Surface Coating with Naphthalene Trisulfonate/Hafnium(IV) Complexes: Versatility and Post-Functionalization.

Naphthalene trisulfonate is found to have versatile surface coating capability when combined with hafnium(IV) ions, thereby forming complexes. Solid substrates such as titanium/titanium dioxide, glass, and nylon immersed in a solution of naphthalene trisulfonate and Hf produces naphthalene trisulfonate/Hf complex coating. The coating is not produced when the Hf ions are absent or when naphthalene monosulfonate replaces naphthalene trisulfonate; this indicates the significance of Hf ions and multiple sulfonates in this coating system. The versatile surface coating property of naphthalene trisulfonate/Hf complexes is attributed to the coexistence of hydrophobic aromatic and hydrophilic side groups in naphthalene trisulfonate. Additionally, Hf ion-mediated cross-linking reactions between naphthalene trisulfonate molecules induce molecular assembly, facilitating versatile surface coating. Post-functionalization of the coating is accomplished through additional Hf-mediated coordinate bond formation; alginate and λ-carrageenan are successfully grafted onto the coating for nonbiofouling applications.