Selective and efficient removal of phosphate from aqueous solution using activated carbon-supported MgFe 2 O 4 -layered double hydroxide (LDH) hierarchically porous nanocomposite

Abstract In the face of the continuous development of novel adsorbents, it remains a scientific challenge to develop robust adsorbents with high efficiency, strong phosphate selectivity, high regenerability, and cost-effectiveness. In the current study, activated carbon-supported MgFe2O4-Layered Double Hydroxide (LDH) nanocomposite was synthesized, and its potential application for phosphate adsorption was investigated. The nanocomposites demonstrated a hierarchical mesoporous structure with BET specific surface area of 193 m2/g and a narrow per-size distribution of ~2 nm. SEM observation revealed the formation of a cubic octahedral structure of the adsorbent with uniform dispersion on the porous activated carbon matrix. The activated carbon-supported MgFe2O4-Layered Double Hydroxide (LDH) exhibited a high point of zero charge (pHzpc) value of 9.8 and robust phosphate adsorption potential over a wide pH range of 4 – 9 due to its high pH buffer capacity. The effect of adsorbent dose, initial phosphate concentration, contact time, and temperature on the phosphate adsorption capacity of the adsorbent was investigated. In the current study up to 99.0% removal of phosphate was achieved at 4 g/L adsorbent dosage in 4 hours at pH 7 and 30°C. The adsorption kinetics, adsorption isotherm, and thermodynamics studies of the adsorbent revealed that the adsorption of phosphate by the activated carbon-supported MgFe2O4 LDH reaches equilibrium within 240 min, with the kinetic experimental data fitting well with the pseudo-first-order kinetics (r2 > 0.99). Langmuir adsorption isotherm model fitted the experimental data well with a maximum adsorption capacity of 25.81mg/g. The intraparticle diffusion model fitted the adsorption data well and demonstrated that the adsorption process is not only controlled by the intraparticle diffusion or micropore diffusion but also by the boundary layer diffusion or macro-pore diffusion effect. The adsorbent displayed strong selectivity of phosphate in the presence of competing anions, and the study demonstrated that AC@ MgFe2O4-LDH would have a promising potential for efficient adsorption of phosphate potential over a wide pH range.