Comparative evaluation of iron-based nanostructures for textile dye adsorption: influence of synthesis routes on physicochemical properties and adsorption mechanisms

Textile dye contamination has become a pressing environmental and public health issue due to the persistent, non-biodegradable, and toxic nature of dye molecules commonly discharged from industrial effluents. This challenge underscores the urgent need for efficient, sustainable, and regenerable adsorbents capable of treating complex wastewater systems. Among available treatments, adsorption has emerged as a leading alternative owing to its operational simplicity, cost-effectiveness, and environmental compatibility. In this context, iron-based nanomaterials, particularly nano-zero-valent iron (nZVI), magnetite (Fe 3 O 4 ), hematite (α-Fe 2 O 3 ), maghemite (γ-Fe 2 O 3 ), and their composites have attracted substantial attention for exceptional surface reactivity, high adsorption efficiency, and magnetic separability. This review systematically compiles, compares, and evaluates the synthesis methods employed for these nanomaterials and critically examines how each route influences their physicochemical properties. The article further analyzes batch adsorption studies across various dye classes, assessing uptake capacities, isotherm and kinetic characteristics, and thermodynamic trends. Notably, the review emphasizes the novelty of correlating synthesis strategies with mechanistic adsorption pathways, thereby providing an integrated understanding of structure–performance relationships. Here we demonstrate that iron-based nanoadsorbents can exhibit high adsorption capacities, varying with dye type and synthesis method, with removal predominantly governed by pseudo-second-order kinetics and Langmuir or Freundlich isotherms. Mechanistically, dye uptake is driven by electrostatic attraction, hydrogen bonding, π–π stacking, van der Waals forces, surface complexation, and redox interactions. The review also highlights key challenges, including nanoparticle aggregation, iron leaching, and scale-up limitations, while emphasizing future directions involving green synthesis, hybrid composites, and continuous-flow applications for practical wastewater treatment.