Microporous organic hydroxyl-functionalized polybenzotriazole for encouraging CO2 capture and separation

We report a mild, hydroxyl functionalized and thermal stable benzotriazole-based aerogel (HO-PBTA), which is inspired by phenolic resin chemistry. Taking advantage of the synergistic adsorption interactions between hydroxy-benzotriazole and CO2, and the phobic effect between benzotriazole and nitrogen (N2), the CO2 uptake capacity of the HO-PBTA reaches an encouraging level (6.41 mmol g−1 at 1.0 bar and 273 K) with high selectivity (CO2/N2 = 76 at 273 K).


The main measurements
FT-IR spectrum was recorded on a Nicolet 6700 FTIR spectrometer. 1 H NMR and 13 C NMR were performed on a Bruker 300MHz NMR spectrometer with dimethylsulfoxide (DMSO-d 6 ) as the solvent. Solid-state cross-polarization magic-angle-spinning (CP/MAS) NMR spectra were recorded on a Bruker Avance III 400 NMR spectrometer.
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 (TEM). Gas adsorption isotherms were measured by a volumetric method using a Micromeritics AR-JW-BK112 instrument. The samples were degassed 10 hours at 120 °C, and the obtained adsorption-desorption isotherms were evaluated to obtain the pore parameters, including Brunauer-Emmett-Teller (BET) specific surface area, pore size, and pore volume. The pore size distribution (PSD) was calculated from the adsorption branch with the nonlocal density functional theory (NLDFT) approach. The selectivity of the aerogels to separate CO 2 from CO 2 /N 2 mixtures was estimated by the ratio between the CO 2 and N 2 adsorption capacities at a selected pressure. The Clausius-Clapeyron equation was employed to calculate the enthalpies of adsorption for CO 2 on the networks. In each case, the data were fit using the S3 equation: (ln P) n = -(Q st /R)(1/T) + C, where P is the pressure, n is thxe amount adsorbed, T is the temperature, R is the universal gas constant and C is a constant. The isosteric heat of adsorption Q st was subsequently obtained from the slope of plots of (ln P) n as a function of 1/T. Synthesis of 4-SO 3 K-BTA: To a one-necked flask equipped with magnetic stirrer, mercury sulfate (0.14 g), oleum (4.6 ml) were added and stirred at room temperature.
Afterwards, benzotriazole (5.95 g) was dissolved in oncentrated sulphuric acid (7 ml) and added to one-necked flask and under below 80 °C. The reaction mixture was heated to 130 °C under stirring for 2 h. The resulting solution was allowed to slowly cool to room temperature, and subsequently dropped into 35ml 20 mol/L KOH solution to PH≥7.

Simulation methods
To illustrate the molecular mechanism, we used density functional theory (DFT) 1,2 to investigate the interaction of indole, amide with CO 2 and to track the CO 2 capture process.
They were calculated at the M06-2X level with the aug-cc-pVDZ basis set and the resolution-of-identity spin-component-scaling Möller-Plesset second-order perturbation theory (RI-scs-MP2) level with the aug-cc-pVTZ basis set. [3][4][5] The geometries were fully optimized without symmetry constraints at each calculation level. The M06-2X S10 functional (hybrid-meta GGA with dispersion correction) has shown good performance in the investigation of the dispersion interaction as well as the electrostatic interaction (Hbonding, H-π interaction, π-π interaction, additional electrostatic and induction energies of neutral and charged dimeric systems). 6,7 Single 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. 8,9 The complete basis set energies were estimated with the extrapolation scheme utilizing the electron correlation error proportional to N -3 for the aug-cc-pVNZ basis set (N=3:T, N=4:Q). It is generally known that the zero-point-energy (ZPE)-uncorrected BE(-ΔE e ) is closer to the experimental CO 2 -adsorption enthalpy (ΔH ads ) than the ZPE-corrected BE(-ΔE 0 ). 10,11 Therefore, the values of -ΔE e are reported as the CO 2 -BEs.