Regeneration and Recyclability of Magnetic Nanomaterials for Multi-Cycle Water Treatment: Toward Circular Adsorption–Desorption Systems

Magnetic nanomaterials (MNMs), particularly magnetically recoverable systems with efficient regeneration capability, have emerged as highly efficient nanoadsorbents for water purification owing to their high surface area, tunable surface chemistry, and facile magnetic separation. This review critically analyzes recent advances (2022-2025) in the multi-cycle use of MNMs, with particular emphasis on regeneration strategies. The major syn-thesis approaches and adsorption mechanisms are discussed in relation to their influence on long-term stability. Recent studies demonstrate that many MNMs retain 85-90% of their removal efficiency over 3-6 cycles, although performance degradation due to aggregation, leaching, and surface passivation remains a key challenge. Regeneration techniques, including chemical, solvent-based, and thermal methods, are evaluated in terms of efficiency and feasibility. Moreover, bibliometric analysis reveals the increasing research focus on recyclable nanomaterial design. Overall, this review elucidates the structure-performance-stability relationships governing multi-cycle operation, with a particular focus on reusable and magnetically separable systems and provides insights into the economic feasibility of regenerable MNMs along with future perspectives for sustainable and scalable water treatment applications.