Browsing by Author "Yan, Qianqian"

Now showing 1 - 4 of 4
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    Metal Oxide Catalysts for the Synthesis of Covalent Organic Frameworks and One-Step Preparation of Covalent Organic Framework-Based Composites
    (American Chemical Society, 2021) Zhu, Yifan; Zhu, Dongyang; Yan, Qianqian; Gao, Guanhui; Xu, Jianan; Liu, Yifeng; Alahakoon, Sampath B.; Rahman, Muhammad M.; Ajayan, Pulickel M.; Egap, Eilaf; Verduzco, Rafael; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    The integration of covalent organic frameworks (COFs) with inorganic materials provides opportunities to develop a new class of composite materials with high surface areas and novel functionalities relevant to photocatalysis, chemical adsorption, and magnetic resonance imaging. However, current methods for the preparation of COF-based composites require challenging, multistep synthetic protocols. Herein, we report a one-pot synthesis approach using a wide range of metal oxides to catalyze the synthesis of highly crystalline and porous COFs. We found that a large variety of metal oxides served as effective catalysts for the synthesis of imine COFs, including niobium(V) oxide (Nb2O5), nickel(II) oxide (NiO), manganese(IV) dioxide (MnO2), ruthenium(IV) oxide (RuO2), zinc(II) oxide (ZnO), lead(II) oxide (PbO), tellurium(IV) dioxide (TeO2), tin(IV) oxide (SnO2), manganese(III) oxide (Mn2O3), zirconium(IV) dioxide (ZrO2), and aluminum(III) oxide (Al2O3). Nb2O5 was effective for the synthesis of a wide range of COFs with different functional groups and pore sizes, and these reactions produced a metal oxide/COF composite. By using Fe3O4 nanoparticles (NPs) as the catalyst, we produced COF-based nanocomposites with Fe3O4 NPs distributed throughout the final COF product. The Fe3O4/COF nanocomposite had a high surface area of 2196 m2 g–1. This work demonstrates a class of novel, low-cost catalysts for synthesizing COFs and a new approach to produce metal oxide/COF composite materials.
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    Porphyrin-based donor–acceptor COFs as efficient and reusable photocatalysts for PET-RAFT polymerization under broad spectrum excitation
    (Royal Society of Chemistry, 2021) Zhu, Yifan; Zhu, Dongyang; Chen, Yu; Yan, Qianqian; Liu, Chun-Yen; Ling, Kexin; Liu, Yifeng; Lee, Dongjoo; Wu, Xiaowei; Senftle, Thomas P.; Verduzco, Rafael
    Covalent organic frameworks (COFs) are crystalline and porous organic materials attractive for photocatalysis applications due to their structural versatility and tunable optical and electronic properties. The use of photocatalysts (PCs) for polymerizations enables the preparation of well-defined polymeric materials under mild reaction conditions. Herein, we report two porphyrin-based donor–acceptor COFs that are effective heterogeneous PCs for photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT). Using density functional theory (DFT) calculations, we designed porphyrin COFs with strong donor–acceptor characteristics and delocalized conduction bands. The COFs were effective PCs for PET-RAFT, successfully polymerizing a variety of monomers in both organic and aqueous media using visible light (λmax from 460 to 635 nm) to produce polymers with tunable molecular weights (MWs), low molecular weight dispersity, and good chain-end fidelity. The heterogeneous COF PCs could also be reused for PET-RAFT polymerization at least 5 times without losing photocatalytic performance. This work demonstrates porphyrin-based COFs that are effective catalysts for photo-RDRP and establishes design principles for the development of highly active COF PCs for a variety of applications.
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    Three-dimensional covalent organic frameworks with pto and mhq-z topologies based on Tri- and tetratopic linkers
    (Springer Nature, 2023) Zhu, Dongyang; Zhu, Yifan; Chen, Yu; Yan, Qianqian; Wu, Han; Liu, Chun-Yen; Wang, Xu; Alemany, Lawrence B.; Gao, Guanhui; Senftle, Thomas P.; Peng, Yongwu; Wu, Xiaowei; Verduzco, Rafael
    Three-dimensional (3D) covalent organic frameworks (COFs) possess higher surface areas, more abundant pore channels, and lower density compared to their two-dimensional counterparts which makes the development of 3D COFs interesting from a fundamental and practical point of view. However, the construction of highly crystalline 3D COF remains challenging. At the same time, the choice of topologies in 3D COFs is limited by the crystallization problem, the lack of availability of suitable building blocks with appropriate reactivity and symmetries, and the difficulties in crystalline structure determination. Herein, we report two highly crystalline 3D COFs with pto and mhq-z topologies designed by rationally selecting rectangular-planar and trigonal-planar building blocks with appropriate conformational strains. The pto 3D COFs show a large pore size of 46 Å with an extremely low calculated density. The mhq-z net topology is solely constructed from totally face-enclosed organic polyhedra displaying a precise uniform micropore size of 1.0 nm. The 3D COFs show a high CO2 adsorption capacity at room temperature and can potentially serve as promising carbon capture adsorbents. This work expands the choice of accessible 3D COF topologies, enriching the structural versatility of COFs.
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    Understanding fragility and engineering activation stability in two-dimensional covalent organic frameworks
    (Royal Society of Chemistry, 2022) Zhu, Dongyang; Zhang, Jun-Jie; Wu, Xiaowei; Yan, Qianqian; Liu, Fangxin; Zhu, Yifan; Gao, Xiaodong; Rahman, Muhammad M.; Yakobson, Boris I.; Ajayan, Pulickel M.; Verduzco, Rafael
    The sensitivity of covalent organic frameworks (COFs) to pore collapse during activation processes is generally termed activation stability, and activation stability is important for achieving and maintaining COF crystallinity and porosity which are relevant to a variety of applications. However, current understanding of COF stability during activation is insufficient, and prior studies have focused primarily on thermal stability or on the activation stability of other porous materials, such as metal–organic frameworks (MOFs). In this work, we demonstrate and implement a versatile experimental approach to quantify activation stability of COFs and use this to establish a number of relationships between their pore size, the type of pore substituents, pore architecture, and structural robustness. Additionally, density functional theory calculations reveal the impact on both inter-and intra-layer interactions, which govern activation stability, and we demonstrate that activation stability can be systematically tuned using a multivariate synthesis approach involving mixtures of functionalized and unfunctionalized COF building blocks. Our findings provide novel fundamental insights into the activation stability of COFs and offer guidance for the design of more robust COFs.