Activation of peroxymonosulfate by MXene-confined micron-sized copper particle catalyst: A new understanding of size effects

The intricate relationship between catalyst size and reactivity has long been debated on the conflicting role of size effects in governing catalytic performance. A series of MXene-confined copper particle catalysts with various sizes ranging from 0.52 μm to 2.06 μm were synthesized via the confined growth strategy. Intriguingly, the pseudo-first removal rate of sulfamethoxazole exhibited a volcano-shaped relationship versus Cu particle size, and the optimal catalytic activity was achieved with the intermediate size of 1.18 μm (Cu@MXene-650 °C catalyst). The Cu particle size also influenced the generation of Cu(I), which was confirmed as the primary electron shuttle for PMS activation. Electrochemical impedance spectroscopy and cyclic voltammetry further revealed that the intermediate-sized Cu particle catalyst exhibited the lowest charge-transfer resistance and the highest electron-transfer efficiency. Hydroxyl radical (HO • ), sulfate radical (SO•- 4), singlet oxygen ( 1 O 2 ) and superoxide radical (O•- 2) were identified as the primary reactive species. Additionally, the micron-sized Cu@MXene catalyst demonstrated excellent performance over the pH range of 3.0 to 9.0, strong resistance towards common water matrix components and good stability in real river water. This work established a volcano-shaped relationship between Cu particle size and catalyst activity, thereby improving understanding of the role of metal particle size effects in advanced oxidation processes.