<p>This work investigates the adsorption of Mn²⁺ ions on hydrothermally synthesized Nb₂O₅ nanoparticles obtained via an oxidant peroxo method, with particular emphasis on the role of functional groups present on the nanoparticle surface. Orthorhombic Nb₂O₅ was formed at a mild temperature (100&#xa0;°C), yielding nanocrystalline particles with high colloidal stability and a strongly negative surface charge. FTIR and zeta potential analyses reveal a carbonyl and hydroxyl-rich surface that promotes electrostatic attraction toward Mn²⁺ species. Adsorption experiments demonstrate rapid Mn²⁺ uptake, reaching equilibrium within minutes, with kinetics best described by a pseudo-first-order model, indicating a physisorption-dominated process. Equilibrium data are best fitted by the Freundlich and Redlich–Peterson isotherms, reflecting surface heterogeneity and multilayer adsorption, with an experimental adsorption capacity approaching 116.67&#xa0;mg&#xa0;g⁻¹. These findings demonstrate that hydrolyzed Nb₂O₅ is an efficient and tunable adsorbent for Mn²⁺ removal, offering strong potential for water treatment and environmental remediation applications.</p> Graphical abstract <p></p>