Kinetics and Mechanisms of ZnO to ZIF‐8 Transformations in Supercritical CO<sub>2</sub>Revealed by In Situ X‐ray Diffraction

Sinnwell, Michael A.; Miller, Quin R. S.; Liu, Lili; Tao, Jinhui; Bowden, Mark E.; Kovařík, Libor; Barpaga, Dushyant; Han, Yi; Motkuri, Radha Kishan; Sushko, Maria L.; Schaef, Herbert T.; Thallapally, Praveen K.

doi:10.1002/cssc.202000434

Cited by 12 publications

(13 citation statements)

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“…As an alternative to conventional solvents, SCFs have been widely used in a range of industrial and laboratory processes . It is noticed, however, that to date, SCFs have not been utilized as platform for MOF membrane synthesis, although they hold great promise for the sustainable production because of the following unique properties: (1) near-zero surface tension, low viscosity, and high diffusivity, which facilitate fast diffusion of reagents in nanoscale intercrystalline defects and easy defect patching through further crystal growth in SCF environments, and (2) controllable phase transition and variable solubility. Since simply altering the operating temperature and pressure in the vicinity of critical points enables facile transition of fluids between supercritical and gaseous states, after the completion of membrane preparation in SCF environments, phase segregation between gaseous fluids and solid solute occurs spontaneously upon evacuation of the reaction chamber so that both SCFs and unreacted reagents can be easily recovered and reutilized, thereby making it possible to realize zero pollutant discharge.…”

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confidence: 99%

Beyond Solution-Based Protocols: MOF Membrane Synthesis in Supercritical Environments for an Elegant Sustainability Performance Balance

Liu

Song

et al. 2020

ACS Materials Lett.

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Supercritical fluids (SCFs) represent materials at temperatures and pressures above their critical points where distinct liquid and gas phases do not exist. SCFs possess several unique properties rendering them excellently adapted for the reaction medium of MOF membranes (like ZIF-8) which, although offering an energyefficient and eco-friendly option for large-scale industrial separation, are still experiencing a dilemma between process sustainability and performance superiority. In this study we addressed this issue through a facile SCF synthetic protocol employing supercritical CO 2 (scCO 2 ) as the reaction medium. Relying on the near-zero surface tension, low viscosity, and high diffusivity of scCO 2 , nanoscale intercrystalline defects could be effectively patched, resulting in the formation of well-intergrown ZIF-8 membranes with commercially attractive olefin/paraffin (C 3 H 6 / C 3 H 8 ) separation performance. Moreover, after the SCF processing, both discharged CO 2 and unreacted ligands could be conveniently recovered and reutilized, resulting in zero pollutant discharge due to the controllable phase transition, variable solubility, and chemical inertness of scCO 2 . This work sheds lights on the promising prospects of SCF processing for sustainable fabrication of high-performing MOF membranes.

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confidence: 99%

Beyond Solution-Based Protocols: MOF Membrane Synthesis in Supercritical Environments for an Elegant Sustainability Performance Balance

Liu

Song

et al. 2020

ACS Materials Lett.

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“…By simple mathematic operation, it transforms into where α is the crystallinity, k is the crystallization rate constant, t is the reaction time, and n is the Avrami exponent. This model is ideal for transformations with sigmoidal reaction profiles and has been successfully applied to solvothermal and hydrothermal reactions at a solid/fluid interface, including the formation of MOFs. − …”

Section: Results and Discussionmentioning

confidence: 99%

“…Second, analysis of the dimensionless Avrami exponent ( n ) can yield mechanistic information. Generally, trends in n as a function of temperature, time, and reaction condition can provide the overall mechanistic insights. , In the analysis of reported n values of 1.28 ± 0.18 for Mg-MOF-74 film formation, a pathway involving a surface reaction-limited process is the most likely since it has been proposed that the values of n are ∼4, ∼1, and <1, which correspond to the homogeneous nucleation of spherical particles, a surface reaction-limited process, and a diffusion-controlled process, respectively. − …”

Section: Results and Discussionmentioning

confidence: 99%

Synthesis of High-Quality Mg-MOF-74 Thin Films via Vapor-Assisted Crystallization

Kim

Culp

Ohodnicki

et al. 2021

ACS Appl. Mater. Interfaces

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The unique features of metal–organic frameworks (MOFs), such as their large surface areas and diversity of structures, make them suitable for a broad range of applications including storage, separation, and sensing of gases. Among all the MOFs, Mg-MOF-74 with the highest CO2 uptake at 1 bar and 25 °C would be particularly beneficial for CO2-related applications. One of the most critical enabling technologies for implementing Mg-MOF-74 is the preparation of dense and continuous films that would maximize the sorption behaviors. However, Mg-MOF-74 thin films present significant challenges in demonstrating large-scale coatings. Herein, we demonstrate for the first time high-quality Mg-MOF-74 films synthesized via a vapor-assisted crystallization (VAC) process. The VAC process described herein provides dense and highly crystalline layers of the Mg-MOF-74 thin film with a low coefficient of variation of film thickness below 7%. By minimizing the solvent use, the VAC process is also more environmentally friendly than conventional techniques. In this work, we first optimized a precursor solution for the VAC process and then investigated the effects of synthesis temperature, time, and droplet volume on the growth, crystallinity, and thickness of VAC Mg-MOF-74 films. The porosity of the MOF film was assessed by measuring the CO2 uptake at room temperature and 1 bar. The obtained VAC Mg-MOF-74 films possess a well-defined microporosity, as deduced from CO2 adsorption studies via quartz crystal microbalance (QCM) and comparison with bulk Mg-MOF-74 reference data. Furthermore, CO2 cyclic adsorption–desorption experiments on the VAC Mg-MOF-74 films showed scaled uptakes to a wide range of CO2 concentration without showing significant variations in the baseline. We specifically demonstrate how the film’s quality of the MOF affects adsorption behavior of CO2 on VAC Mg-MOF-74 and drop-cast Mg-MOF-74 films.

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“…Therefore, researchers capitalized on the in-situ XRD capacities and revealed correlations of the rate of ZIF-8 formation with the surface area of the templating ZnO source. Then, they analysed the kinetics thereof and showed the effect of small changes to isobaric temperature on the variables crucial in the reaction pathway [63].…”

Section: Supercritical Co 2 Synthesis Methodsmentioning

confidence: 99%

Green Synthesis of Zeolitic Imidazolate Frameworks: A Review of Their Characterization and Industrial and Medical Applications

et al. 2022

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Metal organic frameworks (MOF) are a class of hybrid networks of supramolecular solid materials comprising a large number of inorganic and organic linkers, all bound to metal ions in a well-organized fashion. Zeolitic imidazolate frameworks (ZIFs) are a sub-group of MOFs with imidazole as an organic linker to metals; it is rich in carbon, nitrogen, and transition metals. ZIFs combine the classical zeolite characteristics of thermal and chemical stability with pore-size tunability and the rich topological diversity of MOFs. Due to the energy crisis and the existence of organic solvents that lead to environmental hazards, considerable research efforts have been devoted to devising clean and sustainable synthesis routes for ZIFs to reduce the environmental impact of their preparation. Green chemistry is the key to sustainable development, as it will lead to new solutions to existing problems. Moreover, it will present opportunities for new processes and products and, at its heart, is scientific and technological innovation. The green chemistry approach seeks to redesign the materials that make up the basis of our society and our economy, including the materials that generate, store, and transport our energy, in ways that are benign for humans and the environment and that possess intrinsic sustainability. This study covers the principles of green chemistry as used in designing strategies for synthesizing greener, less toxic ZIFs the consume less energy to produce. First, the necessity of green methods in today’s society, their replacement of the usual non-green methods and their benefits are discussed; then, various methods for the green synthesis of ZIF compounds, such as hydrothermally, ionothermally, and by the electrospray technique, are considered. These methods use the least harmful and toxic substances, especially concerning organic solvents, and are also more economical. When a compound is synthesized by a green method, a question arises as to whether these compounds can replace the same compounds as synthesized by non-green methods. For example, is the thermal stability of these compounds (which is one of the most important features of ZIFs) preserved? Therefore, after studying the methods of identifying these compounds, in the last part, there is an in-depth discussion on the various applications of these green-synthesized compounds.

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Kinetics and Mechanisms of ZnO to ZIF‐8 Transformations in Supercritical CO₂Revealed by In Situ X‐ray Diffraction

Cited by 12 publications

References 74 publications

Beyond Solution-Based Protocols: MOF Membrane Synthesis in Supercritical Environments for an Elegant Sustainability Performance Balance

Beyond Solution-Based Protocols: MOF Membrane Synthesis in Supercritical Environments for an Elegant Sustainability Performance Balance

Synthesis of High-Quality Mg-MOF-74 Thin Films via Vapor-Assisted Crystallization

Green Synthesis of Zeolitic Imidazolate Frameworks: A Review of Their Characterization and Industrial and Medical Applications

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Kinetics and Mechanisms of ZnO to ZIF‐8 Transformations in Supercritical CO2Revealed by In Situ X‐ray Diffraction

Cited by 12 publications

References 74 publications

Beyond Solution-Based Protocols: MOF Membrane Synthesis in Supercritical Environments for an Elegant Sustainability Performance Balance

Beyond Solution-Based Protocols: MOF Membrane Synthesis in Supercritical Environments for an Elegant Sustainability Performance Balance

Synthesis of High-Quality Mg-MOF-74 Thin Films via Vapor-Assisted Crystallization

Green Synthesis of Zeolitic Imidazolate Frameworks: A Review of Their Characterization and Industrial and Medical Applications

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Kinetics and Mechanisms of ZnO to ZIF‐8 Transformations in Supercritical CO₂Revealed by In Situ X‐ray Diffraction