Preparation and adsorption study of polyvinyl alcohol-functionalized sodium alginate composite hydrogel for Pb(II) in aqueous solutions

This paper presents the utilization of sodium alginate (SA) as a raw material to construct a double network structure through the incorporation of chitosan (CS) and the electrostatic polymerization of SA. Subsequently, by employing polyvinyl alcohol (PVA) as a functional material, a modified SA/CS/PVA composite hydrogel (SCPH) was prepared via the Ca(II) ion exchange method. The hydrogel exhibited a flocculent form, thereby greatly enhancing the removal of Pb(II). The adsorption process of Pb(II) by the SCPH reached equilibrium within 30 min, achieving a remarkable removal rate of 97.45% and a maximum adsorption capacity of 147.93 mg/g (298 K). A series of characterization analyses have been employed to investigate the structure and adsorption mechanism of hydrogels, and the adsorption mechanism involves ion exchange, electrostatic attraction, as well as the complexation of hydroxyl and carboxyl groups. Batch adsorption experiments were conducted at different temperatures and pH levels, and the kinetics and isotherms were investigated. The Langmuir isotherm and pseudo-second-order kinetic model were found to best fit the experimental data, suggesting the feasibility of using the SCPH as an efficient adsorbent for Pb(II) removal. Moreover, the dual network structure constructed by SA and CS significantly enhances the adsorption performance of SCPH. At the same time, PVA strengthens the mechanical strength of SCPH, which is favorable for recycling. As a low-cost and efficient adsorbent, SCPH can be widely used in water treatment.