Decolorization of Congo Red Using Synthesized Titanate Nanotubes (TNTs)

Congo red (CR, λ_max = 497 nm, C₃₂H₂₂N₆Na₂O₆S₂) removal efficiency from aqueous media was evaluated on synthesized titanate nanotubes (TNTs). TNTs were synthesized hydrothermally and characterized by SEM/EDX and XRD. The as-prepared TNTs were applied on Congo red to adsorb and/or photodegrade. Adsorption, in the absence of light, followed by photodegradation using UV irradiation (UV-C, 360 nm) was conducted. The results of the adsorption experiments suggested that a dose of 4 g/L TNTs could adsorb ~86% CR with a shaking speed of 520–540 rpm within 45 min at room temperature and pH ~6.8 ± 0.2 (pH of de-ionized water), when the initial CR concentration was kept at 6 mg/L. Under the same experimental conditions, the UV light was allowed to irradiate the same experimental suspension for another 5 h to achieve the maximum CR removal efficiency ~98%. The adsorptive behavior of TNTs was evaluated using Langmuir isotherm and was found to be 12.04 mg/g. The feasibility of adsorption was understood by D–R isotherm. Adsorption is followed Langmuir and Freundlich isotherms in a close proximity. Positive free energy change value, ΔG⁰, suggests the process to be non-spontaneous and R_L (dimensionless equilibrium parameter) value implies the favorability of adsorption process.