Fabrication of NiFe2O4@PEI and NiFe2O4@PPy nanospheres for adsorptive and photocatalytic removal of organic dyes

[Display omitted] •Superparamagnetic NiFe2O4 polycrystalline cores were fabricated by hydrothermal method and then coated with PEI or PPy polymers.•The influence of different polymeric shells with various content on surface chemistry, optimization of band gap energy, adsorption, and photocatalytic performance of polycrystalline superparamagnetic cores are studied.•The photocatalytic decomposition of methyl orange (MO) under a visible illumination source was improved after coating NiFe2O4 with PEI and PPy polymers.•Excellent photocatalytic activity under visible light and proper magnetic separation under the magnetic field to remove water pollution was confirmed.•Fabricated core–shell nanostructures are effective candidates for the adsorptive and photocatalytic removal of organic dyes from wastewater. Spinel ferrites (MFe2O4) and their binary composites with polymers are frequently used to remove and degrade organic dyes due to their magnetic, optical, and biocompatible features. In this study, NiFe2O4, as a superparamagnetic core, was coated using the deposition of polyethylenimine (PEI) and in-situ oxidative polymerization of pyrrole (py). Fourier-transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were employed to analyze NiFe2O4, NiFe2O4@PEI, and NiFe2O4@PPy nanospheres. The morphology and chemical composition of nanoparticles were investigated using field emission scanning electron microscopy (FESEM). The formation of core–shell nanostructure was confirmed using transmission electron microscopy (TEM). A vibrating sample magnetometer (VSM) recorded the magnetic behavior of samples before and after coating polymers. NiFe2O4 superparamagnetic core exhibited high saturation magnetization (Ms) (63.6 emu/g) and easy collection by applying an external magnetic field. The maximum magnetic adsorption efficiencies were determined to be 92% and 72% for NiFe2O4@PEI (NiFe2O4/PEI weight ratio of 1:10) and NiFe2O4@PPy (NiFe2O4/PPy weight ratio of 1:50), respectively. Moreover, optical properties and photocatalytic activity were examined using UV–Vis spectroscopy. The band gap energy value was reduced from 2.3 eV for pure NiFe2O4 to 2.0 eV and 1.9 eV for NiFe2O4@PEI and NiFe2O4@PPy nanoparticles, respectively. The photocatalytic decomposition of methyl orange (MO) under visible illumination was improved after coating NiFe2O4 with PEI and PPy polymers. The results denote that NiFe2O4@PEI and NiFe2O4@PPy core–shell nano