid-state properties of bismuth iron oxide during the photocatalytic reformation of formic acid
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DOI：
10.1016/j.cattod.2018.09.003
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发表时间：
2019-04
期刊：
影响因子：
5.3
通讯作者：
W. Ramadan;R. Dillert;J. Koch;C. Tegenkamp;D. Bahnemann
中科院分区：
文献类型：
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作者：
W. Ramadan;R. Dillert;J. Koch;C. Tegenkamp;D. Bahnemann
采用溶胶凝胶法合成了 BiFeO3 纳米颗粒，并首次报道了其对甲酸重整的光催化能力，重点研究了在 ~ pH 3 下光催化反应后 BiFeO3 的稳定性。发现在无 O2 的水悬浮液中甲酸重整会导致 CO2 和 H2 气体的释放。然而，预期的 1:1 摩尔比并未出现。检测到的氢气量明显低于预期。 BiFeO3 导带的位置远低于质子形成分子 H2 的还原电位，因此预计光生电子主要与反应器中存在的其他物质（可能是光催化剂本身）发生反应。为了评估光催化剂发生的变化，使用不同的技术进行光催化反应前后的本体和表面分析。 XRD 揭示了光催化剂主体发生的变化，例如大部分杂质相的浸出，同时应变晶格松弛至理想位置。从XPS中发现，与甲酸光催化反应之前和之后Fe3+与Fe2+的比例分别为86:14和64:36，从而表明导带中的光生电子无法将H+还原成H2，从而对Fe3+进行了还原过程。反应后记录了 Fe 和较小程度的 Bi 离子浸出到溶液中的情况。根据拟合的 XPS，计算出光催化反应前后 BFO 的标称成分为 Bi1Fe0.9O2.9 和 Bi1Fe0.71O2.7。这项工作中提出的结果表明解决铁基光催化剂的体积和表面稳定性以确保长期可用性的重要性。
BiFeO3nanoparticles were synthesized using a sol gel method and its photocatalytic ability for formic acid reformation is reported, for the first time, focusing on the BiFeO3stability after photocatalytic reaction at ∼ pH 3. Reformation of formic acid in O2-free aqueous suspensions was found to result in the evolution of CO2and H2gases. However, the expected molar ratio of 1:1 was not evolved. Significantly lower amounts of H2than expected were detected. The position of the conduction band of BiFeO3resides well below the reduction potential of the protons to form molecular H2, hence it is anticipated that the photoexcited electrons react mainly with other species being present in the reactor, probably the photocatalyst itself. To assess the changes occurring in the photocatalyst, bulk and surface analysis before and after the photocatalytic reaction were performed using different techniques. XRD revealed changes occurring in the bulk of the photocatalyst such as leaching of most of the impurity phases accompanied by the relaxation of the strained lattice to its ideal position. From XPS, the ratio between Fe3+: Fe2+before and after photocatalytic reaction with formic acid was found to be 86:14 and 64:36, respectively, thus evincing a reduction process of Fe3+by the photo generated electrons in the conduction band that were unable to reduce H+into H2. Leaching of Fe and, to less extent, Bi ions into the solution after reaction was recorded. From the fitted XPS, the nominal composition of BFO was calculated to be Bi1Fe0.9O2.9and Bi1Fe0.71O2.7before and after the photocatalytic reaction. The results presented in this work signify the importance of addressing bulk and surface stability of iron-based photocatalysts to ensure long-term usability.