A Ag synchronously deposited and doped TiO2 hybrid as an ultrasensitive SERS substrate: a multifunctional platform for SERS detection and photocatalytic degradation

Abstract

Ag simultaneously deposited and doped TiO₂ (Ag–TiO₂) hybrid nanoparticles (NPs) were prepared via a sol–hydrothermal method, as both a sensitive surface-enhanced Raman scattering (SERS) substrate and a superior photocatalyst for the first time. Ag–TiO₂ hybrid NPs exhibit excellent SERS performance for several probe molecules and the enhancement factor is calculated to be 1.86 × 10⁵. The detection limit of the 4-mercaptobenzoic acid (4-MBA) probe on the Ag–TiO₂ substrate is 1 × 10⁻⁹ mol L⁻¹, which is four orders of magnitude lower than that on pure TiO₂ as a consequence of the synergistic effects of TiO₂ and Ag. This is the highest SERS sensitivity among the reported semiconductor substrates and even comparable to noble metal substrates, and a SERS enhancement mechanism from the synergistic contribution of the semiconductor and noble metal was proposed. And importantly, the Ag–TiO₂ hybrid shows excellent photocatalytic degradation activity for the detected species under UV light irradiation at lower concentration conditions, even for the hard to degrade 4-MBA molecule. This makes the Ag–TiO₂ hybrid promising as a dual-function platform for both highly sensitive SERS detection and photocatalytic degradation of a pollutant system. Moreover, it also proves that the Ag–TiO₂ hybrid can serve as a promising recyclable SERS-active substrate by virtue of its photocatalytic self-cleaning properties for some specific applications, for instance comparative studies of different species on the same SERS platform, in addition to the economic benefit.