# Effect of Pore Size Distribution and Amination on Adsorption Capacities of Polymeric Adsorbents
## 3 Results and Discussion  
### Characterization  
The specific surface area and pore structure of the synthesized resins (NDA-1, NDA-2, NDA-3, and NDA-4) were measured. Their specific surface areas ranged from 448.0 to 565.1 m\({}^{2}\cdot\)g\({}^{-1}\). The characterization results of the resins are shown in Table 1. The mesopore diameter distribution was calculated using the Barret-Joyner-Halenda (BJH) method, as shown in Figure 2. NDA-2 had the largest specific surface area, and the other three resins had similar specific surface areas. The pore diameter distributions of NDA-1 and NDA-2 were relatively narrow, but those of NDA-3 and NDA-4 were relatively wide. The N\({}_{2}\) adsorption isotherms of the synthetic resins were mostly II and IV hybrid adsorption isotherms (see Figure 3). Microporce filling occurred when relative pressure (p/p\({}_{0}\)) was between 0.0 to 0.2 and the adsorption was low. When the relative pressure was slightly higher, the hysteresis curve appeared between the adsorption and desorption curves owing to the occurrence of multilayer adsorption and capillary condensation, indicating that most pores in the resins were mesopores [20]. The low range isotherms (at the logarithmic scale (p/p\({}_{0}\)) scale) were also presented in supporting information (Figure S2). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Number**} & \multicolumn{2}{c}{**Specific Surface Area (m\({}^{2}\) g\({}^{-1}\))**} & \multirow{2}{*}{**S\({}_{\text{ext}}\)**\%**} & \multicolumn{3}{c}{**Pore Volume (cm\({}^{3}\) g\({}^{-1}\))**} & \multirow{2}{*}{**V\({}_{\text{meso}}\)**\%**} & **Average Pore** \\ \cline{2-2} \cline{6-9}  & **Sbet** & & & & & **V\({}_{\text{t}}\)** & **V\({}_{\text{micro}}\)** & **V\({}_{\text{meso}}\)** & \\ \hline NDA-1 & 448.0 & 37.2 & 410.8 & 91.7 & 0.310 & 0.0098 & 0.3002 & 96.8 & 3.80 \\ NDA-2 & 565.1 & 51.8 & 513.3 & 90.8 & 0.474 & 0.0148 & 0.4592 & 96.9 & 4.74 \\ NDA-3 & 452.4 & 43.1 & 409.3 & 90.5 & 0.736 & 0.0213 & 0.7147 & 97.1 & 6.87 \\ NDA-4 & 486.6 & 32.4 & 454.2 & 93.3 & 0.767 & 0.0091 & 0.7579 & 98.8 & 6.72 \\ \hline \hline \end{tabular} Note: S\({}_{\text{BET}}\), S\({}_{\text{micro}}\) and S\({}_{\text{ext}}\) are the BET specific surface area, micropore area and non-micropore area, respectively, V\({}_{\text{t}}\), V\({}_{\text{micro}}\) and V\({}_{\text{meso}}\) are the pore volume, micropore volume and meso-pore volume, respectively, when the relative pressure was 0.98. S\({}_{\text{ext}}\)/\(\psi\) and V\({}_{\text{meso}}\)/\(\psi\) are the percentage of the specific surface area of non-micropores and the percentage of the mesopore volume, respectively.  
\end{table} 
Table 1: Characterization of resins. After modification of NDA-1800 with amines, their characterizations were determined. The infrared spectra of NDA-1800, NDA-1801, NDA-1802, and NDA-1803 resins are shown in Figure S3. Compared with the NDA-1800 resin, the resins modified by primary amines, secondary amines and tertiary amines had a very small peak around 672 cm\({}^{-1}\); this was attributed to the chloromethylal peak. The peaks appearing near 1040 cm\({}^{-1}\) and 1118 cm\({}^{-1}\) were designated as C-N stretching vibration peaks, and they were not present for NDA-1800. In the modified resins, the peaks around 3445 cm\({}^{-1}\) were N-H stretching vibration peaks, which indicated that amine groups had been successfully introduced to the three  
Figure 3: N\({}_{2}\) adsorption isotherms of NDA-1 (**a**), NDA-2 (**b**), NDA-3 (**c**) and NDA-4 (**d**) resins at 77 K.  
Figure 2: Mesopore diameter distribution of NDA-1, NDA-2, NDA-3, and NDA-4. modified resins. Moreover, the chloride content of the resin after amination was decreased, indicating that the chlorine had been partly replaced by the amino groups (Table 2). The exchange capacities of the three modified resins were 1.3, 1.49, and 5.4 mmol-g\({}^{-1}\) for NDA-1801, NDA-1802, and NDA-1803, effectively, showing that the number of exchangeable amino groups increased on the resin skeleton after reaction.