A novel superparamagnetic micro-nano-bio-adsorbent PDA/Fe3O4/BC for removal of hexavalent chromium ions from simulated and electroplating wastewater

In order to improve the adsorption efficiency of the adsorbent and solve the problem of separation difficulty, a novel superparamagnetic micro-nano-bio-adsorbent (PDA/Fe 3 O 4 /BC) was prepared by in situ self-assembly of polydopamine (PDA). The results of scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR), X-ray photoelectron spectrometer (XPS), and vibrating sample magnetometer (VSM) characterization showed that the size of bio-adsorbent was about 200 nm. PDA and Fe 3 O 4 modifications increased the specific surface area of adsorbent, changed the surface functional group of biochar (BC), and made the adsorbent have super-high magnetization (294.76 emu g −1 ). PDA/Fe 3 O 4 /BC was applied to treat Cr wastewater. The results show that the adsorption of Cr by PDA/Fe 3 O 4 /BC includes single-layer and multilayer adsorption. The adsorption follows the pseudo-second-order kinetic model. The adsorption is spontaneous and endothermic, and its maximum adsorption capacity and activation energy are 25.25 mg g −1 at 318 K and 23.108 kJ mol −1 , respectively. After adsorption treatment, PDA/Fe 3 O 4 /BC still possesses high magnetization (233.04 emu g −1 ). PDA/Fe 3 O 4 /BC can treat actual electroplating wastewater with Cr(VI) concentration from 20 mg L −1 to less than 0.2 mg L −1 , which met the PRC discharge standard (GB/21900-2008) of electroplating pollutants. Graphical abstract