Green synthesis of Alginate-nZVIs biosorbent spheres for removal of Rhodamine B and Methylene Blue in aqueous media

Environmental pollution is increasingly negatively affecting our lives, requiring advanced methods and materials that are highly effective for pollutant treatment processes. This study proposes the synthesis of zero-valent iron nanoparticles (nZVIs) through a green chemistry approach, which were then encapsulated in calcium alginate (Alg) spheres for application in the treatment of Rhodamine B (RhB) and Methylene Blue (MB). The morphology and structure of the alginate particles encapsulating zero-valent iron nanoparticles (Alg-nZVIs) were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The analytical results indicate that the material consists of alginate polymer particles with an average diameter of 2.5 mm, containing nZVIs with an average size of 50 nm. Factors affecting the treatment of RhB and MB, including the proportion of components in the material, pH, solution concentration, and treatment time, were studied and evaluated by UV–Vis method. This material showed high removal efficiency for RhB and MB. 0.08 ml nZVIs in 1 g of Alg-nZVIs beads treated 100 mL of RhB 5 mg/L at pH 7 for 180 min with an efficiency of over 90%. The same amount of material effectively treated 100 mL of MB 5 g/L at pH 3 for 120 min with an efficiency of over 90%. The prepared Alg-nZVIs spheres were easy to collect and reuse for up to 6 cycles with a decrease in removal efficiency of less than 15%. Alginate-nZVIs spheres are derived from readily available and natural materials through a clean, cost-effective, and economically sustainable technique.

Graphical Abstract