Abstract
Coffee ground (CG) waste is generated in huge amounts all over the world, constituting a serious environmental issue owing to its low biodegradability. Therefore, processes that simultaneously aim for its valorization while reducing its environmental impact are in great demand. In the current approach, blue luminescent carbon dots (C-dots) were produced in good chemical yields from CGs following hydrothermal carbonization methods under an extended set of reaction parameters. The remarkable fluorescent properties of the synthesized C-dots (quantum yields up to 0.18) allied to their excellent water dispersibility and photostability prompted their use for the first time as sensing elements for detection of noxious nitroanilines (NAs) in aqueous media. Very high levels of NA detection were achieved (e.g., limit of detection of 68 ppb for p-nitroaniline), being the regioisomeric selectivity attributed to its higher hyperpolarizability and dipole moment. Through ground–state and time-resolved fluorescence assays, a static fluorescence quenching mechanism was established. 1H NMR titration data also strongly suggested the formation of ground–state complexes between C-dots and NAs.
Highlights
To improve strategies for polluted areas’ remediation, it is necessary to increase the efficiency of conventional detection/removal of pollutants methodologies or to create innovative approaches
We report the synthesis of Carbon dots (C-dots) from Coffee ground (CG) originating from several coffee beans (CBs) brands following simple and sustainable hydrothermal carbonization (HTC) and microwaveassisted HTC approaches using a comprehensive set of reaction parameters and, for the first time, detailed studies concerning their use as photoluminescent sensors for detection of noxious nitroanilines in aqueous media
The surface state is an important characteristic of C-dots, since it is often related to the photoluminescence of C-dots [54]; the reaction temperature and residence time during their synthesis may have a significant impact on the formation of these surface functionalities and, on the photophysical properties of these nanomaterials [55]
Summary
Environmental pollution continues to be one of the main global challenges resulting from the presence of contaminants with severe impact on human health and the environment. Fluorescent C-dots produced from plant cytoplasm have demonstrated high selectivity in the detection of p-nitroaniline in soil and groundwater [26], while the use of wastewaters from cork boiling [27,28] and olive oil industrial processing [29,30] in C-dots synthesis, with proven application in the detection of (bio)molecules (e.g., hemoglobin and cytochrome c), was recently demonstrated. Another example of biomass material with a strong impact on waste production is that generated by the coffee industry and its derived products. We report the synthesis of C-dots from CGs originating from several CB brands following simple and sustainable hydrothermal carbonization (HTC) and microwaveassisted HTC approaches using a comprehensive set of reaction parameters and, for the first time, detailed studies concerning their use as photoluminescent sensors for detection of noxious nitroanilines in aqueous media
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