Kinetics, isotherm, and thermodynamic studies of methylene blue selective adsorption and photocatalysis of malachite green from aqueous solution using layered Na-intercalated Cu-doped Titania

Abstract

In this study, layered Na-intercalated copper-doped titania (Cu-NaTi) have been synthesized using controlled precipitation method where the sodium ions are self-incorporated. Physio-chemical, microstructural, and optical properties of the prepared materials have been studied using different analytical techniques. Structural data shows that pure and 0.5 wt% Cu-doped samples exhibit pure anatase phase of titania while higher Cu-doped (1 and 2 wt%) titania nanostructures show mainly anatase phase of titania along with a spectrum of monoclinic sodium tritatanate. HRTEM micrographs demonstrate the presence of interlayered architecture. The inner-space of the titania layers may create capillaries with specific size since the adsorption results showed adsorption selectivity towards Methylene blue (MB) from a mixed aqueous solution containing methylene blue and rhodamine B (RhB). The MB adsorption selectivity has been also confirmed from other adsorption experiments mixing with Rose bengal (RB) and bismark brown Y (BB-Y). It is believed that the planner molecular structure and small size of MB makes it unique to enter into the specific capillary to participate in the adsorption process through cation exchange. The 1 wt% Cu-doped sample shows maximum MB removal in just 10 min. of adsorption experiment. Rate kinetics and isotherms of the selective MB adsorption are studied in detail. It has been found that pseudo-second-order kinetic model well describes the adsorption kinetics. Moreover, photodegradation experiment has also been carried out using aqueous solution of malachite green (MG) under direct sunlight. The results indicate approx. 95% photodegradation of MG by 0Cu-NaTi sample with kinetic rate of 0.040 min−1. Results of this study are of great implication for environmental applications, where the layered Na-intercalated copper-doped titania can act as a capable adsorbent and photocatalyst for the purification of water.