Percorrer por autor "Moraes, Bianca"
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- Carbon dots from coffee grounds by a one-pot microwave-assisted methodPublication . Moraes, Bianca; Costa, Alexandra I.; Barata, Patrícia; Prata, José V.Carbon-based nanomaterials, particularly carbon dots (C-dots) have attracted the researchers interest due their excellent luminescence, photostability and biocompatibility, encouraging their use in several areas such as biomedicine, (bio)sensors, photocatalysis and optoelectronics. C-dots could be prepared by a variety of methods (top-down and bottom-up approaches), using a great diversity of carbon sources. Bottom-up processes based on the use of waste materials for producing C-dots are particularly attractive since an effective reduction of environmental impacts of those wastes may be foreseen, while high-valued nanomaterials can be simultaneously obtained. Coffee is one of the most consumed brews all over the world, generating large amounts of coffee waste, a source of a serious environmental problem due to the high content of organic matter such as caffeine, phenols, tannins, and sugars. Herein, we explore the valorization of coffee grounds generated from automatic and vending machines for production of C-dots through a one-pot monomode microwave-assisted method. Structural and photophysical characterization of the as-synthesized nanomaterials have been carried out, and their potential applications as sensing materials for pollutants and explosives (e.g. nitroanilines and nitroaromatics) were evaluated by fluorescence and absorption techniques.
- Carbon dots from coffee grounds: synthesis, characterization, and detection of noxious nitroanilinesPublication . Costa, Alexandra I.; Barata, Patrícia; Moraes, Bianca; Prata, José V.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. H-1 NMR titration data also strongly suggested the formation of ground-state complexes between C-dots and NAs.
- Carbon dots synthesis from coffee grounds, and sensing of nitroanilinesPublication . Moraes, Bianca; Costa, Alexandra I.; Barata, Patrícia; Prata, José V.Fluorescent carbon dots (C-dots) were directly synthesized by a sustainable and eco friendly one-pot microwave-assisted hydrothermal carbonization method from coffee grounds waste. The coffee grounds obtained from automatic coffee machines, after being heated at 190 °C for 1–4 h in the presence of nitrogen additives, furnished the desired carbon nanomaterials. Struc tural and photophysical properties of the as-synthesized nanomaterials were evaluated by FTIR, 1H NMR, UV-Vis, and fluorescence spectroscopies. The ability of the C-dots to behave as probes for isomeric nitroanilines (ortho-, meta- and para-nitroaniline) was explored through fluorimetric titra tion experiments. High sensitivities and selectivities were obtained for the detection of nitroanilines in aqueous media.
- Valorização de borras de café na obtenção de nanopontos de carbono luminescentes: síntese sustentável, caracterização e aplicaçõesPublication . Moraes, Bianca; Costa, Alexandra Isabel Martins Paulo; Barata, Patrícia Alexandra Miranda DavidA presente dissertação apresenta a síntese de nanopontos de carbono (NPsC) luminescentes a partir de borras de café (BsC) com origens distintas, recolhidas em máquinas industriais de cafetarias e de venda automática, através de métodos sustentáveis envolvendo a carbonização hidrotérmica com aquecimento convencional em reator de alta-pressão e por irradiação assistida por microondas. Os produtos obtidos foram purificados por filtração e extração líquido-líquido e as suas propriedades fotofísicas foram analisadas por Espectroscopia de Absorção de Estado Fundamental (UV-Vis) e Espectroscopia de Fluorescência de Estado Estacionário. A caracterização estrutural dos NPsC foi realizada com recurso a Espectroscopia de Infravermelho com Transformada de Fourier e sempre que se justificou, por Ressonância Magnética Nuclear de Protão e Análise Elementar. Os NPsC que apresentaram rendimentos quânticos de fluorescência adequados foram testados como sensores fluorescentes de poluentes ambientais (e.g. nitroanilinas isoméricas; NAs), metais pesados (e.g. Cu(II), Fe(II), Fe(III), Cd(II), Pb(II), Hg(II), Ni(II) e Cr(VI)) e nitroaromáticos precursores de explosivos ((e.g. 2,4,6-trinitrotolueno (TNT), 2,4-dinitrotolueno (DNT) e ácido pícrico (AP)). Recorrendo ao formalismo de Stern-Volmer, os NPsC sintetizados revelaram sensibilidade e seletividade na deteção de p-NA, crómio (VI) e AP.