Green synthesis of iron oxide nanoparticles for tartrazine and bordeaux red dye removal

Dyes are widely used industrially to make various products more attractive to consumers. However, this class of compounds is usually not removed by common effluent treatments, generating a pollutant load. In this context, this work aimed at the application of two samples of iron oxide nanoparticles (NPsFeO) obtained through a green synthesis method using two agroindustry residues: Cucurbita moschataleaves (NPsFeOA) and Beta vulgarisstalks (NPsFeOB), which were applied as adsorbent materials for the removal of tartrazine and bordeaux red dyes. The adsorbents were characterized using Uv–vis spectrophotometry, X-ray diffraction (XRD), transmission electron microscopy and Fourier transform infrared spectroscopy. Synthesis of mixed NPsFeO containing goethite and maghemite with estimated diameter of 2 nm and 20 nm, respectively, were observed by diffraction peaks obtained in XRD. In the adsorption kinetics tests, equilibrium was reached after 1200 min for tartrazine and 240 min for bordeaux red when NPsFeOA was used as adsorbent; and after 180 min for tartrazine and 120 min for bordeaux red when using NPsFeOB. Moreover, NPsFeOB had the higher adsorption capacities, at 59.79 mg g–1for tartrazine and 59.98 mg g–1for bordeaux red. The kinetic model that best represented the adsorption data was pseudo-second order, in both cases. The Langmuir isotherm was the one that better applied to both adsorbents and adsorbates, and the thermodynamic parameters indicated a favorable and endothermic adsorption process.