Efficient singlet oxygen nanogenerator with low-spin iron for selective contaminant decontamination

The hydrogen peroxide (H2O2)-based photo-Fenton-like was a promising technology for the generation of singlet oxygen (1O2), which was highly desirable in water purification. However, the yield of 1O2 in traditional radical system was low due to the radical competition. Targeted construction of the non-radical system could solve the above issue, but it has been a challenge. In this study, we targetedly regulated the Fe spin state to efficiently generate 1O2 in a nonradical path. The experimental and theoretical results demonstrated that low-spin FeIII enhanced H2O2 adsorption, directly extracted electrons from H2O2 to Fe center, and rapidly cleaved O–H bond to accelerate the recombination of *OOH with H2O2 for efficient 1O2 generation. This unique nonradical process differed obviously from the traditional radical pathway for 1O2 generation. The developed 1O2-dominant 50Fh/BiOI/H2O2/vis system degraded 98.4% of TCH, which was higher than that in •OH-dominant Fh/H2O2/vis system (84.2%) and it had excellent resistance to various substances, including inorganic ions, dissolved organic matter and real water matrix (tap water and secondary effluent). This study enhanced our understanding of spin-state-dependent photo-Fenton-like reaction and inspired the targeted development of a new-generation selective wastewater treatment technology.