Metal Ion Release Assembly: A Versatile Strategy for Scalable and Tunable 2D-Material Coatings

Two-dimensional materials (2DMs) exhibit distinctive electronic, electrochemical, and barrier properties, yet scalable production methods for conformal, thick, and uniform coatings across diverse and complex substrates remain limited. We introduce a Metal Ion Release Assembly (MIRA) strategy that uses a gelatin hydrogel preloaded with metal ions (Mⁿ⁺) as a controlled ion-release platform. Upon immersion in a 2DM dispersion, Mⁿ⁺ is released from the hydrogel, screening the surface charges of nanosheets and inducing electrostatic assembly at the gelatin hydrogel surface. This MIRA process enables the formation of Mⁿ⁺-2DM multilayer coatings without the need for additives. The applicability of MIRA is demonstrated using graphene oxide, Ti₃C₂T_x MXene, and montmorillonite nanosheets via spin coating, dip coating, and doctor blading. Coating thicknesses from ∼1 μm to >20 μm are systematically tuned by adjusting immersion time, Mⁿ⁺ concentration, and 2DM dispersion concentration. Interference reflection microscopy confirms rapid nanosheet attachment and assembly driven by burst Mⁿ⁺ release. A diffusion-limited analytical model based on Fick's second law with time-dependent diffusion coefficients accurately predicts coating thickness evolution. Mⁿ⁺ can be removed through mild acid rinsing. Scalability and substrate adaptability in MIRA are demonstrated by fabricating large-area (∼400 cm²) and conformal coatings on curved and cylindrical surfaces. Electrochemical tests show the MXene electrodes fabricated using MIRA and acid rinsing processes perform comparably to pristine MXene electrodes, with similar resistances, specific capacitance, and cycling stability. MIRA provides a tunable and scalable platform for thick 2DM coatings, with applications in sensing, electromagnetic shielding, and corrosion protection.