Eco-friendly production of functionalized few-layer graphene using coffee waste extract and in-situ growth of copper oxide nanoparticles

In this study, we report a facile, one-step and eco-friendly approach to manufacturing functionalized few-layer graphene (FFG) using coffee waste extract. We compared two environmentally friendly methods for exfoliating graphite, bath sonication and shear exfoliation. The effect of pH, initial graphite concentration, coffee waste concentration, and exfoliation time on FFG production was studied. The bath sonication method resulted in a higher lateral flake size of 1.784 mu m and a smaller degree of structural defects. Using the shear exfoliation method, a higher FFG concentration of 3.19 g/L and a smaller thickness were obtained at a shorter exfoliation time of 8 h compared to bath sonication. Raman spectra, transmission electron microscopy, and atomic force microscopy confirmed that the number of layers of FFG were in the range of 5-10. In addition, the surface of the prepared FFG was decorated with copper oxide nanoparticles (CuONPs). Energy dispersive X-ray analysis, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed the formation of CuONPs on FFG. The produced CuO-FFG showed higher 4-nitrophenol reduction (73.2%) than CuONPs (46.5%). CuO-FFG also showed higher peroxidase mimicking activity and antibacterial activity compared to CuONPs.