Solid-phase extraction of food azodyes on magnetite nanoparticles and electrospun nanofibers: A comparative study

In this work, we consider the preparation of magnetic magnetite nanoparticles (MNPs, Fe ₃ O ₄ )) by chemical precipitation method, modified with biocompatible polymers as polyethyleneimine (PEI) and chitosan (CS) to get Fe ₃ O ₄ @PEI and Fe ₃ O ₄ @CS respectively, alongside electrospun polyamide (PA) nanofibers, and their sorption properties towards some of the synthetic food azo dyes (Tartrazine (TRT), Sunset Yellow FCF (SY), Azorubine (AR), Ponceau 4R (P-4R)). Spherical MNPs (7.5 ± 0.2 nm, TEM) and PA electrospun nanofibers (52 ± 3 nm - 104 ± 11 nm, SEM) were prepared, with specific surface area of 101 m ² g ^-1 (MNPs) and 44 m ² g ^-1 (PA) _. The pore space volume of PA nanofibers was 0.024 cm ³ g ^-1 which is much less than for MNPs (Fe ₃ O ₄ – 0.282 cm ³ g ^-1 ; Fe ₃ O ₄ @CS – 0.218 cm ³ g ^-1 and Fe ₃ O ₄ @PEI – 0.154 cm ³ g ^-1 ). The saturation magnetization of Fe ₃ O ₄ @CS (40 emu∙g ^-1 ) and Fe ₃ O ₄ @PEI (43 emu∙g ^-1 ) was slightly lower than that of Fe ₃ O ₄ (48 emu∙g ^-1 ). Sorption studies under optimized conditions (pH, time, sorbent mass) achieved 95–99% dye recovery. The kinetics of dye sorption was studied and pseudo-second order of sorption was preferable. For Fe ₃ O ₄ @PEI the maximum of sorption capacity (q _max , _{mg∙g ^-1 ) values increased 111 (AR), 190 (SY), 274 (P-4R) and 376 (TRT), for Fe 3 O 4 @CS: 57 (SY), 139 (AR), 290 (TRT) and 395 (P-4R); for PA: 27.8 (Ar), 30.6 (TRT), 33.4 (P-4R) and 38.7 (SY) within the Langmuir model. The difference in sorption capacity and recovery may be attributed to steric factors and chemical structure of the azo dye molecule.}