Defect Engineering: Tuning the Porosity and Composition of the Metal–Organic Framework UiO-66 via Modulated Synthesis

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Summary:
The authors from the University of Oslo and University of Torino developed a series of UiO-66 metal–organic frameworks with tunable porosity and composition via modulated synthesis using monocarboxylic acid modulators, achieving significant control over defect concentration and surface area.

Background:
1. To address the challenge of tuning porosity and defectivity in UiO-66, previous researchers used modulators such as acetic or trifluoroacetic acid, achieving increased surface area; however, the nature and origin of defects remained unclear.
2. The authors proposed an innovative systematic modulation approach using monocarboxylic acids of varying acidity (pKa) and concentration, revealing that missing cluster defects dominate and can be finely tuned.

Research Content:
1.Synthesis:
   UiO-66 was synthesized via solvothermal reaction of ZrCl₄ and H₂BDC in DMF at 120°C, with monocarboxylic acid modulators (acetic, formic, difluoroacetic, trifluoroacetic) added in varying equivalents (6–100 eq).
2.Characterizations:
   1) BET surface areas ranged from 1175 m²/g (no modulator) to 1777 m²/g (36 eq trifluoroacetic acid);
   2) PXRD showed broad low-angle peaks indicating reo-phase nanodomains (missing cluster defects);
   3) TGA-DSC confirmed modulator incorporation and linker deficiency; dissolution ¹H/¹⁹F NMR quantified modulator/linker ratios.
3.Application:
   The defective UiO-66 variants exhibited enhanced porosity and tunable surface chemistry, suitable for gas storage, catalysis, and adsorption.
4.Mechanism:
   Defect formation is governed by competitive coordination between modulator and linker; higher modulator acidity and concentration increase missing cluster defect density via deprotonated modulator binding.

Outlook:
This work establishes a rational strategy to engineer defects in UiO-66 MOFs, enabling precise control over porosity and functionality, with broad implications for Zr-MOF design and application.

Defect Engineering: Tuning the Porosity and Composition of the Metal–Organic Framework UiO-66 via Modulated Synthesis
Authors: Greig C. Shearer, Sachin Chavan, Silvia Bordiga, Stian Svelle, Unni Olsbye, Karl Petter Lillerud
DOI: 10.1021/acs.chemmater.6b00602
Link: https://pubs.acs.org/doi/10.1021/acs.chemmater.6b00602

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