Asymmetric Concave Polymer Nanostructures for MB, AF, and Cu²⁺ Ions Adsorption

Methylene blue (MB), acid fuchsin (AF), and divalent copper ions (Cu²⁺) are common aquatic pollutants known for their environmental persistence and biotoxicity, posing considerable risks to ecosystem integrity and human health. Therefore, developing efficient adsorbents for their elimination is crucial. In this study, an asymmetric concave polymer was synthesized through a one-step self-assembly method employing 3-aminophenol (3-AP) as the monomer, formaldehyde as the cross-linker, and ammonia as the catalyst, and then subjected to etching with acetone to refine its concave structure. The polymer demonstrated outstanding synchronous adsorption performance in both Cu²⁺/AF and AF/MB binary systems, achieving maximum adsorption capacities of 473.5 mg/g for MB, 1250.6 mg/g for AF, and 988.64 mg/g for Cu²⁺. The adsorption behaviors of AF and Cu²⁺ conformed to the Langmuir model, implying monolayer, spontaneous, and endothermic chemisorption. While MB adsorption was more accurately represented by the Freundlich model, reflecting a heterogeneous surface-based, spontaneous, and endothermic process. The adsorption kinetics for all three contaminants were best described by the pseudo-second-order model, affirming chemisorption as the rate-controlling step. These results reveal that the asymmetric concave adsorbent functions through a synergistic mechanism involving electrostatic attraction, hydrogen bonding, and chemical complexation. This study underscores the material's wide application potential in treating complex water pollutants.