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Scholarly Works (6 results)

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UC Berkeley Electronic Theses and Dissertations (2022)

This dissertation details several projects that focus on the development of advanced materials and technologies capable of achieving precise molecular separations. This work is based on a materials class of exceptionally microporous and tunable polymers known as porous aromatic frameworks, which are also often referred to as porous polymer networks and porous organic frameworks. These frameworks were designed and tailored to feature pore properties and chemical functionalities that lead to the selective capture of various targeted solutes from water. The synthesized frameworks were also placed into versatile polymer membranes that achieve multifunctional water treatment separations or generalizable gas separations. Specifically, applications are demonstrated for selective desalination, target solute capture (Hg2+, Cu2+, Fe3+, B(OH)3, Cr(VI), As(V), Ag(I), Au(III), Os(IV), Pd(II), Pt(II), or Ru(III)), and gas separations (CO2, O2, H2, He, N2, CH4, C2H4, C2H6). Investigations to characterize the synthesized materials and their separation mechanisms are also covered.

Chapter 1 begins by first introducing pertinent water-related issues encountered around the world, along with explanations for why various ion separations in water treatment are technologically challenging. This chapter then presents a brief overview of top technological approaches currently used to achieve selective ion separations. These technologies include desalination membranes, extraction processes, adsorbents, and ion-exchangers. Descriptions of the separation mechanisms and materials employed in these technologies are additionally mentioned. This chapter concludes by introducing porous aromatic frameworks and their use as promising next-generation materials for these separations.

Chapter 2 describes one-step approaches to accomplish selective solute capture during the desalination of various complex water sources (e.g., groundwater, brackish water, industrial wastewater). The first and major approach described in this chapter, which uses adsorptive membranes placed in electrodialysis configurations, is referred to as “ion-capture electrodialysis.” These coupled desalination and solute extraction methods utilize robust composite membranes that consist of adsorbent materials embedded into polymer matrices. We show that the solute selectivity of the desalination membranes can be easily tuned according to the choice of adsorbent filler. The unique material properties of the model membranes demonstrated in this process, consisting of composite cation-exchange membranes incorporated with porous aromatic frameworks, are additionally characterized.

Chapter 3 highlights a method for selectively removing toxic chromium and arsenic oxyanions from water, using aminopolyol-functionalized porous aromatic framework adsorbents. Notably, adsorption tests reveal that the synthesized materials exhibit record-high kinetic uptake rates and can be regenerated and reused with negligible performance loss over at least 10 adsorption-desorption cycles. Through an assortment of additional adsorption investigations, spectroscopic measurements, and modeling efforts, the binding mechanisms that allow for these selective capture performances are also characterized.

Chapter 4 presents techniques to selectively recover high-value metals from aqueous mixtures, using sulfur-rich porous aromatic framework adsorbents. Polymer frameworks functionalized with different sulfur-based moieties were synthesized, tested for separation performances, and systematically characterized. Methods are shown for the selective separation of gold, osmium, palladium, platinum, ruthenium, and silver from other common waterborne competing ions and transition metals. Furthermore, we demonstrate that the chemistries of our polymer adsorbents can be exploited to create a unique separation treatment train capable of isolating each individual precious metal from mixtures containing each of the six precious metals. Finally, processes are established to regenerate and reuse the sorbents and harvest the captured metals.

Chapter 5 builds upon the separation fundamentals developed in Chapter 2 and chemical insights uncovered in Chapter 4, by creating membrane-based extraction approaches to recover precious metals with exceptional selectivity using cation- and anion-capture electrodialysis. Composite anion-exchange membranes incorporated with selective porous aromatic framework adsorbents were fabricated and characterized; their unique material properties are reported in this chapter. By exploiting speciation effects (e.g., using solutions with high Cl– concentrations to form PtCl42– anions), we show that our membrane separation approach may improve metal recovery selectivities even beyond those accessible with bulk adsorption separations.

Chapter 6 expands upon the material fundamentals elucidated in the previous chapters. Here, porous aromatic framework-based membranes are applied to other climate-related separations: gas separations. In this chapter, the ultra-high porosities of porous aromatic frameworks are used to incorporate high-diffusivity gas transport channels into membranes. We demonstrate that this effect leads to greatly improved gas permeabilities yet retained selectivities for various industrially relevant gas separations. Specifically, composite gas separation membranes were synthesized using high-performance polymers incorporated with porous aromatic frameworks, with the gas selectivity tuned by the choice of polymer used. Finally, we also show that porous aromatic frameworks act as a promising filler material due to their high dispersibility in various casting solvent types, arising from solvent nanoconfinement effects.

    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2021)
    Technologies that can efficiently purify nontraditional water sources are needed to meet rising global demand for clean water. Water treatment plants typically require a series of costly separation units to achieve desalination and the removal of toxic trace contaminants such as heavy metals and boron. We report a series of robust, selective, and tunable adsorptive membranes that feature porous aromatic framework nanoparticles embedded within ion exchange polymers and demonstrate their use in an efficient, one-step separation strategy termed ion-capture electrodialysis. This process uses electrodialysis configurations with adsorptive membranes to simultaneously desalinate complex water sources and capture diverse target solutes with negligible capture of competing ions. Our methods are applicable to the development of efficient and selective multifunctional separations that use adsorptive membranes.
      Cover page: Ion-capture electrodialysis using multifunctional adsorptive membranes
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2021)
      Fluoroarenes are widely used in medicinal, agricultural, and materials chemistry, and yet their production remains a critical challenge in organic synthesis. Indeed, the nearly identical physical properties of these vital building blocks hinders their purification by traditional methods, such as flash chromatography or distillation. As a result, the Balz-Schiemann reaction is currently employed to prepare fluoroarenes instead of more atom-economical C-H fluorination reactions, which produce inseparable mixtures of regioisomers. Herein, we propose an alternative solution to this problem: the purification of mixtures of fluoroarenes using metal-organic frameworks (MOFs). Specifically, we demonstrate that controlling the interaction of fluoroarenes with adjacent coordinatively unsaturated Mg2+ centers within a MOF enables the separation of fluoroarene mixtures with unparalleled selectivities. Liquid-phase multicomponent equilibrium adsorption data and breakthrough measurements coupled with van der Waals-corrected density functional theory calculations reveal that the materials Mg2(dobdc) (dobdc4- = 2,5-dioxidobenzene-1,4-dicarboxylate) and Mg2(m-dobdc) (m-dobdc4- = 2,4-dioxidobenzene-1,5-dicarboxylate) are capable of separating the difluorobenzene isomers from one another. Additionally, these frameworks facilitate the separations of fluoroanisoles, fluorotoluenes, and fluorochlorobenzenes. In addition to enabling currently unfeasible separations for the production of fluoroarenes, our results suggest that carefully controlling the interaction of isomers with not one but two strong binding sites within a MOF provides a general strategy for achieving challenging liquid-phase separations.
        Cover page: Fluoroarene Separations in Metal–Organic Frameworks with Two Proximal Mg2+ Coordination Sites
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2024)
        Chromium and arsenic are two of the most problematic water pollutants due to their high toxicity and prevalence in various water streams. While adsorption and ion-exchange processes have been applied for the efficient removal of numerous toxic contaminants, including heavy metals, from water, these technologies display relatively low overall performances and stabilities for the remediation of chromium and arsenic oxyanions. This work presents the use of polyol-functionalized porous aromatic framework (PAF) adsorbent materials that use chelation, ion-exchange, redox activity, and hydrogen-bonding interactions for the highly selective capture of chromium and arsenic from water. The chromium and arsenic binding mechanisms within these materials are probed using an array of characterization techniques, including X-ray absorption and X-ray photoelectron spectroscopies. Adsorption studies reveal that the functionalized porous aromatic frameworks (PAFs) achieve selective, near-instantaneous (reaching equilibrium capacity within 10 s), and high-capacity (2.5 mmol/g) binding performances owing to their targeted chemistries, high porosities, and high functional group loadings. Cycling tests further demonstrate that the top-performing PAF material can be recycled using mild acid and base washes without any measurable performance loss over at least ten adsorption-desorption cycles. Finally, we establish chemical design principles enabling the selective removal of chromium, arsenic, and boron from water. To achieve this, we show that PAFs appended with analogous binding groups exhibit differences in adsorption behavior, revealing the importance of binding group length and chemical identity.
          Cover page: Removal of Chromium and Arsenic from Water Using Polyol-Functionalized Porous Aromatic FrameworksCreative Commons 'BY-NC-ND' version 4.0 license
          • Article
          • Peer Reviewed
          LBL Publications (2023)
          Diamine-appended Mg2(dobpdc) (dobpdc4- = 4,4-dioxidobiphenyl-3,3-dicarboxylate) metal-organic frameworks have emerged as promising candidates for carbon capture owing to their exceptional CO2 selectivities, high separation capacities, and step-shaped adsorption profiles, which arise from a unique cooperative adsorption mechanism resulting in the formation of ammonium carbamate chains. Materials appended with primary,secondary-diamines featuring bulky substituents, in particular, exhibit excellent stabilities and CO2 adsorption properties. However, these frameworks display double-step adsorption behavior arising from steric repulsion between ammonium carbamates, which ultimately results in increased regeneration energies. Herein, we report frameworks of the type diamine-Mg2(olz) (olz4- = (E)-5,5-(diazene-1,2-diyl)bis(2-oxidobenzoate)) that feature diverse diamines with bulky substituents and display desirable single-step CO2 adsorption across a wide range of pressures and temperatures. Analysis of CO2 adsorption data reveals that the basicity of the pore-dwelling amine─in addition to its steric bulk─is an important factor influencing adsorption step pressure; furthermore, the amine steric bulk is found to be inversely correlated with the degree of cooperativity in CO2 uptake. One material, ee-2-Mg2(olz) (ee-2 = N,N-diethylethylenediamine), adsorbs >90% of the CO2 from a simulated coal flue stream and exhibits exceptional thermal and oxidative stability over the course of extensive adsorption/desorption cycling, placing it among top-performing adsorbents to date for CO2 capture from a coal flue gas. Spectroscopic characterization and van der Waals-corrected density functional theory calculations indicate that diamine-Mg2(olz) materials capture CO2 via the formation of ammonium carbamate chains. These results point more broadly to the opportunity for fundamentally advancing materials in this class through judicious design.
            Cover page: Cooperative Carbon Dioxide Capture in Diamine-Appended Magnesium-Olsalazine Frameworks.Creative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2019)
            Iron is one of the most abundant elements in the environment and in the human body. As an essential nutrient, iron homeostasis is tightly regulated, and iron dysregulation is implicated in numerous pathologies, including neuro-degenerative diseases, atherosclerosis, and diabetes. Endogenous iron pool concentrations are directly linked to iron ion uptake from environmental sources such as drinking water, providing motivation for developing new technologies for assessing iron(ii) and iron(iii) levels in water. However, conventional methods for measuring aqueous iron pools remain laborious and costly and often require sophisticated equipment and/or additional processing steps to remove the iron ions from the original environmental source. We now report a simplified and accurate chemical platform for capturing and quantifying the iron present in aqueous samples through use of a post-synthetically modified porous aromatic framework (PAF). The ether/thioether-functionalized network polymer, PAF-1-ET, exhibits high selectivity for the uptake of iron(ii) and iron(iii) over other physiologically and environmentally relevant metal ions. Mössbauer spectroscopy, XANES, and EXAFS measurements provide evidence to support iron(iii) coordination to oxygen-based ligands within the material. The polymer is further successfully employed to adsorb and remove iron ions from groundwater, including field sources in West Bengal, India. Combined with an 8-hydroxyquinoline colorimetric indicator, PAF-1-ET enables the simple and direct determination of the iron(ii) and iron(iii) ion concentrations in these samples, providing a starting point for the design and use of molecularly-functionalized porous materials for potential dual detection and remediation applications.
              Cover page: Iron detection and remediation with a functionalized porous polymer applied to environmental water samples
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