Innovative anodic treatment to obtain stable metallic silver micropatches on TiO₂ nanotubes: structural, electrochemical, and photochemical properties

Abstract

Electrochemical modification of the Ti surface to obtain TiO₂ nanotubes (NT-Ti) has been proposed to enhance osseointegration in medical applications. However, susceptibility to microbial adhesion, linked to biomaterial-associated infections, and the high TiO₂ band gap energy, which allows light absorption almost exclusively in the ultraviolet (UV) region, limit its applications. Modifying the TiO₂ semiconductor with metals such as Ag has been suggested both for antimicrobial purposes and for absorbing light in the visible region. The formation of NT-Ti with Ag micropatches (Ag-NT-Ti) is pursued with the objective of enhancing the stability of the deposits and preventing cytotoxic levels of Ag cellular uptake. The innovative process proposed here involves immersing NT-Ti in a AgNO₃ solution as the initial step. Diverging from previously reported electrochemical methods, this process incorporates anodization within the TiO₂ oxide formation region instead of cathodic reduction generally employed by other researchers. The final step encompasses an annealing treatment. The treatments result in the in situ Ag¹⁺ reduction and formation of stable and active micropatches of metallic Ag on the NT-Ti surface. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman, diffuse reflectance spectroscopy (DRS), wettability assessment, and electrochemical characterizations were conducted to evaluate the modified surfaces. The well-known properties of NT-Ti surfaces were enhanced, leading to improved photocatalytic activity across both visible and UV regions, significant stability against detachment, and controlled release of Ag¹⁺ for promising antimicrobial effects.