Enhanced Cu2+ adsorption through double cross-linking of hydrogel with in situ CaCO3

Hydrogel systems formed with polymers possessing functional groups are widely explored for the removal of heavy metal ions due to their high adsorption capability, while numerous inorganic micro-nano-particles have been investigated as well due to their potential to bring in complementary properties to organic constituents. However, challenges still remain to design an efficient system for water purification. Here, a double cross-linked system with polyvinyl alcohol (PVA) and sodium alginate (SA) was developed by freeze-thaw cycles and Ca2+-induced cross-linking. Importantly, calcium carbonate (CaCO3) particles with a high adsorption capacity were doped via an in-situ method, which enhanced mechanical properties of PVA/SA hybrid films. Additionally, CaCO3 doubled the Cu2+ adsorption efficiency of PVA/SA/CaCO3 compared to that of PVA/SA, and finally reached an adsorption equilibrium (Ae) of 95 %. PVA/SA/CaCO3 experienced a typical pseudo-second-order adsorption kinetic model and the Langmuir model of adsorption isotherm, indicating that the adsorption process was more inclined to monolayer chemisorption. The adsorption thermodynamic revealed that the adsorption process was spontaneous and exothermic. The highly efficient adsorption of Cu2+ ions by PVA/SA/CaCO3 was the result of the synergistic adsorption mechanism of electrostatic interaction, complexation, cation exchange and ionic reaction. Regeneration experiment and comparative results shows that PVA/SA/CaCO3 has greater application potential for wastewater purification.