Eco-friendly Photocatalytic Removal of Synthetic Dye Wastewater using Spent Coffee Grounds (SCGs)-derived Reduced Graphene Oxide (rGO)

Photocatalysts are distinguished materials that can easily convert solar energy for the uses in oxidation and reduction activities. The escalating global consumption of coffee has led to a surge in the generation of spent coffee grounds (SCGs), contributing significantly to environmental pollution when disposed of in landfills. This study proposes a sustainable approach to repurpose SCGs by synthesizing reduced graphene oxide (rGO) and apply as a photocatalyst for the degradation of methylene blue (MB), a common dye pollutant. SCGs were pre-treated by hydrothermal and used as the precursor to synthesize graphene oxide (GO) via modified Hummer’s method, then reduced into rGO. The sample was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy (UV-Vis). XPS analysis showed that the decrease in carbon bonds as carbonyl functional groups increased from graphite to rGO indicated successful oxidation and reduction. Graphite generally exhibits more extensive π-binding than rGO due to its composition of pristine graphene layers with intact π-electron systems. The XRD analysis revealed that graphite (commercial) exhibits a peak at approximately 26.7o on (002) plane, while coffee grounds derived rGO displays a leftward shift with a peak appearing around 24o, due to the amorphous structure of SCGs. Photocatalytic experiment was carried out by continuously stirring under UV light (254 nm). Within 2h of irradiation, approximately 60% of MB has been reduced by using only 0.25 mg of rGO. To enhance the removal efficiency, rGO can be used to improve the photocatalytic activity of titanium dioxide (TiO2).