2D Nanomaterials, with unique structural and electronic features, have shown enormous potential toward photocatalysis fields. However, the photocatalytic behavior of pristine 2D photocatalysts are still unsatisfactory, and far below the requirements of practical applications. In this regard, surface defect engineering can serve as an effective means to tune photoelectric parameters of 2D photocatalysts through tailoring the local surface microstructure, electronic structure, and carrier concentration. In this review, recent progress in the design of surface defects with the classified anion vacancy, cation vacancy, vacancy associates, pits, distortions, and disorder on 2D photocatalysts to boost the photocatalytic performance is summarized. The strategies for controlling defects formation and technique to distinguish various surface defects are presented. The crucial roles of surface defects for photocatalysis performance optimization are proposed and advancement of defective 2D photocatalysts toward versatile applications such as water oxidation, hydrogen production, CO 2 reduction, nitrogen fixation, organic synthesis, and pollutants removal are discussed. Surface defect modulated 2D photocatalysts thus represent a powerful configuration for further development toward photocatalysis.

a great deal of research interest for diverse applications such as field effect transistors, optoelectronic devices, catalysis, energy storage, and conversion. [1][2][3][4][5] Benefiting from the features of atomic thickness, large specific surface area, intrinsic quantum confined electrons, and high ratio of surface atoms to entire atoms, the ultrathin 2D materials exhibit unique physicochemical properties, such as planar conductivity, electronic anisotropy, tunable energy band structure, and high surface activity. [6,7] When the thickness of bulk materials is reduced to the atomic level, the local atomic structures will suffer from obvious distinctions including coordination number, bond angle, bond length, and disorder degree of the surface atoms and may even result in the formation of numerous surface defects. As a consequence, the ultrathin 2D materials can not only display improved inherent properties of the bulk materials but also give birth to new properties that the corresponding bulk materials do not possess. [8,9] Semiconductor photocatalysis has attracted massive research interest since it has been regarded as one of the most promising solutions to deal with the energy shortage and environmental-pollution issues. [10][11][12][13][14] With the solar light as the external driving force, the semiconductor could split water into hydrogen and oxygen, reduce the CO 2 to chemicals and valuable fuel, as well as completely eliminate pollutants. [15][16][17][18] Generally, the major critical steps in the photocatalytic process can be classified as light absorption, charge separation and migration, as well as surface redox reactions. Under the irradiation, the photocatalysts can absorb the solar light and are excited to produce electron-hole pairs when the photon energy equal to or higher the bandgap, leaving the electrons in the conduction band (CB) and holes in the valence band (VB), respectively. Subsequently, the photogenerated electrons and holes will diffuse to the materials surface and further migrate to the surface active sites before involving in the surface reactions. During this process, the recombination of charge carriers will happen and the crystal structure, crystallinity, particle size, surface atomic structure, etc., will strongly affect the separation efficiency. Finally, the target molecule will be adsorbed on the materials surface, and will undergo charge injection process and desorption to form the ultimate products. [19] Up to now, hundreds of semiconductor materials are available for different photocatalytic applications with the help As a sustainable technology, semiconductor photocatalysis has attracted considerable interest in the past several decades owing to the potential to relieve or resolve energy and environmental-pollution issues. By virtue of their unique structural and electronic properties, emerging ultrathin 2D materials with appropriate band structure show enormous potential to achieve efficient photocatalytic performance. Here, the state-of-the-art progress on ultrathin 2D...

The design of efficient and stable photocatalysts for robust CO 2 reduction without sacrifice reagent or extra photosensitizer is still challenging. Herein, a single-atom catalyst of isolated single atom cobalt incorporated into Bi 3 O 4 Br atomic layers is successfully prepared. The cobalt single atoms in the Bi 3 O 4 Br favors the charge transition, carrier separation, CO 2 adsorption and activation. It can lower the CO 2 activation energy barrier through stabilizing the COOH* intermediates and tune the rate-limiting step from the formation of adsorbed intermediate COOH* to be CO* desorption. Taking advantage of cobalt single atoms and two-dimensional ultrathin Bi 3 O 4 Br atomic layers, the optimized catalyst can perform light-driven CO 2 reduction with a selective CO formation rate of 107.1 µmol g −1 h −1 , roughly 4 and 32 times higher than that of atomic layer Bi 3 O 4 Br and bulk Bi 3 O 4 Br, respectively.