Hidrogéis de poli(ácido acrílico)/poli(álcool vinílico) e íons Fe3+ com propriedades de autocura para aplicação na adsorção seletiva de corante catiônico

Abstract

The pollution of aquatic environments by organic contaminants, mainly dyes, is a worrying reality. As a result, the demand for robust materials and innovative systems aimed at remediating these environments has been growing. As an option, this work proposes the development and application of a hydrogel synthesized from the formation of multiple polymeric networks with self-healing properties using poly(acrylic acid) (PAAc), poly(vinyl alcohol) (PVA), and Fe3+ ions. The presence of Fe3+ ions in the polymer matrix, in addition to making it more thermally and mechanically stable, also influences the swelling capacity of the hydrogel and gives it a self-healing ability. This last property is due to the formation of dynamic ionic bonds between Fe3+ ions and PAAc carboxyl groups. Connections of this nature allowed the PAAc/PVA@Fe3+ hydrogel to reach a self healing percentage of about 68.0% in only 8 h. Batch studies using methylene blue (MB) and methyl orange (MO) were done to investigate the best conditions for using these hydrogels as adsorbents. Moreover, experiments demonstrated that there is selective adsorption of MB towards MO, likely due to the electrostatic interactions between the cationic MB and the anionic groups in the hydrogel. In binary dye mixtures, the PAAc/PVA@Fe3+ hydrogel removed around 81.0% of the MB, while the removal of MO was only 15.1%. According to the Langmuir isotherm, the maximum adsorption capacity of MB on the hydrogel was 27.4 mg/g when relatively mild working conditions were used (pH 6–7, 180 min, 25 ºC). Furthermore, the hydrogel demonstrated a good capacity for regeneration and reuse, maintaining the adsorption efficiency above 60.0% even after 10 cycles. The removal efficiency was kept even after the self-healing process. In short, the multi-network and self-healing PAAc/PVA@Fe3+ hydrogel is a promising candidate for practical application in environmental remediation, useful in the selective removal of cationic dyes from the aqueous medium.