Dual-Electronic Nanomaterial (Synthetic Clay) for Effective Removal of Toxic Cationic and Oxyanionic Metal Ions from Water
Van Phuong Nguyen, Khanh T. Nguyen, Loc Ton-That, Dong Thanh Nguyen, Khuong Quoc Nguyen, Mai Thị Vũ, Hai Nguyen Tran
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 (Cd 2+ , Cu 2+ , Pb 2+ , Ni 2+ , and Cr 3+ ) and oxyanions (MnO 4 – and Cr 2 O 7 2– ) from a single aqueous solution. The result demonstrated that LDH exhibited a poor porosity (its specific surface area and total pore volume: 23.2 m 2 /g and 0.161 cm 3 /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 CO 3 2– 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, pH Equilibrium 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 Ni 2+ adsorption) > 0.880 mmol/g (Cd 2+ ) > 0.701 mmol/g (Cr 3+ ) > 0.657 mmol/g (Pb 2+ ) > 0.601 mmol/g (Cu 2+ ) > 0.589 mmol/g (Cr 2 O 7 2– ) > <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mn>0.522</mml:mn><mml:mtext> </mml:mtext><mml:mtext>mmol</mml:mtext><mml:mo>/</mml:mo><mml:mtext>g</mml:mtext><mml:mtext> </mml:mtext><mml:mfenced open="(" close=")"><mml:mrow><mml:mtext>Mn</mml:mtext><mml:msup><mml:mrow><mml:msub><mml:mrow><mml:mtext>O</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:mo>–</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:mfenced></mml:math>. 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.