Analyzing ultrafast liquid-phase reactions in real time presents signifi cant challenges owing to their rapid kinetics. In this

study, by employing the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as a model reaction, we demonstrate the

feasibility of real-time kinetic analysis using UV–Vis absorption spectroscopy. This reaction, which was completed within

10 s, was successfully monitored and analyzed to understand the limitations of conventional ultrafast reaction methods and

explore steps to overcome them. A novel coral-like ultrasonic-treated Cu (UCu) mesh fabricated via sulfi dation and ultrasonic

treatments was utilized as the catalyst for this reaction, resulting in a high specifi c surface area and abundant active sites.

The UCu mesh exhibited an apparent rate constant of 0.353 s −1 , signifi cantly outperforming other reported catalysts, such

as ZnO@Cu (0.043 s −1 ) and Cu nanowires (0.076 s −1 ). Compared to Cu and CuS meshes, the UCu mesh demonstrated a

29- to 58-fold improvement in catalytic performance under identical conditions. These results demonstrate the eff ectiveness

of integrating real-time UV–Vis spectroscopy with advanced nanostructured catalysts for ultrafast reaction analyses. This

study establishes the UCu mesh as a highly effi cient and reusable catalyst with promising applications in environmental and

industrial processes requiring rapid catalytic reactions.