<p>This study presents the synthesis, physicochemical evaluation, and practical application of powder-nano magnesium oxide (P-MgO) for the adsorption of fluoride from fluoride-polluted subsurface environments. A key innovation in the synthesis strategy was the use of polyethylene glycol (PEG) as both a structure-directing and end-capping agent, which played a pivotal role in restricting particle growth, preventing agglomeration, and promoting morphological uniformity. The synthesized P-MgO possessed a mesoporous framework with a high specific surface area of 90.1 m²/g and a particle diameter of 298 nm. Batch adsorption studies determined that a dosage of 0.4 g/L was optimal, achieving approximately 95% fluoride removal (initial fluoride concentration: 11.3 mg/L) efficiency across a wide pH range (4–11) and in the presence of common competing anions. The fluoride adsorption process adhered closely to the pseudo-second-order model, indicative of chemisorption, while equilibrium data aligned with the Langmuir isotherm, suggesting monolayer coverage and a maximum adsorption capacity of 113.5 mg/g. Results confirmed the formation of Mg–F chemical bonds and highlighted the role of surface ligand exchange in the fluoride capture mechanism. In column experiments using groundwater from a fluoride-polluted site (initial fluoride concentration: 12.08 mg/L), P-MgO rapidly reduced fluoride levels, achieving 95.4% of fluoride removal at the first column pore volume (PV), and effective treatment continued up to 15 PVs. Results highlight P-MgO’s potential as a fast-acting, chemically stable, and environmentally compatible adsorbent. Its high removal efficiency makes it a promising candidate for scalable fluoride remediation, particularly in rapid-response or emergency groundwater treatment applications.</p> Graphical Abstract <p></p>