Solvent-free fabrication of ultrathin two-dimensional metal oxides/sulfides in a fixed interlayer by geometric confinement

Two-dimensional (2D) nanomaterials display unique characteristics owing to their ultrahigh surface-to-volume ratio and quantum confinement effects. Nonetheless, seeking a versatile and facile method to rationally shape ultrathin 2D frameworks is still an appealing challenge. Herein, a series of ultrathin 2D metal oxide crystals (2D MOs), including 3d transition metals (Ti, Cr, Mn, Fe, Co, Ni, Cu, Zr, W), lanthanide (Ce) and nontransition metal (In, Sn, Bi) oxides, were created through a confined interlayer growth strategy in combination with melt infiltration, in which no complicated chemistry or sophisticated equipment was needed. The 2D oxides presented lamellar constructions with high crystallinity, and the thickness was strictly limited to ~ 1 nm. The crystallization process, including the Frank-van der Merwe mode and the Volmer-Weber mode, was described. The defects and distortions of 2D TiO₂ reduced the optical band gap and improved the sunlight utilization efficiency, thus accelerating the photocatalytic activity. This method could be extended to the preparation of 2D polymetallic oxides, metal sulfides etc., which enables the development of versatile systems for ultrathin 2D frameworks, especially for nonlayered structures originally.