Sodium titanate (Na2Ti4O9) nanoribbons for effective removal of organic dyes from water: Experimental and computational studies

In this work, Na₂Ti₄O₉ nanoribbons (NTRs) were synthesized using the hydrothermal method for its potential application in water treatment. The NTRs were characterized by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, zeta potential, Fourier Transform infrared spectroscopy, and surface area analyzer. The adsorption of organic dyes, including cationic methyl green (MeG) and methylene blue (MB) model pollutants, onto the NTRs was explored for the first time. Various parameters such as pH, adsorbent dose, initial dye concentration, regeneration, contact time, the effect of temperature, and thermodynamics were studied to determine the efficiency of NTRs for removing both dyes from water. A variety of isotherm and kinetic models were applied to fit the dye adsorption data at pH 7.0, providing insights into the adsorption mechanism and process kinetics. Kinetic data for both dyes fit well with pseudo-second-order and mixed 1,2-order models. The isotherm data agreed well with Langmuir-Freundlich and Sips models. At the studied temperatures of 298.2, 318.2, and 328.2 K, the maximum adsorption capacities for MeG (353.2, 367.7, and 443.2 mg·g⁻¹) are significantly higher than for MB (29.3, 52.6, and 67.2 mg·g⁻¹), indicating a stronger affinity for MeG, with adsorption efficiency improving as temperature increases. The MeG samples at 328.2 K exhibited interesting behavior. After adsorption, the samples became colorless, with a final pH near 7.0, indicating effective dye removal. However, the color faintly reappeared at pH 4.0, suggesting pH-dependent behavior and incomplete dye removal. The adsorption mechanism on the NTRs surface was investigated using Monte Carlo and molecular dynamics simulations.