Hydrogels consist of three-dimensional polymer networks, which have the ability to absorb large amounts of water and swell to a very high degree, while remaining insoluble in water due to the presence of chemical crosslinks in the polymer network. These unique properties make hydrogels highly adaptable materials, with potential for use in areas such as controlled drug release, nanomaterial incorporation and semiconductor technologies. More specifically, their ability to purify water is particularly important in effectively binding and retaining a wide range of water-soluble pollutants.

Another way to remove pollutants is biochar, which is characterized by a highly porous structure, large specific surface area and the presence of functional groups on their surface, which makes them particularly effective in the adsorption of organic and inorganic pollutants from aqueous solutions. Their usefulness is found in environmental protection applications, such as the removal of heavy metals, the binding of nutrients and the improvement of soil quality.

In the present work, UV-vis spectrophotometry and high-performance liquid chromatography (HPLC) are applied to investigate the adsorption of the preservative Propyl Paraben and the herbicide Metribuzin (MEB) by the negatively charged hydrogels P(DMAM-co-ANax), and biochars from lime peel, callistemon seeds and olive kernel. The initial concentration of the solutions was 5 mg·L⁻¹, while the adsorbents were placed with a mass ratio of 0.1-0.5 g. The evaluation of the pollutants was conductedat three different concentrations (5 mg·L⁻¹, 2.5 mg·L⁻¹ and 1 mg·L⁻¹). The samples remained in the adsorption state for 4 hours, then, both the swelling ratio (Swelling Ratio %) and the sorption capacity were evaluated. The results showed satisfactory removal for both pollutants.