Lactose intercalated layered double hydroxide as a green sorbent for efficient and selective removal of heavy metals from aqueous solution

In recent years, layered double hydroxides (LDHs) have shown a remarkable potential for effective removal of heavy metals owing to their large surface area, high anion exchange capacity and good thermal stability [1]. This study represents the efficient removal of heavy metals from aqueous solution by layered double hydroxide intercalated with biomolecule as a green and economical sorbent. The Lactose (LA) was intercalated into copper-aluminium layered double hydroxide (CuAl-LA-LDH) to produce an adsorbent which indicates highly selective and extremely efficient removal of heavy metal such as Hg+2 and Pb+2. LA-LDH was prepared using the co-precipitation method. The structure of sorbent was investigated using X-ray diffraction, scanning electron microscopy, Fourier transform infrared, Brunauer-Emmett-Teller, Barret-Joyner-Halenderm and transmission electron microscopy. X-Ray diffraction showed that with the presence of lactose, distance between the layers has increased compared with the NO3-LDH. To extract the analytes, 20 mg of sorbent was added into 20 mL of the solution containing a certain concentrations of heavy metals. The mixture was stirred for 1 h at a constant temperature of 25 °C. After extraction of the ions at equilibrium time, the sorbent was setteled by centrifugation. The metal ions concentrations in the supernatant solutions were determined using ICP-AES. Sorption isotherm for Hg+2 and Pb+2 agrees with the Langmuir model suggesting a monolayer adsorption and maximum adsorption capacity was 303.0 mg g-1 for Hg+2 and 322.6 mg g-1 for Pb+2. The sorption kinetics for mentioned ions follows a pseudu-second-order model, suggesting a chemisorption process. The distribution coefficient (Kd) values using CuAl-LA-LDH was 6.07×104 ml g-1 for Hg+2 and 6.41×102 ml g-1 for Pb+2. The results were shown that the sorbent has high capability to remove heavy metals from aqueous solutions.