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24. Piezofluorochromism in Covalent Organic Frameworks: Pressure‐Induced Emission Enhancement and Blue‐Shifted Emission.

Author

Fang, Jing, Yu, Xihan, Liu, Yaozu, Yusran, Yusran, Wang, Yujie, Valtchev, Valentin, Qiu, Shilun, Zou, Bo, and Fang, Qianrong

Subjects
DIAMOND anvil cell, HYDROSTATIC pressure, FLEXIBLE structures, OPTICAL properties, SMALL molecules
Abstract

Achieving enhanced or blue‐shifted emission from piezochromic materials remains a major challenge. Covalent organic frameworks (COFs) are promising candidates for the development of piezochromic materials owing to their dynamic structures and adjustable optical properties, where the emission behaviors are not solely determined by the functional groups, but are also greatly influenced by the specific geometric arrangement. Nevertheless, this area remains relatively understudied. In this study, a successful synthesis of a series of bicarbazole‐based COFs with varying topologies, dimensions, and linkages was conducted, followed by an investigation of their structural and emission properties under hydrostatic pressure generated by a diamond anvil cell. Consequently, these COFs exhibited distinct piezochromic behaviors, particularly a remarkable pressure‐induced emission enhancement (PIEE) phenomenon with a 16‐fold increase in fluorescence intensity from three‐dimensional COFs, surpassing the performance of CPMs and most organic small molecules with PIEE behavior. On the contrary, three two‐dimensional COFs with flexible structures exhibited rare blue‐shifted emission, whereas the variants with rigid and conjugated structures showed common red‐shifted and reduced emission. Mechanism research further revealed that these different piezochromic behaviors were primarily determined by interlayer distance and interaction. This study represents the first systematic exploration of the structures and emission properties of COFs through pressure‐treated engineering and provides a new perspective on the design of piezochromic materials. [ABSTRACT FROM AUTHOR]

Published
2024
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25. Structural Modulation of Covalent Organic Frameworks for Efficient Hydrogen Peroxide Electrocatalysis.

Author

Wang, Rui, Zhang, Ziqi, Zhou, Haiping, Yu, Mingrui, Liao, Li, Wang, Yan, Wan, Sheng, Lu, Haiyan, Xing, Wei, Valtchev, Valentin, Qiu, Shilun, and Fang, Qianrong

Subjects
HYDROGEN peroxide, ELECTROCATALYSIS, OXYGEN reduction, HYDROGEN production, ARCHITECTURAL design, STRUCTURAL engineering
Abstract

The electrochemical production of hydrogen peroxide (H2O2) using metal‐free catalysts has emerged as a viable and sustainable alternative to the conventional anthraquinone process. However, the precise architectural design of these electrocatalysts poses a significant challenge, requiring intricate structural engineering to optimize electron transfer during the oxygen reduction reaction (ORR). Herein, we introduce a novel design of covalent organic frameworks (COFs) that effectively shift the ORR from a four‐electron to a more advantageous two‐electron pathway. Notably, the JUC‐660 COF, with strategically charge‐modified benzyl moieties, achieved a continuous high H2O2 yield of over 1200 mmol g−1 h−1 for an impressive duration of over 85 hours in a flow cell setting, marking it as one of the most efficient metal‐free and non‐pyrolyzed H2O2 electrocatalysts reported to date. Theoretical computations alongside in situ infrared spectroscopy indicate that JUC‐660 markedly diminishes the adsorption of the OOH* intermediate, thereby steering the ORR towards the desired pathway. Furthermore, the versatility of JUC‐660 was demonstrated through its application in the electro‐Fenton reaction, where it efficiently and rapidly removed aqueous contaminants. This work delineates a pioneering approach to altering the ORR pathway, ultimately paving the way for the development of highly effective metal‐free H2O2 electrocatalysts. [ABSTRACT FROM AUTHOR]

Published
2024
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27. Recent Advances in Hydrodeoxygenation of Lignin‐Derived Phenolics over Metal‐Zeolite Bifunctional Catalysts.

Author

He, Ping, Li, Lin, Shao, Yuanchao, Yi, Qisong, Liu, Zhifeng, Geng, Huawei, Liu, Yuanshuai, and Valtchev, Valentin

Subjects
ALTERNATIVE fuels, CATALYST poisoning, PHENOLS, CATALYSTS, THERMAL stability, ZEOLITES
Abstract

The hydrodeoxygenation (HDO) reaction provides a promising catalytic strategy to remove oxygen in biomass‐derived bio‐oil to produce renewable transportation fuels and value‐added chemicals. The development of highly efficient and stable HDO catalysts plays an essential role in biomass valorization. Metal‐zeolite bifunctional catalysts have been well‐developed as the effective HDO catalysts in upgrading lignin‐derived phenolics due to their excellent activity, selectivity, and thermal and hydrothermal stability. However, clarifying the roles of the active sites and their synergistic effect, and establishing effective structure‐performance relationships in the HDO process still face challenges. In this review, we first survey the conventional catalysts applied in the HDO of bio‐oil, followed by thoroughly discussing the roles of metal centers, acid sites, supports, and their impacts on the HDO process of phenolic model compounds or bio‐oil. Finally, a discussion on the stability and deactivation of metal‐zeolite catalysts, especially in the aqueous‐phase HDO reaction, is provided. This critical review offers new insights into the development of state‐of‐the‐art metal‐zeolite bifunctional catalysts with well‐defined porosity and metal‐acid properties for viable biomass valorization. [ABSTRACT FROM AUTHOR]

Published
2024
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