Modification of the Zeolite Heulandite with N-(3-Triethoxysilylpropyl)guanidines Offers an Effective Approach to Enhancing Its Adsorption Capacity for Heavy Metal Ions

Zeolites are widely used as adsorbents due to their porous structure and ion-exchange capabilities. However, their adsorption efficiency for heavy metal ions remains limited. To enhance their performance, the natural zeolite heulandite (<b>Z</b>) was functionalized with guanidine derivatives: N-[3-(triethoxysilyl)propyl]guanidine (<b>1</b>), -aminoguanidine (<b>2</b>), and -acetyl-guanidine (<b>3</b>). The resulting materials (<b>Z1</b>-<b>Z3</b>) were evaluated for their ability to adsorb Co²⁺, Cu²⁺, and Ni²⁺ from aqueous solutions. The composition and structure of silanes <b>1</b>-<b>3</b> were confirmed by FT-IR and ¹H and ¹³C NMR spectroscopy methods. The modified zeolites were characterized using nitrogen adsorption/desorption (BET) and SEM-EDX to confirm their functionalization and assess the structural changes. A TGA-DSC was used to determine the thermal stability. The adsorption experiments were conducted in single and multi-ionic aqueous solutions at pH 5.0 to evaluate metal uptake. Functionalization significantly improved the adsorption efficiency, with <b>Z1</b>-<b>Z3</b> showing a three to six times greater adsorption capacity than the unmodified zeolite. The adsorption efficiency followed the trend Cu²⁺ > Co²⁺ > Ni²⁺, primarily due to chelate complex formation between the metal ions and guanidine groups. The SEM-EDX confirmed the co-localization of nitrogen atoms and metal ions. The functional materials (<b>Z1</b>-<b>Z3</b>) exhibited strong potential as adsorbents for noble, heavy, and toxic metal ions, and could find applications in industry, agriculture, ecology, medicine, chemistry, wastewater treatment, soil remediation, chemisorption, filtration, chromatography, etc.