Silk-based microparticles for the adsorption of methylene blue: formulations, characterization, adsorption study, in...

Although silk-derived biomaterials have garnered attention for environmental remediation due to their sustainability, biocompatibility, and biodegradability, the application of silk fibroin-based microparticles (FNP) for pollutant dye adsorption remains vastly underexplored. Hence, this study pioneers the fabrication and characterization of FNP for the removal of methylene blue (MB), offering a comprehensive comparison with two other silk-based states of raw silk cocoon pieces (SC) and sericin-degummed silk fibers (SD). Remarkably, FNP achieved an adsorption capacity of 122.98 mg g^-1, over 32-fold higher than both SC and SD (3.8 mg g^-1), highlighting its superior efficiency. The adsorption performance of FNP was strongly influenced by experimental variables including pH, contact time, initial dye concentration, and adsorbent dosage. Structurally, FNP exhibited favorable physicochemical properties for adsorption, including uniform spherical morphology (∼2.45 μm), moderate surface area (21.894 m² g^-1), a mesoporous-to-macroporous structure (pore diameter 21.911 Å), and a point of zero charge (pH_pzc) of 6.7, contributing to its effective electrostatic interactions with the cationic dye MB. Importantly, the adsorption data fitted the Dubinin-Radushkevich isotherm, indicating a chemisorption-dominated mechanism. Molecular docking further revealed specific fibroin-dye interactions at Lys62 (hydrogen bonding, -0.2 kcal mol^-1) and Glu94 (ionic bonding, -1.9 kcal mol^-1). Additionally, molecular dynamics simulations in water confirmed the docking results and demonstrated the aqueous stability of the fibroin-MB complex. Conclusively, this work not only establishes FNP as a high-performance, eco-friendly adsorbent for MB removal, but also provides mechanistic insights at the molecular level, offering a scientific foundation for the rational design of protein-based adsorbents in future environmental technologies.