Water Vapor Condensation on Iron Minerals Spontaneously Produces Hydroxyl Radical

Water vaporcondensation on iron minerals spontaneouslyproduces hydroxyl radicals, driving surface-bound pollutant degradation. The hydroxyl radical ((OH)-O-center dot) is a potentoxidantand key reactive species in mediating element cycles and pollutantdynamics in the natural environment. The natural source of (OH)-O-center dot is historically linked to photochemical processes (e.g., photoactivationof natural organic matter or iron minerals) or redox chemical processes(e.g., reaction of microbe-excreted or reduced iron/natural organicmatter/sulfide-released electrons with O-2 in soils andsediments). This study revealed a ubiquitous source of (OH)-O-center dot production via water vapor condensation on iron mineral surfaces.Distinct (OH)-O-center dot productions (15-478 nM via watervapor condensation) were observed on all investigated iron mineralsof abundant natural occurrence (i.e., goethite, hematite, and magnetite).The spontaneous (OH)-O-center dot productions were triggered bycontact electrification and Fenton-like activation of hydrogen peroxide(H2O2) at the water-iron mineral interface.Those (OH)-O-center dot drove efficient transformation of organicpollutants associated on iron mineral surfaces. After 240 cycles ofwater vapor condensation and evaporation, bisphenol A and carbamazepinedegraded by 25%-100% and 16%-51%, respectively, forming (OH)-O-center dot-mediated arene/alkene hydroxylation products. Ourfindings largely broaden the natural source of (OH)-O-center dot. Given the ubiquitous existence of iron minerals on Earth'ssurface, those newly discovered (OH)-O-center dot could play arole in the transformation of pollutants and organic carbon associatedwith iron mineral surfaces.

Automated summary

Water vapor condensation on iron minerals leads to the production of hydroxyl radicals, which play a vital role in degrading surface-bound pollutants. This study identified a widespread source of hydroxyl radicals through water vapor condensation on iron mineral surfaces. Distinct hydroxyl radical productions were observed on various iron minerals, and these radicals efficiently transformed organic pollutants associated with the mineral surfaces. These findings expand our understanding of the natural sources of hydroxyl radicals and their potential involvement in pollutant transformation on Earth's surface.