Facile one-pot synthesis of urchin-like Fe–Mn binary oxide nanoparticles for effective adsorption of Cd(ii) from water

Abstract

The development of efficient and low-cost adsorbent is critical for water treatment, but still presents great challenges. Herein, we report the synthesis of three-dimensional (3D) hierarchical nanostructured adsorbent, urchin-like Fe–Mn binary oxides (UFMBO), by simple heating without any template/surfactant. The surface morphology, crystalline and pore structure were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and nitrogen adsorption–desorption isotherm, respectively. Results revealed that the UFMBO had a 3D hierarchical nanostructure with a high specific surface area of 142 m² g⁻¹, which was conducive to pollutant adsorption and adsorbent separation. Cd(II) removal using the UFMBO was evaluated by batch adsorption experiments. The adsorption equilibrium was established within 3 h, and the adsorption process was better described by pseudo second-order kinetics model. The adsorption isotherm data fitted well to Langmuir model, and the maximum adsorption capacity was 74.76 mg g⁻¹ at pH 6.0. Influence by ionic strength on the adsorption was significant, implying that Cd(II) may form outer-sphere complexes on the adsorbent surface. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis suggested hydroxyl group played an important role in Cd(II) uptake. The highly effective 3D UFMBO adsorbent can be easily separated and regenerated, demonstrating its great potential in cadmium removal from contaminated water source.