[Water-Stable HKUST-1] Methyl-Shield Cu-BTC with High Water Stability

Home > News > [Water-Stable HKUST-1] Methyl-Shield Cu-BTC with High Water Stability

Abstract:
This articl presents a novel approach to enhancing the water stability of the metal-organic framework (MOF) Cu-BTC by incorporating isopropanol (IPA) during its synthesis. The resulting material, Cu-BTC-IPA, retains high Brunauer-Emmett-Teller (BET) surface areas and gas adsorption capacities even after prolonged exposure to water, making it a promising candidate for practical applications in gas storage and separation.

Research Background:
1.Industry Problem: Metal-organic frameworks (MOFs) are highly promising materials for applications in gas storage and separation due to their high surface areas and tunable pore structures. However, many MOFs, including Cu-BTC, suffer from poor water stability, which significantly limits their practical applications.
2.Existing Solutions: Previous strategies to enhance the water stability of MOFs include coating the surface with hydrophobic materials, introducing hydrophobic functional groups into the framework, strengthening coordination bonds, and generating framework interpenetration. These methods often involve complex synthesis processes or secondary treatments.
3.Innovative Approach: The authors propose a one-step synthesis method to incorporate isopropanol (IPA) into Cu-BTC, creating a hydrophobic microenvironment around the unsaturated Cu sites. This method is simpler and more scalable compared to previous approaches, and it effectively enhances the water stability of Cu-BTC.

Experimental Section:
1.Material Synthesis:
   -Cu-BTC-IPA Synthesis: Cu(NO₃)₂·3H₂O and 1,3,5-benzenetricarboxylic acid (H₃BTC) were dissolved in deionized water and ethanol, respectively. IPA was added to the mixture, and the solution was heated at 120°C for 12 hours. The resulting blue crystals were washed with ethanol and dried at 150°C.
   -Comparison Sample: Cu-BTC was synthesized similarly but without IPA.
2.Characterization:
   -X-ray Diffraction (XRD): Patterns were obtained using a Bruker D8 ADVANCE X-ray diffractometer.
   -N₂ Adsorption-Desorption: Measurements were performed using a Micromeritics ASAP 2020 instrument.
   -Scanning Electron Microscopy (SEM): Images were captured using a Hitachi S-4800 microscope.
   -Fourier Transform Infrared Spectroscopy (FT-IR): Spectra were measured using a Bruker TENSOR II FT-IR spectrometer.
   -X-ray Photoelectron Spectroscopy (XPS): Spectra were obtained using a Thermo Fisher K-Alpha instrument.
   -Proton Nuclear Magnetic Resonance (¹H NMR): Spectra were recorded using a Bruker ADVANCE III HD 400 MHz spectrometer.
   -Thermogravimetry (TG): Experiments were conducted on a TA-SDT Q600 instrument.
3.Gas Adsorption Measurements:
   - CO₂, N₂, and CH₄ adsorption capacities were measured using a Micromeretics ASAP 2020 instrument at room temperature.

Analysis and Testing:
1.XRD Analysis:
   - The XRD patterns of Cu-BTC and Cu-BTC-IPA3 showed well-defined diffraction lines consistent with the simulated Cu-BTC patterns, indicating successful synthesis.
   - After immersion in water for 4 days, Cu-BTC-IPA3 retained its crystalline structure, while Cu-BTC decomposed.
2.N₂ Adsorption-Desorption:
   - Cu-BTC exhibited a BET surface area of 1529 m²/g, while Cu-BTC-IPA3 had a BET surface area of 1365 m²/g.
   - After 4 days in water, Cu-BTC-IPA3 retained 95% of its initial BET surface area.
3.SEM Imaging:
   - SEM images showed that Cu-BTC-IPA particles had a similar morphology to Cu-BTC but with slightly smaller crystal sizes.
4.FT-IR and ¹H NMR Spectroscopy:
   - FT-IR spectra confirmed the presence of IPA in Cu-BTC-IPA3 through a new absorption peak at 1411 cm⁻¹.
   - ¹H NMR spectra showed new resonances at 4.4 and 1.1 ppm, confirming the presence of IPA molecules.
5.XPS Analysis:
   - XPS spectra indicated the formation of new Cu−OIPA bonds in Cu-BTC-IPA3.
6.Thermogravimetry (TG):
   - TG analysis showed no significant improvement in thermal stability for Cu-BTC-IPA3 compared to Cu-BTC.
7.Gas Adsorption Properties:
   - Cu-BTC-IPA3 retained high CO₂, N₂, and CH₄ adsorption capacities even after 4 days in water, demonstrating its stability and potential for practical applications.

Summary:
The study demonstrates a one-step synthesis method for enhancing the water stability of Cu-BTC by incorporating IPA. The resulting Cu-BTC-IPA3 retains high BET surface areas and gas adsorption capacities even after prolonged exposure to water. The enhanced stability is attributed to the hydrophobic microenvironment created by the methyl groups of IPA, which shields the Cu sites from water molecules. This method is simpler and more scalable than previous approaches, making it a promising strategy for improving the stability of other MOFs.

Methyl-Shield Cu-BTC with High Water Stability through One-Step Synthesis and In Situ Functionalization
Authors: Shanshan Xu, Xiangyu Guo, Zhihua Qiao, Hongliang Huang, Chongli Zhong
DOI: 10.1021/acs.iecr.0c02156
Link: https://pubs.acs.org/doi/10.1021/acs.iecr.0c02156

The above review is for academic progress sharing. For any errors or copyright issues, please contact us for correction or removal.