In Situ Measurement of CO2 and H2O Adsorption by
ZIF-8 Films
Fangyuan Tian, Amber M. Mosier, Aileen Park, Elizabeth R. Webster, Andrew M. Cerro, Ryan
S. Shine and Lauren Benz*
Department of Chemistry & Biochemistry, University of San Diego, San Diego, CA 92110, USA
Corresponding Author
* E-mail: [email protected]
Supporting Information
Temperature programmed desorption (TPD)
First-order desorption kinetics were assumed for CO2 desorption from pore sites (α1 peak), and
the Redhead method1 was used to calculate the activation energy of desorption:
𝐸𝑎 ⁄𝑅𝑇𝑃 = ln(𝜈𝑇𝑃 /𝛽) − 3.64
(Eq S1)
Ea – activation energy of desorption
R – molar gas constant
TP – peak temperature when the rate is maximum and its first derivative is zero (also known as
maximum desorption temperature), 116 K was observed for 4-cycle sample and 114 K was
observed for 2-cycle sample.
ν – pre-exponential factor, assumed to be 1013 here as is typical for small molecules with firstorder desorption. For 108< ν<1014 the relation between Ea and TP is given to an error within
1.5%.
β – heating rate, 2 K/s
The reported error on the activation energy comes predominantly from error propagation of the
peak max (± 3 K).
TPD studies of CO2 and H2O on a TiO2(110) surface
Figure S1. TPD spectra of (a) CO2 and (b) water desorption from a TiO2(110) surface, the black
spectra indicate the CO2 and water monolayers formed on a TiO2(110) surface.
TPD studies of CO2 desorption from a ZIF-8 thin film at elevated adsorption temperature
Figure S2. TPD spectra of CO2 desorption from a 2-cycle ZIF-8 sample at different temperatures
after dosing the same large amount of CO2 (900 Langmuir).
TPD studies of CO2 desorption from a ZIF-8 thin film
Figure S3. TPD spectra of CO2 desorption from a 2-cycle ZIF-8 film after exposure to the same
amount of CO2 with and without a 60 min wait time.
Control TPD studies of water and CO2 on a gold surface.
Figure S4. TPD spectra of water desorption from (a) a gold surface and (b) a 2-cycle ZIF-8/Au
sample. (c) An example of exposure of 15 L CO2 to both surfaces: the large TPD peak area
difference indicates that the ZIF-8 thin film captures significantly more CO2 than the gold
surface.
Time-dependent TPD studies of CO2 at low uptake
Figure S5. TPD spectra of CO2 (only α1 can be observed) desorption from a 2-cycle ZIF-8 film
with and without a 45 min waiting time (post-exposure, pre-desorption).
Quartz crystal microbalance (QCM):
CO2 uptake amounts for both 2-cycle and 4-cycle samples were calculated based on TPD and
QCM results (shown in Table S1 and Figure 4). The amount of CO2 molecules adsorbed by the
ZIF-8 film was determined from the TPD peak area (compared with CO2 adsorption on a TiO2
(110) surface: 5.2x1014 CO2 molecules corresponding to a single molecular layer on a 1 x 1 cm2
TiO2 (110) surface).2 The ZIF-8 film mass was calculated from frequency changes measured by
QCM using the Sauerbrey model.
Table S1. CO2 uptake amount
# Cycles
Delta Mass (ng)
(from QCM)
CO2 uptake amount
(mmol/g)
2
4
2129±398
4716±898
10.1±1.9
11.9±2.3
Theoretical maximum CO2 loading for ZIF-8 calculations:
Assuming CO2 fills all pore space in the ZIF-8 films, the loading amount was calculated by the
following equation:
 Free Volume ( ZIF 8)


Density ZIF 8   Density CO2
 Total Volume

( ZIF 8 )


CO2 loading amount 
 1000
Molar Mass of CO2
( Eq S2)
The total volume and free volume of microcrystalline ZIF-8:
Free Volume(ZIF-8) / Total Volume(ZIF-8) – 43.3%3
Density of microcrystalline ZIF-8: DensityZIF-8 – 0.924 g/cm3 3
Density of solid state CO2: DensityCO2 – 1.562 g/cm3
Molar Mass of CO2 – 44.01 g/mol
By applying the above into Eq S2, the maximum CO2 loading amount was calculated to be 16.6 mmol/g.
References
1.
Redhead, P. A., "Thermal Desorption of Gases." Vacuum 1962, 12, 203-211.
2.
Lin, X.; Yoon, Y.; Petrik, N. G.; Li, Z. J.; Wang, Z. T.; Glezakou, V. A.; Kay, B. D.; Lyubinetsky,
I.; Kimmel, G. A.; Rousseau, R.; Dohnalek, Z., "Structure and Dynamics of CO2 on Rutile TiO2(110)1x1." J. Phys. Chem. C 2012, 116, 26322-26334.
3.
Battisti, A.; Taioli, S.; Garberoglio, G., "Zeolitic Imidazolate Frameworks for Separation of
Binary Mixtures of CO2, CH4, N2 and H2: A Computer Simulation Investigation." Microporous
Mesoporous Mater. 2011, 143, 46-53.