Layered double hydroxide-loaded biochar as a sorbent for the removal of aquatic phosphorus: behavior and mechanism insights

This study was aimed to enhance the phosphorus (P) sorption capability of biochar through embedding of Mg-Fe layered double hydroxide (LDH) particles within its matrix. The structure, morphology, and surface chemistry of the prepared LDH/biochar composite were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared (FTIR) analysis. The P sorption behavior of LDH/biochar composite was assessed in comparison with the raw biochar under batch conditions. The effects of initial P concentrations, pH levels, and contact times on P sorption were examined. Results showed that the P sorption on LDH/biochar composite was pH-dependent, and the maximum P sorption was found at the pH range of 2-4. The sorption isotherm and kinetic data were best fitted with the Langmuir and pseudo-second-order models, respectively. The maximum P sorption capacity (Q(max)) improved from 1.39 mg g(-1) for raw biochar to 17.46 mg g(-1) for LDH/biochar composite, respectively. Also, the equilibrium contact time decreased from 8 h for raw biochar to 1 h for LDH/biochar composite, respectively. The sorption process followed electrostatic attraction, ligand exchange, and surface inner-sphere complex formation mechanisms. Overall, the results of the present study revealed that the synthesized LDH/biochar composite can be potentially used as a carbon-based sorbent for the removal of phosphorus from aqueous solutions.