Fast removal of malachite green dye using novel superparamagnetic sodium alginate-coated Fe3O4 nanoparticles

• Sodium alginate coated Fe3O4 nanoparticles (Alg–Fe3O4) as a novel superparamagnetic adsorbent were prepared by in situ coprecipitation method.
• The Alg–Fe3O4 nanoparticles were used for removal of malachite green (MG) from aqueous solutions using batch adsorption technique.
• The results of FTIR and TGA confirmed that sodium alginate was successfully coated on the surface of Fe3O4 nanoparticles.
• The maximum adsorption capacity obtained from Langmuir isotherm equation was 47.84 mg/g.
• The adsorption of MG onto Alg–Fe3O4 nanoparticles followed the pseudo-second-order kinetic model.

In this study, superparamagnetic sodium alginate-coated Fe3O4 nanoparticles (Alg–Fe3O4) as a novel magnetic adsorbent were prepared by in situ coprecipitation method, in which Fe3O4 nanoparticles were precipitated from FeCl3 and FeCl2 under alkaline medium in the presence of sodium alginate. The Alg–Fe3O4 nanoparticles were used for removal of malachite green (MG) from aqueous solutions using batch adsorption technique. The characterization of synthesized nanoparticles was performed using XRD, FTIR, TEM, TGA and vibrating sample magnetometer (VSM) techniques. FTIR analysis of synthesized nanoparticles provided the evidence that sodium alginate was successfully coated on the surface of Fe3O4 nanoparticles. The FT-IR and TGA characterization showed that the Alg–Fe3O4 nanoparticles contained about 14% (w/w) of sodium alginate. Moreover, TEM analysis indicated that the average diameter of the Alg–Fe3O4 nanoparticles was about 12 nm. The effects of adsorbent dosage, pH and temperature were investigated on the adsorption properties of MG onto Alg–Fe3O4 nanoparticles. The equilibrium adsorption data were modeled using the Langmuir and Freundlich isotherms. The maximum adsorption capacity obtained from Langmuir isotherm equation was 47.84 mg/g. The kinetics of adsorption of MG onto Alg–Fe3O4 nanoparticles were investigated using the pseudo-first-order and pseudo-second-order kinetic models. The results showed that the adsorption of MG onto nanoparticles followed pseudo-second-order kinetic model.