Photocatalytic Degradation of Organic Pollutants Using Graphene Quantum Dot-Loaded Sodium Alginate Hydrogels: Synthesis and Characterization

Abstract

Rapid industrialization and population growth are placing increasing pressure on global clean water resources, resulting in a decline in water quality and associated environmental and health risks. Nanotechnology offers promising and cost-effective solutions for water remediation. Among nanomaterials, graphene quantum dots (GQDs) exhibit strong potential due to their chemical stability, high surface area, and photo luminescent properties. Embedding GQDs within hydrogels enhances their stability, dispersion, and photocatalytic performance. This study aimed to synthesize GQDs from organic waste—specifically waste tea leaves (WTL)—using an environmentally friendly microwave- assisted method. The synthesized GQDs were characterized using UV–Vis spectroscopy, dynamic light scattering (DLS), zeta potential, and scanning electron microscopy (SEM), revealing an absorption peak at 272 nm, particle sizes below 100 nm, high colloidal stability, and spherical morphology. GQDs were embedded in sodium alginate (SA) hydrogels through ionic crosslinking. The resulting GQDs-loaded hydrogels were characterized by UV–Vis spectroscopy, swelling behavior tests, and visual inspection under UV light. Photocatalytic degradation tests against methylene blue (MB) demonstrated effective dye removal under both UV light (25.1%) and dark conditions (17.85%), confirming both photoreactive and passive adsorption capabilities. These results highlight the synergistic effect of GQDs and SA hydrogels and offer a sustainable, dual-function platform for wastewater treatment applications.