The development of recyclable and stimuli-regulated interfacial coatings with tunable wettability remains a significant challenge in surface and materials chemistry. Herein, we report a facile and controllable strategy for constructing two-dimensional (2D) metal-polyphenol Janus nanosheets (Fe/PPG-ODA JNSs) with tunable cross-linking degrees and demonstrate their application in dynamic assembly and reversible superhydrophobic coatings. The Janus nanosheets were fabricated using an octadecylamine (ODA) bilayer dispersed in the bulk EtOH/H₂O medium as a soft template, where pyrogallol (PG) molecules were first adsorbed and subsequently underwent oxidative polymerization to form a poly(pyrogallol) (PPG) network. Fe³⁺ ions were then introduced to coordinate with phenolic hydroxyl groups, forming a metal-polyphenol cross-linked structure. By precisely regulating the FeCl₃ concentration (0.05-0.25 mmol/L), a series of Fe/PPG-ODA JNSs with different cross-linking densities were obtained.
The chemical structure, morphology, and elemental composition of the nanosheets were systematically characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The spectroscopic results support covalent coupling between PG-derived quinone intermediates and ODA through Schiff-base and Michael-addition pathways, together with the formation of Fe³⁺-polyphenol coordination networks. AFM analysis reveals a gradual increase in nanosheet thickness with increasing Fe³⁺ content, indicating enhanced network rigidity. Thermogravimetric analysis (TGA) further demonstrates improved thermal stability with increasing cross-linking degree.
Upon ultrasonication in an n-hexane/ethanol mixed solvent, the Janus nanosheets undergo controllable disassembly into secondary nanosheet-like building units (SJNSs-Fe). The lateral size of these disassembled units increases with increasing cross-linking degree, indicating that metal coordination significantly enhances structural integrity against solvent-induced fragmentation. During solvent evaporation-induced self-assembly on solid substrates (including silicon wafers, glass, copper, stainless steel, and PTFE), these building units reassemble into hierarchical supraparticles. The assembly behavior is strongly dependent on multiple parameters, including Fe³⁺ cross-linking degree, solvent polarity (hexane/ethanol ratio from 6:1 to 1:1), particle concentration, and evaporation temperature (-20 to 50 °C). As a result, a variety of morphologies including flower-like aggregates, spherical supraparticles, helical nanowires, and dense films are obtained.
Small-angle X-ray scattering (SAXS) analysis reveals ordered hierarchical packing with characteristic lamellar spacing, supporting the formation of ordered supraparticle architectures. Importantly, the macroscopic wettability of the resulting coatings can be tuned by adjusting the cross-linking degree. The water contact angle decreases continuously from 153.4° to 117.5° with increasing Fe³⁺ content, accompanied by a transition from a superhydrophobic low-adhesion state displaying Cassie-Baxter-like composite wetting behavior to a hydrophobic high-adhesion state. The wettability variation is attributed to the combined effects of reduced hierarchical roughness and changes in surface chemical composition/polarity associated with Fe-polyphenol coordination.
Furthermore, the coatings exhibit excellent substrate universality and mechanical robustness. More importantly, they possess reversible disassembly-reassembly capability: the coatings can be disassembled into nanosheet building units under ultrasonic treatment in mixed solvent and subsequently reassembled into functional coatings upon solvent evaporation, with negligible loss in morphology or wettability after repeated cycles. This work demonstrates that metal coordination cross-linking provides an effective strategy to regulate the balance between structural stability and dynamic assembly in 2D Janus systems, offering a general platform for designing recyclable, adaptive, and functionally tunable interfacial materials.

Key words: metal-polyphenol, Janus nanosheets, disassembly-reassembly, superparticles, hydrophobic coatings, wettability