Methylene blue dye removal utilizing biomass of the macroalgae (Padina sp.): Adsorption, kinetic studies and mechanism

Macroalgae, which are abundant in marine ecosystems, are promising natural adsorbents for water purification because of their high surface area, rich functional groups, and natural adsorption capabilities. In this study, the adsorption capacity of Padina sp., a brown macroalgae in dried powdered form, was evaluated for the removal of toxic methylene blue (MB) dye from water. A series of batch adsorption tests were conducted to investigate the effects of several operational parameters, as initial MB concentrations (2, 5, 10, 20, and 50 mg L-1), pH levels (2, 4, 7, and 11), and contact time (0, 0.08, 0.5, 1, 2, 4, 6, and 24 h) on MB removal. Furthermore, powdered Padina sp. was analyzed before and after MB adsorption using Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy. The results showed optimal removal efficiency under neutral and alkaline conditions, as opposed to acidic environments. The Freundlich model accurately represents experimental adsorption data (R2= 0.9902). Kinetic analysis revealed that MB adsorption onto Padina sp. primarily followed a pseudo-second order mechanism (R2= 0.9982). The characterization and experimental findings suggest that the proposed mechanisms for MB adsorption by Padina sp. involve electrostatic interactions, pore filling, and hydrogen bonding. The experimental results suggest that powdered Padina sp. is a promising adsorbent for removing MB from water.