Highly-dispersed TiO2 nanoparticles with abundant active sites induced by surfactants as a prominent substrate for SERS: charge transfer contribution

Abstract

In this study, highly-dispersed TiO₂ nanoparticles (NPs) with abundant active sites were synthesized by a simple sol-hydrothermal method with the assistance of surfactant polyethylene glycol (PEG) which served as an effective SERS-active substrate for the first time. The observed considerable SERS enhancement of 4-mercaptobenzoic acid (4-MBA) probe molecules on TiO₂ NPs is attributed to the contribution of the charge transfer mechanism from the substrate to the probe molecule. It is suggested that PEG can act as a protective agent in the reductive calcination of the surfactant-coated nanocrystallite and consequently brings about abundant surface oxygen vacancies for TiO₂ NPs, which provide more effective sites for the adsorption of probe molecules and promote the charge transfer effect and its consequent SERS enhancement. Moreover, the prepared TiO₂ NPs can serve as an effective substrate for highly sensitive detection of p-aminobenzoic acid (PABA). The detection limit of PABA is as low as 1 × 10⁻⁸ M, which is the highest sensitivity among the reported determination methods. And, it proves that the prepared TiO₂ substrate with abundant active sites is characterized by high stability, which offers a unique long service lifetime for SERS detection without losing its activity.