Direct identification of reaction sites on ferrihydrite

Abstract

Hydroxyl groups are the cornerstone species driving catalytic reactions on mineral nanoparticles of Earth's crust, water, and atmosphere. Here we directly identify populations of these groups on ferrihydrite, a key yet misunderstood iron oxyhydroxide nanomineral in natural sciences. This is achieved by resolving an enigmatic set of vibrational spectroscopic signatures of reactive hydroxo groups and chemisorbed water molecules embedded in specific chemical environments. We assist these findings by exploring a vast array of configurations of computer-generated nanoparticles. We find that these groups are mainly disposed along rows at edges of sheets of iron octahedra. Molecular dynamics of nanoparticles as large as 10 nm show that the most reactive surface hydroxo groups are predominantly free, yet are hydrogen bond acceptors in an intricate network formed with less reactive groups. The resolved vibrational spectroscopic signatures open new possibilities for tracking catalytic reactions on ferrihydrite, directly from the unique viewpoint of its reactive hydroxyl groups.

Unveiling the Hydration Structure of Ferrihydrite for Hole Storage in Photoelectrochemical Water Oxidation

“…Impressively, the crystal water molecules have been widely demonstrated to play a significant role in the physic‐chemical properties such as chirality, capacitance, and electrocatalytic activity [12] . Recently, although surface hydroxyl groups disposed at edges of iron octahedra, have been identified as reaction sites of Fh, there are lack of sufficient evidences for structure‐property relationship [13] . It is therefore much more intriguing to unravel the intrinsic structure of Fh for its hole storage function.…”

Thermal Stability and Decomposition Products of P-Doped Ferrihydrite

“…Ferrihydrite (Fe 5 HO 8 ∙4H 2 O) is a widely known hydrous ferric oxyhydroxide that is widespread in both terrestrial and aquatic systems [ 1 ]. It is formed in near-surface environments during the oxidation reaction of Fe(II) to Fe(III), as a nearly amorphous nanomineral with a high surface area [ 2 , 3 , 4 , 5 ], and a high concentration of active hydroxyl sites [ 6 ]. It plays an essential role as a sorbent of various major and trace elements and controls their availability in the environment [ 7 , 8 , 9 , 10 , 11 ].…”

Arsenite photo-oxidation and removal by ferrihydrite in the presence of oxalate: a pH dependence and surface-mediated process

“…Previous studies showed that the surface hydroxyl groups on the surface of iron oxides served as the active sites of the catalyst and contributed to the degradation of pollutants. 49 The results of XPS in our study showed that the content of surface hydroxyl groups of ferrihydrite varied after a 90 min reaction and the FTIR spectra also indicated that the surface hydroxyl group was involved in the photo-oxidation process, which implied that the surface hydroxyl groups (available -OH group and Fe-OH at the surface of ferrihydrite) acted as the active sites and played an important role in the generation of reactive oxygen species and then the photo-oxidation of As(III).…”