Wet‐Chemical Etching and Delamination of MoAlB into MBene and Its Outstanding Photocatalytic Performance

Abstract MBenes are post‐MXene materials that contain boron in their structure instead of carbon and nitrogen. This unique composition offers an opportunity to explore the role of boron in the performance of 2D materials. However, wet‐chemical etching and delamination of the starting MoAlB phase are challenging due to the persistent bonding of aluminum atoms with their neighboring elements. Herein, it is overcome by processing MoAlB for 24, 48, and 72 h with an aqueous HCl/H 2 O 2 solution. The time‐wise etching and delamination delivers individual single‐to‐few layered 48‐MBene flakes. The theoretical‐to‐experimental XRD analysis revealed the best‐delaminated 48‐MBene having Mo 2 B 2 orthorhombic lattice arrangement. The presence of Mo oxide allows direct 1.2 eV and indirect 0.2 eV optical band gaps and outstanding photocatalytic activity in decomposing methylene blue as a model organic contaminant. The 48‐MBene photocatalyst achieves about 90% of MB decomposition under ultraviolet and simulated white light irradiation with three times faster kinetics outperforming even hybridized MXenes. In addition, 48‐MBene appeared best suited to utilize the full spectrum of visible light into reactive oxygen species. Conversely, 24‐MBene and 72‐MBene shows incomplete delamination or oxidation, hampering their photocatalytic activity. The obtained results open an experimental pathway to apply MBenes in environmental remediation.