Effects of Fullerol and Graphene Oxide on the Phase Transformation of Two-Line Ferrihydrite

Abstract

Two-line ferrihydrite (Fh) is an omnipresent iron oxyhydroxide nanomineral with high surface reactivity and weak crystallinity, and its phase transformation in nature has drawn significant concerns. A number of studies have investigated the effects of coexisting natural substances (e.g., ions, organic molecules, and clay minerals) on the phase transformation processes of Fh. This work, for the first time, studied the effects of coexisting carbon nanomaterials (CNM) on the phase transformation of Fh, and CNM with different morphologies, that is, graphene oxide (GO) and fullerol (PHF), were applied. Characterization results from X-ray diffraction, transmission electron microscopy, and Mossbauer spectroscopy showed that the transformed products of Fh are mainly hematite (Hem) with a small amount of goethite (Gth) in the absence/presence of CNM; however, the transformation kinetics, morphologies, and Hem/Gth ratio of the transformed products are distinctly different in each system. In particular, GO decreased the transformation rate of Fh (compared with the Fh system), whereas PHF not only accelerated the transformation rate but also favored the formation of larger Hem particles and higher Hem/Gth ratios in the transformed products. We hypothesized that these results could be attributed to the different behaviors of CNM in affecting the aggregation of Fh as the transformation of Fh into Hem is a solid phase transformation process (via dehydration), which strongly relies on the aggregation of Fh particles. In this term, the samples of CNM−Fh mixtures before transformation were characterized. The results obtained from atomic force microscopy and sedimentation experiments showed that the large lamellar GO could act as a dispersing agent and inhibit the aggregation and contact of Fh particles while the nanogranular PHF functioned as a "bridge" and enhanced the aggregation of Fh particles. This study revealed that the coexisting nanoparticles (e.g., PHF and GO) could exert different influences on the transformation of Fh by influencing its aggregation and dispersion.

Effect of Mn(II) and Phytic Acid on Cr(VI) in the Ferrihydrite-Cr(VI) Co-precipitates: Implication for the Migration Behavior of Cr(VI)

“…Hematite was formed by aggregation and rearrangement and internal dehydration in ferrihydrite, while goethite was formed by the dissolution of ferrihydrite, followed by its recrystallization. 41 The XRD spectra of the Fh−Cr with different PA/Fe molar ratios after aging for 4 days and 9 days are displayed in Figure 1c,d. The Fh−Cr showed peaks of hematite and goethite after aging for 4 days and 9 days, indicating that Fh− Cr was converted into hematite and goethite.…”

“…According to the results of Figure4a, there was almost no M-OH 2 component on Fh−Cr, while 0.05PA-Fh-Cr and 0.05PA-Fh-Cr+Mn contained 41.4 and 40.9% M-OH 2 components, respectively. The difference in the M-OH 2 component among the Fh−Cr, 0.05PA-Fh-Cr, and 0.05PA-Fh-Cr+Mn systems can be explained by the process of dehydration that occurs during the conversion of ferrihydrite to hematite41 and the contribution of the C−O−P bond on PA 63,64.…”

Adsorption of phosphate and cadmium on iron (oxyhydr)oxides: A comparative study on ferrihydrite, goethite, and hematite

“…The nanocrystalline Fh is ubiquitous in groundwater, stagnant water soils, and paddy soils (Barrón and Torrent, 2013). The metastable Fh can transform into Hm and Gt, which are very common constitutes in tropical soils such as ferralsols or oxisols (Barrón and Torrent, 2013; Yan et al, 2020). Generally, Fh converts to Gt through dissolution-recrystallization under acid or alkaline conditions, and to Hm under neutral pH through internal rearrangement (Barrón and Torrent, 2013;Cornell et al, 2003;Jiang et al, 2018).…”

Carbonate-Enhanced Transformation of Ferrihydrite to Hematite

“…In natural environments, the transformation process of ferrihydrite is also controlled by the complexation of common cations (e.g., zinc, nickel, cobalt, iron, and calcium), oxyanions (e.g., phosphate, silicate, sulfate, and arsenic), organic ligands (e.g., carboxylic acid, simple sugars, cysteine, and phytic acid), clay minerals (e.g., montmorillonite), and carbon nanomaterials (e.g., fullerol and graphene oxides). − Among them, different oxyanions exert different interactions with ferrihydrite particles, which accordingly may alter the transformation process of ferrihydrite. For example, phosphate, silicate, and arsenic strongly adsorb to ferrihydrite under alkaline conditions through inner-sphere complexation (e.g., (FeO) 2 PO 2 , (FeO) 2 Si­(OH) 2 , and (FeO)­AsO­(OH) 2 ). ,, These surface complexes generally slow down the rate of ferrihydrite transformation by retarding ferrihydrite aggregation and dissolution. − Sulfate can be adsorbed onto the ferrihydrite surface via both outer-sphere complexes and inner-sphere complexes, which also retards the transformation rate of ferrihydrite. , In a sulfate solution at 80 °C, goethite is the dominant product under slightly acidic conditions, whereas the formation of hematite is favored under slightly alkaline conditions .…”