Kinetic and equilibrium of methylene blue adsorption on amino-acid functionalized dendritic mesoporous silica nanoparticles

In this work, we fabricated dendritic mesoporous silica nanoparticles (DMSNs) functionalized with amino acids (leucine, serine, and ornithine) for removal of methylene blue (MB) from aqueous solutions. Structural characterization showed mesoporous architecture, with TEM showing almost uniform particle size of approximately 210 nm for DMSNs. Dynamic light scattering (DLS) analysis showed that the nanoparticles had hydrodynamic diameters of 232 nm for leucine-modified DMSNs (LE-DMSN), 247 nm for serine-modified DMSNs (SE-DMSN), and 256 nm for ornithine-modified DMSNs (OR-DMSN). FT-IR spectroscopy showed the appearance of characteristic amide carbonyl stretching at ∼1690 cm⁻ ¹ . Batch adsorption investigations showed pH 10 as optimal for maximum MB removal efficiency. The adsorption data exhibited agreement with the Langmuir isotherm model, suggesting monolayer adsorption on homogeneous binding sites. Kinetic studies showed that the adsorption process followed pseudo-second-order kinetics with rate constants ( k ₂ ) ranging from 0.03 to 0.15 g·mg⁻ ¹ ·min⁻ ¹ and calculated equilibrium capacities ( q _e ) between 4.34 and 7.23 mg·g⁻ ¹ within a contact time of 120 minutes. From the first to the third regeneration cycle, the removal efficiency of LE-DMSN decreased from ∼83% to ∼60%, while the efficiencies of OR-DMSN and SE-DMSN decreased from ∼64%/63% to ∼46%.