Catalysts that can rapidly degrade tetracycline (TC) in water without introducing secondary ion pollution have always been challenging. Herein, a cobalt-based catalyst (CoO@P-C) is prepared so that CoO quantum particles (5–10 nm) are uniformly distributed on a linear substrate, and the outer layer is covered with a shell (P-C). The quantum particles of CoO provide many active sites for the reaction, which ensures the efficient degradation effect of the catalyst, and 30 mg/L TC can be completely degraded in only 5 min. The shell of the quantum particles' outer layer can effectively reduce ions' extravasation. The combination of the shell-like structure and the linear substrate greatly enhances the catalysis's stability and ensures that the catalyst is prepared into a film for practical application. The high catalytic activity of CoO@P-C is mainly due to the following factors: (1) Uniformly distributed ultra-small nanoparticles can provide many active sites. (2) The microenvironment formed by the core-shell structure enhances not only catalytic stability but also provides the driving force to improve the reaction rate. (3) The composite of CoO and P-C core-shell structure can accelerate electron transfer and generate many reactive oxygen species in a short time, which makes TC degrade extremely rapidly.

Nickel cobalt sulfides (Ni-Co-S) have attracted extensive attention for application in electronic devices owing to their excellent conductivity and high electrochemical capacitance. To facilitate the large-scale practical application of Ni-Co-S, the excellent rate capability and cyclic stability of these compounds must be fully exploited. Thus, hierarchical Ni-Co-S@Ni-W-O (Ni-Co-S-W) core/shell hybrid nanosheet arrays on nickel foam were designed and synthesized herein via a facile three-step hydrothermal method, followed by annealing in a tubular furnace under argon atmosphere. The hybrid structure was directly assembled as a free-standing electrode, which exhibited a high specific capacitance of 1, 988 F·g^-1 at 2 A·g^-1 and retained an excellent capacitance of approximately 1, 500 F·g^-1 at 30 A·g^-1, which is superior to the performance of the pristine Ni-Co-S nanosheet electrode. The assembled asymmetric supercapacitors achieved high specific capacitance (155 F·g^-1 at 1 A·g^-1), electrochemical stability, and a high energy density of 55.1 W·h·kg^-1 at a power density of 799.8 W·kg^-1 with the optimized Ni-Co-S-W core/shell nanosheets as the positive electrode, activated carbon as the negative electrode, and 6 M KOH as the electrolyte.