Browsing by Author "Ling, Kexin"

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    Exploring the Photophysical Properties of UiO-67 MOF Doped with Rhenium Carbonyl Complexes
    (Elsevier, 2022) Ling, Kexin; Ogle, Meredith M.; Flores, Erick; Godoy, Fernando; Martí, Angel A.
    Directly coordinating transition metal catalysts to the linkers of stable metal organic frameworks (MOFs) is a sleek solution to increasing the longevity of the catalyst. Photoluminescence metal complexes incorporated in MOFs have risen in interest lately. Particularly, Re(bpydc)(CO)3Cl (bpydc = 2,2’-bipyridine-5,5’-dicarboxylic acid) doped zirconium-based MOFs (Re-UiO-67) and their use in the photocatalytic reduction of CO2 have attracted considerable attention. Nonetheless, the photophysical characteristics of Re-UiO-67 as a function of loading have not been well explored. Here we analyzed the structural and compositional properties of Re-UiO-67 and showed that the photoluminescence properties of rhenium doped MOFs, including emission intensity, maximum, and lifetime, can be tuned by changing the rhenium loading. The photoluminescence of the film made of Re-UiO-67 exposed to different vapors also exhibited vapoluminescence, luminescence vapochromism, and vapotemporism. Understanding of photophysical properties of the Re-doped MOFs material could provide guidance for further photocatalytic, solar energy conversion and sensing applications.
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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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    Synthesis, Modifications, and Applications of Porous Nanostructures
    (2022-11-22) Ling, Kexin; Martí, Angel A
    Porous materials, with their high surface areas, controllable structures, and tunable pore sizes, comprise an interdisciplinary research field in focus today, and one that is developing rapidly. Various porous materials have been adopted for different applications, including adsorption, separation, catalysis, energy conservation, sensing, and drug delivery. Thus, there is an ever-increasing demand for synthesizing porous materials with desired structures and compositions to meet specific requirements. In this thesis, three distinct porous materials will be covered: iron oxide/carbon composite, rhenium carbonyl complex incorporated UiO-67 MOFs, and fluorinated boron nitride nanotubes. Chapter 1 generally summarized the fundamentals about synthetic methods and structural properties of porous materials. The development of the three materials covered in this thesis will also be introduced in detail. Activated carbon is one of the most ever studied porous materials. Its composites with metal oxides show potential for desulfurization. In Chapter 2, we explored the synergic effects in composites of iron oxide (Fe2O3) and oxygenated porous carbon (OPC) for the removal of H2S at room temperature. Two types of Fe2O3-OPC composite samples were prepared: physically mixed (PM) and chemically mixed (CM). The two types of composites were tested for H2S uptake performance at ambient conditions, and a systematic study of the synergic effects of Fe2O3 and OPC was performed. Thorough characterization and analysis were used to reveal detailed structural and compositional properties of these samples. The CM sample with the best uptake capacity was also tested further for the desulfurization rate and the mechanism of action. The PM samples showed a lower H2S uptake capacity within 24 h compared to the theoretical value for the Fe2O3 and OPC working independently, indicating a negative synergic effect. The CM samples reached a maximum uptake capacity higher than the components working independently and importantly an increased rate of H2S uptake, which indicates positive synergy, showing potential in applications where rapid adsorption is required. Directly coordinating transition metal catalysts to the linkers of stable metal organic frameworks (MOFs) is a sleek solution to increasing the longevity of the catalyst. In Chapter 3, Re(bpydc)(CO)3Cl (bpydc = 2,2’-bipyridine-5,5’-dicarboxylic acid) doped zirconium-based MOFs (Re-UiO-67) were synthesized. The photophysical characteristics of Re-UiO-67 as a function of loading were explored. We analyzed the structural and compositional properties of Re-UiO67 and showed that the photoluminescence properties of rhenium doped MOFs, including emission intensity, maximum, and lifetime, can be tuned by changing the rhenium loading. The photoluminescence of the film made of Re-UiO-67 exposed to different vapors also exhibited vapoluminescence, luminescence vapochromism, and vapotemporism. Understanding of photophysical properties of the Re-doped MOFs material could provide guidance for further photocatalytic, solar energy conversion and sensing applications. In Chapter 4, we developed a covalent fluorine functionalization protocol using hydrofluoric acid at room temperature and reached up to 3.7 wt% of fluorine content on the BNNTs. Using spectroscopic methods and thermal analysis, we verified that fluorine was chemically bonded to boron site. Further nucleophilic BNNTs substitution reactions were performed using alkyl alcohol, providing insights into subsequently tuning surface properties of BNNTs from the fluorinated precursor. In addition, we showed that tuning the hydrophobicity of the surface functional groups leads to dispersibility differentiation in different solvents. This sequential chemical functionalization protocol brings a chance to improve the compatibility of BNNTs towards developing composite materials.