A microporous, amino acid functionalized Zn(II)-organic framework nanoflower for selective CO2 capture and solvent encapsulation†

A robust Zn-CBS nanoflower is utilized for selective sorption of CO2 and encapsulation of solvents.


Analysis of Sorption Isotherm
For this analysis, the BET equation is considered: where, x = p/p0,is the volume of nitrogen adsorbed per gram of Zn-CBS at STP, mis the monolayer capacity, and c is related to the heat of adsorption. It is noted that the line is fit to the low pressure isotherm data with range 0.05 < x < 0.3.
The surface area is then calculated from: where, 0 is the cross-sectional area of nitrogen at liquid density (16.2 Å) and Navis Avogadro's number.
These calculations are done through the "BET analysis" and "Langmuir analysis" function embedded in the Belsorp Adsorption/Desorption Data Analysis software version 6.3.1.0.
Pore size was calculated using microporous (MP) analysis method embedded in the Belsorp Adsorption/Desorption Data Analysis software.

Calculation of Isosteric Heats of Adsorption:
Using the Clausius-Clapeyron equation Isosteric heats of adsorption (Qst) were calculated using the Clausius-Clapeyron equation based on pure-component isotherms collected at two different temperatures of 273 K and 298 K. Qst is defined as: where, x is the pressure, T is the temperature, R is the gas constant and y is the adsorption amount.
These calculations are done through the "Heat of Adsorption" function embedded in the Belsorp Adsorption/Desorption Data Analysis software version 6.3.1.0. S12 where, p is the pressure of the bulk gas at equilibrium with the adsorbed phase (kPa); y is the adsorbed amount per mass of adsorbent (mmol/g), qm1 and qm2 are the saturation capacities of sites 1 and 2 (mmol/g); b1 and b2 are the affinity coefficients of sites 1 and 2, n1 and n2 represent the deviation from an ideal homogeneous surface.
The predicted adsorption selectivity is defined as

Density Functional Theory (DFT) and Configurational Bias Monte Carlo (CBMC) molecular simulation:
Ligand H3(D-2,4-cbs) was optimized in DFT and put in a (1 x 1 x 1) cell for further calculation.
The simulation boxes representing the ligand consist of (1 x 1 x 1) unit cells for CO2, N2 and CH4 (optimized). All the calculations were perfomed at 298 K at fixed pressure 1 bar. Interatomic interactions were modeled with standard Lennard-Jones potential and Columbic potentials.
Lorentz-Berthelot mixing rules were employed to compute the Lennard-Jones parameters between unlike atom types. The pairwise interactions between host and guest atoms of the particular force field were analysed by utilizing the non-bonding parameter. The long-range part of electrostatic interactions was handled using the Ewald summation technique with a relative precision of 10 −6 . Periodic boundary conditions were applied in all three dimensions. For each state point, the CBMC simulation consists of 1 x 10 7 steps to guarantee equilibration, followed by 1 x 10 7 steps to sample the desired thermodynamic properties.