Browsing by Author "Wu, Xiaowei"

Now showing 1 - 7 of 7
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    3D Covalent Organic Frameworks with Interpenetrated pcb Topology Based on 8-Connected Cubic Nodes
    (American Chemical Society, 2022) Shan, Zhen; Wu, Miaomiao; Zhu, Dongyang; Wu, Xiaowei; Zhang, Kan; Verduzco, Rafael; Zhang, Gen
    The connectivity of building units for 3D covalent organic frameworks (COFs) has long been primarily 4 and 6, which have severely curtailed the structural diversity of 3D COFs. Here we demonstrate the successful design and synthesis of a porphyrin based, 8-connected building block with cubic configuration, which could be further reticulated into an unprecedented interpenetrated pcb topology by imine condensation with linear amine monomers. This study presents the first case of high-connectivity building units bearing 8-connected cubic nodes, thus greatly enriching the topological possibilities of 3D COFs.
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    Branching processes with biological applications
    (2010) Wu, Xiaowei; Kimmel, Marek
    Branching processes play an important role in models of genetics, molecular biology, microbiology, ecology and evolutionary theory. This thesis explores three aspects of branching processes with biological applications. The first part of the thesis focuses on fluctuation analysis, with the main purpose to estimate mutation rates in microbial populations. We propose a novel estimator of mutation rates, and apply it to a number of Luria-Delbruck type fluctuation experiments in Saccharomyces cerevisiae. Second, we study the extinction of Markov branching processes, and derived theorems for the path to extinction in the critical case, as an extension to Jagers' theory. The third part of the thesis introduces infinite-allele Markov branching processes. As an important non-trivial example, the limiting frequency spectrum for the birth-death process has been derived. Potential application of modeling the proliferation and mutation of human Alu sequences is also discussed.
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    Functional wood for carbon dioxide capture
    (Cell Press, 2023) Roy, Soumyabrata; Philip, Firuz Alam; Oliveira, Eliezer Fernando; Singh, Gurwinder; Joseph, Stalin; Yadav, Ram Manohar; Adumbumkulath, Aparna; Hassan, Sakib; Khater, Ali; Wu, Xiaowei; Bollini, Praveen; Vinu, Ajayan; Shimizu, George; Ajayan, Pulickel M.; Kibria, Md Golam; Rahman, Muhammad M.
    With increasing global climate change, integrated concepts to innovate sustainable structures that can multiaxially address CO2 mitigation are crucial. Here, we fabricate a functional wood structure with enhanced mechanical performance via a top-down approach incorporating a high-performance metal-organic framework (MOF), Calgary framework 20 (CALF-20). The functional wood with 10% (w/w) CALF-20 can capture CO2 with an overall gravimetric capacity of 0.45 mmol/g at 1 bar and 303 K that scales linearly with the MOF loading. Interestingly, the functional wood surpasses the calculated normalized adsorption capacity of CALF-20 stemming from the mesoporous wood framework, pore geometry modulation in CALF-20, and favorable CO2 uptake interactions. Density functional theory (DFT) calculations elucidate strong interactions between CALF-20 and the cellulose backbone and an understanding of how such interactions can favorably modulate the pore geometry and CO2 physisorption energies. Thus, our work opens an avenue for developing sustainable composites that can be utilized in CO2 capture and structural applications.
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    Modeling neutral evolution using an in nite-allele Markov branching process
    (Hindawi, 2013) Wu, Xiaowei; Kimmel, Marek; Bioengineering; Statistics
    We consider an in nite-allele Markov branching process (IAMBP). Our main focus is the frequency spectrum of this process, i.e., the proportion of alleles having a given number of copies at a speci ed time point. We derive the variance of the frequency spectrum, which is useful for interval estimation and hypothesis testing for process parameters. In addition, for a class of special IAMBP with birth and death o spring distribution, we show that the mean of its limiting frequency spectrum has an explicit form in terms of the hypergeometric function. We also derive an asymptotic expression for convergence rate to the limit. Simulations are used to illustrate the results for the birth and death process.
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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.