In this study, the green synthesis of iron oxide nanoparticles (IONPs) using an aqueous extract of Centaurea cyanus plant, as an appropriate regenerative and stabilising agent, was evaluated. This low-cost adsorbent was then investigated to adsorb a cationic dye such as methylene blue (MB) from an aqueous solution. The various tests such as XRD, BET, FTIR and FE-SEM were applied to characterise the crystalline structure, size, morphology, chemical composition, and properties of nanoparticles. The mean distribution of nanoparticles size was at 24 nm and their shapes were in spherical. Central Composite Design (CCD) under Response Surface Methodology (RSM) was served to model and optimise the MB adsorption from an aqueous solution using the synthesised nanoparticles. Several parameters (such as pH, time, initial concentration of dye and adsorbent dosage) effects on the adsorption process were studied. The optimum MB removal was around 83.96% at MB initial concentration of 90 mg.L−1 , pH of 5, adsorbent dosage of 3.6 g.L−1 and time of 93 min. Moreover, isotherm and kinetic of MB adsorption onto the synthesised nanoparticles were carefully investigated. Freundlich isotherm and pseudo-second-order kinetic models could properly legitimise this process. The results showed that the synthesised nanoparticles can be used as an efficient and inexpensive adsorbent for the MB removal.
