skip to main content

Attention:

The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Friday, December 13 until 2:00 AM ET on Saturday, December 14 due to maintenance. We apologize for the inconvenience.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Implications of Defect Density and Polymer Interactions for CO 2 Capture on Amine‐Functionalized MIL‐101(Cr)
Abstract

Rising anthropogenic carbon emissions have dire environmental consequences, necessitating remediative approaches, which includes use of solid sorbents. Here, aminopolymers (poly(ethylene imine) (PEI) and poly(propylene imine) (PPI)) are supported within solid mesoporous MIL‐101(Cr) to examine effects of support defect density on aminopolymer‐MOF interactions for CO2uptake and stability during uptake‐regeneration cycles. Using simulated flue gas (10 % CO2in He), MIL‐101(Cr)‐ρhigh(higher defect density) shows 33 % higher uptake capacity per gram adsorbent than MIL‐101(Cr)‐ρlow(lower defect density) at 308 K, consistent with increased availability of undercoordinated Cr adsorption sites at missing linker defects. Increasing aminopolymer weight loadings (10–50 wt.%) within MIL‐101(Cr)‐ρlowand MIL‐101(Cr)‐ρhighincreases amine efficiencies and CO2uptake capacities relative to bare MOFs, though both incur CO2diffusion limitations through confined, viscous polymer phases at higher (40–50 wt.%) loadings. Benchmarked against SBA‐15, lower polymer packing densities (PPI>PEI), weaker and less abundant van der Waals interactions between aminopolymers and pore walls, and open framework topology increase amine efficiencies. Interactions between amines and Cr defect sites incur amine efficiency losses but grant higher thermal and oxidative stability during uptake‐regeneration cycling. Finally, >25 % higher CO2uptake capacities are achieved for aminopolymer/MIL‐101(Cr)‐ρhighunder humid conditions, demonstrating promise for realistic applications.

  more » « less
PAR ID:
10507635
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
ChemSusChem
ISSN:
1864-5631
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ( , ACS Applied Polymer Materials)
    null (Ed.)
    Energy-efficient adsorptive CO2 capture requires both adsorbent materials with high CO2 capacity and structured adsorption contactors possessing fast mass transfer kinetics and low pressure drop. The state-of-the-art research primarily focuses on “hard” adsorbents such as mesoporous zeolites and metal–organic frameworks, which exhibit high CO2 capacities but are challenging to translate into structured contactors. Polymer of intrinsic microporosity 1 (PIM-1), a solution-processable microporous polymer, is a “softer” alternative that can be easily fabricated into structured adsorption contactors. In prior research, PIM-1 has been utilized as a “molecular basket” for poly(ethylene imine) (PEI). Despite nanoscale amine dispersion and excellent processability, PEI/PIM-1 composites possess an unstable micropore structure, which collapses at high PEI loadings (∼30%) and results in lower CO2 adsorption capacity than PEI-loaded hard oxides. Here, we applied a post-fabrication polymer stabilization method, vapor phase infiltration (VPI), to improve the CO2 capacity of the PEI/PIM-1 composite without sacrificing its processibility. PIM-1 is fabricated into structured adsorption contactors and then reinforced with amorphous aluminum oxyhydroxide (AlOx) nanostrands via VPI. The resulting AlOx/PIM-1 is a stable, hierarchically porous support, which can be loaded with 40% PEI without pore collapse. Owing to the combination of processibility, comparable CO2 capacity, and high amine efficiency, PEI/AlOx/PIM-1 composites are a promising alternative to PEI-loaded mesoporous oxides. 
    more » « less
  2. ; ( , Catalysis Science & Technology)
    Isostructural Cr and Fe nanoporous MIL-101, synthesized without mineralizing agents, are investigated for styrene oxidation utilizing aqueous hydrogen peroxide to yield valuable oxygenates for chemical synthesis applications. Styrene conversion rates and oxygenate product distributions both depend on metal identity, as MIL-101(Fe) is more reactive for total styrene oxidation and is more pathway selective, preferring aldehyde (benzaldehyde) formation at the α-carbon to the aromatic ring, where MIL-101(Cr) sustains epoxide (styrene oxide) production at the same α-carbon. These pathways often involve hydrogen peroxide derived radical intermediates (O, –HOO˙, –HO − ˙) and metallocycle transition states. We postulate that the higher reactivity of one of these surface intermediates, Fe( iv )O relative to Cr( iv )O, leads to higher styrene oxidation rates for MIL-101(Fe), while higher electrophilicity of Cr( iii )–OOH intermediates translates to the higher styrene oxide selectivity observed for MIL-101(Cr). Secondary styrene oxide and benzaldehyde conversions are observed over both analogs, but the former is more prevalent over MIL-101(Fe) due to higher Lewis/Brønsted acid site density and strength compared to MIL-101(Cr). Recyclability experiments combined with characterization via XRD, SEM/EDXS, and FT-IR and UV-vis spectroscopies show that the nature of MIL-101(Fe) sites does not change significantly with each cycle, whereas MIL-101(Cr) suffers from metal leaching, which impacts styrene conversion rates and product distribution. Both catalysts require active site regeneration, though MIL-101(Fe) sites are more susceptible to reactivation, even under mild conditions. Finally, examination of styrene conversion for three unique synthesized phases of MIL-101(Cr) rationalizes that nodal defects are largely responsible for observed reactivity and selectivity but predispose the framework to metal leaching as a predominant deactivation mechanism. 
    more » « less
  3. ; ; ; ; ( , Catalysis Science & Technology)
    Precious metals have been shown to play a vital role in the selective hydrogenation of α,β-unsaturated aldehydes, but still suffer from challenges to control selectivity. Herein, we have advanced the design of catalysts made out of Pt–Co intermetallic nanoparticles (IMNs) supported on a MIL-101(Cr) MOF (3%Pt y %Co/MIL-101(Cr)), prepared by using a polyol reduction method, as an effective approach to enhance selectivity toward the production of α,β-unsaturated alcohol, the desired product. XRD, N 2 adsorption–desorption, FTIR spectroscopy, SEM, TEM, XPS, CO adsorption, NH 3 -TPD, XANES and EXAFS measurements were used to investigate the structure and surface properties of our 3%Pt y %Co/MIL-101(Cr) catalysts. It was found that the Co-modified 3%Pt y %Co/MIL-101(Cr) catalysts can indeed improve the hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL), reaching a higher selectivity under mild conditions than the monometallic Pt/MIL-101(Cr) catalysts: 95% conversion of CAL with 91% selectivity to COL can be reached with 3%Pt3%Co/MIL-101(Cr). Additionally, high conversion of furfural (97%) along with high selectivity to furfural alcohol (94%) was also attained with the 3%Pt3%Co/MIL-101(Cr) catalyst. The enhanced activity and selectivity toward the unsaturated alcohols are attributed to the electronic and geometric effects derived from the partial charge transfer between Co and Pt through the formation of uniformly dispersed Pt–Co IMNs. Moreover, various characterization results revealed that the addition of Co to the IMPs can promote the Lewis acid sites that facilitate the polarization of the charge-rich CO bonds and their adsorption via their oxygen atom, and also generate new interfacial acid sites. 
    more » « less
  4. ; ; ; ; ( , Environmental Science: Water Research & Technology)
    Toxic oxyanions of Cr(VI) can be potentially removed by adsorbents with positively charged surfaces. In this study, we synthesized a stable and insoluble amine-rich polymer composite (CS–PEI–GLA) by crosslinking polyethyleneimine (PEI), a soluble amine-rich synthetic polymer, and chitosan (CS) with glutaraldehyde (GLA). The positively charged amine groups were the main adsorption sites. The batch investigation demonstrated that the adsorbent was able to remove ≥90% of chromium at pH ranging from 2 to 8. Due to deprotonation of the amine groups, chromium removal decreased at higher pH values. The adsorption was fast and reached equilibrium after 45 min. The maximum adsorption capacity was 500 mg g−1 according to the Langmuir isotherm and did not decrease in the presence of monovalent anions. In the column study, the adsorption capacity was the highest when the flow rate was the lowest (5 mL min−1), influent concentration was medium (225 mg L−1), and the bed height was the shortest (3.5 cm). NaOH was the best recovery reagent with recovery of 67% in batch and 31% in the column. The CS–PEI–GLA composite was able to remove 97.1 ± 0.1% chromium in batch and treat 750 mL of electroplating wastewater with a 3.5 cm packed-bed column. 
    more » « less
  5. ; ; ; ; ; ; ; ; ( , ChemCatChem)
    Abstract

    Lactic acid is a renewable and versatile chemical for food, pharmaceuticals, cosmetics, and other chemicals. Lactic acid can be produced from biomass‐derived dihydroxyacetone. However, selective and recyclable water‐tolerant acid catalysts need to be developed for the specific production of lactic acid. Here we show that the MIL‐101(Al)−NH2metal‐organic framework (MOF) is a water‐tolerant and selective solid Lewis acid catalyst for dihydroxyacetone isomerization to lactic acid. The Lewis acidic MIL‐101(Al)−NH2catalyst promoted a high lactic acid selectivity of 91 % at 96 % dihydroxyacetone conversion at 120 °C in water. The reaction proceeded by temperature and/or MIL‐101(Al)−NH2MOFs mediated dihydroxyacetone dehydration to pyruvaldehyde. Subsequently, the MIL‐101(Al)−NH2facilitated rehydration of the pyruvaldehyde to lactic acid. The Lewis acidic MIL‐101(Al)−NH2catalyst was stable and reusable four times without any decrease in catalytic performance.

     
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email