The ESR spin-trapping technique (with BMPO) was employed to detect the reactive oxygen KX2-391 (ROS) involved in the suspension of the catalyst with H2O2. As shown in Fig. 8, no significant signals were attributed to OH in the control experiments without catalyst (curve a) or in the M0 aqueous dispersion (curve b), while four characteristic peaks of BMPO-OH were observed in the aqueous dispersion of Cu-MSMs with H2O2 (curve c–f). The intensities of these peaks in the suspension with H2O2 had the sequence: M2 > M1 > M3 > M4. The formation of HO2/O2− radicals was also detected in methanol, and the similar rule with the formation of OH radicals was found in the systems. The result was in agreement with the catalytic activity of Cu-MSMs for the degradation of PhACs, indicating that H2O2 was more effectively converted to OH and HO2/O2− radicals at the interface of M2 where the copper species were primarily in the framework of Cu-MSMs.