MXene-based 2D/2D Ti3C2/TiO2 heterojunction with spatially separated redox sites for efficient photocatalytic N2 reduction towards NH3

Herein, a new type of two-dimensional (2D)/2D Ti 3 C 2 /TiO 2 heterojunction was developed for efficient photocatalytic nitrogen reduction reaction (NRR), in which TiO 2 nanosheets (TiO 2 Ns) were designed as the main catalyst, while Ti 3 C 2 MXene served as the co-catalyst. Experimental and theoretical results revealed that Ti 3 C 2 MXene introduced electron-rich unsaturated Ti sites, serving as highly active sites for both the adsorption and activation of N 2 on the Ti 3 C 2 /TiO 2 heterojunction. Furthermore, the 2D/2D Ti 3 C 2 /TiO 2 heterostructure greatly promoted the directional separation and transfer of charge carriers, facilitated by the internal electric field. This structural feature enabled the spatial separation of the N 2 reduction and H 2 O oxidation half-reactions on the distinct surfaces of Ti 3 C 2 (001) and TiO 2 (001), consequently reducing the reaction energy barrier for each respective process. The synergistic effects arising from the interface and surface interactions within the heterojunction conspicuously improved the photocatalytic NRR activity. As a result, the optimized Ti 3 C 2 /TiO 2 heterojunction exhibited a high NH 3 production rate of 24.4 μmol g -1 h -1 in the absence of sacrificial agents, representing a remarkable 12.8-fold increase compared to individual TiO 2 Ns. This work provides new insights into rational design of high-performance heterogeneous photocatalysts and offers a deeper understanding of the mechanism underlying surface active sites in the photocatalytic NRR process.