Evolution of the reactive surface area of ferrihydrite: time, pH, and temperature dependency of growth by Ostwald ripening

Abstract

Surface area is a crucial property of ferrihydrite that has been assessed by probing it with PO4.

How crucial is the impact of calcium on the reactivity of iron-organic matter aggregates? Insights from arsenic

“…Calcium interacts with the OM COOH sites that partially screen the interactions between Fe and OM [8]. As a consequence, the size of the Fh-like Nps increases, which should involve a decrease in their SSA and q max [40,[44][45][46]. Surprisingly, our results did not confirm these expectations: q max and the SSA increased concomitantly with the increasing size of Fh-like Nps (Figure 6).…”

Assessing the Reactive Surface Area of Soils and the Association of Soil Organic Carbon with Natural Oxide Nanoparticles Using Ferrihydrite as Proxy

“…The fraction of metal ions forming surface groups increases when the particle size decreases, leading to an increase in n H 2 O. Consequently, M nano increases when the particle size decreases, whereas ρ nano simultaneously decreases because the surface groups (−OH 2 and −OH) contribute more to the particle volume than to the mass. 36 …”

“… 23 , 25 , 32 In this approach, the nanocrystalline fraction of metal-(hydr)oxides is assessed using a traditional acid ammonium oxalate (AO) extraction 33 , 34 and next converted to the RSA (m 2 /g soil) using, for the extracted metal-(hydr)oxides, a standard value for the specific surface area (SSA) and a fixed value for the molar mass ( M nano ). However, this may lead to inconsistent results because both properties are particle size-dependent 35 , 36 and can greatly vary among soil samples. 37 − 39 …”

Iron speciation in iron–organic matter nanoaggregates: a kinetic approach coupling Quick-EXAFS and MCR-ALS chemometrics

“…As an example, a small difference in the Fh-NP size such as 1.68 vs 1.65 nm would not lead to any modification of the Fh-NP EXAFS spectrum but can lead to a difference in the solubility product from Ks ~5.4 to Ks ~5.6 which leads to different Fh/oligomer ratios. 25,54 Accordingly, the observed slow decrease of the oligomer/Fh ratio after Fe(II) oxidation ( Figure 3a) can be explained by the ferrihydrite solubility decrease with its size growth over time.…”

“…Furthermore, it has been demonstrated that ferrihydrite particle size grows with ageing and pH increase, which leads to a decrease of the ferrihydrite solubility. 25,54 This phenomenon also contributes to the increase of the Fh/oligomer ratio over time. Figure 3a shows that, at the beginning of the reaction, Fh-NP and oligomers concentration grow concomitantly during Fe(II) oxidation, whatever the rate of Fe(II) oxidation.…”