Tannic acid-functionalized chitosan/sodium dodecyl sulfate composite beads for methylene blue removal: adsorption performance and ecotoxicological assessment

Introduction: The development of environmentally friendly adsorbent materials has emerged as an important strategy to mitigate water contamination caused by synthetic dyes released from industrial activities. Materials and methods: This study aimed to synthesize and evaluate a novel bioadsorbent based on chitosan modified with tannic acid and gelled with sodium dodecyl sulfate for the removal of methylene blue from aqueous solutions. Spheres composed of chitosan with 30% tannic acid stabilized with sodium dodecyl sulfate (CS-TA30/SDS) were synthesized by ionic gelation and characterized using UV-Vis and FTIR spectroscopy to investigate the interactions among chitosan, tannic acid, and sodium dodecyl sulfate. Adsorption experiments were conducted to evaluate the effects of pH, adsorbent dosage, and initial dye concentration on methylene blue removal. The ecotoxicological safety of the composite was assessed using the Artemia salina lethality assay. Results: Spectroscopic analyses confirmed the successful interaction between chitosan, tannic acid, and sodium dodecyl sulfate through electrostatic interactions and supramolecular associations. The incorporation of tannic acid significantly enhanced the adsorption performance by introducing additional phenolic and aromatic functional groups capable of interacting with methylene blue molecules. The dry chitosan (CS)-30% tannic acid (TA30)/sodium dodecyl sulfate (SDS) composite exhibited a maximum adsorption capacity removal of 263 mg g−1, representing an approximately 11-fold increase compared to the CS/SDS system without tannic acid. Adsorption efficiency was strongly influenced by pH, adsorbent dosage, and initial dye concentration, indicating the combined contribution of electrostatic attraction, hydrogen bonding, and π–π interactions. Furthermore, the composite demonstrated negligible toxicity toward Artemia salina even at high concentrations. Conclusions: The CS-TA30/SDS composite showed high adsorption efficiency and low ecotoxicological impact, demonstrating its potential as a sustainable and environmentally compatible adsorbent for dye removal in wastewater treatment applications.