Comprehensive characterization of Fe₃O₄@Ag nanoparticles using cross-techniques: inference of the type of Ag-Fe₃O₄ interaction and its impact on anion adsorption

In this study, magnetite nanoparticles were functionalized with metallic silver using a chemical reduction method, and their structural, morphological, thermal, electrokinetic and magnetic properties were characterised using thirteen complementary techniques. Combined analysis by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy (Raman) and X-ray Photoelectron Spectroscopy (XPS) revealed a promising surface configuration, where silver is deposited on the surface of magnetite as metallic Ag⁰, forming nanoclusters without penetrating the spinel crystal lattice or altering the iron's oxidation state. This configuration generates a biphasic system, where magnetite retains its magnetic properties while silver provides a modulated surface capable of interacting electrostatically with anionic species. The synthesis and characterization approach were comprehensive, following a multi-technique strategy where each technique reinforced or limited the interpretations of others: XRD confirmed the crystalline identity, XPS ruled out chemical bonding, and Raman–FTIR complemented vibrational analysis. TEM and SEM revealed surface organization, while Brunauer–Emmett–Teller Surface Area Analysis (BET) and laser diffraction characterized porosity and dispersion. Thermogravimetry (TG)– Differential Scanning Calorimetry (DSC) studies demonstrated enhanced thermal stability and Point of Zero Charge (PZC) analysis provided evidence of electrostatic modulation, with magnetometry confirming the magnetic retention after functionalization. This integrative strategy not only validated the physical nature of the silver–magnetite interaction but also demonstrated that silver acts as an electrostatic modulator without compromising internal magnetism. The combination of Van der Waals interactions, increased surface area, and localized positive charge regions favours the adsorption of anionic pollutants. This was corroborated in previous adsorption experiments (e.g., nitrate and amoxicillin removal), confirming the material’s potential in environmental decontamination applications. In conclusion, the rational design of Fe₃O₄@Ag systems through surface functionalization with silver enables the integration of physical, thermal and electrostatic enhancements, which, when analysed through a coherent multi-technique methodology, converge toward a single functional objective: the development of effective adsorbent nanomaterials for water treatment.