Structural Control of Uniform MOF-74 Microcrystals for the Study of Adsorption Kinetics

We report a unique naturally derived activated carbon with optimally incorporated nitrogen functional groups and ultra-microporous structure to enable high CO 2 adsorption capacity. The coprocessing of biomass (Citrus aurantium waste leaves) and microalgae (Spirulina) as the N-doping agent was investigated by probing the parameter space (biomass/microalgae weight ratio, reaction temperature, and reaction time) of hydrothermal carbonization and activation process (via the ZnCl 2 /CO 2 activation) to generate hydrochars and activated carbons, respectively, with tunable nitrogen content and pore sizes. The central composite-based design of the experiment was applied to optimize the parameters of the prehydrothermal carbonization procedure resulting in the fabrication of N-enriched carbonaceous products with the highest possible mass yield and nitrogen content. The resulting hydrochars and activated carbon samples were characterized using elemental analysis, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and Brunauer−Emmett−Teller surface area analysis. We observe that while N-doping and the activation process can individually enhance the CO 2 adsorption capacity to some extent, it is the combined effect of the two processes that synergistically work to greatly increase the adsorption capacity of the N-doped activated carbon by an amount which is more than the sum of individual contributions. We analyze the origins of this synergy with both physical and chemical characterization techniques. The resulting naturally derived activated carbon demonstrates one of the highest CO 2 adsorption capacities (8.43 mmol/g) with rapid adsorption kinetics and good selectivity and reusability.

Section: Resultsmentioning

confidence: 94%

Section: Structural and Morphologicalmentioning

confidence: 99%

Synergistic Effect of Nitrogen Doping and Ultra-Microporosity on the Performance of Biomass and Microalgae-Derived Activated Carbons for CO₂ Capture

Balou

Babak

Priye

2020

“…27,28 The MOF-74 series consists of prototypical MOFs fabricated from divalent metal cations, such as Mg(II), Ni(II), Co(II), Fe(II), or Zn(II), and their combination by coordinating them with the organic linker of 2,5-dihydroxy-1,4-benzendicarboxylic acid (H 4 DOBDC) to form tailored nanoparticles with a honeycomb-like structure. 29 The resulting robust lattice comprises hexacoordinated metal oxide backbones within a three-dimensional architecture containing 1D channels. 30 Therefore, Zn-MOF-74, with a unique 1D channel and nanoscale pore size, should be a viable alternative that addresses the problem of restricted aperture size inhibiting larger substrate penetration and the associated mass transfer limitations inside the cross-linked networks due to the fewer degrees of freedom.…”

Section: Introductionmentioning

confidence: 99%

Rapid Fabrication of Biocomposites by Encapsulating Enzymes into Zn-MOF-74 via a Mild Water-Based Approach

Hsu

Chang

Wang

et al. 2021

Self Cite

A zinc-based metal organic framework, Zn-MOF-74, which has a unique one-dimensional (1D) channel and nanoscale aperture size, was rapidly obtained in 10 min using a de novo mild water-based system at room temperature, which is an example of green and sustainable chemistry. First, catalase (CAT) enzyme was encapsulated into Zn-MOF-74 (denoted as CAT@Zn-MOF-74), and comparative assays of biocatalysis, size-selective protection, and framework-confined effects were investigated. Electron microscopy and powder X-ray diffraction were used for characterization, while electrophoresis and confocal microscopy confirmed the immobilization of CAT molecules inside the single hexagonal MOF crystals at loading of ∼15 wt %. Furthermore, the CAT@Zn-MOF-74 hybrid was exposed to a denaturing reagent (urea) and proteolytic conditions (proteinase K) to evaluate its efficacy. The encapsulated CAT maintained its catalytic activity in the decomposition of hydrogen peroxide (H 2 O 2 ), even when exposed to 0.05 M urea and proteinase K, yielding an apparent observed rate constant (k obs ) of 6.0 × 10 −2 and 6.6 × 10 −2 s −1 , respectively. In contrast, free CAT exhibited sharply decreased activity under these conditions. Additionally, the bioactivity of CAT@Zn-MOF-74 for H 2 O 2 decomposition was over three times better than that of the biocomposites based on zeolitic imidazolate framework 90 (ZIF-90) owing to the nanometer-scaled apertures, 1D channel, and less confinement effects in Zn-MOF-74 crystallites. To demonstrate the general applicability of this strategy, another enzyme, α-chymotrypsin (CHT), was also encapsulated in Zn-MOF-74 (denoted as CHT@Zn-MOF-74) for action against a substrate larger than H 2 O 2 . In particular, CHT@Zn-MOF-74 demonstrated a biological function in the hydrolysis of Lphenylalanine p-nitroanilide (HPNA), the activity of ZIF-90-encapsulated CHT was undetectable due to aperture size limitations. Thus, we not only present a rapid eco-friendly approach for Zn-MOF-74 synthesis but also demonstrate the broader feasibility of enzyme encapsulation in MOFs, which may help to meet the increasing demand for their industrial applications.

“…By applying this concept to ZIF-67@ZIF-8 core–shell structures, defined hollow ZIF-8 microcrystals could be obtained. Prof. Tsung further extended this concept to design hollow MOF-74 . Because Mg-MOF-74 is the most acid-labile analog in the MOF-74 family, Mg-MOF-74 can be selectively removed through chemical etching with HCl.…”

Section: Above and Belowmentioning

confidence: 99%

“…Prof. Tsung further extended this concept to design hollow MOF-74. 145 Because Mg-MOF-74 is the most acid-labile analog in the MOF-74 family, Mg-MOF-74 can be selectively removed through chemical etching with HCl. Core−shell MOF-74 structures were prepared through the epitaxial growth of Ni-MOF-74 shells on Mg-MOF-74 cores.…”

Section: Above and Belowmentioning

confidence: 99%

Tailoring Heterogeneous Catalysts at the Atomic Level: In Memoriam, Prof. Chia-Kuang (Frank) Tsung

Williams

Morabito

et al. 2021

Self Cite

Professor Chia-Kuang (Frank) Tsung made his scientific impact primarily through the atomic-level design of nanoscale materials for application in heterogeneous catalysis. He approached this challenge from two directions: above and below the material surface. Below the surface, Prof. Tsung synthesized finely controlled nanoparticles, primarily of noble metals and metal oxides, tailoring their composition and surface structure for efficient catalysis. Above the surface, he was among the first to leverage the tunability and stability of metal–organic frameworks (MOFs) to improve heterogeneous, molecular, and biocatalysts. This article, written by his former students, seeks first to commemorate Prof. Tsung’s scientific accomplishments in three parts: (1) rationally designing nanocrystal surfaces to promote catalytic activity; (2) encapsulating nanocrystals in MOFs to improve catalyst selectivity; and (3) tuning the host–guest interaction between MOFs and guest molecules to inhibit catalyst degradation. The subsequent discussion focuses on building on the foundation laid by Prof. Tsung and on his considerable influence on his former group members and collaborators, both inside and outside of the lab.