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/Fe3O4/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 200nm. PDA and Fe3O4 modifications increased the specific surface area of adsorbent, changed the surface functional group of biochar (BC), and made the adsorbent have super-high magnetization (294.76emug(-1)). PDA/Fe3O4/BC was applied to treat Cr wastewater. The results show that the adsorption of Cr by PDA/Fe3O4/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 25.25mgg(-1) at 318K and 23.108kJmol(-1), respectively. After adsorption treatment, PDA/Fe3O4/BC still possesses high magnetization (233.04emug(-1)). PDA/Fe3O4/BC can treat actual electroplating wastewater with Cr(VI) concentration from 20mgL(-1) to less than 0.2mgL(-1), which met the PRC discharge standard (GB/21900-2008) of electroplating pollutants.