An In Situ Oxidation Strategy for Ti ₃ C ₂ @TiO ₂ Heterojunction: Narrow‐Band Photodetection and Trace Chromium Ion Determination

Ti 3 C 2 MXene has frequently been applied in photodetection, while there are few works directly utilizing Ti 3 C 2 MXene as an active material due to the fast carrier recombination. The construction of MXene‐based heterojunctions have been demonstrated to further enhance the photo‐response performance. In this work, a Ti 3 C 2 @TiO 2 heterojunction was fabricated by an in situ oxidation approach and used to construct a photoelectrochemical photodetector. The as‐fabricated photodetector exhibits a narrow‐spectrum response (334–380 nm), with an optimized photocurrent density of 6.43 µA/cm 2 and a photoresponsivity of 5057.14 µA/W. Benefiting from interface engineering, the Ti 3 C 2 @TiO 2 ‐based photodetector possesses excellent stability and sensitive response to chromium. A large range of 10 −12 –10 −6 M could be achieved in a tea water matrix with an ultra‐low detection limit of 7.6 × 10 −12 M. We anticipate that this study will provide an effective approach for the design of MXene‐based photodetectors and pave the way for online chromium monitoring sensors in particular.