Monolithic magnetic carbonaceous beads for efficient Cr(VI) removal from water

Monolithic magnetic carbonaceous materials as adsorbents can provide easy recovery and quickly separate pollutants in wastewater treatment; however, the development of designed fabrication processes remains a great challenge. Herein, a supermagnetic monolithic material was synthesized for the first time via the controllable carbonization of ferric alginate beads, and its Cr(VI) adsorption behaviour was investigated in detail. This new adsorbent was characterized using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), N2 adsorption–desorption isotherms, X-ray diffraction (XRD), Raman spectroscopy, vibrating sample magnetometry (VSM), zeta potential measurements, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Kinetic and equilibrium studies indicated that the experimental data for Cr(VI) adsorption were best described by pseudo-second-order kinetic and Langmuir models. The maximum adsorption capacity of the material for Cr(VI) was calculated to be 143.20 mg g−1 at room temperature. Evaluation of the thermodynamic parameters (ΔH > 0, ΔS > 0, and ΔG < 0) revealed that the adsorption process was endothermic and spontaneous. The mechanistic studies showed that the adsorption of Cr(VI) likely involved electrostatic attraction and a redox reaction. It was demonstrated that the material was an effective adsorbent for Cr(VI) removal with quick separation; most importantly, compared to conventional powdery adsorbents, this bead-like material could be handled much more conveniently for reuse and scale-up for practical applications, owing to its ease of operation and separation.