Facile synthesis of aminated indole-based porous organic polymer for highly selective capture of CO2 by the coefficient effect of π–π-stacking and hydrogen bonding

A new aromatic aminated indole-based porous organic polymer, PIN-NH2, has been successfully constructed, and it was demonstrated that the coefficient effect endows this porous material with outstanding CO2 absorption capacity (27.7 wt%, 1.0 bar, 273 K) and high CO2/N2 (137 at 273 K and 1 bar) and CO2/CH4 (34 at 273 K and 1 bar) selectivity.


Measurements
FT-IR spectrum was recorded on a Nicolet 6700 FTIR spectrometer.Solid-state crosspolarization magic-angle-spinning (CP/MAS) NMR spectrum was recorded on a Bruker Avance III 400 NMR spectrometer.The elemental analysis characterization technique was performed using a Vario EL III apparatus.Thermogravimetric analysis (TGA) was performed on a Setarma TG-92 at a heating rate of 10 °C/min under nitrogen atmosphere.
Scanning electron microscopy (SEM) was recorded on an S-4800 (Hitachi Ltd) field emission scanning electron microscope.Morphological observation was performed with a Tecnai G2 F20 S-TWIN (FEI Company) transmission electron microscope.The nitrogen adsorption and desorption isotherms were measured at 77 K using a Micromeritics AR-JW-BK112 instrument.The sample was treated at 120 °C for 24 h before the measurement.The surface area was calculated by Brunauer-Emmett-Teller (BET) equation (0.01 < P/P 0 < 0.1).The pore-size-distribution (PSD) curve was obtained from the adsorption branch using non-local density functional theory (NL-DFT) method.

Preparation of porous organic polymer material PIN-NH 2 aerogel
4-Aminoindole (0.528 g, 4 mmol) was added to anhydrous 1,2-dichloroethane (40 mL) under a flow of N 2 , followed by formaldehyde dimethyl acetal (0.4566 g, 6 mmol).FeCl 3 (1.30g, 8 mmol) was added and heated to 80 °C for 18 h (Scheme S1).The solid product was collected by filtration and washed with methanol, HCl (10%) and deionized water to remove the residual FeCl 3 .The product was further purified by soxhlet extraction in methanol, dried in vacuum at 60 °C for 24 h.

The adsorption measurements
The CO 2 , N 2 and CH 4 adsorption measurements were carried out using a Micromeritics AR-JW-BK112 analyzer at 273, 291 and 303 K and up to 1 bar.The temperature during all of the pure gases were regulated by mass flow controllers (0-100 mL min -1 ).The gas mixture was first sent to the gas chromatograph through bypass line and measured its component before the breakthrough measurements.The relative amounts of the effluent gases passing through the column were monitored by GC.

Simulation method
To illustrate the molecular mechanism, we used density functional theory (DFT) 7,8 to investigate the interaction of the PIN-NH 2 model compound with CO 2 .0][11] The geometries were fully optimized without symmetry constraints at each calculation level.The M06-2X functional (hybrid-meta GGA with dispersion correction) has shown good performance in the investigation of the dispersion interaction as well as the electrostatic interaction (H-bonding, H-π interaction, π-π interaction, additional electrostatic and induction energies of neutral and charged dimeric systems). 12,13Single point calculations using the RI-coupled cluster theory with single, double and perturbative triple excitations (RI-CCSD(T)) were performed by employing the aVTZ and aug-cc-pVQZ (aVQZ) basis sets at the RI-scs-MP2/aVTZ geometries.The CO 2 -BEs were calculated at the complete basis set (CBS) limit at the RI-CCSD(T) level with the aVTZ and aVQZ basis sets by employing the extrapolation approximation. 14,15The complete basis set energies were S-19 estimated with the extrapolation scheme utilizing the electron correlation error proportional to N-3 for the Figure S1. 13C CP/MAS NMR spectrum of PIN-NH 2 .

Figure S10 .
Figure S10.The dynamic breakthrough separation curves for CO 2 /N 2 mixture gas.