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

Singlet oxygen (1O2), which is difficult to generate, plays an important role in chemosynthesis, biomedicine and environment. Molecular oxygen (O2) is a green oxidant to produce 1O2 cost-effectively. However, O2 activation is difficult due to its spin-forbidden nature. Moreover, the main products of O2 activation are basically hydrogen peroxide (H2O2) and hydroxyl radical (•OH), but rarely 1O2. Herein, we innovatively realize the selective generation of 1O2 via O2 activation by a facile molybdenum (Mo)/Cu2+ system. In this system, Mo firstly reduces Cu2+ in solution to low-valence Cu0/Cu+ on its surface. Cu0/Cu+ activates O2 to generate superoxide radical (O2•-). Importantly, O2•- can be captured immediately and oxidized to 1O2 by surface-bound Mo6+ rather than reduced to H2O2. As a result, the Mo/Cu2+ system can selectively produce 1O2. Under air and O2 conditions, the degradation efficiency of ibuprofen by Mo/Cu2+ 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 Cu2+ 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 1O2 for advanced oxidation processes.