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.
Recently, surface-enhanced Raman scattering (SERS) has been the subject of great interest because of its ultrasensitive, rapid and nondestructive analysis, detection, and imaging. Highly sensitive, stable and recyclable substrates are of great importance in fulfilling the practical potential of the technique in various fields, such as trace analysis, diagnosis and criminal investigation. In this work, we introduce wafer-scale Ag-modified hydrogenated black TiO2 nanowires as active SERS substrate by hydrogenation. The Ag/H–TiO2 NWs substrates deliver a relative enhancement factor of up to ∼102 compared with the substrate before hydrogenation and a detection limitation improved by at least three orders of magnitude compared with R6G detection. Moreover, hydrogenated TiO2/Ag also exhibits outstanding stability, and is recyclable by self-cleaning under UV irradiation. The excellent SERS performance is ascribed to the abundant surface electronic states induced by the hydrogenated amorphous layers and trivalent titanium, and more photogenerated charge carriers may contribute to the chemical and electromagnetic enhancement. The relative standard deviation (RSD) value for Raman signals less than 0.15 confirms the reproducibility of the hydrogenated composite SERS substrate. Therefore, the hybrid SERS substrates have great advantages in self-cleaning, reproducibility and stability, making them promising candidates for sensitive and recyclable SERS detection.
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