Propriedades fotoluminescentes de pontos quânticos de carbono sintetizados a partir de ácido cítrico e da técnica hidrotermal
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2020-07-14
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Universidade Estadual Paulista (Unesp)
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Pontos quânticos de carbono (CQDs) têm recebido bastante atenção devido às suas inúmeras propriedades físicas e químicas, entre as quais: baixa toxicidade, emissão luminescente, boa condutividade e produção com custo moderado. Tem sido relatado que os pontos quânticos de grafeno (GQDs) apresentam características ópticas e eletrônicas singulares, tendo como principal atrativo a luminescência, pois podem exibir absorção na região ultravioleta (UV) e ultravioleta-visível (UV-Vis). Estudos apontam também que a dopagem de GQDs com nitrogênio (N) causa um aumento na sua intensidade de emissão fotoluminescente (PL). Outra classe de material que também está chamando a atenção são os pontos quânticos de óxido de grafeno (GO). Ele possui uma extensa banda no espectro de luminescência que abrange a faixa UV até o infravermelho próximo (NIR) e apresenta o “efeito de borda vermelha”, que faz seu comprimento de onda de emissão e excitação serem conexos. Há diversos métodos para síntese de GQDs e GO, e neste trabalho fizemos o uso do método hidrotermal, pois ele possibilita o controle das características físico-químicas das amostras. O material utilizado como precursor para tal produção foi o ácido cítrico (CA) e como bases, o hidróxido de sódio (NaOH) e o hidróxido de amônio (NH4OH). As técnicas de caracterização escolhidas para análises foram as espectroscopias de absorção e fluorescência e a partir delas foi verificada a influência que as bases podem causar. Notou-se que a adição de NaOH provocou dependência entre os comprimentos de onda de excitação e emissão PL, causando o deslocamento do pico de emissão PL para a região do vermelho (efeito de borda vermelha). Esta característica é um indício de que houve formação GO na estrutura do material. Com o NH4OH foi observado o oposto, ele apresenta um único comprimento de onda de emissão PL independente da excitação, isto é um indicativo para formação de GQD. Em ambos os casos ocorreram emissão PL entre 425 e 450 nm exibindo, portanto, a emissão de luz azul.
Carbon quantum dots (CQDs) have received a lot of attention due to their numerous physical and chemical properties, among which are: low toxicity, luminescent emission, good conductivity and moderate cost production. It has been reported that the graphene quantum dots (GQDs) have unique optical and electronic characteristics, having as main attraction the luminescence, because they can exhibit absorption in the ultraviolet (UV) and ultraviolet-visible (UV-Vis) region. Studies also point out that the doping of GQDs with nitrogen (N) causes an increase in its intensity of photoluminescent (PL) emission. Another class of material that is also attracting attention are the graphene oxide (GO) quantum dots. It has an extensive band in the luminescence spectrum that covers the UV to near infrared (NIR) range and has the "red edge effect", which makes its wavelength of emission and excitation be connected. There are several methods for the synthesis of GQDs and GO, and in this work we used the hydrothermal method, as it allows the control of the physical and chemical characteristics of the samples. The material used as precursor for such production was citric acid (CA) and as bases, sodium hydroxide (NaOH) and ammonium hydroxide (NH4OH). The characterization techniques chosen for analysis were absorption and fluorescence spectroscopies and the influence that the bases can cause was verified. It was noted that the addition of NaOH caused dependence between the wavelengths of excitation and PL emission, causing the displacement of the peak of PL emission to the red region (red border effect). This characteristic is an indication that GO formation has occurred in the structure of the material. With the NH4OH the opposite was observed, it presents a single wavelength of PL emission independent of excitation, this is indicative for the formation of GQD. In both cases there was a PL emission between 425 and 450 nm, thus showing blue light emission.
Carbon quantum dots (CQDs) have received a lot of attention due to their numerous physical and chemical properties, among which are: low toxicity, luminescent emission, good conductivity and moderate cost production. It has been reported that the graphene quantum dots (GQDs) have unique optical and electronic characteristics, having as main attraction the luminescence, because they can exhibit absorption in the ultraviolet (UV) and ultraviolet-visible (UV-Vis) region. Studies also point out that the doping of GQDs with nitrogen (N) causes an increase in its intensity of photoluminescent (PL) emission. Another class of material that is also attracting attention are the graphene oxide (GO) quantum dots. It has an extensive band in the luminescence spectrum that covers the UV to near infrared (NIR) range and has the "red edge effect", which makes its wavelength of emission and excitation be connected. There are several methods for the synthesis of GQDs and GO, and in this work we used the hydrothermal method, as it allows the control of the physical and chemical characteristics of the samples. The material used as precursor for such production was citric acid (CA) and as bases, sodium hydroxide (NaOH) and ammonium hydroxide (NH4OH). The characterization techniques chosen for analysis were absorption and fluorescence spectroscopies and the influence that the bases can cause was verified. It was noted that the addition of NaOH caused dependence between the wavelengths of excitation and PL emission, causing the displacement of the peak of PL emission to the red region (red border effect). This characteristic is an indication that GO formation has occurred in the structure of the material. With the NH4OH the opposite was observed, it presents a single wavelength of PL emission independent of excitation, this is indicative for the formation of GQD. In both cases there was a PL emission between 425 and 450 nm, thus showing blue light emission.
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Grafeno, Pontos quânticos de carbono, Pontos quânticos de grafeno, Óxido de grafeno, Luminescência, Fotoluminescência, Fluorescência, Emissão óptica, Graphene, Carbon quantum dots, Graphene quantum dots, Graphene oxide, Luminescence, Photoluminescence, Fluorescence, Optical emission