Surface localized p-n homojunctions in two-dimensional ultrathin titanium oxide with remarkable photocatalytic activity

Constructing p-n homojunctions while confining them on the surface of two-dimensional (2D) photocatalyst is a highly promising way to promote charge separation and thus improve the photocatalytic performance, yet they have rarely been achieved thus far. Here, we prepare 2D titanium oxide nanosheets enriched with both n-type oxygen vacancies and p-type titanium vacancies that form surface localized p-n homojunctions. The built-in electric field of the homojunctions promotes the unidirectional movement and separation of photogenerated carriers. Moreover, the p-n homojunctions confined to the surface of the ultrathin nanosheet can interact directly with the reactants, which reduces the recombination probability of electron-hole pairs. As a result, these p-n homojunctions enable an outstanding photocatalytic activity for water decontamination which is 30 times higher than that of benchmark titanium oxide. These results provide new opportunities for design and engineering of defects of 2D photocatalysts, potentially driving technological breakthroughs for energy conversion and environmental remediation.