Controllable synthesis of coral-like hierarchical porous magnesium hydroxide with various surface area and pore volume for lead and cadmium ion adsorption

A coral-like hierarchical porous magnesium hydroxide (HPMH) with various surface area and pore volume was controllably prepared using a simple one-step hydrothermal process, for which MgO, water and citric acid were applied. The citric acid (CA), as a structure-directing molecule, is a key factor in regulating the pore structure of HPMH products. With different additive dosages, the nanostructure, surface area and pore volume of HPMH products can be controllably regulated. The MH-CA20 product (prepared in the presence of 20 wt% CA) with high BET surface area (159 m2/g) and pore volume (0.75 cm3/g) was used to investigate the adsorption properties for Pb(II) and Cd(II) ions. The experimental adsorption capabilities of the MH-CA20 for Pb(II) and Cd(II) are respectively 4535 and 3530 mg g-1, very close to the maximum adsorption capabilities calculated by Langmuir equation (4545 and 3571 mg g-1). According to the adsorption kinetics and adsorption isotherm data, the adsorption process conforms to the Pseudo-second-order and Langmuir model, indicating that heavy metal ions conduct monolayer chemical adsorption mechanism. Since the preparation of HPMH is simple, low-cost and filtrate recycling, the process can easily be scaled up and could be a good candidate for application in tackling different wastewater.

Automated summary

A coral-like hierarchical porous magnesium hydroxide (HPMH) with controllable nanostructure, surface area, and pore volume was successfully prepared using a simple one-step hydrothermal process. The addition of citric acid (CA) played a key role in regulating the pore structure of the HPMH products. The HPMH showed high adsorption capabilities for Pb(II) and Cd(II) ions, following a Pseudo-second-order and Langmuir adsorption mechanism, suggesting a monolayer chemical adsorption process for heavy metal ions.