# Controllable Synthesis of 1, 3, 5-tris (1H-benzo[d]imidazole-2-yl) Benzene-Based MOFs
## 2 Results
### CO\({}_{2}\) and N\({}_{2}\) Adsorption Measurements  
To examine the CO\({}_{2}\)-capture performance of all the samples, CO\({}_{2}\) and N\({}_{2}\) adsorption properties were measured at 298 K and 0-1 bar. As reported in Figure 6, TIBM-Cu showed the highest CO\({}_{2}\) adsorption capacity (3.60 mmol/g) at 1 bar, compared to the TIBM-Al (2.04 mmol/g) and TIBM-Cr (1.67 mmol/g). This result is ascribable to both the metal site exposure and the metal oxide chelation of the TIBM host precursor for Cu\({}^{2+}\) ions [83]. The Cu-Cu magnetic interaction of TIBM-Cu is stronger than the Al-Al and Cr-Cr magnetic interactions of TIBM-Al and TIBM-Cr, respectively, and results in a strong interaction between CO\({}_{2}\) and the two available electrons of the Cu\({}^{2+}\) metal in the TIBM-Cu MOF [84; 85]. Conversely, TIBM-Cr showed the highest surface area (2141.1 m\({}^{2}\)/g) and total pore volume 2.116 cm\({}^{3}\)/g, compared to the other examined MOFs (Table 1), while a reverse adsorption trend was found for N\({}_{2}\) adsorption for the TIBM MOFs. With regards to the CO\({}_{2}\)/N\({}_{2}\) adsorption selectivity, which is defined as the ratio between CO\({}_{2}\) adsorption capacity at 0.15 bar and N\({}_{2}\) adsorption capacity at 0.85 bar, TIBM-Cu showed the highest value (53.69) compared to TIBM-Cr (11.16) and TIBM-Al (33.33), as reported in Figure 7, mainly in virtue of its high CO\({}_{2}\) adsorption capacity, and concurrent low N\({}_{2}\) adsorption capacity. In addition, CO\({}_{2}\)/N\({}_{2}\) selectivity is different for each of the TIBM MOFs and depends on different factors,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Synthesized MOFs** & **Matching Peak Angles (20)** & **Reported MOFs with Matching Peaks** & **Known Structure** \\ \hline TIBM-Al & 9.1, 12.5–20, 24–29 & Cu-BTC, Ni-BTC [67; 68; 72] & Hexagonal, cubic \\ \hline TIBM-Cu & 9.4–20, 28.8, 35.3, 38.9 & Cu-BTC, HKUST-1 [64; 65] & Cubic, pyramidal \\ \hline TIBM-Cr & 10.9, 14, 20, 24 & Fe-BTC, MIL-100, MOF-235 [67; 68; 69; 71; 73] & Irregular spherical \\ \hline \hline \end{tabular}
\end{table}
Table 2: Matching the characteristics peaks of TIMB MOFs with reported MOFs.  
such as MOF pore size and available open metal sites for CO\({}_{2}\). The pore sizes of TIBM-Cu (0.5 and 1 nm) are more suited to selective adsorption of CO\({}_{2}\) (0.33 nm) over N\({}_{2}\) (0.35 nm) than TIMB-Al (1.9 nm) and TIBM-Cr (2.2 nm), owing to the size-selective separation. The CO\({}_{2}\)/N\({}_{2}\) adsorption selectivity of TIBM-Cu is promising, compared to other MOFs reported in the literature (e.g., 6 for CuDABCO [86], 8 for ZIF-8 [87], 12 for MIL-101 (Cr) [88], 18 for MOF-5 [89], 16.5 for MOF-177 [89]). However, the adsorption capacities of the TIBM MOFs are comparable to those of previously reported MOFs (Table 3). TIBM-Cu was selected for the performance evaluation, showing that the CO\({}_{2}\) adsorption capacity (Figure 8) gradually decreased with increasing temperature from 298 to 338 K.  
Figure 4: FTIR spectra of (**a**) TIBM\(-\)Al, TIBM\(-\)Cr, and TIBM\(-\)Cu, and (**b**) TIBM.  
Figure 5: Thermal degradation graphs for TIBM-Al, TIBM-Cr, and TIBM-Cu.  
Figure 6: (a) CO\({}_{2}\) and (b) N\({}_{2}\) adsorption capacities at 298 K for TIBM-Al, TIBM-Cr, and TIBM-Cu. MOFs.