Synthesis and characterization of PVA/rGO composite hydrogel for efficient removal of dyes and heavy metals from aqueous solutions

Abstract The contamination of water resources by synthetic dyes and heavy metal ions poses significant environmental and health risks worldwide. In this study, we report the synthesis of polyvinyl alcohol/reduced graphene oxide (PVA/rGO) composite hydrogels via a facile aqueous mixing method employing borax crosslinking and repeated freeze–thaw cycles. The structural, chemical, morphological, and adsorption properties of the synthesized composite were comprehensively characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, and thermogravimetric analysis (TGA). The results demonstrate successful integration of rGO nanosheets into the PVA matrix, forming a porous threedimensional network with enhanced thermal stability and surface area. Batch adsorption experiments were conducted using methylene blue (MB), Congo Red (CR), and representative heavy metal ions (Pb2+, Cu2+, Cd2+). The composite hydrogel exhibited remarkable adsorption capacities of 185.6 mg g-1 for MB, 142.3 mg g-1 for CR, 98.7 mg g-1for Pb2+, 76.4 mg g-1 for Cu2+, and 62.1 mg g-1 for Cd2+. Isotherm data were best described by the Langmuir model for MB and heavy metals, while the Freundlich model provided superior fitting for CR adsorption. . The adsorption mechanisms involve π-π interactions, hydrogen bonding, electrostatic attractions, and surface complexation. The PVA/rGO hydrogel demonstrated excellent reusability, maintaining over 85% of its initial adsorption capacity after six consecutive adsorption–desorption cycles. The facile synthesis approach, coupled with high adsorption performance and good recyclability, positions PVA/rGO composite hydrogels as promising, cost-effective adsorbents for wastewater treatment applications.