Spin‐State Switching Modulates Lewis Acidity in Ferrihydrite for Enhanced Phosphate Capture

filling ≈0.983). Compared to pristine Fh, the HS S-Fh exhibits an elevated number of unpaired d electrons (2.36→3.45), thereby significantly increasing its Lewis acidity. Mechanistic studies reveal that improved electron transfer between P-O bonds and Fe centers, together with strengthened d-p orbital hybridization, promotes phosphate adsorption, resulting in a 146-fold improvement in adsorption kinetics. Remarkably, S-Fh continuous-flow reactor maintains ≈100% phosphate removal after treating over 1200 bed volumes of wastewater. This work emphasizes the crucial role of spin state in regulating Lewis acidity and provides a new design strategy for highly efficient adsorbents.