Insights into clay/cationic and anionic dye interactions

Various environmental remediation methods have been employed to address dye contamination in water. Among these, adsorption stands out as a particularly advantageous process due to its simplicity, cost-effectiveness, high efficiency, and environmental friendliness. Clay-based adsorbents, in particular, have attracted considerable interest because of their unique physicochemical properties. Previous research has demonstrated the efficacy of Cuban natural palygorskite (PAL) in removing both anionic and cationic dyes, specifically Congo red (CR) and methylene blue (MB), respectively. Building on these findings, this study provides a detailed characterization of the resulting PAL-CR and PAL-MB composites to elucidate the interactions governing clay/dye affinity. The composites were analyzed using attenuated total reflection infrared spectroscopy (ATR-FTIR) and thermogravimetric analysis (TGA), complemented by preliminary desorption studies in distilled water. The results indicate that the efficient adsorption of MB onto PAL is primarily governed by electrostatic interactions, whereas CR binding is dominated by hydrogen bonding. Desorption tests further confirmed the strong clay/dye interactions, indicating that the adsorption process is largely irreversible for both systems.