Nanoparticles (NPs) play a vital role in the energy catalysis process, so understanding the heterogeneous catalytic properties of nanocatalysts is of great significance for rationally guiding the design of catalysts. However, the traditional method obtains the average information based on the whole and cannot study the catalytic activity of a single nanoparticle. It is critical to investigate the catalytic activity of individual nanoparticles using in situ techniques. This review summarizes some of Prof. Xu’s recent accomplishments in studying the catalytic behavior of nanoparticles at the single-particle level using single-molecule fluorescence microscopy (SMFM). These achievements include revealing the effect of size, shape, and surface atoms of Pd nanoparticles on catalytic kinetics and dynamics as well as obtaining the activation energy of single Au nanoparticles for catalytic reactions by single-molecule methods. It is the first time to study the kinetics and dynamics of single-atom Pt catalysts. Furthermore, the method was extended to study the Pt deactivation process for hydrogen oxidation reactions as well as the catalytic kinetics of two-electron oxygen reduction reactions of individual Fe₃O₄ nanoparticles in electrocatalysis. Finally, single-molecule super-resolution techniques were used to observe the evolution of the activity of single Sb doped TiO₂ nanorod domains. These studies are of guiding significance for in-depth understanding and realization of rational design of optimal catalysts.

Densely packed and ordered "suprastructures" are new types of nanomaterials exhibiting broad applications. The direct self-assembly of cetyltrimethylammonium bromide (CTAB)-capped gold nanotriangles to form "suprastructures" was systematically investigated by varying the temperature and tilt angle of the silicon wafer used in the assembly process. Under optimal conditions, nanotriangles form into regular patterns, maintain their integrity, and form edge-to-edge, point-to-point, and face-to-face connections to form ordered "suprastructures" within an area of hundreds of square microns, achieving a high level of regularity. The formation of the "suprastructures" under optimal conditions could be mainly attributed to the complex balance between multiple temperature-dependent factors, including the atom diffusion rate, solvent evaporation rate, self-assembly rate, and the time for which the nanoparticle stays in the wet medium.