Browsing by Author "Khalil, Safiya"

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    Enabling Solution Processable COFs through Suppression of Precipitation during Solvothermal Synthesis
    (American Chemical Society, 2022) Khalil, Safiya; Meyer, Matthew D.; Alazmi, Abdullah; Samani, Mohammad H. K.; Huang, Po-Chun; Barnes, Morgan; Marciel, Amanda B.; Verduzco, Rafael; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    Covalent organic frameworks (COFs) are crystalline, nanoporous materials of interest for various applications, but current COF synthetic routes lead to insoluble aggregates which precludes processing for practical implementation. Here, we report a COF synthesis method that produces a stable, homogeneous suspension of crystalline COF nanoparticles that enables the preparation of COF monoliths, membranes, and films using conventional solution-processing techniques. Our approach involves the use of a polar solvent, diacid catalyst, and slow reagent mixing procedure at elevated temperatures which altogether enable access to crystalline COF nanoparticle suspension that does not aggregate or precipitate when kept at elevated temperatures. On cooling, the suspension undergoes a thermoreversible gelation transition to produce crystalline and highly porous COF materials. We further show that the modified synthesis approach is compatible with various COF chemistries, including both large- and small-pore imine COFs, hydrazone-linked COFs, and COFs with rhombic and hexagonal topologies, and in each case, we demonstrate that the final product has excellent crystallinity and porosity. The final materials contain both micro- and macropores, and the total porosity can be tuned through variation of sample annealing. Dynamic light scattering measurements reveal the presence of COF nanoparticles that grow with time at room temperature, transitioning from a homogeneous suspension to a gel. Finally, we prepare imine COF membranes and measure their rejection of polyethylene glycol (PEG) polymers and oligomers, and these measurements exhibit size-dependent rejection and adsorption of PEG solutes. This work demonstrates a versatile processing strategy to create crystalline and porous COF materials using solution-processing techniques and will greatly advance the development of COFs for various applications.
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    Rapid, Ambient Temperature Synthesis of Imine Covalent Organic Frameworks Catalyzed by Transition-Metal Nitrates
    (American Chemical Society, 2021) Zhu, Dongyang; Zhang, Zhuqing; Alemany, Lawrence B.; Li, Yilin; Nnorom, Njideka; Barnes, Morgan; Khalil, Safiya; Rahman, Muhammad M.; Ajayan, Pulickel M.; Verduzco, Rafael
    Covalent organic frameworks (COFs) are crystalline, porous organic materials that are promising for applications including catalysis, energy storage, electronics, gas storage, water treatment, and drug delivery. Conventional solvothermal synthesis approaches require elevated temperatures, inert environments, and long reaction times. Herein, we show that transition-metal nitrates can catalyze the rapid synthesis of imine COFs under ambient conditions. We first tested a series of transition metals for the synthesis of a model COF and found that all transition-metal nitrates tested produced crystalline COF products even in the presence of oxygen. Fe(NO3)3·9H2O was found to produce the most crystalline product, and crystalline COFs could be produced within 10 min by optimizing the catalyst loading. Fe(NO3)3·9H2O was further tested as a catalyst for six different COF targets varying in linker lengths, substituents, and stabilities, and it effectively catalyzed the synthesis of all imine COFs tested. This catalyst was also successful in the synthesis of 2D imine COFs with different geometries, 3D COFs, and azine-linked COFs. This work demonstrates a simple, low-cost approach for the synthesis of imine COFs and will significantly lower the barrier for the development of imine COFs for applications.
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    Transformation of One-Dimensional Linear Polymers into Two-Dimensional Covalent Organic Frameworks Through Sequential Reversible and Irreversible Chemistries
    (American Chemical Society, 2021) Zhu, Dongyang; Li, Xiaoyi; Li, Yilin; Barnes, Morgan; Tseng, Chia-Ping; Khalil, Safiya; Rahman, Muhammad M.; Ajayan, Pulickel M.; Verduzco, Rafael
    Covalent organic frameworks (COFs) are crystalline porous materials linked by dynamic covalent bonds. Dynamic chemistries enable the transformation of an initially amorphous network into a porous and crystalline COF. While dynamic chemistries have been leveraged to realize transformations between different types of COFs, including transformations from two-dimensional (2D) to three-dimensional (3D) COFs and insertion of different linking groups, the transformation of linear polymers into COFs has not yet been reported. Herein, we demonstrate an approach to transform linear imine-linked polymers into ketone-linked COFs through a linker replacement strategy with triformylphloroglucinol (TPG). TPG first reacts through dynamic chemistry to replace linkers in the linear polymers and then undergoes irreversible tautomerism to produce ketone linkages. We have analyzed the time-dependent transformation from the linear polymer into COF through powder X-ray diffraction, Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) to understand the transition and substitution mechanisms. This work demonstrates another route to produce COFs through sequential reversible and irreversible chemistries and provides a potential approach to synthesizing COFs through the solution processing of linear polymers followed by transformation into the desired COF structure.
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    Transforming Covalent Organic Framework Synthesis for Advanced Applications: From Solution Processing to High- Throughput Production in Flow Reactors
    (2023-08-10) Khalil, Safiya; Verduzco, Rafael
    Water and energy are essential for sustaining life on earth. As the population grows and living standards improve, the demand for clean water and energy continues to rise simultaneously. In this regard, fossil-fuel consumption, CO2 emissions and byproduct formation will continue to grow in these industries. Integrating advanced nanomaterials in the water and energy sectors emerges as a pivotal strategy for satisfying global water and energy demands in a secure, affordable, and sustainable manner. In light of the foregoing, My PhD is centered on a newly emerging class of nanomaterials known as covalent organic frameworks (COFs). Owing to their porosity, crystallinity, modularity and tunability, COFs have emerged as attractive candidates for various applications including membrane-based separations, photocatalysis and ion transport. However, their wide-scale implementation is hindered by complications related to their synthesis, upscaling, and processing, which also impedes their commercialization and industrialization. In my thesis, I discuss my attempts to tackle the synthetic, scalability and processability challenges of COFs to accelerate their commercialization and facilitate their employment in the water and energy sectors to help us meet escalating demands securely, affordably, and sustainably.