Silver nanoparticle-decorated titanium dioxide nanowire systems via bioinspired poly(l-DOPA) thin film as a surface-enhanced Raman spectroscopy (SERS) platform, and photocatalyst

Abstract

Silver nanostructure decorated-titanium dioxide (TiO₂) nanocomposite systems with their unique characteristics provide extraordinary performance in various applications including surface-enhanced Raman spectroscopy (SERS), and photocatalysis. Despite the recent progress, novel, simple, effective, low-cost, reducing and stabilizing agent-free, and easy-to-tune approaches are heavily demanded for the preparation of these nanocomposites. In this context, we propose the fabrication of silver nanostructure decorated TiO₂ nanowires (TiO₂ NWs) through a thin interphase layer of the polymer of 3,4-dihydroxyphenyl-L-alanine (PLDOPA). In the first step, TiO₂ NWs were synthesized through the hydrothermal method and then a conformal thin film of PLDOPA was deposited onto the TiO₂ NWs (TiO₂@PLDOPA) by oxidative polymerization of L-DOPA. Having various functional groups including catechol and amine, the PLDOPA thin-film reduced the silver ions onto the TiO₂ NWs and stabilized the resultant nanocomposites without the employment of any surfactant, reducing agent, and seed material. By simply tuning the amount of silver ions, we could manipulate the size, morphology, and interparticle distance of silver nanostructures decorated onto the TiO₂@PLDOPA colloidal composite system (TiO₂@PLDOPA@Ag NP). The TiO₂@PLDOPA@Ag nanocomposite systems provided unique properties as an ideal SERS platform and photocatalyst. The optimized TiO₂@PLDOPA@Ag nanosystem demonstrated a high SERS activity, reproducibility, and self-cleaning property with an enhancement factor of 5.1 × 10⁵. As a photocatalyst, the TiO₂@PLDOPA@Ag NP systems provided remarkable performance under visible light irradiation in the catalytic degradation of methylene blue.