In situ turning defects of exfoliated Ti
 3
 C
 2
 MXene into Fenton-like catalytic active sites


 Controllable in situ formation of nanoclusters with discrete active sites is highly desirable in heterogeneous catalysis. Herein, a titanium oxide–based Fenton-like catalyst is constructed using exfoliated Ti
 3
 C
 2
 MXene as a template. Theoretical calculations reveal that a redox reaction between the surface Ti-deficit vacancies of the exfoliated Ti
 3
 C
 2
 MXene and H
 2
 O
 2
 molecules facilitates the in situ conversion of surface defects into titanium oxide nanoclusters anchoring on amorphous carbon (TiO
 x
 @C). The presence of mixed-valence Ti
 δ+
 (δ = 0, 2, 3, and 4) within TiO
 x
 @C is confirmed by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) characterizations. The abundant surface defects within TiO
 x
 @C effectively promote the generation of reactive oxygen species (ROS) leading to superior and stable Fenton-like catalytic degradation of atrazine, a typical agricultural herbicide. Such an in situ construction of Fenton-like catalysts through defect engineering also applies to other MXene family materials, such as V
 2
 C and Nb
 2
 C.
