Green and Sensitive Flexible Semiconductor SERS Substrates: Hydrogenated Black TiO2 Nanowires

Hydrogenation was discovered to be an effective method to improve the surfaced-enhanced Raman scattering (SERS) performance of semiconductor TiO2 and enhance its enhancement factor (EF) by at least 3 orders of magnitude. The TiO2 substrate hydrogenated for 3 h showed the most remarkable SERS activity with a detection limit of 1 × 10–7 M for R6G and an EF of 1.20 × 106, which can be comparable to the Ag substrate. The remarkable SERS activities can be attributed to the chemical enhancement mechanism dominated by the enhanced photoinduced charge transfer (PICT) process between R6G and the oxygen vacancy-containing partly amorphous black TiO2 NWs substrate, as well as the electromagnetic enhancement (EM) derived from the metal-like local surface plasma resonance (LSPR) of the hydrogenated randomly oriented TiO2 nanowires. The first principle based on the density functional theory has been applied to demonstrate the appearance of tailed electron energy state produced by hydrogenation and provide the reasonable explanation for an easier PICT process, a stronger light absorption, and the enhanced SERS performance of our hydrogenated TiO2 substrates. Another impressive fact was that the photodegradation capability of TiO2 was also evidently improved. After 14 cycles of detection-and-degradation of R6G molecules, the substrates can still maintain regenerative and remarkable SERS activity. Ultrasensitive SERS activity and self-cleaning performance were successfully integrated on the black TiO2 NWs substrate by hydrogenation. Moreover, our substrate exhibited the excellent signal reproducibility and the outstanding stability of antioxidation in atmosphere thanks to the protection of the surface amorphous layer.