# Aminated Covalent Organic Polymers for Anionic Dye Adsorption in Aqueous Systems
## 4 Conclusions  
The ACOPs were prepared by means of a catalyst-free Schiff base reaction involving terephthalaldehyde and melamine. The FT-IR spectra, XPS spectra, and N\({}_{2}\) adsorption-desorption hysteresis loop indicated that ACOP with a high specific surface area (582.07 m\({}^{2}\)/g) and average pore size of 88.71 A was successfully synthesized. Furthermore, the surface charge of the ACOP was shifted from +21.85 mV to \(-\)16.23 mV in the pH range of 4-10, and the pH\({}_{\text{pzc}}\) was determined to be pH 8.26. The prepared ACOP exhibited rapid adsorption on MO and OG within 1 min. According to the intraparticle diffusion model, the single-step rapid adsorption of the anionic dyes on ACOP can be attributed to the high specific area and dispersibility of ACOP. According to the Langmuir isotherm model, the maximum adsorption capacities (\(q_{\text{m}}\)) of ACOP were 351.9 and 227.9 mg/g for MO and OG, respectively; these values are considerably higher than those of other well-known adsorbents. According to the dye adsorption results as a function of pH in the presence/absence of cationic dye (MB), dye adsorption on the prepared ACOP occurred through charge-charge and \(\pi\)-\(\pi\) interactions. Furthermore, the presence of cationic dye enhanced the dye adsorption capacity, owing to the synergistic effect of the positively charged quaternized nitrogen atoms. The FT-IR and XPS spectra of the prepared ACOP after dye adsorption indicated that adsorption occurred through charge-charge and \(\pi\)-\(\pi\) interactions. The outstanding rapid adsorption and high adsorption efficiency of ACOP over a wide pH range and in the presence of cationic dye make it possible to use ACOP for environmental remediation, especially in aqueous systems. Further studies, including recycling tests, applicability to different organic pollutants, and column operation of granulated ACOP will be beneficial to enhance the practical relevance of ACOP in environmental remediation.  
Figure 10: Schematic illustration of suggested interaction between ACOP and dye molecules.  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13042043/s1](https://www.mdpi.com/article/10.3390/app13042043/s1)]([https://www.mdpi.com/article/10.3390/app13042043/s1](https://www.mdpi.com/article/10.3390/app13042043/s1)), Figure S1: Dye adsorption kinetics fitted using the intraparticle diffusion model, Table S1: Intraparticle diffusion model parameters of ACOP for MO and OG, Figure S2: Zeta-potential distribution graphs of ACOP after MO and OG adsorption, Figure S3: The influence of coexisting ions of MO and OG adsorption by ACOP, Figure S4: FT-IR spectra of dye molecules, ACOP, and ACOP after dye adsorption.  
**Author Contributions:** Conceptualization, T.-H.K. and Y.H.; methodology, J.P. and S.K.; validation, T.-H.K. and Y.P.; formal analysis, J.P. and S.K.; investigation, J.P. and S.K.; resources, Y.H.; data curation, T.-H.K., Y.P. and S.K.; writing--original draft preparation, J.P., S.K. and T.-H.K.; writing--review and editing, T.-H.K., Y.P. and Y.H.; visualization, J.P.; supervision, T.-H.K. and Y.H.; project administration, Y.H.; funding acquisition, Y.H. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This study was financially supported by Seoul National University of Science and Technology.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest.