Defect hydroxides in UiO-66 shuttle protons
Simulations of missing-linker UiO-66 put charge-balancing OH on under-coordinated Zr and show those sites swap between hydroxide and water by rapid proton transfer with extra-framework water.
Source
Dynamic acidity in defective UiO-66
Study at a glance
- Design
- Computational / modelling — PBE0+D3 and AIMD of defective UiO-66 proton transfer and NH3 binding
- N
- Periodic DFT/AIMD study of MOF defects — no sample N
- Population
- Defective UiO-66 zirconium MOF models
- Outcome
- Dynamic Brønsted acidity and proton-transfer barriers at defect sites
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
Authors ran PBE0+D3 static optimisations and AIMD at 100–700 K on defective UiO-66, compared Zr–O distances to diffraction, estimated proton-transfer barriers, and used NH3 binding as a Brønsted-acidity probe.
What they found
Average Zr⋯O = 2.23 Å matches 300 K experiment. Direct O0–O1 proton transfer barrier is only 6.5 kJ mol−1 versus 27.5 for an O3-mediated path. NH3 binds 110.1 vs 75.8 kJ mol−1 at defect vs perfect regions. Water can leave, exposing frustrated Lewis pair-like Zr sites.
The limits
What it doesn't show
The dynamics are computed; they are invisible to time-averaged XRD and are not a measured catalytic turnover of a substrate.
Key terms
- UiO-66
- Zr6-oxo MOF with 12 BDC linkers per cluster in the ideal structure.
- Missing-linker defect
- A removed BDC2− compensated here by bound hydroxide/water.
- AIMD
- Ab initio molecular dynamics following nuclei on a DFT potential.
- μ3-OH
- Hydroxide bridging three Zr atoms on the intact cluster face.
- Frustrated Lewis pair
- Under highly activated conditions, a bare Zr and hydroxide that could cooperate.
Flashcards
Research intelligence for this paper
See its role on concept claims, tensions it is part of, placement history, and related discoveries.
Quiz yourself
Missing BDC2− charge is balanced by:
Common questions
What balances the missing BDC2− charge?
Hydroxide bound to under-coordinated Zr.
How fast is proton transfer at 300 K?
About one double transfer per 15 ps with water at O3.
Direct proton-transfer barrier?
6.5 kJ mol−1 per defect.
NH3 binding at the defect vs bulk?
110.1 vs 75.8 kJ mol−1.
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