Recent advances in two-dimensional ultrathin Bi-based photocatalysts

Bi-based layered material shows its great potential in constructing ultrathin two-dimensional (2D) structure, which has been demonstrated to be an effective strategy to improve the photocatalytic performance of various semiconductors. The ultrathin 2D configuration endows Bi-based photocatalyst with many inherent advantages, including large specific surface area, short charge migration distance, increased redox capability, and abundant surface reactive sites. While these unique features contribute to the superior activity of the 2D Bi-based nanosheet, the unique electronic properties of the 2D configuration also endue the material with great potential in a number of energy-related photoreactions (e.g., water splitting, CO2 reduction and N2 fixation) that are thermodynamically unfavorable on bulk photocatalyst. Herein, we provide a review on recent literatures relevant to Bi-based (layered or nonlayered) photocatalysts by distinguishing the ultrathin 2D architecture from bulk counterparts. This review focuses on the synthesis techniques and provides a fundamental understanding of the physicochemical, electronic, and optical properties of the 2D Bi-based photocatalysts. Recent advances of these ultrathin 2D Bibased photocatalysts in a multitude of photocatalytic applications such as molecular oxygen activation, water splitting, CO2 reduction, and N2 fixation are appraised. Given that there remain challenges in realizing highly efficient solar energy conversion on ultrathin Bi-based photocatalyst, strategies regarding to increasing light absorption, facilitating charge separation and migration, and accelerating surface reaction kinetics, are therefore introduced. This review aims to provide a comprehensive survey and deep understanding on ultrathin 2D Bi-based photocatalysts from various aspects in order to inspire new research directions in designing highperforming photocatalysts.