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Valorização de borras de café na obtenção de nanopontos de carbono luminescentes: síntese sustentável, caracterização e aplicações
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Resumo(s)
A 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.
Abstract The present work reports the synthesis of luminescent carbon nanodots (CNDs) prepared from spent coffee grounds (SCGs) with distinct origins, collected from industrial coffee shops and vending machines, through sustainable methods, involving hydrothermal carbonization with conventional heating in a high-pressure reactor and by microwave-assisted irradiation. The obtained products were purified by filtration and liquid-liquid extraction and their photophysical properties were analyzed by ground state absorption spectroscopy (UV-Vis) and steady-state fluorescence. Structural characterization of the CNDs was performed using Fourier Transform Infrared Spectroscopy and, whenever justified, by Proton Nuclear Magnetic Resonance and Elemental Analysis. CNDs that showed adequate fluorescence quantum yields were tested as fluorescent sensors for environmental pollutants (e.g. isomeric nitroanilines; NAs), heavy metals (e.g. Cu(II), Fe(II), Fe(III), Cd(II), Pb(II), Hg(II), Ni(II) and Cr(VI)) and nitroaromatic explosives precursors (e.g. 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and picric acid (PA)). Using Stern-Volmer formalism’, the synthesized CNDs showed sensitivity and selectivity in the detection of p-NA, chromium (IV) and PA.
Abstract The present work reports the synthesis of luminescent carbon nanodots (CNDs) prepared from spent coffee grounds (SCGs) with distinct origins, collected from industrial coffee shops and vending machines, through sustainable methods, involving hydrothermal carbonization with conventional heating in a high-pressure reactor and by microwave-assisted irradiation. The obtained products were purified by filtration and liquid-liquid extraction and their photophysical properties were analyzed by ground state absorption spectroscopy (UV-Vis) and steady-state fluorescence. Structural characterization of the CNDs was performed using Fourier Transform Infrared Spectroscopy and, whenever justified, by Proton Nuclear Magnetic Resonance and Elemental Analysis. CNDs that showed adequate fluorescence quantum yields were tested as fluorescent sensors for environmental pollutants (e.g. isomeric nitroanilines; NAs), heavy metals (e.g. Cu(II), Fe(II), Fe(III), Cd(II), Pb(II), Hg(II), Ni(II) and Cr(VI)) and nitroaromatic explosives precursors (e.g. 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and picric acid (PA)). Using Stern-Volmer formalism’, the synthesized CNDs showed sensitivity and selectivity in the detection of p-NA, chromium (IV) and PA.
Descrição
Palavras-chave
Nanopontos de carbono (NPsC) luminescentes Borras de café Poluentes Metais pesados Explosivos Valorização de resíduo Luminescent carbon nanodots (CNDs) Spent coffee grounds (SCGs) pollutants Heavy metals Explosives Waste recovery