Design of structure of hierarchically porous carbon monoliths with magnetic properties for high efficiency in adsorption of lead (II) ions

Abstract

Pb (II) is one of the toxic heavy metal ions, which is released from the industry, especially the manufacture of batteries and electronics-devices. Its release into the water effluents causes environmental problems and affects the humans’ and animals’ health. Adsorption is one of the conventional techniques for removal of Pb (II) in water treatment processes. The adsorbents with effective adsorption properties with their easy operation are then desired. In this study, hierarchically porous carbon monoliths with magnetic properties have been designed and successfully fabricated by incorporating sodium alginate and black liquor in ferric chloride solution. The resulting monoliths have been used to study their adsorption efficiency towards Pb (II) in aqueous solution. The interconnected macroporous structures of the materials were generated by the freeze-drying process, while the increase in microporosity was observed after pyrolysis at 700 °C (SA-BL-Fe-700). SA-BL-Fe-700 showed a magnetization of 8.79 emu/g, and high porosity, with a BET specific surface area of 945.45 m2/g and pore size distribution calculated by DFT was less than 2 nm, which is suitable to adsorb Pb (II) ions. Furthermore, the materials obtained showed a monolith feature in a cylindrical shape with strong mechanical stability, which renders them with the easy operation. The adsorption properties of SA-BL-Fe-700 monolith toward Pb (II) ions demonstrated a maximum adsorption capacity of 75.19 mg/g at pH 5 with retaining the magnetic properties. The study of adsorption behaviours illustrated that equilibrium data and kinetic study fitted with Langmuir isotherm model and pseudo-second-order model, respectively.