In the adsorption complex S[O.sub.2]/Sc@COF-105, the total interaction energy between the absorbed S[O.sub.2] molecule and the Sc-doped COF-105 complex is -41.36 kcal/mol, much larger than those of the adsorption complexes S[O.sub.2]/Li@COF105, S[O.sub.2]/Na@COF-105, and S[O.sub.2]/K@COF-105.
Here, the adsorption complexes were regarded as S[O.sub.2]/Li@COF105, S[O.sub.2]/Na@COF-105, S[O.sub.2]/K@COF-105, and S[O.sub.2]/Sc@ COF-105, respectively, where sulfur dioxide gas molecule was absorbed onto the Li, Na, K, and Sc metal-doped COF105 complexes.
Figure 4 and Table 3 display all the optimized geometries of the adsorption complexes S[O.sub.2]/metal@COF-105, in which the metals (Li, Na, K, and Sc) are doped at the top of the phenyl of the TBPS building blocks in the COF-105 cluster model.
When a Li atom, doped at the top of the phenyls in the TBPS building block of COFs, is positively charged, it can absorb one S[O.sub.2] molecule with the interaction energy of -25.46 kcal/mol obtained by subtracting the energies of sulfur dioxide and the metal-doped covalent organic frameworks from the energy of the adsorption complexes S[O.sub.2]/Li@COF-105.
Charge densities of [BCP.sub.O7-Na] and [BCP.sub.O7-K] in the adsorption complexes S[O.sub.2]/Na@COF-105 and S[O.sub.2]/K@COF-105 are 0.0205 a.u.
On the contrary, the interaction energy between the absorbed S[O.sub.2] molecule and the Sc-doped covalent organic frameworks is -41.36 kcal/mol, obtained by subtracting the energies of sulfur dioxide and the metal-doped covalent organic frameworks from the energy of the adsorption complexes S[O.sub.2]/Sc@COF-105.
In the adsorption complexes S[O.sub.2]/Li@COF-105, S[O.sub.2]/Na@COF-105, and S[O.sub.2]/K@COF-105, the calculated interaction energy between the absorbed S[O.sub.2] gas molecule and the metal-doped COF-105 complexes is -25.46, -21.87, and -19.14 kcal/mol, respectively.