Blend of polyvinylpyrrolidone/thermally reduced graphene for adsorption of heavy metal ions in water

This paper presents the preparation of a modified polyvinylpyrrolidone (PVP)/graphene mixture and evaluates its adsorption capacity for heavy metal ions in water. Graphene with a high specific surface area of about 362 m² g⁻¹ was obtained through the thermal separation of graphite oxide (GO), which had been synthesised from graphite by the Hummer method. The graphene-PVP blend was prepared by dispersing the graphene into a PVP solution and then crosslinking it to prevent washout by water. This crosslinking ensured a well-dispersed and stable graphene-PVP blend. The maximum adsorption capacity of graphene-PVP for Cu²⁺ and Cd²⁺ ions was found to be 158 mg g⁻¹ and 134 mg g⁻¹, respectively, at pH 3 and a contact time of 30 min. The experimental results were found to be consistent with Langmuir and pseudo-second-order kinetic models. The study further reveals that the adsorption mechanism of Cu²⁺ and Cd²⁺ ions on graphene-PVP follows an ion exchange mechanism, driven by strong interactions between PVP and metal ions. The study provides an easy, low-cost, and eco-friendly method to produce highly adsorptive graphene-PVP materials.