Competitive adsorption between natural organic matter and sodium tripolyphosphate cross-linked chitosan microspheres by Cd(II) ions in aqueous media
Carregando...
Arquivos
Data
2022-08-26
Autores
Faria, Carol Christina de [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
Níveis elevados de metais potencialmente tóxicos em ambientes aquosos têm chamado a atenção devido à sua toxicidade em seres vivos. Dentre as várias abordagens sustentáveis de tratamento / monitoramento, o método de adsorção tem se mostrado uma ferramenta atrativa, simples e poderosa para a remoção desses compostos. A quitosana (CTS) é um abundante biossorvente natural amplamente conhecido por suas propriedades de formar complexos estáveis com muitos íons metálicos. Neste trabalho, esferas de CTS reticuladas com tripolifosfato de sódio (CTS – TPP) foram produzidas para experimentos de adsorção de íons Cd(II) em batelada na presença e ausência de matéria orgânica natural (MON), um importante competidor para íons metálicos em águas naturais. Microscopia eletrônica de varredura, espectroscopia de infravermelho com transformada de Fourier, e difração de raios-X foram utilizadas para caracterizar CTS – TPP antes e depois dos experimentos de adsorção na ausência e presença de MON. As análises elementares foram feitas usando espectroscopia de energia dispersiva. Foram estudados a influência do tempo de contato, pH, quantidade de adsorbato em solução no equilíbrio adsortivo, os mecanismos da cinética e do equilíbrio de adsorção, bem como o efeito de competição com MON. O espectro de FTIR mostrou que ocorreram mudanças importantes na estrutura química da quitosana, confirmando assim o sucesso do processo de reticulação com TPP. Além disso, os espectros também mostraram o protagonismo de grupos amina no processo de adsorção de íons Cd(II) e MON. O adsorvente utilizado neste estudo apresentou boa taxa de sorção ( ≈ 82%) em todas as faixas de pH e concentrações iniciais em ausência de MON. Nos estudos de competição, visto que íons Cd(II) e MON estiveram em contato prévio antes de serem adicionadas à solução as esferas de CTS, cerca de 94% dos íons Cd(II) foram adsorvidos pela MON, portanto, CTS – TPP sofre grande interferência da MON devido à competição por íons cádmio. Os íons Cd(II) remanescentes em solução foram adsorvidos numa taxa de 85%. Nos estudos de tempo de contato, uma taxa de remoção de Cd(II) de 50% foi observada nas concentrações iniciais de 0,1 e 0,2 mg L-1 após 120 min de experimento. No entanto, para a concentração de 5,0 mg L-1, é possível observar um processo cinético mais lento. A cinética do Cd(II) apresentou duas fases muito distintas; sendo a primeira bastante rápida e a segunda mais lenta. Para o estudo cinético, foram aplicados aos dados experimentais os modelos de pseudo-primeira-ordem e pseudo-segunda ordem, sendo que a cinética de pseudo-segunda-ordem descreveu melhor o processo adsortivo. O estudo do equilíbrio de adsorção foi realizado por meio dos modelos não-lineares de Langmuir e Freundlich. O dado de equilíbrio ajustou-se melhor ao modelo de Langmuir (R2 de 0,98 – 0,99) na faixa de pH estudada. A capacidade máxima de adsorção atingida por CTS – TPP foi de 1,61 mg g-1 em pH 6,5. Em geral, CTS – TPP mostrou-se bastante promissora na remoção de Cd(II) de meios aquosos em diferentes concentrações iniciais e intervalo de pH em ausência de MON.
High levels of potentially toxic metals in aqueous environments have drawn attention due to their toxicity in living beings. Among the several sustainable treatment / monitoring approaches, the adsorption method has proved to be an attractive, simple and powerful tool for the removal of these compounds. Chitosan (CTS) is an abundant natural biosorbent widely known for its properties of forming stable complexes with many metal ions. In this work, sodium tripolyphosphate (CTS – TPP) crosslinked CTS spheres were produced for batch Cd(II) ion adsorption experiments in the presence and absence of natural organic matter (NOM), an important competitor of metallic ions in natural water. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction were used to characterize CTS – TPP before and after adsorption experiments in the absence and presence of NOM. Elemental analyzes were performed using Energy dispersive spectroscopy. The influence of contact time, pH, amount of adsorbate in solution on the adsorptive equilibrium, the mecanisms of kinetics and adsorption equilibrium, as well as the effect of competition with NOM were studied. The FTIR spectrum showed that there were important changes in the chemical structure of CTS, thus confirming the success of the crosslinking process with TPP. In addition, the spectra also showed the role of amine groups in the adsorption process of Cd(II) and NOM ions. The adsorbent used in this study showed good sorption rate (≈ 82%) in all pH ranges and initial concentrations in the absence of NOM. In competition studies, since Cd(II) and NOM ions were in previous contact before the CTS beads were added to the solution, about 94% of the Cd(II) ions were adsorbed by NOM, therefore, CTS – TPP undergoes high NOM interference due to competition for cadmium ions. The remaining Cd(II) ions in solution were adsorbed at a rate of 85%. In the contact time studies, a Cd(II) removal rate of 50% was observed at initial concentrations of 0.1 and 0.2 mg L-1 after 120 min of experiment. However, for the concentration of 5.0 mg L-1, it is possible to observe a slower kinetic process. The kinetics of Cd(II) showed two very distinct phases; the first being quite fast and the second being slower. For the kinetic study, pseudo-first-order and pseudo-second-order models were applied to the experimental data and the pseudo-second-order kinetics better described the adsorptive process. The study of the adsorption equilibrium was carried out using non-linear models of Langmuir and Freundlich. The equilibrium data fitted better to the Langmuir model (R2 of 0.98 – 0.99) in the studied pH range. The maximum adsorption capacity achieved by CTS – TPP was 1.61 mg g-1 at pH 6.5. In general, CTS – TPP showed to be quite promising in removing Cd(II) from aqueous media at different initial concentrations and pH range in the absence of NOM.
High levels of potentially toxic metals in aqueous environments have drawn attention due to their toxicity in living beings. Among the several sustainable treatment / monitoring approaches, the adsorption method has proved to be an attractive, simple and powerful tool for the removal of these compounds. Chitosan (CTS) is an abundant natural biosorbent widely known for its properties of forming stable complexes with many metal ions. In this work, sodium tripolyphosphate (CTS – TPP) crosslinked CTS spheres were produced for batch Cd(II) ion adsorption experiments in the presence and absence of natural organic matter (NOM), an important competitor of metallic ions in natural water. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction were used to characterize CTS – TPP before and after adsorption experiments in the absence and presence of NOM. Elemental analyzes were performed using Energy dispersive spectroscopy. The influence of contact time, pH, amount of adsorbate in solution on the adsorptive equilibrium, the mecanisms of kinetics and adsorption equilibrium, as well as the effect of competition with NOM were studied. The FTIR spectrum showed that there were important changes in the chemical structure of CTS, thus confirming the success of the crosslinking process with TPP. In addition, the spectra also showed the role of amine groups in the adsorption process of Cd(II) and NOM ions. The adsorbent used in this study showed good sorption rate (≈ 82%) in all pH ranges and initial concentrations in the absence of NOM. In competition studies, since Cd(II) and NOM ions were in previous contact before the CTS beads were added to the solution, about 94% of the Cd(II) ions were adsorbed by NOM, therefore, CTS – TPP undergoes high NOM interference due to competition for cadmium ions. The remaining Cd(II) ions in solution were adsorbed at a rate of 85%. In the contact time studies, a Cd(II) removal rate of 50% was observed at initial concentrations of 0.1 and 0.2 mg L-1 after 120 min of experiment. However, for the concentration of 5.0 mg L-1, it is possible to observe a slower kinetic process. The kinetics of Cd(II) showed two very distinct phases; the first being quite fast and the second being slower. For the kinetic study, pseudo-first-order and pseudo-second-order models were applied to the experimental data and the pseudo-second-order kinetics better described the adsorptive process. The study of the adsorption equilibrium was carried out using non-linear models of Langmuir and Freundlich. The equilibrium data fitted better to the Langmuir model (R2 of 0.98 – 0.99) in the studied pH range. The maximum adsorption capacity achieved by CTS – TPP was 1.61 mg g-1 at pH 6.5. In general, CTS – TPP showed to be quite promising in removing Cd(II) from aqueous media at different initial concentrations and pH range in the absence of NOM.
Descrição
Palavras-chave
Química ambiental, Sorção, Biopolímero, Metais, Environmental chemistry, Sorption, Biopolymer, Metals