Aminated Covalent Organic Polymers for Anionic Dye Adsorption in Aqueous Systems

Aminated covalent organic polymer (ACOP) was synthesized through a catalyst-free Schiff base reaction involving terephthalaldehyde and melamine, and the prepared ACOP was used for the adsorption of anionic dyes. The prepared ACOP possessed a high specific surface area (582.07 m2/g) with an average pore size of 88.71 Å. Its point of zero charge was determined as pH 8.26. Anionic dye molecules, methyl orange (MO) and orange G (OG), were used to evaluate the dye adsorption efficiency of the prepared ACOP, and it was found that they were adsorbed rapidly on ACOP within 1 min. The maximum adsorption capacities (qm) of the prepared ACOP for MO and OG were 351.9 and 227.9 mg/g, respectively. Furthermore, the results of dye adsorption as a function of the initial pH and presence/absence of cationic dye (methylene blue; MB) revealed that dye adsorption on ACOP proceeded through charge–charge and π–π interactions. The presence of MB along with MO and OG enhanced the dye adsorption capacity because of the synergistic effect of the positively charged quaternized nitrogen atoms in the prepared ACOP. The dye adsorption mechanism was further investigated using Fourier transform infrared (FT-IR) analysis and X-ray photoelectron spectrometry (XPS). The ACOP adsorbent prepared herein using a facile catalyst-free reaction offers rapid adsorption with a high adsorption efficiency over a wide pH range and in the presence of cationic dye. For these reasons, it can be used for environmental remediation, especially in aqueous systems.