Adsorptive removal of alizarin red-S and alizarin yellow GG from aqueous solutions using polypyrrole-coated magnetic nanoparticles

The potential of polypyrrole-coated Fe3O4 nanoparticles (Fe3O4@PPy NPs) for removal of two anionic dyes from aqueous solutions was studied. The dye removal process was affected by several parameters such as pH, sorbent amount, and contact time, and were optimized using the response surface methodology (RSM) based on orthogonal central composite design (OCCD). The maximum removal of dyes was achieved at the adsorbent amount of 0.1–0.12 g/100 mL at pH 4–5.4 in 60 min. Three kinetic models; namely, pseudo-first-order, pseudo-second-order, and intra-particle diffusion were used to analyze the adsorption mechanism. The kinetic results showed that the pseudo-second-order equation was the best model. The isotherm analysis indicated that the equilibrium data were well fitted to the Langmuir isotherm model, showing a monolayer adsorption manner of the dyes onto a homogeneous surface of the modified nanoparticles. According to the experimental results, about 97.8% of alizarin yellow and 78.7% of alizarin red were removed from aqueous solutions under optimal conditions. The maximum adsorption capacities for alizarin red-S and alizarin yellow GG in the concentration ranges studied were 116.3 and 113.6 mg g−1, respectively, which were higher than the recent reports for potential adsorbents in the literature. The results obtained showed that the Fe3O4@PPy NPs are an appropriate adsorbent for removal of anionic dyes from aqueous solutions.