Dual-Electronic Nanomaterial (Synthetic Clay) for Effective Removal of Toxic Cationic and Oxyanionic Metal Ions from Water

Abstract

A synthetic clay (Mg/Al-layered double hydroxides; LDH) was directly synthesized through a simple coprecipitation method under a low-supersaturation condition. The clay was applied to remove metal cations (Cd2+, Cu2+, Pb2+, Ni2+, and Cr3+) and oxyanions (MnO4– and Cr2O72–) from a single aqueous solution. The result demonstrated that LDH exhibited a poor porosity (its specific surface area and total pore volume: 23.2 m2/g and 0.161 cm3/g, respectively) and positively charged surface within solution pH from 3.0 to 12. The X-ray powder diffraction (XRD) data suggested that the basal spacing of LDH was 0.773 nm. The presence of active CO32– anions in the interlayer region of LDH that played an extremely important role in the adsorption process was identified by XRD and Fourier-transform infrared spectroscopy (FTIR). Energy-dispersive X-ray spectroscopy (SEM) analysis indicated that LDH possessed a surface morphology like a plate with a hexagonal shape. The adsorption isotherms of LDH towards various potentially toxic metals were conducted at 1.0 g/L, pHEquilibrium 5.0, 30°C, and 24 h. The Langmuir maximum adsorption capacity of LDH towards the target metals exhibited the following order: 1.299 mmol/g (for Ni2+ adsorption) > 0.880 mmol/g (Cd2+) > 0.701 mmol/g (Cr3+) > 0.657 mmol/g (Pb2+) > 0.601 mmol/g (Cu2+) > 0.589 mmol/g (Cr2O72–) > 0.522 mmol/g MnO4–. The synthetic clay can adsorb both cations and anions in the solution. Therefore, such LDH material can serve as a potential dual-electronic adsorbent for effectively eliminating various oxyanionic and cationic metal ions from water media.