Adsorption/photodegradation of methylene blue from synthetic wastewater on titanate nanotubes surfaces.

ABSTRACT

Titanate nanotubes (TNTs) were hydrothermally synthesized from commercially available TiO2 powder and were characterized by XRD, SEM/EDX, and TEM. The as-prepared TNTs were used to remove organic dye, Methylene Blue (MB) from aqueous media by batch mode at 25 ± 2 °C, at pH 6.8 ± 0.2. The MB removal process followed two mechanisms of adsorption (absence of UV light) and photodegradation on precursor's surfaces. Photo-illumination study revealed the ∼98% MB removal with the dose of 3 g/L TNT with an initial concentration of 10 mg/L. Adsorptive capacity of TNT was evaluated from the Langmuir isotherm and found to be 151.51 mg/g. Dimensionless equilibrium parameter RL value suggested the favourable but the free energy changes (ΔG°) value (10.752 kJ/mol) suggested the non-spontaneity of the adsorption process. Adsorption followed the pseudo-second order kinetics model best. MB adsorption onto TNT surfaces followed neither pore diffusion nor film diffusion. Studies conducted in the presence of different foreign ions as well as varying pH of the media to understand their effects in the process if any. Turnover studies were also conducted. A probable photodegradation mechanism was proposed. Finally, TNT was used to remove MB from spiked pond water collecting from the KISS University, including pre- and post analysis of water quality.