Desenvolvimento de fotocatalisadores a partir de óxidos metálicos dopados com lantanídeos para o tratamento de efluentes de vinícolas
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Data
2022-02-01
Autores
Campos, Mariana Bizari Machado de
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Universidade Estadual Paulista (Unesp)
Resumo
O vinho é uma bebida alcoólica milenar amplamente consumida em todo mundo. No Brasil existem mais de 74 mil hectares de produção vitivinícola, espalhados em 6 regiões de produção. Dentre as cidades produtoras do Estado de São Paulo, destaca-se São Roque, que vem apresentando um crescimento desse setor produtivo. No entanto, a geração de resíduos sólidos e líquidos provenientes desse setor vêm se tornando uma preocupação local. No caso dos efluentes líquidos, estes apresentam alto teor de matéria orgânica, especialmente polifenóis, o que dificulta o uso de tratamentos convencionais. Assim, este projeto visou desenvolver fotocatalisadores a partir da síntese de óxidos metálicos (TiO2 e CeO2) puros e dopados com lantanídeos (Pr e Tb), que sejam eficientes no tratamento dos efluentes vinícolas. As amostras obtidas foram tratadas termicamente (500 e 900oC) e caracterizadas estrutural, morfológica e espectroscopicamente (DRX, FTIR, DRS, MEV-FEG e EDS). Os resultados indicaram que os métodos de síntese escolhidos foram eficientes, resultando nas dopagens de interesse. Para as amostras de TiO2 tratadas a 500oC, verificou-se que a presença do dopante favoreceu a redução da cristalinidade e a formação de TiO2 da fase anatase, além de apresentarem absorção no UV e band gaps próximos a 3,20 eV. As amostras tratadas a 900oC apresentaram a fase rutilo e a formação de fase secundária, sendo por este motivo, descartadas para os testes fotocatalíticos. Já as amostras de CeO2 pura e dopadas, apresentaram estrutura cristalina do tipo fluorita, redução do band gap, além de absorção no visível, característica dos íons Pr4+ e/ou Tb4+. Devido maior cristalinidade observada a 900oC, estas amostras foram escolhidas para os testes fotocatalíticos. Posteriomente, a atividade fotocatalítica das amostras escolhidas foi investigada diante da degradação do azul de metileno e do ácido gálico, sob excitação de radiação UV e solar. Para o azul de metileno, observou-se uma redução da atividade fotocatalítica a medida que o % de lantanídeo aumenta, além de melhor desempenho das amostras quando excitadas por radiação solar, especiamente as de TiO2 puro e as com pequenos % de dopante. No degradação do ácido gálico, as amostras de TiO2 (puro e/ou dopagens) apresentaram resultados superiores às amostras de CeO2, além de melhor eficiência fotocatalítica a medida que o % de dopante aumenta, o que pode ser explicada pela capacidade quelante do lantanídeo diante desse composto fenólico. Por fim, realizou-se a caracterização físico-química do efluente vínícola fornecido por vínícola local e o tratamento fotocatalítico do efluente usando os óxidos sintetizados. O efluente vinícola apresentou pH ácido, grande quantidade de sólidos, altos valores de DQO, de COT e concentração significativa de compostos fenólicos, confirmando seu potencial nocivo e a necessidade de tratamento. Após o tratamento fotocatalítico, verificou-se redução considerável na DQO (de 50 a 60%) e no COT (de 30 a 40%) especialmente nas amostras com maior % de dopante excitadas por radiação solar. Tais resultados indicaram que os óxidos obtidos nesse trabalho são capazes de degradar parte dos compostos orgânicos presentes, apresentando potencial para aplicação no tratamento desse tipo de efluente, especialmente se combinados a tratamentos convencionais.
Wine is an age-old alcoholic beverage consumed worldwide. In Brazil there are more than 74 thousand hectares of wine production, spread across 6 production regions. Among the producing cities in the State of São Paulo, São Roque stands out, which has been growth in this productive sector. However, the generation of solid and liquid waste from this sector is becoming a local concern. In case of liquid effluents, they have a high content of organic matter, especially polyphenols, which difficult the use of conventional treatments. Thus, this project aimed to develop photocatalysts from the synthesis of pure metallic oxides (TiO2 and CeO2) and doped with lanthanides (Pr and Tb), which are efficient in the treatment of winery effluents. The samples obtained were thermally treated (500 and 900oC) and structurally, morphologically and spectroscopically characterized (XRD, FTIR, DRS, SEM and EDS). The results shows that the chosen synthesis methods were efficient, resulting in the dopings of interest. For TiO2 samples treated at 500oC, it was found that the presence of the dopant favored the reduction of crystallinity and the formation of TiO2 in the anatase phase, in addition showed UV absorption and band gaps close to 3.20 eV. The samples treated at 900oC showed the rutile phase and the formation of secondary phase, and for this reason, they were discarded for photocatalytic tests. The pure and doped CeO2 samples, on the other hand, showed a fluorite-type crystalline structure, band gap reduction, in addition to visible absorption, characteristic of Pr4+ and/or Tb4+ ions. Due to the greater crystallinity observed at 900oC, these samples were chosen for photocatalytic tests. Afterwards, the photocatalytic activity of the chosen samples was investigated against the degradation of methylene blue and gallic acid, under excitation by UV and solar radiation. For methylene blue, a reduction in photocatalytic activity was observed as the % of lanthanide increased, in addition to a better performance of the samples when excited by solar radiation, especially those with pure TiO2 and those with a small % of dopant. In the degradation of gallic acid, TiO2 samples (pure and/or doping) showed better results than CeO2 samples, in addition to better photocatalytic efficiency as the % of dopant increases, which can be explained by the lanthanide chelating capacity against this phenolic compound. Finally, the physicochemical characterization of the wine effluent supplied by local winery and the photocatalytic treatment of the effluent using the synthesized oxides were carried out. The winery effluent showed acid pH, large amount of solids, high values of COD, TOC and significant concentration of phenolic compounds, confirming its harmful potential and the need of treatment. After the photocatalytic treatment, there was a considerable reduction in COD (50 to 60%) and TOC (30 to 40%), especially in samples with higher % of dopant excited by solar radiation. These results indicated that the oxides obtained in this work are capable of degrading part of the organic compounds present, showing potential for application in the treatment of this type of effluent, especially if associated with conventional treatments.
Wine is an age-old alcoholic beverage consumed worldwide. In Brazil there are more than 74 thousand hectares of wine production, spread across 6 production regions. Among the producing cities in the State of São Paulo, São Roque stands out, which has been growth in this productive sector. However, the generation of solid and liquid waste from this sector is becoming a local concern. In case of liquid effluents, they have a high content of organic matter, especially polyphenols, which difficult the use of conventional treatments. Thus, this project aimed to develop photocatalysts from the synthesis of pure metallic oxides (TiO2 and CeO2) and doped with lanthanides (Pr and Tb), which are efficient in the treatment of winery effluents. The samples obtained were thermally treated (500 and 900oC) and structurally, morphologically and spectroscopically characterized (XRD, FTIR, DRS, SEM and EDS). The results shows that the chosen synthesis methods were efficient, resulting in the dopings of interest. For TiO2 samples treated at 500oC, it was found that the presence of the dopant favored the reduction of crystallinity and the formation of TiO2 in the anatase phase, in addition showed UV absorption and band gaps close to 3.20 eV. The samples treated at 900oC showed the rutile phase and the formation of secondary phase, and for this reason, they were discarded for photocatalytic tests. The pure and doped CeO2 samples, on the other hand, showed a fluorite-type crystalline structure, band gap reduction, in addition to visible absorption, characteristic of Pr4+ and/or Tb4+ ions. Due to the greater crystallinity observed at 900oC, these samples were chosen for photocatalytic tests. Afterwards, the photocatalytic activity of the chosen samples was investigated against the degradation of methylene blue and gallic acid, under excitation by UV and solar radiation. For methylene blue, a reduction in photocatalytic activity was observed as the % of lanthanide increased, in addition to a better performance of the samples when excited by solar radiation, especially those with pure TiO2 and those with a small % of dopant. In the degradation of gallic acid, TiO2 samples (pure and/or doping) showed better results than CeO2 samples, in addition to better photocatalytic efficiency as the % of dopant increases, which can be explained by the lanthanide chelating capacity against this phenolic compound. Finally, the physicochemical characterization of the wine effluent supplied by local winery and the photocatalytic treatment of the effluent using the synthesized oxides were carried out. The winery effluent showed acid pH, large amount of solids, high values of COD, TOC and significant concentration of phenolic compounds, confirming its harmful potential and the need of treatment. After the photocatalytic treatment, there was a considerable reduction in COD (50 to 60%) and TOC (30 to 40%), especially in samples with higher % of dopant excited by solar radiation. These results indicated that the oxides obtained in this work are capable of degrading part of the organic compounds present, showing potential for application in the treatment of this type of effluent, especially if associated with conventional treatments.
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Palavras-chave
Fotocatálise heterogênea, TiO2, CeO2, Dopagem, Lantanídeos, Efluente vinícola, TiO2, CeO2, Doping, Lanthanides, Winery eflluent, Heterogeneous photocatalysis