Magnetic Fishing: A pH-Responsive "Capture and Release" Strategy for Up-Concentrating Exfoliated 2D Nanosheets in Water

Nanoparticle-2D material composites represent a pivotal class of advanced materials, offering synergistic enhancements in electrical, thermal, and mechanical properties that surpass those of individual components. In contrast to traditional synthesis methods, electrostatic self-assembly provides a green, scalable, and cost-effective alternative, leveraging charge-regulated adhesion for precise control over loading without toxic agents or extreme temperatures. This study employs electrostatic self-assembly to fabricate a versatile library of magnetic 0D-2D composites, demonstrating flexibility in component selection. Monodispersed nanoparticles, including iron oxides, previously unreported medium entropy ferrites, and cubic morphologies, are uniformly integrated with 2D materials like graphene and MoS2. Characterization via PXRD, TEM, and STEM-EDS confirms cubic spinel phases, uniform distribution, and controllable loading of the nanoparticles. Furthermore, this electrostatic interaction addresses a critical challenge in 2D material production: the low-concentration bottleneck of liquid-phase exfoliation, particularly in water where yields are limited to 2–5%. By utilizing zwitterionic magnetic nanoparticles in a pH-responsive "capture and release" mechanism, the approach iteratively up-concentrates dilute nanosheet dispersions, achieving enhancements exceeding 10-fold for MoS2, WS2 and MoSe2, as evidenced by UV-Vis spectroscopy and visual color changes. This strategy advances sustainable, high-yield 2D material production for industrial and biomedical applications.