# Zinc-Decorated and Nitrogen-Functionalized Hierarchical Porous Carbons for Carbon Dioxide Capture
## 4 Conclusions  
The ZIF-8 polyhedrons prepared in this study showed a uniform rhombic dodecahedron morphology, which was maintained after carbonization at temperatures of up to 1223 K. The decomposition of ZIF-8 upon high-temperature pyrolysis might generate significant shrinkage from outside to inside. Using N\({}_{2}\) adsorption isotherms at 77 K and CO\({}_{2}\) adsorption isotherms at 273 K, the pore size distributions of the adsorbents with ultramicropores were determined using the NLDFT method. The ZIF-8 polyhedrons had the largest SSA; however, all the ZDCs had superior CO\({}_{2}\) adsorption performances compared to ZIF-8. It was expected that the dissociation of ZIF-8 during pyrolysis would generate more active sites, exposing nitrogen and zinc atoms, and convert them to more active functional groups. The adsorption process occurs favorably and spontaneously, is exothermic and tends to be orderly. Physical adsorption was the predominant adsorption behavior in this study, but under a low CO\({}_{2}\) loading, some chemosorption might occur on the adsorbents with a high isosteric heat of adsorption. At 15 kPa, Z8-750 exhibited a better CO\({}_{2}\) adsorption performance, while at 101.3 kPa, Z8-850 showed the highest CO\({}_{2}\) adsorption capacity. Strong interactions between CO\({}_{2}\) and the adsorbents resulted in a higher adsorption selectivity for CO\({}_{2}\) over N\({}_{2}\) at higher adsorption temperatures. The CO\({}_{2}\) adsorption capacities of the adsorbents are a compromise between surface structures and surface chemistry.  
Conceptualization, Y.-C.C.; methodology, Y.-C.C.; software, W.-T.C. and I.-C.C.; validation, Y.-C.C.; investigation, W.-T.C.; data curation, W.-T.C.; writing--original draft preparation, Y.-C.C. and I.-C.C.; writing--review and editing, Y.-C.C.; visualization, Y.-C.C.; supervision, Y.-C.C.; project administration, Y.-C.C.; funding acquisition, Y.-C.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Science and Technology Council, Taiwan (grant numbers: MOST 109-2221-E-155-012, MOST 111-2221-E-155-010, and NSTC 112-2221-E-155-004-MY2).  
Not applicable.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Material** & **S\({}_{\text{BET}}\) (m\({}^{2}\)/g)** & **CO\({}_{2}\) Conc.** & **Temp. (K)** & **CO\({}_{2}\) Capacity (mmol/g)** & **Reference** \\ \hline Z8-850 & 1309 & 15 kPa & 298 & 1.13 & This study \\  & 101.3 kPa & & 3.57 & \\ Z8-750 & 963 & 15 kPa & 1.26 & This study \\  & 101.3 kPa & & 3.40 & \\ ZIF-8 (773 K, 24 h) & 942 & 0.15 bar & 298 & 0.4 & [33] \\ ZIF-8 & 1016 & 1 bar & 298 & 0.60 & [61] \\ ZIF-7-8s & 283 & 1 bar & 293 & 1.44 & [62] \\ ZIF-8 & 1169 & 1 bar & 298 & 1.06 & [63] \\ NH\({}_{2}\)-ZIF-8 & 886 & 1 bar & 298 & 1.94 & [63] \\ NH\({}_{2}\)-ZIF- & & & & & \\
8/bacterial & 455 & 1 bar & 298 & 1.63 & [63] \\ cellulose foams & & & & & \\ ZIF-100 & 595 & 1 atm & 298 & 0.6 & [64] \\ Deep eutectic & 1147 & 1 bar & 293 & 3.03 & [65] \\ solvent-ZIF-8 & 2491 & 1 bar & 298 & 1.72 & [66] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of CO\({}_{2}\) adsorption performance of the materials developed in this study with various ZIF-8-related products from the literature.  
Data Availability Statement: The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy restrictions.  
The authors would like to thank the Instrumentation Center at NTU for performing the FESEM, TEM, STEM, and EA analyses and the Instrumentation Center at NTHU for performing the XRD and XPS analyses.  
The authors declare no conflicts of interest.