From one-dimensional to two-dimensional wurtzite CuGaS2 nanocrystals: non-injection synthesis and photocatalytic evolution.

Multinary copper-based chalcogenides exhibit significant performance in photocatalytic hydrogen evolution due to their suitable optical bandgap for visible light absorption and environmentally friendly character. Herein, high-quality wurtzite CuGaS2 (CGS) nanocrystals (NCs) were synthesized by using a one-step heating-up process without any injection, and the morphology could be tuned from one-dimensional (1D) to two-dimensional (2D) by precise choice of surface ligands and gallium precursors. The formation mechanism of CGS NCs was studied comprehensively by means of the temporal-evolution of the morphology, crystal structure and optical absorption results. The reaction started from djurleite Cu31S16 NCs, and then proceeded with the formation of Cu31S16-CGS heteronanostructures (HNS), and finally the transformation from HNS to monophasic CGS nanorods took place with prolonging of the synthesis time. The optical bandgap and the energy level of the different-dimensional CGS NCs exhibited a strong dependence on the morphology change, which correlated with the percentage of the exposed {001} and {100} facets. The theoretical calculation based on density functional theory (DFT) revealed that the (001) surface facilitated the charge transport rather than the (100) surface, which was consistent with the electrochemical impedance spectroscopy (EIS) results. As a result, the 2D CGS nanoplates with more exposed {001} facets exhibited an attractive photocatalytic hydrogen production activity under simulated solar illumination as compared to 1D and quasi-2D counterparts. This study demonstrates that control over the dimension of I-III-V group semiconductor NCs could lead to a significant improvement of the photocatalytic hydrogen evolution.