Low-valent copper on molybdenum triggers molecular oxygen activation to selectively generate singlet oxygen for advanced oxidation processes.

Singlet oxygen (O), which is difficult to generate, plays an important role in chemosynthesis, biomedicine and environment. Molecular oxygen (O) is a green oxidant to produce O cost-effectively. However, O activation is difficult due to its spin-forbidden nature. Moreover, the main products of O activation are basically hydrogen peroxide (HO) and hydroxyl radical (•OH), but rarely O. Herein, we innovatively realize the selective generation of O via O activation by a facile molybdenum (Mo)/Cu system. In this system, Mo firstly reduces Cu in solution to low-valence Cu/Cu on its surface. Cu/Cu activates O to generate superoxide radical (O). Importantly, O can be captured immediately and oxidized to O by surface-bound Mo rather than reduced to HO. As a result, the Mo/Cu system can selectively produce O. Under air and O conditions, the degradation efficiency of ibuprofen by Mo/Cu system is 67.2 % and 76.6 %, respectively. The degradation efficiencies of bisphenol A, rhodamine B and furfuryl alcohol are 77.1 %, 87.7 % and 91.1 %, respectively. The dosages of Mo and Cu are 0.4 g/L and 3 mM, respectively, and the reaction time is 2 h. Interestingly, the activity of Mo decreased by only 4.2 % after 4 cycles. Therefore, this study provides a green pathway to selectively generate O for advanced oxidation processes.