High-Efficiency Capture of Indole-3-Acetic Acid (IAA) from Water Using AgNPs-Decorated Silicate-Based Nanocomposites

The ubiquitous use of the plant hormone indole-3-acetic acid (IAA) or auxin in modern agriculture has led to its emergence as a water contaminant, necessitating efficient removal technologies. Addressing the need for high-performance sorbent materials, this study reports the synthesis and characterization of four novel nanocomposites based on halloysite (Hal), bentonite (Ben), sepiolite (Sep), and diatomaceous earth (DE) functionalized with silver nanoparticles (AgNPs). Successful immobilization and morphological features were confirmed via XRD and SEM-EDS. Crucially, post-adsorption EDS analysis provided direct solid-state evidence of pollutant capture through the distinct quantification of organic carbon. High-Performance Liquid Chromatography (HPLC) tests demonstrated that all functionalized materials exhibited a drastically enhanced IAA adsorption capacity over their pristine counterparts during a 96-h kinetic monitoring window. Kinetic profiling revealed a biphasic adsorption pathway characterized by a rapid initial sequestration within the first 10 h followed by a diffusion-limited equilibration, while thermodynamic modeling converged excellently with Langmuir and Sips equations, confirming a surface-confined chemisorption mechanism governed by uniform monolayer deposition. Notably, the performance ranking was found to be primarily governed by the architectural accessibility of the silicate frameworks rather than the absolute magnitude of their specific surface area. Furthermore, solution-phase spectroscopic studies coupled with Dynamic Light Scattering (DLS) and Zeta Potential measurements unraveled a robust, surface-confined ligand exchange mechanism. Rather than triggering colloidal aggregation, IAA coordination induced a controlled, systematic development of an organic molecular shell around the individual silver cores. This work underscores the potential of these engineered AgNPs@silicate platforms as sustainable, high-efficiency materials for the environmental remediation of emerging phytohormone contaminants.