Ti${}_3$C${}_2$: An ideal co‐catalyst?

How 2D Ti${}_3$C${}_2$ enhances photocatalytic efficiency remains unclear. Now, it is shown that it is graphene quantum dots (GQDs) derived from Ti${}_3$C${}_2$, rather than 2D Ti${}_3$C${}_2$ itself, that play the role of co‐catalyst for La${}_2$Ti${}_2$O${}_7$/Ti${}_3$C${}_2$ (LTC) composites during the photocatalytic reaction. After modification of Ti${}_3$C${}_2$ derivatives, the photocatalytic efficiency of La${}_2$Ti${}_2$O${}_7$ is enhanced 16 times over pure La${}_2$Ti${}_2$O${}_7$. Solid‐state NMR, Raman, and HRTEM results confirm the existence of GQDs in Ti${}_3$C${}_2$ and LTC composites. The GQDs are formed during the chemical change from Ti${}_3$AlC${}_2$ to Ti${}_3$C${}_2$ via HF etching, as Ti atoms are removed and unsaturated carbon bonds are left, which react with each other to form sp${}^2$ π‐conjugation GQDs. 2D Ti${}_3$C${}_2$ is completely oxidized to CO${}_x$ modified TiO${}_x$ species, causing Ti${}_3$C${}_2$ to lose its electrical conductivity and the role as co‐catalyst. GQDs largely suppress the photogenerated charge recombination of La${}_2$Ti${}_2$O${}_7$, as revealed by the photoluminescence (PL) and transient photocurrent. (© 2020 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)