Multifunctional ethylenediaminetetraacetic acid/chitosan-attapulgite composite for methylene blue removal: Performance optimization and synergistic adsorption mechanisms

In order to improve the adsorption capacity of attapulgite, a novel composite adsorbent EDTA/CS-ATP was synthesized by integrating attapulgite (ATP), chitosan (CS), and ethylenediaminetetraacetic acid (EDTA) by hydrothermal carbonization and grafting method. Under optimized conditions, the composite adsorbent achieved a removal ratio of 92.46 % and an adsorption capacity of 66.31 mg/g for methylene blue (MB) removal. Characterizations revealed that introducing CS and EDTA to ATP enhanced the electrostatic and hydrophobic interactions of ATP, which is beneficial for MB adsorption. Kinetic and thermodynamics studies showed that the adsorption followed pseudo-second-order kinetics and the Langmuir model, indicating a chemisorption-driven monolayer binding mechanism. Hydrogen bonding, electrostatic attraction, and π-π interactions were identified as the key mechanisms contributing to MB capture. Notably, compared to traditional EDTA-based materials mainly used for heavy metal removal, the EDTA/CS-ATP composite has the multifunctional sites to match the cationic and aromatic structure of MB, exhibiting highly selective and efficient MB removal. This work presents an environmentally friendly and scalable strategy for treating wastewater contaminated with cationic dyes, offering a promising solution for practical applications in water purification.