Dispersões altamente concentradas de nanopartículas de prata em meio aquoso: preparação, caracterização, imobilização em celulose não modificada e aplicações
Data
2023-07-31
Autores
Nunes, Rodolfo Pedro Pereira 
Orientadores
Camilo, Fernanda Ferraz
Tipo
Dissertação de mestrado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Atualmente, ainda há uma escassez na literatura de trabalhos que se concentrem na obtenção de dispersões com altas concentrações de nanopartículas de prata (AgNPs). Portanto, este trabalho apresenta um novo método de síntese de AgNPs por redução química para obter dispersões com concentrações de 5, 10, 25, 50 e 100 mM em meio aquoso, na presença do agente estabilizante polivinilpirrolidona (PVP). As dispersões produzidas consistem em partículas esféricas com diâmetros inferiores a 100 nm, baixa polidispersividade e estabilidade razoável ao longo do tempo. Com o objetivo de aumentar a estabilidade das AgNPs, elas foram imobilizadas em filmes de celulose em duas etapas. Na primeira etapa, a celulose microcristalina foi dissolvida em um líquido iônico chamado 1-butil-3-metilimidazólio (BMlmCl), e na segunda etapa, o filme foi formado usando um anti-solvente para a celulose. Foram obtidos cinco filmes por meio do contato dos filmes de celulose com as dispersões contendo 5, 10, 25, 50 e 100 mM de prata. As análises indicam que os filmes obtidos eram amorfos, contendo celulose do tipo 2, com superfície lisa e homogênea, e uma porcentagem de prata variando de 1% a 5%, dependendo da dispersão utilizada. A atividade catalítica dos filmes produzidos com diferentes concentrações de prata foi avaliada em relação à degradação do 4-nitrofenol. Os filmes utilizados resultaram na redução do 4-nitrofenol em 25 a 40 minutos, dependendo do filme utilizado. Embora a atividade catalítica diminua após o primeiro ciclo de uso, os filmes podem ser utilizados com atividade parcial por pelo menos cinco ciclos. A grande vantagem do uso de filmes em vez de dispersões de AgNP é que o filme pode ser facilmente removido do meio racional e possui um maior potencial de reutilização. Esses resultados contribuem para o avanço na obtenção de dispersões de AgNPs concentradas e sua aplicação catalítica. Estudos futuros podem otimizar as condições de síntese e imobilização, bem como explorar outras aplicações desses filmes de celulose com AgNPs.
Currently, there is still a scarcity in the literature of works focusing on obtaining dispersions with high concentrations of silver nanoparticles (AgNPs). Therefore, this study presents a new method for synthesizing AgNPs through chemical reduction to obtain dispersions with concentrations of 5, 10, 25, 50, and 100 mM of silver in aqueous medium, in the presence of the stabilizing agent polyvinylpyrrolidone (PVP). The produced dispersions consist of spherical particles with diameters smaller than 100 nm, low polydispersity, and reasonable stability over time. To enhance the stability of AgNPs, they were immobilized in cellulose films through a two-step process. In the first step, microcrystalline cellulose was dissolved in an ionic liquid called 1-butyl-3- methylimidazolium chloride (BMImCl), and in the second step, the film was formed using an anti-solvent for cellulose. Five films were obtained from the contact of the cellulose films with the silver nanoparticle dispersions. The characterizations indicate that the obtained films were amorphous, containing cellulose type II, with a smooth and homogeneous surface, and a silver percentage ranging from 1% to 5%, depending on the dispersion used. The catalytic activity of the films produced with different silver concentrations was evaluated in the degradation of 4-nitrophenol. The films used resulted in the reduction of 4-nitrophenol in 25 to 40 minutes, depending on the film used. Although the catalytic activity decreases after the first cycle of use, the films can be partially active for at least five cycles. The significant advantage of using films instead of AgNP dispersions is that the film can be easily removed from the reaction medium and has a higher potential for reuse. These results contribute to the advancement in obtaining concentrated AgNP dispersions and their catalytic application. Future studies can optimize the synthesis and immobilization conditions, as well as explore other applications of these cellulose films with AgNPs.
Currently, there is still a scarcity in the literature of works focusing on obtaining dispersions with high concentrations of silver nanoparticles (AgNPs). Therefore, this study presents a new method for synthesizing AgNPs through chemical reduction to obtain dispersions with concentrations of 5, 10, 25, 50, and 100 mM of silver in aqueous medium, in the presence of the stabilizing agent polyvinylpyrrolidone (PVP). The produced dispersions consist of spherical particles with diameters smaller than 100 nm, low polydispersity, and reasonable stability over time. To enhance the stability of AgNPs, they were immobilized in cellulose films through a two-step process. In the first step, microcrystalline cellulose was dissolved in an ionic liquid called 1-butyl-3- methylimidazolium chloride (BMImCl), and in the second step, the film was formed using an anti-solvent for cellulose. Five films were obtained from the contact of the cellulose films with the silver nanoparticle dispersions. The characterizations indicate that the obtained films were amorphous, containing cellulose type II, with a smooth and homogeneous surface, and a silver percentage ranging from 1% to 5%, depending on the dispersion used. The catalytic activity of the films produced with different silver concentrations was evaluated in the degradation of 4-nitrophenol. The films used resulted in the reduction of 4-nitrophenol in 25 to 40 minutes, depending on the film used. Although the catalytic activity decreases after the first cycle of use, the films can be partially active for at least five cycles. The significant advantage of using films instead of AgNP dispersions is that the film can be easily removed from the reaction medium and has a higher potential for reuse. These results contribute to the advancement in obtaining concentrated AgNP dispersions and their catalytic application. Future studies can optimize the synthesis and immobilization conditions, as well as explore other applications of these cellulose films with AgNPs.