Validation of Spent Coffee Grounds as Precursors for the Development of Sustainable Carbon Dot-based for Fe³⁺ Optical Sensing

Carbon dots (CDs) are fluorescence carbon-based nanomaterials that possess several properties such as (photo)chemical stability, biocompatibility and good water solubility.[1, 2] They can be fabricated from a large variety of precursors, however, most available organic molecules are still expensive and their use or synthesis can lead to significant challenges to the environment and human health. It has become desirable to use biomass waste as alternative precursors in the synthesis of CDs, given that biomass waste material is ubiquitous, nontoxic, cheap, and renewable.

The significant increasement of coffee consumption has consequently led to an increase in waste products, including spent coffee grounds (SCGs), which are the residues of coffee brewing.

In this work, we fabricated SCG-based CDs via one-pot and solvent-free carbonization of solid samples generating particles with sizes between 2.1 and 3.9 nm. These carbon nanoparticles exhibited blue fluorescence and excitation-dependent emission of CDs with moderate quantum yields (2.9-5.8%).[3]

More importantly, SCG-based CDs showed potential for being used as optical Fe³⁺ optical sensors, with Life Cycle Assessment (LCA) studies validating the SCGs as more sustainable precursors than classical precursors, both considering a weight- or function-based functional unit.

Acknowledgments: Fundação para a Ciência e Tecnologia (FCT) is acknowledged for funding projects PTDC/QUI-QFI/2870/2020 and UIDB/00081/2020, the Ph.D. Grant SFRH/BD/144423/2019 (D.M.A.C.), and scientific employment stimulus CEECIND/01425/2017 (L.P.d.S.).

References

1. Crista, D.M.A., J.C.G. Esteves da Silva, and L. Pinto da Silva, Evaluation of Different Bottom-up Routes for the Fabrication of Carbon Dots. Nanomaterials (Basel), 2020. 10(7).
2. Vale, N., et al., Normal breast epithelial MCF-10A cells to evaluate the safety of carbon dots. RSC Medicinal Chemistry, 2021. 12(2): p. 245-253.
3. Crista, D.M.A., et al., Turning Spent Coffee Grounds into Sustainable Precursors for the Fabrication of Carbon Dots. Nanomaterials, 2020. 10(6): p. 1209.