Theory and experiment on SERS sensitivity tuning of TiO2 aerogels based on surface oxygen vacancy engineering

The exploration of new and high-performance semiconductor substrates has always been one of the most important research directions in SERS technology. However, the low sensitivity of semiconductor SERS substrates limits their application. Herein, TiO2 aerogels with high surface oxygen vacancies were fabricated by sol-gel method followed by supercritical drying. Compared with traditional semiconductor materials, TiO2 aerogels exhibit low detection limits (1 x 10-7 M) for 4-mercaptobenzoic acid molecules. Moreover, density functional theory further revealed that abundant surface oxygen vacancies endow TiO2 aerogels with high electrostatic potential, which promotes the formation of stable surface charge transfer complexes and allows significant charge transfer from molecules to TiO2 aerogels. It is worth noting that the narrower band gap and higher electron density of states of TiO2 aerogels effectively enhance the vibrational coupling in the substratemolecule system, leading to significant SERS activity of TiO2 aerogels.