Spatial Ice Confinement Enabled Chemical Reaction Acceleration for Water Purification

The frozen environment is recognized as an important physical and chemical sink for various environmental substances. However, progress in unraveling the fundamental mechanisms governing the reaction process and the conversion of substances within ice matrices remains limited. Here, we discovered that the direct electron transfer process of environmental contaminants is drastically accelerated during freezing, with pseudo-first-order rate constants increasing by orders of magnitude relative to ambient conditions. Contaminants were observed to significantly concentrate within the liquid regions between ice crystals. The interface adsorption layers greatly influenced the molecular packing behavior, inducing migration and anchoring of reactants at the ice-water interface. Theoretical calculations further demonstrated that the spatial confinement imposed by the ice crystals profoundly reshaped the reactants' electron distribution, reduced their energy gap, and lowered the reaction free energy, collectively providing both thermodynamic and kinetic driving forces. Kinetics simulation quantitatively showed that a new chemical reaction acceleration paradigm, referred to as the ice confinement effect, overwhelmingly drove degradation of micropollutants. This work overturns the traditional mechanism of freeze-accelerated reactions, which may lead to a paradigm shift in the understanding of environmental substance fate in frozen environments.