Selective photocatalytic conversion of alcohol to aldehydes by singlet oxygen over Bi-based metal-organic frameworks under UV–vis light irradiation

• Published in: Applied catalysis. B, Environmental Vol. 254; pp. 463 - 470
• Main Authors: Zhang, Ruoqian, Liu, Yuanyuan, Wang, Zeyan, Wang, Peng, Zheng, Zhaoke, Qin, Xiaoyan, Zhang, Xiaoyang, Dai, Ying, Whangbo, Myung-Hwan, Huang, Baibiao
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05.10.2019; Elsevier BV
• Subjects: Alcohol; Alcohols; Aldehydes; Atomic energy levels; Benzaldehyde; Benzyl alcohol; Bi-based MOFs; Bismuth; Carboxylates; Emission; Energy transfer; Excitons; Fluorescence; Heavy metals; Holes (electron deficiencies); Irradiation; Ligands; Light irradiation; Materials selection; Metal-organic frameworks; Oxidation; Oxygen; Phosphorescence; Photocatalysis; Photooxidation; Selective oxidation; Singlet oxygen; TATB; Triazine; Triazine pesticides; Triplet state; Ultraviolet radiation; Selective oxidation; Bi-based MOFs; Excitons; Singlet oxygen; Photocatalysis
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2019.05.024

[Display omitted] The presence of Bi3+ in Bi-MOFs promotes the singlet → triplet intersystem crossing of the organic ligand due to the heavy metal effect, which in turn induces the 3O2 → 1O2 conversion and results in high selective oxidation of alcohol to aldehydes. [Display omitted] •1O2 was proved to be the dominant reactive oxygen species over Bi-based MOFs.•The reason for the singlet oxygen production is attributed to the presence of Bi.•The coordination with Bi promotes the singlet → triplet intersystem crossing of the ligand. So far, most efforts in photocatalysis have been devoted to the separation of photogenerated electron-hole pairs, and possible use of excitons (i.e., electron-hole pairs) for photocatalytic processes has not received much attention. In this work, we studied the effect of metal dots on the excitonic behaviors of two bismuth-based MOFs, Bi-TATB and Bi-BTC (here the tridentate ligands TATB3− and BTC3− represent the carboxylates of 4,4′,4′'-s-triazine-2,4,6-triyl-tribenzoic and 1,3,5-benzenetricarboxylic acids, respectively). The organic ligands (TATB and BTC) display different emission properties from the corresponding Bi based MOFs. Specifically, TATB and BTC display strong fluorescence emission while Bi-TATB and Bi-BTC display strong phosphorescence emission, suggesting the higher efficiency of intersystem crossing for Bi-TATB and Bi-BTC. The reason is attributed to the coordination with Bi, which promotes the singlet→ triplet intersystem crossing of the organic ligand due to the heavy metal effect. The enhanced triplet excited emission of Bi-TATB and Bi-BTC was further confirmed by the detection of 1O2, as 1O2 is well known to be formed due to energy transfer from the triplet state of photosensitizers to the ground-state oxygen (3O2). With above understanding, Bi-TATB and Bi-BTC were finally used to high selective photooxidation of benzyl alcohol to benzaldehyde. This work presents new understanding of the photophysical properties of Bi based MOFs, which provides alternative ideas on designing materials for selective photo-oxidation.