Cashew Gum/Pure and Modified Hydroxyapatite Nanocomposite Aerogels for Water-Pollutant Removal

The pollution of aquatic environments by synthetic dyes, especially those from the textile industry, represents a significant environmental challenge. In this work, nanocomposite aerogels based on cashew gum (CG) and pure and aminosilane-modified hydroxyapatite (HAp) were synthesized and characterized for their application in the adsorption of the methylene blue dye. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), CHN elemental analysis, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were used to characterize the materials. Characterization results confirmed the incorporation of HAp into the polymer matrix and its modification, as well as changes in the morphological and thermal properties of the aerogels. The materials exhibited swelling capacity, with a higher degree of swelling observed in basic media. Regarding methylene blue adsorption, equilibrium was reached after 180 min, with varying adsorption capacities among the aerogels. The highest adsorption capacity was observed at pH 12, and kinetic data was best described by the pseudo-first-order model. Equilibrium data showed the best fit to the Langmuir and Dubinin-Radushkevich models, depending on the material. The temperature had no significant effect on the amount of dye adsorbed by the aerogels in the 25 to 55 °C range. The results demonstrate that combining cashew gum with hydroxyapatite, alongside modification of the mineral phase, enables the production of aerogels with tunable structural and adsorptive properties, highlighting their potential for removing cationic dyes from aqueous media.