Patterned Bi Nanoparticles\non a Layer-by-Layer MXene\nFilm for Highly Improved Photodetection

To improve the photodetction performance of MXene titanium\ncarbide\n(Ti<sub>3</sub>C<sub>2</sub>), a MXene film assembled by two-dimensional\n(2D) MXene Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> nanosheets (NSs) via a layer-by-layer technique is employed to facilely\npattern zero-dimensional (0D) bismuth nanoparticles (Bi NPs), abbreviated\nas patterned Bi NP@MXene Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> NS, for the construction of a prototypical photoelectrochemical\n(PEC)-type photodetector. Compared to individual 2D MXene Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> NSs and 0D Bi NPs, the\npatterned Bi NP@MXene Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> NS displays remarkably better PEC performance, including photocurrent\ndensity, photoresponsivity, and detectivity under the same conditions.\nA theoretical investigation demonstrates that monolayer Bi shows a\nsemiconducting property on the MXene Ti<sub>3</sub>C<sub>2</sub> that\nusually yields a strict bandgap match with an incident light, while\nmultilayer (≥2) Bi tends to be conductive, which not only facilitates\nelectron transport but also promotes the generation of photoinduced\ncurrent by overcoming the work function. The intriguing experimental\nand theoretical results indicate that 2D MXene Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> NSs can be employed as building\nblocks to construct many promising hydrides for various photoelectronic\ndevices, further greatly widening the application prospects of 2D\nMXenes.