Adsorption toward Pb(II) occurring on three-dimensional reticular-structured montmorillonite hydrogel surface

Two-dimensional montmorillonite nanosheets (2DMMT), acrylic acid and acrylamide were used as raw materials to synthesize the three-dimensional reticular-structured hydrogel via hydrogen-bond, polymerization, amidation and electrostatic interactions. Morphology characteristics shown the porous structure of montmorillonite hydrogel, offering an open-access for Pb(II) to react with internal adsorption sites. Adsorption tests indicated that 2DMMT hydrogel could achieve the effective removal (99%) for high concentrated Pb(II) solution (125 mg/L) via small hydrogel dosage (1 g/L) within short contact time (60 min). High removal of Pb(II) (70%, adsorption capacity: 90 mg/g) could be still achieved even after five adsorption-regeneration cycles, achieving the long-term servicing for wastewater treatment with cost-optimal operation. Adsorption kinetics and isotherm tests indicating the homogeneous monolayer physical and chemical adsorption between Pb(II) and hydrogel, and the adsorption capacity of Pb(II) was controlled by the amount of adsorption sites on hydrogel. Characteristics of XPS and EDS revealed the adsorption mechanism of ion exchange, chelation reaction and chemical precipitation. Two-dimension montmorillonite with high surface area and fully-exposed active sites formed the reticular-structured hydrogel, showing high removal ability for Pb(II).