Abstract: A kind of 2D-layered material, Ti3C2 MXenes, was successfully used as a new and efficient co-catalyst to improve the photocatalytic NH3 synthesis performance of P25, due to its large surface area/2D-layered structure, large electric capacity, excellent electrical conductivity and effective chemisorption/activation of N-2 molecules. The generation yield of NH3 was improved by five times on the optimized sample of 6% Ti3C2 MXenes-P25 compared with pure P25 under full spectrum light irradiation, consistent with the measured both photocurrent densities and charge lifetime. The further mechanistic study showed that Ti3C2 MXenes played an important role in the separation of photogenerated electron-hole pairs by accumulating the excited electrons from the excited P25. Most importantly, Ti3C2 MXenes could dramatically improve chemisorption and activation of N-2 as demonstrated by ESR spectra and DFT calculations. In addition, Ti3C2 MXenes loading on P25 could introduce oxygen vacancies in P25, also beneficial for photocatalytic NH3 synthesis. Thus this study provides an efficient and promising co-catalyst for the photocatalytic NH3 synthesis process from N-2 in air