Green, HF-Free Synthesis of MXene Quantum Dots and their Photocatalytic Activity for Hydrogen Evolution

A general methodology to prepare MXene quantum dots (MxQDs) with yields over 20% by liquid-phase laser ablation of the MAX phase is reported. Mechanical and thermal shock by 532 nm laser pulses (7 ns fwhp, 50 mJ × pulse^-1 , 1 Hz pulse frequency) produces MAX etching and exfoliation to form MXene QDs, avoiding the use of HF. The process can be followed by absorption and emission spectroscopy and by dynamic laser scattering and it appears to be general, being applied to Ti₃ AlC₂ , Ti₂ AlC, Nb₂ AlC, and V₂ AlC MAX phases. Density functional theory calculations indicate that, depending on the surface terminal groups, the diminution of the MXene size to the nanometric scale makes it possible to control the band gap of the MXene. The photocatalytic activity of these MXene QDs for hydrogen evolution has been observed, reaching an H₂ production for the most efficient Ti₃ C₂ QDs as high as 2.02 mmol × g^-1 × h^-1 .