Aquatic macrophytes as natural biosorbents: Transforming invasive plants into solutions

The contamination of aquatic environments by organic dyes and other pollutants has become an increasing concern, especially in regions affected by industrial and agricultural discharges. In these areas, the uncontrolled proliferation of aquatic macrophytes is a common consequence. Eichhornia crassipes (MEC) and Egeria najas (MEN) stand out as invasive specimens frequently found in the Paraná River, Brazil. Despite their ecological impact, these plants may serve a useful role in pollutant removal due to their natural adsorptive and phytoremediation capabilities. This study investigated the potential use of MEC and MEN in their natural form as low‐cost biosorbents for the removal of methylene blue (MB), a synthetic dye widely used in textile and plastic industries and known for its resistance to degradation. The characterization of both biomasses included immediate analysis, thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) analysis. Egeria najas presented a significantly higher ash content (51.94%) than MEC (6.22%), suggesting a richer inorganic fraction. Thermogravimetric analysis revealed similar thermal degradation profiles for both, whereas FTIR confirmed the presence of functional groups typically associated with lignocellulosic materials. SEM analysis showed heterogeneous surface morphologies with irregular structures. In adsorption tests, MEN achieved rapid initial removal (82%) and reached 87.01% after 1440 min. Eichhornia crassipes demonstrated slower kinetics, starting at 47.40% and reaching a maximum of 89.76%. These results highlight the potential of native aquatic macrophytes as an accessible alternative for MB removal from wastewater, especially when considering specific requirements for treatment efficiency, availability, and sustainability.