Facet-Specific Stability of ZIF -8 in the Presence ... - EFRC · Scientific Achievement . ZIF-8 metal-organic frameworks were examined for stability in the presence of mild acidic
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Scientific Achievement ZIF-8 metal-organic frameworks were examined for stability in the presence of mild acidic conditions. It was found that material stability is controlled by the exposed surface facets. Significance and ImpactThis study represents the first comprehensive investigation of differences between exposed surface facets of a MOF and provides guidelines for synthesizing sulfur resistant ZIFs.
Pang, S. H.; Han, C.; Sholl, D. S.; Jones, C. W.; Lively, R. P. “Facet-Specific Stability of ZIF-8 in the Presence of Acid Gases Dissolved in Aqueous Solutions” Chem. Mater., Accepted (2016). DOI: 10.1021/acs.chemmater.6b02643
(L) Representation of crystallographic planes examined to modeldifferent surface facets of ZIF-8 and (R) microscopy images offacet-specific ZIF-8 crystals before exposure to SO2.
Facet-Specific Stability of ZIF-8 in the Presence of Acid Gases Dissolved in Aqueous Solutions
Research Details– ZIF-8 particles were synthesized to yield either {110} rhombic
dodecahedra (RD) facets or {100} truncated cubes.– Electron microscopy, BET surface area, XPS, FTIR, and
diffusion studies were performed to characterize differences in stability between exposed surface facets after exposure to aqueous SO2 solutions.
– Studies revealed the {110} RD facet was more susceptible to degradation; it is hypothesized that the mechanism for degradation follows a shrinking-core model, with surface imidazolates being replaced by hydroxyls.
– Computational investigations support this degradation mechanism and suggest that the reaction is more favorable on the {110} facet than the {100} facet due to steric constraints.
Particles exposing a single facet can be synthesized using crystal engineering techniques
1 μm 2 μm
J. Cravillon, M. Wiebcke, et al. CrystEngComm 2012Y. Pan, Z. Lai, et al. CrystEngComm 2011
10 μm
(100)
(110)
The surfaces of (100)-terminated cubes appear more stable than the surfaces of (110)-terminated RD
1 μm 1 μm 1 μm
500 nm 500 nm 500 nm
cube
RD
as synthesized 3 days 14 days
Bulk textural properties are not significantly affected, suggesting a shrinking-core model of degradation
10-6 10-5 10-4 10-3 10-2 10-1 100
0
100
200
300
400
500
600
N2 A
dsor
bed
(cm
3 /g S
TP)
P/P°
RD RD, after SO2
cube cube, after SO2
Pre-SO2(m2/g)
Post-SO2(m2/g)
RD 1440 1290Cube 1420 1220
1 μm
500 nm
XPS studies suggest that imidazole is removed from the surface region and is replaced by hydroxyl
980 985 990 995 10000.0
0.1
0.2
0.3
0.4
0.5
Zn(OH)2
Nor
mal
ized
Inte
nsity
(a.u
.)
Kinetic Energy (eV)
RD RD, after SO2
cube cube, after SO2
Zn(OH)2
ZnO
Zn LMM
ZnO
294 292 290 288 286 284 2820.0
0.2
0.4
0.6
0.8
1.0
Nor
mal
ized
Inte
nsity
(a.u
.)
Binding Energy (eV)
RD RD, after SO2
cube cube, after SO2
C1s
542 540 538 536 534 532 530 528 5260.0
0.1
0.2
0.3
0.4
0.5
Nor
mal
ized
Inte
nsity
(a.u
.)
Binding Energy (eV)
ZnO Zn(OH)2
RD RD, after SO2
cube cube, after SO2
O1sZn(OH)2
174 172 170 168 166 164 162 160
0.00
0.05
0.10
0.15
0.20
Nor
mal
ized
Inte
nsity
(a.u
.)Binding Energy (eV)
RD RD, after SO2
cube cube, after SO2
S2p
1 μm
500 nm
N
NH
IR studies confirm formation of hydroxyl and sulfite species, likely on the external surfaces
3800 3600 3400 3200 3000 2800 2600
Abs
orba
nce
(a.u
.)
Wavenumber (cm-1)
RD RD, after SO2
cube cube, after SO2
1400 1200 1000 800 600 400
Abs
orba
nce
(a.u
.)Wavenumber (cm-1)
ν(NH/OH) ν(SO3)
ρ(SO2)
N N ZnZn
H2O N NH
ZnZn
OH2O SO2HN NH
ZnZn
OHH2OH2SO3
OSHO
OH
N N ZnZn
H2O OSOH
O
H H2O
Proposed sulfite-assisted degradation reactions at ZIF-8 surfaces. Imidazole is removed from the framework, and is replaced by surface sulfites or hydroxyls.
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