Sintese e caracterização de um derivado da pectina para estudos de fenômenos de sorção de íons chumbo (II)
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Data
2017-03-17
Autores
Santana, Ana Paula Reis [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Os íons metálicos estão cada vez mais presentes nos efluentes industriais e sua destinação incorreta pode promover impactos ambientais desastrosos. O desenvolvimento de processos e metodologias para remoção destes diferentes metais em níveis tóxicos deve apresentar baixo custo e serem sustentáveis de forma geral. Nos últimos anos tem havido um considerável interesse nos estudos de materiais sorventes obtidos a partir de biomassa, como as pectinas, que são provenientes principalmente de resíduos de frutas. A utilização da pectina traz vantagens por possuir uma estrutura potencialmente propícia a modificações químicas, além de poder ter sua seletividade modulada devido aos seus diferentes graus de esterificação. Tendo isso em vista, foi sintetizado e caracterizado um derivado ácido hidroxâmico da pectina de frutas cítricas visando seu emprego em estudos de sorção para chumbo. As caracterizações foram realizadas através da determinação do grau de esterificação, espectrofotometria na região do infravermelho, titulação potenciométrica, estudo da afinidade por vapor d‟água, análises térmicas e análise elementar. A caracterização da pectina quanto ao seu grau de esterificação, pelas técnicas de infravermelho e titulação revelaram resultados coerentes, com graus de esterificação de 49,9% e de 51,5% respectivamente. A caracterização do biopolímero modificado foi realizada por espectrofotometria na região do infravermelho e possibilitou a identificação de duas novas bandas em 1548 cm-1 e 1646 cm-1 quando comparado ao material de partida, comprovando sua modificação. Por meio da técnica de titulação potenciométrica o valor do pKa da pectina comercial foi de 4,4. Com respeito aos testes de afinidade com água, observou-se uma afinidade semelhante para ambos os materiais. A análise de DSC comprovou a modificação da pectina comercial, no qual o derivado apresentou uma menor estabilidade térmica comparada ao material de partida. Com a análise elementar foi possível determinar o grau de substituição dos grupos ácidos carboxílicos por ácidos hidroxâmicos do material de partida em 18,05% e a mesma técnica revelou que o aumento do tempo de síntese provoca uma reação de hidrólise, consequentemente diminuindo o grau de substituição do derivado. Os estudos de sorção de íons chumbo (II) com ambos os materiais poliméricos mostraram que após 50 minutos a taxa de sorção pectina hidroxâmica foi estatisticamente significativamente superior comparada com a da pectina comercial, comprovando ser um excelente material para sorção de íons chumbo (II).
The metal ions are increasingly present in industrial effluents and their improper disposal can result in environmental impacts. The development of processes and methodologies for removing these toxic metals must be low cost and sustainable. In the last years, there has been a considerable interest in studies of sorbent materials obtained from biomass, such as pectin, which are extracted from fruit residue. The use of pectin brings advantages for having a structure potentially favorable to chemical modifications, besides having its selectivity modulated due to different degrees of esterification. Keeping this in view, a pectin hydroxamic acid derivative was synthesized, which was characterized with commercial citrus fruit pectin for the purpose of both being used in metal ion sorption tests. The characterizations include determination the degree of esterification, spectroscophotometry in the mid-infrared region, potentiometric titration, the water uptake, thermal analysis and CHN. The characterization of pectin as to its degree of esterification, by spectroscophotometry in the mid-infrared region and titration, techniques revealed consistent results, with degrees of esterification of 49.9% and 51.5% respectively. The characterization of the modified biopolymer was performed by infrared radiation absorption and allowed the identification of two new bands at 1548 cm-1 and 1646 cm-1 compared to the starting material, showing its modification. Through of potentiometric titration technique, the pKa value of the commercial pectin was 4.4. The experiments regarding affinity to water, showed a similarity hydrophilic character of commercial pectin compared to its hydroxamic acid derivative. DSC analysis showing the modification of commercial pectin, in which the derivative showed a higher thermal stability compared to the starting material. The CHN results determined the degree of substitution of carboxylic acid groups by hydroxamic acids in 18.05%. The same technique has shown that increasing the time of the synthesis causes a hydrolysis reaction, thereby reducing the degree of substitution of the derivative. Sorption studies of lead (II) with both polymeric materials showed that after 50 minutes of reaction the hydroxamic pectin sorption rate was statistically significantly higher compared of commercial pectin, proving to be an excellent material for sorption of lead (II).
The metal ions are increasingly present in industrial effluents and their improper disposal can result in environmental impacts. The development of processes and methodologies for removing these toxic metals must be low cost and sustainable. In the last years, there has been a considerable interest in studies of sorbent materials obtained from biomass, such as pectin, which are extracted from fruit residue. The use of pectin brings advantages for having a structure potentially favorable to chemical modifications, besides having its selectivity modulated due to different degrees of esterification. Keeping this in view, a pectin hydroxamic acid derivative was synthesized, which was characterized with commercial citrus fruit pectin for the purpose of both being used in metal ion sorption tests. The characterizations include determination the degree of esterification, spectroscophotometry in the mid-infrared region, potentiometric titration, the water uptake, thermal analysis and CHN. The characterization of pectin as to its degree of esterification, by spectroscophotometry in the mid-infrared region and titration, techniques revealed consistent results, with degrees of esterification of 49.9% and 51.5% respectively. The characterization of the modified biopolymer was performed by infrared radiation absorption and allowed the identification of two new bands at 1548 cm-1 and 1646 cm-1 compared to the starting material, showing its modification. Through of potentiometric titration technique, the pKa value of the commercial pectin was 4.4. The experiments regarding affinity to water, showed a similarity hydrophilic character of commercial pectin compared to its hydroxamic acid derivative. DSC analysis showing the modification of commercial pectin, in which the derivative showed a higher thermal stability compared to the starting material. The CHN results determined the degree of substitution of carboxylic acid groups by hydroxamic acids in 18.05%. The same technique has shown that increasing the time of the synthesis causes a hydrolysis reaction, thereby reducing the degree of substitution of the derivative. Sorption studies of lead (II) with both polymeric materials showed that after 50 minutes of reaction the hydroxamic pectin sorption rate was statistically significantly higher compared of commercial pectin, proving to be an excellent material for sorption of lead (II).
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Palavras-chave
Pectina, Ácido hidroxâmico, Sorção, Pectin, Hydroxamic acid, Sorption