While heterogeneous photocatalysis is regarded as a sustainable strategy to achieve organic reactions for the production of high-value-added organics, photocatalytic efficiency is generally limited by poor charge separation, dull surface catalytic activity and the consequently caused insufficient generation of active species. Herein, the hybrid structures of metal–organic frameworks (MOFs) incorporated with Pd ultrasmall nanocrystals are synthesized, and their photocatalytic performance is evaluated by the oxidative coupling of benzylamine as a model reaction. The photocatalytic activity of the Pd/MIL-125-NH₂ hybrid material with an optimal Pd loading is greatly superior to that of the pristine MIL-125-NH₂, achieving a high benzylamine conversion rate of 3136 μmol h⁻¹ g_cat⁻¹ at 94.08% conversion. The enhanced charge transfer and separation in Pd/MIL-125-NH₂ are verified by photoluminescence spectroscopy and photoelectrochemical experiments. Photogenerated reactive oxygen species are probed by 3,3′,5,5′-tetramethylbenzidine (TMB) as an indicator and the reactive intermediates in the photocatalytic systems are identified by in situ ESR detection. The results confirm that the optimized Pd/MIL-125-NH₂ hybrid catalyst possesses higher ability for molecule activation and that both superoxide radical (˙O₂⁻) and singlet oxygen (¹O₂) are the dominant oxidative species in the present photocatalytic system. Therefore, the dual advantages of Pd/MIL-125-NH₂ hybrid structures for promoting the photogenerated charge transfer/separation and providing highly catalytic sites for molecule activation contribute to higher photocatalytic activity.

中文翻译：

---

Pd / MIL-125-NH2杂化结构促进选择性氧化反应的电荷分离和分子活化

尽管非均相光催化被认为是实现有机反应以生产高附加值有机物的可持续策略，但光催化效率通常受电荷分离差，表面催化活性钝以及由此导致的活性物种生成不足的限制。在此，合成了掺入钯超小纳米晶体的金属有机骨架（MOF）的杂化结构，并通过苄胺的氧化偶联作为模型反应来评估其光催化性能。具有最佳Pd负载的Pd / MIL-125-NH ₂杂化材料的光催化活性大大优于原始MIL-125-NH ₂的光催化活性，实现了3136μmolh ^-1的高苄基胺转化率。g _cat ^-1，转化率为94.08％。通过光致发光光谱和光电化学实验证实了Pd / MIL-125-NH ₂中增强的电荷转移和分离。通过3,3'，5,5'-四甲基联苯胺（TMB）探测光生的活性氧物质，并通过原位ESR检测鉴定光催化体系中的活性中间体。结果证实，在优化的Pd / MIL-125-NH ₂混合催化剂具有用于分子活化，并且两个超氧自由基（O能力较高的₂ ^- ）和单线态氧（¹ Ò ₂）是目前光催化系统中的主要氧化物种。因此，Pd / MIL-125-NH ₂杂化结构在促进光生电荷转移/分离以及为分子活化提供高度催化位点方面的双重优势有助于提高光催化活性。