A research team from Shandong Normal University has published a groundbreaking study in the journal Science, marking the university's first-ever paper in this top-tier journal as the primary contributing institution.

The study, led by Professor Luo Tao from the College of Chemistry, Chemical Engineering and Materials Science, reveals for the first time that a single freeze-thaw cycle can induce irreversible aggregation of ferrihydrite nanoparticles, shifting their transformation pathway from goethite to hematite.

Ferrihydrite, a ubiquitous nanomineral found in nature, is often described as the "infant" of the iron mineral world. It serves as both a precursor to many iron minerals and a "super sponge" that adsorbs heavy metals, phosphorus, and organic carbon. Until now, the scientific community viewed freezing as merely a "pause button" that slows down reactions. The team's research upends this conventional understanding, demonstrating that freezing itself acts as an active "chemical reactor".

Using cryo-transmission electron microscopy and other multi-scale techniques, the researchers quantitatively revealed how ice crystals compress ferrihydrite nanoparticles into a thin liquid boundary layer just tens to hundreds of nanometers thick. There, dehydration and surface hydroxyl reactions form stable Fe–O–Fe chemical bonds, effectively "welding" the particles together. This single freeze event alters the mineral's evolution path for months, a phenomenon the team calls the "memory effect."

The discovery carries profound implications beyond mineralogy. As global warming accelerates permafrost degradation and glacier melt, the findings provide a new theoretical framework for understanding iron cycling, carbon sequestration, and pollutant migration in cold regions.