The presence of metal ions from industrial processes in water has led to great concern regarding their effects on human health. The frequency of metal ions in water is apprehensive because they present several harmful effects on human health. In addition, they are non-biodegradable, and their toxicity, observed even at low concentrations, can be aggravated by bioaccumulation and biomagnification phenomena, which increase the degree of exposure along the food chain.
Conventional techniques can remove metal ions, such as solvent extraction, ion exchange, chemical precipitation, and reverse osmosis. However, these processes are limited because of high costs, the generation of toxic by-products, or long treatment times. Based on these limitations, new alternatives have been researched, and the adsorption process has shown the potential to meet the demands of metal contaminant removal. The adsorption is based on the presence of binding sites on the surface of the adsorbent material, which makes it a process highly influenced by its surface area.
Porous materials are promising for adsorption applications due to their high surface area, for which hydrogels can be highlighted. Hydrogels are three-dimensional polymeric structures produced by crosslinking, which exhibit high hydrophilicity and the ability to absorb large volumes of water. Polysaccharides have attracted much attention in developing hydrogels due to their biodegradability, biocompatibility, non-toxicity, and low cost. Chitosan has drawn attention among these materials due to its high natural abundance. Moreover, its chemical structure presents amine and hydroxyl groups that guarantee the chitosan hydrogel's capacity to remove metal ions.
However, the available groups can be consumed during the crosslinking process, so optimizing the hydrogel preparation conditions is a challenge to obtain a material with attractive properties. Therefore, the present work aims to investigate the effect of chitosan and crosslinker molar ratio on chitosan hydrogel properties, using the design of experiments methodology.
For the development of chitosan hydrogels, an experimental planning study was carried out to select the optimal condition for hydrogel production. The chitosan was previously solubilized in an acetic acid solution (2% v/v) in different concentrations (1, 2 and 3% w/v). Glutaraldehyde was used as a crosslinking agent at different concentrations (1 and 10% v/m). Response surface planning was employed to evaluate the effect of the proportion of chitosan and crosslinking agent, and 18 formulations were generated.
The water absorption capacity of the hydrogels was evaluated through the degree of swelling, considering mass variation as a function of the time of a sample kept in an aqueous medium. To evaluate the adsorption potential of the hydrogels, a selectivity study was performed using an equimolar solution of copper, nickel, zinc, manganese, cadmium, and chromium where each metal was at a concentration of 0.17 mmol/L so that the solution had a total concentration of 1.02 mmol/L. The solution was prepared at pH 4 to avoid precipitation effects that could affect the analysis of the results.
All hydrogels showed a high degree of water absorption, greater than 100%, after 1 day, which is a typical behavior of hydrogels. Furthermore, it was observed that some samples stood out with more than 200% water absorption. It was observed that the samples with higher water absorption presented the use of a lower content of glutaraldehyde, which may indicate a lower crosslinking of the hydrogel structure and higher availability of functional groups capable of absorbing water.
Evaluating the metal adsorption experiments, it was worth noticing that the hydrogels presented a significant removal potential for copper (up to 75%) and chromium (up to 100%). In the case of copper removal, a significant variation of removal was observed depending on the composition employed, which indicates that the degree of crosslinking of the sample should directly influence the groups available for interaction and removal of the metal ion. Regarding chromium, a total removal was observed under the test conditions, considering the deviation between the samples, indicating that the chitosan matrix presents a high affinity for chromium removal.
The results of water absorption and removal of metal ions were used as a response to the experimental planning developed to select the conditions of preparation of hydrogels that enhance the properties obtained. It was obtained that the condition minimizing both the chitosan content and crosslinking content presented the best properties for the developed hydrogels.
Therefore, the success of producing hydrogels was observed, aiming to understand the optimal formulation conditions, which can serve as a basis for functionalizing these materials and developing new functional products to remove and recover metals in contaminated water.
Bem-vindo(a) aos Anais do VII NanoMat, evento organizado pela Pós-graduação em Nanociências e Materiais Avançados da Universidade Federal do ABC (UFABC) com o intuito de reunir e debater trabalhos desenvolvidos por alunos e pós-doutorandos em Materiais e áreas afins.
Comissão Organizadora
Pedro Alves da Silva Autreto
Andre Luiz Martins de Freitas
Aryane Tofanello
Comissão Científica
Ferramenta completa de submissão, avaliação e publicação de anais para eventos científicos.
