Hydrogels and Metallo-Hydrogels: Characterization, and Their Environmental and Pharmaceutical Applications

VIVIANA CAMPODALL'ORTO; YAMILA GARRO LINCK; AYELÉN F. CRESPI; GUILLERMO COPELLO; JUAN MANUEAL LÁZARO-MARTÍNEZ

Microgels: Synthesis, Properties and Applications

Nova Science Publishers, Inc.

Año: 2018; p. 193 - 228

The increase in the concentration of extremely dangerous environmental pollutants such as heavy metal ions, cyanide ions, perfluorinated alkanes and organic dyes, could be solved by designing and synthesizing new highly functionalized polymeric materials. Particularly, the decontamination of heavy metal ions from water needs special consideration since these ions are non-biodegradable and are being excessively released into the environment due to rapid industrialization. In this scenario, the use of hydrogel materials as adsorbents is a practical and efficient option for decontamination purposes. Although other materials, such as activated carbon, mineral materials and natural polymers, are also being used due to their low cost and good mechanical stability, in some cases they do not have a high loading capacity or high avidity for the contaminants. Regarding the decontamination of organic pollutants, the technique used is generally adsorption, but in order to achieve the total mineralization of these pollutants, this technique needs to be complemented with advanced oxidation systems. These oxidation systems are mainly based on metal ions coordinated into polymeric matrixes as well as on hybrid materials or mesoporous systems, being copper and cobalt ions the most relevant cations used for the activation of hydrogen peroxide (H2O2) and the generation of reactive oxygen species (ROS), which vary depending on the metal ion supported in the catalyst. H2O2 is a powerful oxidant used in the degradation of pollutants, which can be combined with catalysts and/or UV light to give rise to ROS, being the Fenton-like reactions widely used but only effective in acidic conditions. On the other hand, the copper(II)-complexes coupled with H2O2 can be used in a broader pH range. It is interesting to point out that the catalytic activity of copper(II) ions in the activation of H2O2 is enhanced after coordination with pyridine, organic acids and other coordinating agents, but the recovery of soluble complexes is expensive. In this sense, heterogeneous catalysts are an attractive alternative for decontamination, combining effectiveness, ease of recovery and reuse potential. Additionally, cobalt complexes are very useful for soft oxidative procedures in organic synthesis, but there are only a few reports related to Co(II)-complexes supported in polymeric hydrogel structures. As an example, a Co(II)-crosslinked polyacrylamide has been used as a selective catalyst for the oxidation of olefins and alkyl halides with H2O2 in aqueous media [1]. The main difference with copper complexes is that the metal ion is converted to Co(III) from the corresponding Co(II) in the presence of H2O2 and that the main oxidant species are the superoxide radicals in contrast with the hydroxyl radicals generated by Cu(II)-complexes [1?3].Concerning pharmaceutical applications, hydrogels loaded with small molecules or large molecular weight proteins are available due to recent advances in the field of molecular biology and organic synthesis, and have given rise to new ways to treat a high number of diseases. Once a drug for a particular disease or chemotherapy treatment is discovered, its delivery needs to be adequate for the success of the therapy. To this end, crosslinked hydrophilic polymer structures can be synthesized to respond to a broad number of physiological stimuli present in the body, such as pH, ionic strength and temperature.