Misfortune Begets Fortune? Tailoring Facets in the MXene Oxidation Process for a Sensitive and Recyclable SERS Platform

Low SERS activity and poor environmental stability of MXenes limit their potential to become universal substrates comparable to noble metals. Herein, a crystal surface engineering technique that kills two birds with one stone is proposed. By customizing the exposed surface of TiO2 during the oxidation of Ti3C2 MXene, the hybrid Ti3C2-TiO2 substrate with a narrower bandgap and higher density of state was optimized. The stable lattice and heterostructure addressed the material's intrinsic susceptibility to oxidation (no signal drop over 180 days), while achieving a stronger charge transfer resonance effect (5.52 × 104 times higher than that of fresh Ti3C2). In addition, the Schottky barrier formed between Ti3C2 and TiO2 promotes the separation of photogenerated electron-hole pairs, enabling the substrate to be recycled (the degradation rate of MeB was 92.7% at 80 min). This work provides guidance for utilizing crystal facet engineering to regulate the SERS performance of substrates.