The removal of methylene blue (basic dye) from spiked pond water through adsorption and photodegradation using TNTs

Titanate nanotubes (TNTs) were synthesized hydrothermally at 150–160°C, characterized by TEM, XRD, FESEM and FTIR to understand the surface morphology and crystallinity. Prepared TNTs were used to remove methylene blue (MB) from spiked pond water in conjugation with adsorption and photodegradation at room temperature. Initially, complete photo-illumination study conducted to find out the optimum conditions for maximum MB degradation. In dark, ~69% dye adsorbed within 3.0 h whereas final removal was achieved to ~98% during photo-illumination within another 3.5 h of photo-irradiation in presence of oxygen in suspension. Optimal conditions for degradation were, 8 mgL–1 dye concentration, dosage of 3 gL–1, pH 6.8 ± 0.2, 6.5 h. Adsorptivity of TNTs was found to 33.55 mgg–1 as determined from the Langmuir isotherm and is followed in a better way than Freundlich isotherm. Kinetic analysis indicated that adsorption followed pseudo-second-order model. Adsorption did not follow either by physisorption or chemisorption and was elucidated from D-R isotherm or by film or pore diffusion controlled. Photodegradation is supposed to the redox reactions onto TNTs surfaces due to the generation of ROS during transition of photo-generated electron(s) from VB to CV. Three times recycling study conducted with suppression removal efficiency. Cost analysis of degradation was calculated.