M. P. Suh and L.-H. Xie
rate of 10 mLminꢀ1 until pressurized CO2 in the syringe pump was
empty, which was then filled with CO2 again. The cycle of refilling with
CO2, pressurizing, and venting was repeated over 8 h. Finally, the super-
critical-CO2-activated sample of SNU-C1 was obtained as a pale yellow
powder.
during the water treatment and subsequent activation. This
is also supported by the color change of SNU-C1-sca from
pale yellow to orange, which is the color of SNU-C1-va,
after activation of the water-treated sample. We assume that
drying the water-adsorbed SNU-C1-sca sample under 608C
induces a structural change to the one that vacuum drying
of the as-synthesized SNU-C1 does.
Gas-sorption experiments: The gas adsorption–desorption experiments
were performed using an automated micropore gas analyzer, Autosorb-1
(Quantachrome Instruments). All the gases used were of 99.9999%
purity. The N2-sorption isotherms were measured at 77 K and 298 K,
CH4-sorption isotherms were measured at 298 K, and CO2-sorption iso-
therms were measured at 273 K, 285 K, and 298 K. The adsorption tem-
peratures were achieved by using baths of liquid nitrogen (77 K), ice/
water (273 K), dry ice/dioxane (285 K), and water (298 K). N2-adsorption
isotherms measured at 77 K were used for porosity analyses. Brunauer—
Emmett–Teller (BET) and Langmuir surface areas were calculated from
the adsorption data in the pressure range of 0.005–0.01 atm (see Fig-
ure S5 in the Supporting Information). Micropore analyses were per-
formed by using the Dubinin–Radushkevich (DR) method[47] in the pres-
sure range of 0.005–0.01 atm (see Figure S6 in the Supporting Informa-
tion). By using nonlocal density-functional theory[41] (NLDFT), pore-size-
distribution calculations were performed with the adsorption data in the
pressure range of 0.005–0.025 atm and with the desorption data in the
pressure range of 0.025–0.95 atm. The NLDFT equilibrium model—N2 at
77 K on carbon (slit pore)—was used for the calculations because it pro-
vided the best fit (see Figure S7 in the Supporting Information).
Conclusion
We have synthesized a new porous organic polymer, SNU-
C1, which contains two kinds of moderately CO2-attracting
functional moieties, carboxy and triazole groups. After
SNU-C1 was activated by the conventional evacuation
method and the supercritical-CO2 drying method, respec-
tively, the CO2-capture ability of each guest-free material
was evaluated by the experimental sorption studies as well
as calculation of five VSA separation parameters, that is,
CO2-adsorption-capacity, working-capacity, regenerability,
selectivity, and sorbent-selection parameters. The results
reveal that porosity and CO2-capture performance of the
POP depend upon the activation method used. In addition,
the POP described herein has high CO2-uptake capacity at
room temperature, high selectivity, high regenerability, and
good stability against water, and thus it has great potential
application in CO2 capture.
Gas-cycling experiments: A sample (around 20 mg) introduced to a TA-
Q50 thermogravimetric analyzer was heated at 608C for 5 h to remove
adsorbed water under a pure N2 flow (99.9999%). After the temperature
of the furnace was reduced and stabilized at 308C, a CO2/N2 mixture
(15:85 v/v) was introduced into the furnace for 40 min and then pure N2
was introduced for another 40 min. This cycle was repeated 12 times. A
flow rate of 60 mLminꢀ1 was employed for both gases. The weights of
the sample were recorded during the cycles.
Estimation of isosteric heat of CO2 adsorption: Isosteric heat of CO2 ad-
sorption was estimated from the CO2-sorption data measured at 273, 285
and 298 K. Firstly, the Toth equation,[48,49] Equation (1), was used for in-
dependent fittings of the isotherms (see Figure S9 in the Supporting In-
formation), where N is the amount of adsorbed gas in cm3 gꢀ1, Nsat is the
saturated adsorption amount, P is the pressure in atm, b and t are the
equation constants. It is noteworthy that the Toth equation reduces to
the Langmuir equation when t has the value of 1.
Experimental Section
Synthesis of SNU-C1: To a round-bottom flask (100 mL) containing 3,5-
diazidobenzoic acid (Hdab; 0.082 g, 0.4 mmol, 1.0 equiv), 1,3,5,7-tetra-
kis(4-ethynylphenyl)adamantane (tepa; 0.107 g, 0.2 mmol, 0.5 equiv), and
a magnetic stirring bar, DMSO (20 mL) was added. The flask containing
the resultant clear solution was placed in a preheated 908C oil bath and
the solution was stirred. Then, an aqueous solution (0.5 mL) of
CuSO4·5H2O (0.020 g, 0.08 mmol, 0.2 equiv) and l-ascorbic acid (0.028 g,
0.16 mmol, 0.4 equiv) was added dropwise to the solution, which immedi-
ately became cloudy. After addition, the flask was capped with a rubber
septum and the heterogeneous mixture was stirred at 908C for 96 h. The
reaction mixture was cooled to room temperature and filtered under re-
duced pressure. The solid product was washed with DMSO (100 mL) and
MeOH (300 mL). This as-synthesized sample of SNU-C1 was immersed
in MeOH for further activations, which are described below. Yield:
0.175 g (93% of weight sum of the two reactants). Elemental analysis
calcd (%) for C56H40N12O4·3H2O ([tepa][Hdab]2·3H2O): C 67.32, H 4.64,
N 16.82; found: C 65.70, H 4.67, N 17.04 (for SNU-C1-va); C 65.83, H
4.55, N 16.94 (for SNU-C1-sca). The elemental-analysis data indicate that
activated SNU-C1 samples adsorb water from air to various degrees
during the sample handling.
NsatbP
N ¼
ð1Þ
1
t
t
ð1 þ bP Þ
Then, the expression for the pressure, P, in terms of the CO2-adsorption
amount, N, could be obtained by using Equation (2).
N
P ¼
ð2Þ
1
t
ðbtNsat ꢀ bN Þ
t
t
Isosteric heats of the CO2 adsorption (Qst) were calculated with the Clau-
sius–Clapeyron equation[6,50] Equation (3), where T is the temperature, R
is the universal gas constant, and C is a constant. The Qst values at differ-
ent CO2 loading, N, were obtained from the slopes of the plots of (lnP)N
as a function of (1/T).
Qst
R T
1
Activation of SNU-C1: The guest solvent molecules included in SNU-C1
were removed by two different activation methods, namely, high dynamic
vacuum activation at room temperature for 12 h, and supercritical-CO2
treatment. Vacuum activation is a common method; supercritical-CO2
treatment is described as follows. As-synthesized SNU-C1 was immersed
in 30 mL MeOH for 3 h, during which time, the solution was replaced
with fresh MeOH three times. The sample was then transferred to a su-
percritical dryer together with a small amount of MeOH. The tempera-
ture and pressure of the chamber were raised to 408C and 200 bar with
CO2 by using a CO2 syringe pump, above the critical point (318C,
73 atm) of CO2. The supercritical CO2 in the chamber was vented at a
ð3Þ
ðln PÞN ¼ ꢀ
þ C
Calculation of CO2-separation parameters: Ideal adsorbed solution
theory (IAST)[44] enables prediction of adsorption equilibriums of the
binary gas mixtures from the related single-component isotherms. Ac-
cording to IAST:
y1 þ y2 ¼ 1
x1 þ x2 ¼ 1
ð4Þ
ð5Þ
&
6
&
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!