Formation of Metal–Phytic Acid Surface Coatings via Oxidation-Mediated Coordination Assembly

Substrate-independent, chemical-durable, and homogeneous coatings are attracting great interest because of their potential applications in various fields. Surface coatings based on polydopamine and metal–phenol networks have been widely investigated. Phytic acid (PA), a plant-derived compound with six phosphate groups, can coordinate with multivalent ions to generate metal–phytic acid complex coatings. However, the formation of the coatings generally proceeds in a discrete step with a thickness of only about 8 nm via conventional methods. Herein, the continuous assembly of PA–FeIII coatings has been proposed by employing an oxidation-mediated assembly strategy. PA coordinates with an FeII precursor to form soluble complexes, which are then converted into insoluble PA–FeIII aggregates continuously, enabling coating thickness to be controllable and time-dependent. The formation and the kinetic growth process of the coatings are investigated systematically. Highly visible colors induced by the thin-film interference effect have been observed on silicon wafers and tailored by modulating the coating thickness. Moreover, benefiting from the superior chemical resistance and superhydrophilicity of the PA–FeIII coatings, potential applications in membrane modification for oil/water emulsion separation have been demonstrated. The modified membranes exhibit both high flux and separation efficiency. This work provides a feasible route to form effective PA–FeIII coatings and expands the versatile platform of metal–phytic acid surface coatings.