Synthesis of graphene quantum dots from rice husk for water treatment applications

This study aims to develop a sustainable method for synthesizing graphene quantum dots (GQDs) from biomass waste for water treatment applications. Rice husk, a carbon-rich waste material, was used as a precursor for GQDs synthesis via a simple boiling method, providing a sustainable and cost-effective approach. The optimal GQDs sample (2.5% w/v) was prepared from 5 g of rice husk and 200 mL of deionized water, exhibiting greenish fluorescence under UV light, indicating successful GQD formation. The synthesized GQDs were characterized by ultraviolet–visible (UV–Vis), Fourier-transform infrared (FTIR) and fluorescence spectroscopy, as well as zeta potential analysis. The 2.5% w/v filtered GQDs showed low absorption beyond 230 nm in the UV region, a zeta potential of −20.6 ± 1.0 mV indicating good colloidal stability, and the presence of oxygen-containing functional groups that enhance adsorption capability, as confirmed by FTIR analysis. The adsorption performance of GQDs was evaluated using methylene blue (an organic dye) and copper ions (a heavy metal). The electrical conductivity (EC) of the copper sulphate (CuSO₄) solution decreased by 54.2%, demonstrating significant removal of copper ions. In contrast, the EC of the methylene blue solution increased slightly by 21.5%, possibly due to the release of smaller ionic species during degradation or interactions between GQDs and dye molecules. In summary, this study presents an eco-friendly approach for converting biomass waste into functional nanomaterials for water purification, contributing to sustainable waste management and clean water initiatives aligned with the United Nations Sustainable Development Goals (SDGs).