Liquid phase laser ablation as a general green physical etching method to prepare MXene dots with arbitrary surface functionalization. Implications in overall water splitting photocatalysis

A novel green, fluoride-free etching method allowing installation of surface groups at will for the preparation 0D MXene dots with notable photocatalytic activity is reported. The method consists in the liquid-phase laser ablation using a pulsed Nd-YAG laser (532 nm, 7 ns fwhp, 30 mJ pulse −1 , 10 Hz) that produces the physical Al etching of the Ti 3 AlC 2 precursor forming nanometric Ti 3 C 2 particles. Simultaneously with etching, the surface of the MXene dots become functionalized with organic moieties inherited from the liquid phase as confirmed by XPS and in several cases by FT-IR spectroscopy. The lateral particle size of the Ti 3 C 2 dots depends on the viscosity of the liquid medium and varies from a few nm to above 50 nm. Crystallinity and structure of the Ti 3 C 2 dot is confirmed by high resolution TEM and by selected area electron diffraction of the samples. Ti 3 C 2 dots promote photocatalytic overall water splitting into H 2 and O 2 , the activity depending on the nature of the surface terminal groups. However, upon reuse the Ti 3 C 2 dots become significantly degraded into amorphous material, decreasing gradually in photocatalytic activity. This degradation is proposed to be caused by self-oxidation of Ti 3 C 2 dots by the photogenerated holes, as evidenced by the fact that the use of methanol as hole quencher stops deactivation during H 2 production. In sharp contrast with the decay in photocatalytic activity the presence of hole quenchers, the Ti 3 C 2 dots even increase substantially their photocatalytic activity upon reuse, a fact that has been attributed to the optimization of the nature of the surface terminal groups during the photocatalytic process. • MXene dots having tunable surface functionalization have been prepared by laser ablation. • MXene dots exhibit photocatalytic activity for H 2 generation depending on the surface groups. • The optimal MXene dot evolves 7800 μmol H2 g catalyst −1 using 150 W Xe lamp in the presence of MeOH. • Photocatalytic activity of MXene dots increases in four consecutive uses in MeOH. • MXene dots can also promote overall water splitting, but they undergo self-oxidation.