A green cross-linking method for the preparation of renewable threedimensional graphene sponges for efficient adsorption of Congo red dye

Graphene-based materials possess significant potential for the treatment of dye wastewater due to their exceptional adsorption properties toward stubborn pollutants. However, their utilization is hindered by high preparation costs, low yields, environmental pollution during synthesis, and challenges in regenerating the adsorbent. This study proposes a novel approach to address these limitations by developing nitrogen-doped three-dimensional(3D) polyvinyl alcohol(PVA) crosslinked graphene sponges(N-PGA) using a cross-linking method with ammonium carbonate. This method offers a relatively mild, environmentally friendly approach. Ammonium carbonate serves as both a reducing and modifying agent, facilitating the formation of the intrinsic structure of N-PGA and acting as a nitrogen source. Meanwhile, PVA is utilized as the cross-linking agent. The results demonstrate that N-PGA exhibits a favorable internal 3D hierarchical porous structure and possesses robust mechanical properties. The measured specific surface area(BET) of N-PGA was as high as406.538 m2·g-1, which was favorable for its efficient adsorption of Congo red(CR) dye molecules. At an initial concentration of 50 mg·L-1, N-PGA achieved an impressive removal rate of 89.6% and an adsorption capacity of 112 mg·g-1for CR dye. Furthermore, it retained 79% of its initial adsorption capacity after 10 cycles, demonstrating excellent regeneration performance. In summary, the synthesized N-PGA displays remarkable efficacy in the adsorption of CR dye in wastewater, opening up new possibilities for utilizing 3D porous graphene nanomaterials as efficient adsorbents in wastewater treatment.