Facile synthesis of hollow Ti₃AlC₂ microrods in molten salts via Kirkendall effect

The microstructure and morphology of Ti₃AlC₂ powders not only affect the preparation of Ti₃C₂ MXene but also have a great influence on their potential applications, such as microwave absorbers, alloy additives, or catalytic supports. However, the synthesis of Ti₃AlC₂ powders with desired microstructure and morphology remains a challenge. Herein, hollow Ti₃AlC₂ microrods were prepared for the first time in NaCl/KCl molten salts by using titanium, aluminum, and short carbon fibers as starting materials. It was found that the short carbon fibers not only performed as carbon source but also acted as sacrificial template. Furthermore, it was revealed that TiC and Ti₂AlC were initially formed on the surface of carbon fibers. The subsequent reactions between the outer Ti, Al and the inner carbon were dominated by the Kirkendall effect which gave rise to the formation of a hollow structure. Based on this mechanism, hollow Ti₃AlC₂ microspheres and a series of hollow TiC, Ti₂AlC, and V₂AlC powders were also successfully fabricated. This work provides a facile route to synthesize hollow MAX phases and may give enlightenment on preparing other hollow carbide powders via the Kirkendall effect in the molten salts.