Comparing and quantifying goethite, hematite, lepidocrocite, and ferrihydrite by FTIR

Comparing and quantifying goethite, hematite, lepidocrocite, and ferrihydrite by FTIR | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Comparing and quantifying goethite, hematite, lepidocrocite, and ferrihydrite by FTIR Ruth H. Ellerbrock, Nisha Bhattarai, Jörg Schaller This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8741763/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 11 You are reading this latest preprint version Abstract Iron-(oxyhydr)-oxides like goethite, hematite and ferrhydrite affect soil properties like sorption capacity and can be distinguished by their specific surface and spectroscopic data like XRD. During dissolution–recrystallization the iron (oxyhydr)-oxide can convert from one into the other. Some studies used Fourier-transform infrared spectroscopy (FTIR) to analyze hematite and goethite. The objective of this study was to identify absorption bands in FTIR that allow to distinguish hematite, goethite, lepidocrocite, and ferrihydrite and to compare the FTIR of laboratory synthesized with those of natural iron (oxyhydr)-oxides. Comparing the FTIR spectra of the different iron minerals indicate that all studied iron (oxyhydr)-oxides show absorption band located at different WN in the WN region from 1180 to 400 cm − 1 typical for each of them. Distinct differences allow to distinguish and quantify, especially goethite from the other oxides. Hence, FTIR is a suitable method to distinguish between the different iron (oxyhydr)-oxides. Physical sciences/Chemistry Earth and environmental sciences/Environmental sciences Physical sciences/Materials science Earth and environmental sciences/Solid earth sciences crystal structure FTIR ferrihydrite goethite hematite crystallinity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Importance of crystallinity for iron (oxyhydr)-oxides Iron-(oxyhydr)-oxides show relatively high specific surface areas. Since they also offer a significant amount of hydroxyl sites 1 , 2 they considerably contribute to the soil sorption properties 3 , 4 . In soils the iron(III) (oxyhydr)-oxides are frequently present as ocre colored goethite (α-FeOOH) and red-colored hematite (α-Fe 2 O 3 ). Additionally, orange colored lepidocrocite (γ-FeOOH), redish-brown colored maghemite (γ-Fe 2 O 3 ), and the low crystalized water holding ferrihydrite (5Fe 2 O 3 *H 2 O). These iron(III) (oxyhydr)-oxides are formed from octahedral units which have an iron in the center and at the corners either of 6 O atoms (Fig. 1 a) or 3 O atom plus 3 OH groups (Fig. 1 b). In hematite the octahedral units are connected via the octahedral surfaces such the units are connected via three O atoms (turquoise circles; Fig. 2 a left): these arrangement results in a hexagonal dense packing of oxygens (Fig. 2 a right) with the cations distributed in the interstice-spaces of the octahedra 1 , 6 . In goethite and lepidocrocite the octahedral units are connected via octahedral edges (connection via two O atoms; Fig. 2 c left). In goethite the octahedra form double chains are interconnected via H-bridges between octahedral corners 1 , 6 (Fig. 2 b right). In lepidocrocite the double chains are formed via octahedral edges in zick-zack pattern. The structure of ferrihydrite is similar to the Baker-Figgis δ-Keggin clusters and the ferrihydrite particles are within the diameters of 2–10 nm 1,7 resulting in a 3D arrangement that is isostructural to akdalaite) (Fig. 2 d; https://www.mindat.org/min-69.html ). The structures and morphologies of the minerals control the surface properties of iron (oxyhydr)-oxides. The specific surface area values decrease in the sequence: ferrihydrite (200–600 m 2 /g) > goethite (30–90 m 2 /g) > hematite (10–90 m 2 /g). Their pH values of point of zero charge range from 7.5 to 9.5 6,8 , indicating the surface of these minerals are (under environmental conditions) mostly positively charged. Formation of iron oxides in soil: dissolution – precipitation In case of fast Fe 3+ dissolution or fast Fe 2+ oxidation, high amounts of Fe 3+ were offered to the formation of iron-(oxydr)oxides which will cause a fast precipitation of iron hydroxides at relatively high pH resulting in ferrihydrite formation 5 . Such fast hydrolysis of Fe(III) or rapid oxidation of aqueous Fe(II) oxides will form poorly crystalline Fe(II) ferrihydrite with a grain size of 2–10 nm 12 . Ferrihydrite can be found across a diversity of soil and aquatic environments on Earth 9 . For such poorly ordered material a precise analysis of its structure remains difficult. However, the most common ferrihydrite types can be distinguished by the number of peaks present in the XRD pattern into 2- and 6-line ferrihydrites. Despite the XRD-based differentiation, the X-ray pair distribution function analyses suggest that there are no significant structural differences between 2- and 6-line ferrihydrites. The differences in XRD seem instead to reflect variations in the average size of coherent scattering domains 13 . Please note, dissolved silicates, phosphates and organics may be entrapped within the ferrihydrite because of its fast precipitation. The entrapped silicates etc. will mostly prohibit the restructuring of naturally formed ferrihydrite into goethite or hematite 5 . If the Fe 3+ is dissolved slowly in low amounts, it becomes hydrolyzed, and in presence of hydroxyl anions a slow precipitation of iron hydroxides will start. Such slow processes will result in goethite (FeO(OH); Fig. 2 b) in soils in the temperate region in long-term. While at higher temperature hematite will be formed, since at higher temperature each pair of FeO(OH) will lose one water molecule resulting in a Fe 2 O 3 unit of hematite. By slow processes of dissolution and precipitation at colder conditions mostly goethite will be formed, while at higher temperatures preferably hematite will be formed. In soils both hematite and goethite, are stable minerals distributed ubiquitously in soils. Through dissolution–recrystallization under acid or alkaline conditions the iron hydroxides and ferrihydrite converts generally to goethite, and under neutral pH to hematite through internal rearrangement 1 , 6 , 14 . Hence, the distributions of iron (oxyhydr)-oxides can vary under different geological conditions. However, under laboratory conditions goethite can be transformed into hematite especially at higher temperature (e.g., Cornell and Schwertmann 6 and Ruan, et al. 15 . Iron (oxyhydr)-oxides As the structure and properties of iron (oxyhydr)-oxides control their abilities in interacting with environmental chemicals, determining the exact surface reactivity of each iron (oxyhydr)-oxides is needed for understanding their roles in affecting the character of soils 9 (Fig. 1 ). The adsorption processes of ions on iron (oxyhydr)-oxides determines the transport of the ions and the cycling of elements, which has been intensively studied 8 , 16 – 22 . The conditions during formation of the oxides affect the lattice structure and such the Fourier transform infrared spectroscopy (FTIR) spectra. Such it can be hypothesized that difference in the “crystal” structure (crystallinity) of the iron (oxyhydr)-oxides should be reflected in their FTIR spectra 11 , 23 . Table 1 Assignment of WN ranges of absorption bands from 3800 to 400 cm − 1 in Fourier transform infrared spectroscopy (FTIR) spectra of iron (oxyhydr)-oxides towards defined stretching and bending modes. With the bold letters indicating the WN range of each band in total, and the normal letters indicating the WN of the band maxima specific to the respective oxide species (e.g. goethite). WN region Abbrev. Vibration WN of band maxima for the oxides synthesized here, cm − 1 type group cm − 1 Goethite* Hematite Ferrihydrite 3400 to 3250 ν O-H Water molecules at minerals surface 3375s 3366 3357 3250 to 2900 ν O-H OH in minerals 3108 3151 2951 930 to 850 Goe-I δ Fe- O-H Fe-O goethite 892 - 835 to 772 Goe-II δ Fe- O-H 795 - 660 to 620 Goe-III 636 607 to 546 Hem-I 584 577 511 to 400 Hem-II ν Fe-O 478 463 463 There are several studies that either (i) characterize mixtures of iron (oxyhdr)-oxides, (ii) analyze changes in goethite caused by heating using FTIR or (iii) investigate the adsorption behaviors / mechanisms of typical cations and oxyanions (i.e., cadmium and phosphate) on the omnipresent iron oxide minerals: Prasad, et al. 24 followed the hematite formation during dehydration of natural goethite by heating, while Ruan, et al. 15 followed the transformation from goethite to hematite during heating processes by using defined absorption bands in FTIR spectra of goethite characteristic for OH deformation modes (WN at 888 to 884 cm - 1 ; 800 to 798 cm - 1 ). Furthermore, in archeology FTIR was used to study nature and composition natural earth pigments used as Byzantine ochre´s palette 25 or for rubrications / illustrations of ancient texts 26 and to identify the pigments in the manufacture of the ceramic artifacts 27 , among others. However, the above given studies did not reflect on differences in the FTIR spectra with respect to differences in the 3D structure or crystallinity of the iron (oxyhydr)-oxides. Our aim was to compare spectra of laboratory synthesized hematite with those of naturally occurring minerals (raw hematite), and to find characteristic absorption bands in FTIR that allows to distinguish between hematite, goethite, lepidocrocite and ferrihydrite. Additionally, we tested if we could determine the amount of the different iron minerals in mixture. Results & Discussion Hematite The samples collected during hematite samples from the 2nd, 3rd and 4th run of synthesis (2.V, 3.V and 4.V) did not show differences in FTIR spectra (Fig. 3a) suggesting that the samples are not different in their “crystalline” structure 28 . The FTIR spectra of the hematite samples show nearly identical FTIR pattern (Fig. 3b). All spectra of the hematite samples from the 2nd, 3rd and 4th run of synthesis (2.V, 3.V and 4.V) show two band maxima (at WN 567 and WN 478 cm − 1 ) which is in accordance with the data shown by Hu, et al. 23 . The broad band in FTIR of hematite with the maximum at WN 3426 cm – 1 is related to O–H stretching modes of water molecules within the crystal structure 29 . Its broadness is caused by hydrogen bridges between the water molecules. The band with the maximum at 3111 to 3236 cm − 1 is mostly caused by O–H stretching modes of OH groups within the iron (oxyhydr)-oxide. This band also becomes broad in case hydrogen bridges are formed. Comparison with the spectra of raw hematite 29 indicate sample from the 3rd run of synthesis (3.V) to be contaminated with silicate traces (yellow arrow in Fig. 3b). During the 3rd run of synthesis (3.V) samples we used glass ware. From the surfaces of the glass ware some silicate may be partly dissolved in small amounts during the heating procedure. Such silicate traces may co-precipitate together with the iron oxide and which will be reflected by bands at WN of about 1080 cm - 1 (yellow arrow, Fig. 3b) 30 , 31 . The WN of this band is in accordance with that of the silicate band detected in the FTIR spectrum of raw hematite (Fig. 3c, adopted from Khorshidi and Azadmehr 29 ). Goethite The FTIR spectra of the goethite samples (Fig. 4 a) from synthesis 28 are mostly identical among each other. Additionally, these spectra are similar to the ones published by others for goethite synthesized by the same procedure 24 , for goethite nano particles 32 , 33 (and goethite precipitated from pH regulated FeCl 2 propylenoxide mixtures by bubbling air through it 11 , despite the WN range 3800 to 2700 cm - 1 . Comparing the FTIR of the goethite samples synthesized here with goethite collected at an Indian site (natural 1 and 2) indicated the natural samples to contain significant amounts of silicate (Band at WN 1076/1082 cm - 1 ) 24 . The lower intensity of the OH bands (WN range 3800 to 2700 cm - 1 ) in the FTIR spectra of the goethite samples studied here compared to already published FTIR spectra 11 , 32 , 33 can be explained by the drying procedures since the bands at WN range 3800 to 2700 cm - 1 reflect to large extent the presence of water molecules at the surface and within the iron (oxyhydr)-oxides structures. The samples studied here were freeze-dried. Please note, the water content of freeze-dried samples is lower as compared to samples dried in an air ventilated oven at 60°C 32,33 or 80°C 11 . Such lower water content in the freeze-dried goethite samples studied here is reflected by relatively lower OH bands in the respective FTIR spectra compared to more intense OH bands in the FTIR of the goethite samples studied by Prasad, et al. 24 or Cui, et al. 11 . Ferrihydrite In the spectra of the line 6 ferrihydrite (Fig. 5 d) compared to the spectra of ferrihydrite published by Eusterhues, et al. 34 (Fig. 5 a) the sharp band at 1384 cm - 1 is missing. This band appears in the spectra of the ferrihydrite line 2 sample (Fig. 5 b) indicating line 2 and line 6 samples to be different in general. However, the band at 1384 cm - 1 may be caused by nitrate residues in the ferrihydrite line 2 sample which are missing in the ferrihydrite line 6 sample. For ferrihydrite line 2 synthesis an iron nitrate solution is used 6 . An incomplete washing of the precipitates may have caused nitrate residues in the ferrihydrite samples, such that the ferrihydrite samples may show a sharp intense band of the nitrate at 1384 cm - 1 (green arrow in Fig. 5 ). A similar sharp and intense band was found in FTIR of sodium nitrate (Fig. 5 c). Comparing hematite, goethite, lepidocrocite and ferrihydrite Comparing the FTIR spectra of the different iron (oxyhydr)oxides at WN range 1000 to 400 cm - 1 (Fig. 6 ) indicates for (i) hematite samples two intense bands with maxima at WN of about 600 and 480 cm - 1 (greenish), (ii) for goethite samples three intense bands at about 885, 702, 635 cm - 1 , and a small one at WN 400 cm - 1 , and (iii) for ferrihydrite samples three maxima located at WN 604, 563 and 442 cm - 1 (Fig. 6 b). For ferrihydrite these absorption bands are broader as compared to the ones in the FTIR of hematite and goethite samples and their maxima are more difficult to identify (Fig. 6 , bottom). In comparison to the FTIR of goethite the one of lepidocrocite shows a sharp band at WN 1021 cm -1 11 . Please note lepidocrocite is formed from octahedral units that are very similar to those of goethite (Fig. 2 b and 2 c, left hand side) but the 3D arrangement structures of these octahedral units are different (Figs. 2 b and 2 c, center) 9 , 10 . Such differences in the 3D arrangement may cause an increase in the energy needed to cause deformation modes into the Fe-O-H groups which will result in a shift of the Fe-O-H band maximum towards higher WN. Note, differences in the bands at WN range 1200 to 400 cm - 1 are mostly related to difference in the content of Fe-OH groups within the iron (oxyhydr)-oxides since all iron (oxyhydr)-oxides studied here are formed by octahedral units, with an iron cation in the center and either O or OH at the edges. An OH group is located at the edge of the FTIR will show δFe-O-H bands in FTIR. In general, the Fe-O-H group shows two bending modes that result in two δ Fe-O-H bands: one at WN range 876 to 892 cm - 1 , and the second at WN range 790 to 798 cm - 1 , as it was found for goethite (Fig. 6 ). These δ Fe-O-H bands are present in the FTIR of goethite and ferrihydrite but missing in the FTIR of hematite (Fig. 6 ) and magnetite 15 . This difference in FTIR spectra can be explained by the relatively lower OH and water content of hematite compared to goethite samples 15 . The FTIR spectra of hematite samples show relatively strong ν Fe-O-Fe band at WN 561 cm - 1 (Fig. 6 ) because the structure of hematite is dominated by a large number of Fe-O-Fe bonds (connecting the octahedral units; Fig. 2 a). Note, such ν Fe-O-Fe bands were also found in magnetite but at a different WN (WN 592 cm - 1 ; 15 ). However, magnetite was not studied here since it is formed from Fe 2+ instead of Fe 3+ 35 . In the FTIR spectra of goethite the ν Fe-O-Fe band is of much lower intensity compared to the one in the FTIR spectra of hematite, caused by the lower number of Fe-O-Fe bonds compared to hematite (see structures in Fig. 2 a to c). Additionally, in FTIR of goethite the ν Fe-O-Fe band is located at a different WN (621 to 674 cm - 1 ). This is because goethite shows a less condensed 3D structure of the octahedral units inter-connected by Fe-O-Fe bonds (Fig. 2 b) as compared to hematite (Fig. 2 a). Please note in FTIR spectra of raw hematite the ν Fe-O-Fe band is hard to identify because it is overlapped by Si-O-Si and OH bands 31 . Comparing the spectra of the different iron (oxyhydr)-oxides (Fig. 6 ) indicate differences in the WN range from 3700 to 2900 cm - 1 (blue oval in Fig. 6 ): The spectra of ferrihydrite shows the largest intensity of the OH bands, caused by the higher content of OH groups in the ferrihydrite (Fe 10 O 14 (OH) 2 nH₂O compared to Fe 2 O 3 for hematite) and the potentially higher water content within the minerals structure of ferrihydrite because of its higher surface area. Compared to the FTIR spectra of hematite, ferrihydrite and lepicrocite, the FTIR spectra of goethite shows a group of three distinct absorption bands (WN 889, 794 and 636 cm - 1 ; Figs. 4 a to 4 c, red circle). This is in accordance with findings of Xia et al. (2017) who used these absorption bands to determine the goethite concentration in different artificial goethite-ferrihydrite, or with findings of Prasad, et al. 24 and Ruan, et al. 15 who used these bands to study the formation of hematite when heating goethite samples. Hematite-Goethite mixtures The FTIR spectra of goethite hematite mixtures show bands at 892 and 795 characteristic for goethite (Goe-I and Goe-II; yellowish arrows Fig. 7 ) and at 569 cm - 1 characteristic for hematite (Hem-I; reddish arrow Fig. 7 ). When normalizing the FTIR spectra to the Goe-I band (All spectra show the same intensity of the Goe-I band) the intensity of the Hem-I band was found to increase with increasing Hem/Goe ratio (Fig. 7 , reddish arrow). The intensity of the Hem-I band was linearly related to the Goethite/Hematite ratio (for ratios from 95/5 to 30/70) (Fig. S1 ). Additionally, the ratio between the intensities of the Hem-I and the Goe-I band maxima (Hem-I/Goe-I) increases linearly with the Hem/Goe weight ratio (Fig. S2b) from 5/95 to 30/70 with an r 2 = 0.94 (Fig. S2b). While the ration between the intensities of the Goe-I to Hem-I band maxima increases linearly with increasing Goe/Hem ratio (r 2 = 0.99) (Fig. S2c) for the Goe/Hem weight ratios from 5/95 to 30/70. This finding suggests that the ratio between the intensities of the Hem-I and Goe-I band maxima can be used to estimate the Hem/Goe ratio. Conclusion The FTIR spectra of the different iron (oxyhydr)-oxides differ according to their OH and water content. For the minerals studied here the δ Fe-O-H bands at WN 900 and 794 cm − 1 characteristic for bending modes of the Fe-O-H group are only detectable in the FTIR spectra of goethite and ferrihydrite. While only in the FTIR spectra of the hematite samples a ν Fe-O-Fe band (WN 561 cm − 1 ) was found. These differences suggest that FTIR analysis in general allows to distinguish between the iron (oxyhydr)-oxides studied here. Hence, FTIR is a suitable method to distinguish between different iron minerals and may allow a quantification of goethite in mixtures. Please note the spectra of hematite and ferrihydrite cannot be distinguished that easily. However, when applying the FTIR approach to soil derived samples one has to consider that several absorption bands characteristic for the iron (oxyhydr)-oxides may become overlapped with bands that are caused by vibration modes within silicates and soil organic matter. Material and Methods Hematite (Fe 2 O 3 ) synthesis Hematite synthesis was done according to a procedure described by Schwertmann and Cornell 28 : Briefly 30.42 g of iron perchlorate (Fe(OCl 4 ) 3 hydrate were mixed with 500 mL of deionized water in a beaker until the solid was completely dissolved. The beaker was put in an oven at 97°C for seven days (evaporation needs to be prohibited). After 24h of storage at 97°C the precipitation started. After seven days the mixture was centrifuged at 3600 min - 1 for 20 minutes to separate the precipitate from the acidic supernatant. Afterwards, the precipitate was washed three times with distilled water to eliminate the acid as far as possible. Then the sample was frozen at -20°C and freeze-dried before FTIR analysis. Goethite FeOOH synthesis Goethite was obtained according to Atkinson, et al. 36 as follows: 135 g of FeCl 3 * 6 H 2 O were dissolved in in a beaker within 1000 mL of deionized and degassed water (pH of obtained solution < 1). The solution was cooled down to 0°C in an ice bath, then 150 ml of 10 M NaOH solution was added carefully until a pH value of 10 to 11. The pH was controlled automatically using a pH meter (Schott, Germany). The formation of a homogeneous dark brownish suspension (ferrihydrite) started, and temperature of the suspension increased. If temperature increases above 45°C, the dropwise addition of NaOH was slowed down until a pH of 12 is reached. The hot solution protected from evaporation was then stored for 24 h in an oven at 55°C to allow a crystallized of the precipitate into goethite. The color of suspension changed from reddish-brown to ochre. To allow for complete crystallisation the suspension was repeatedly mixed using a silicone spatula. The solid was separated by filtration and washed with distilled water until the pH of the filtrates shows a pH value of about 7. Ferrihydrite Fe 10 O 14 (OH) 2 synthesis 6-Line ferrihydrite was prepared using the method described by Schwertmann and Cornell 28 . Specifically, 20 g of Fe(NO₃)₃·9H₂O were dissolved in 2 L of nanopure water preheated to 75°C in an oven. The solution was returned to the oven for another 10 minutes, then rapidly cooled in ice water. It was subsequently transferred to a dialysis bag (Spectrum Labs, 6–8 kDa MWCO) and dialyzed with regular water changes for 7 days until a brown precipitate formed. The product was shock-frozen in liquid N₂ and freeze-dried. For comparison, 2-Line ferrihydrite was synthesized using a modified method of Schwertmann and Cornell 28 . Briefly, 40 g of Fe(NO₃)₃·9H₂O were dissolved in 500 mL of distilled water, followed by the addition of 330 mL of 1 M NaOH to adjust the pH to 7–8. The resulting suspension was centrifuged, the supernatant was decanted, and the obtained solide were freeze-dried. X-ray diffraction (XRD) analysis confirmed the successful formation of 2-Line and 6-Line ferrihydrite, respectively. Preparation of goethite-hematite-mixtures The freeze dried oxides were mixed in weight based ratios (Table 2 ) as follows: For preparing 500mg of a goethite to hematite mixture with a 5 to 95 weight % ratio 25 mg of goethite was mixed with 475 mg of hematite and carefully homogenized within an agate mortar. From this mixture 1mg was used for FTIR analysis. The same procedure was used to prepare the other goethite to hematite weight % ratios (Table 2 ). Table 2 The weights of hematite (Hem) and goethite (Goe) used to produce the goethite hematite mixtures studied here as well as the mMol of Fe offered by hematite in the mixtures and the intensities of the Hem-I, Goe-I and Goe-I band maxima in FTIR spectra of the mixtures. Mixture Goethite Hematite Hematite-Fe in the mixture Band intensities Goe/Hem mg mg mMol Hem-I Goe-I Goe-II 5/95 25 475 5.938 2.978 0.555 0.576 10/90 50 450 5.625 2.702 0.510 0.517 15/85 75 425 20/80 100 400 5.000 2.365 0.507 0.503 30/70 150 350 4.375 3.161 0.832 0.803 40/60 200 300 3.750 2.474 0.837 0.782 50/50 250 250 3.125 1.463 0.617 0.553 60/40 300 200 2.500 1.39 0.715 0.64 70/30 350 150 1.875 1.133 0.906 0.791 80/20 400 100 1.250 0.383 0.384 0.364 85/15 425 75 0.938 0.959 1.088 0.962 90/10 450 50 0.625 0.258899 0.792 0.623 95/5 475 25 0.313 0.316 0.799 0.672 FTIR analysis : KBr technique: 2 mg of finely ground samples (Table 2 ) were combined with 98 mg of KBr, finely ground in an agate mortar, dried for 12 h over silica gel in a desiccator to standardize the water content and were then pressed into pellets. Note for the goethite-hematite mixture we used 1mg of mixture diluted in 99 mg of KBr. The pellets were analyzed using a FTS135 (BioRad, Krefeld, Germany) 37 in transmission mode. All spectra were recorded in 2 replicates at a resolution of 2 cm – 1 and 16 scans (= 16 repetitions of a single spectra; Ellerbrock, et al. 37 ) to obtain the absorption spectra in a range of wavenumbers between 4000 and 400 cm – 1 . All spectra were corrected for ambient air 38 , and baseline-corrected (BioRad Winirez software). The baseline-corrected spectra (e.g., Ellerbrock, et al. 37 ) were analyzed for the WN and the intensity of absorption bands characteristic for stretching and bending modes in the iron (oxyhydr)-oxide octahedra (Figs. 1 a and 1 b). The characteristic absorption bands caused by (1) stretching vibrations of (1a) O-H groups at the particles surfaces able to interact with H 2 O appear at WN 3400 to 3250 cm − 1 (ν O-H H2O ; 39 ), (2) O-H groups within the matrix of the iron (oxyhydr)-oxides at WN 3250 to 2900 (ν O-H Ox ; 39 ), those of (3) the Fe - O-H bending at WN 930 to 850 and 835 to 772 cm − 1 (δ Fe-O-H;) as well as (4) the Fe-O-Fe stretching vibrations at WN 720 − 583 and 511 to 400 (ν Fe-O-Fe) within the iron (oxyhydr)-oxides (Table 2 ; 11,23 ). When interpreting the spectra, we focus on the δ Fe-OH, and the ν Fe-O-Fe bands within the iron (oxyhydr)-oxides which were assumed to mostly reflect potential differences in the structure of the studied iron (oxyhydr)-oxide species ( 11,23,39 ) compared to the hematite. Table 2 The iron (oxyhydr)-oxides studied here by FTIR spectroscopy, their origin and references for the FTIR spectra used for comparison. Fe- species Origin / reference Ref. for spectra Goethite Own synth. Cui, et al. 11 Hematite Own synth. Hu, et al. 23, Khorshidi and Azadmehr 29 Ferrihydrite Line 2 : Own synth. Line 6 Own synth. Xiao, et al. 40 Lepidocrocite Cui, et al. 11 Cui, et al. 11 The FTIR of the goethite-hematite mixture was interpreted for the intensity of the hematite (Hem)-I, goethite (Goe)-I and Goe-II bands. The maxima of the δ Fe-OH (Goe-I), and the ν Fe-O-Fe (Goe-II), and Hem-I bands were identified using an automated identification procedure of the BioRad WINIREZ Software (BioRad Corp, Krefeld, Germany) as follows: the left and right limits of the WN region characteristic for each band (Table 1 ) were used to construct so called ‘‘def’’-files (offered by WINIREZ) that were than applied within the automated BioRad WINIREZ procedure. Note, we focus the interpretation of the hematite content in the goethite-hematite mixtures on the Hem-I band located at WN region from 607 to 546 cm − 1 (Table 1 ) since the second band of hematite located at about 475 cm − 1 is overlapping with a ν Fe-O band of goethite (Table 1 ). The band of the hydroxyl groups at WN 3700 to 3250 cm – 1 (νO–H band) were only considered with respect to the water content of the studied iron (oxyhydr)-oxides. Declarations Competing interests The authors declare no competing interests. Funding Open Access funding enabled and organized by Projekt DEAL. Author Contribution J.S. had the idea. Measurements were done by R.E. and N.B.. The manuscript was written by R.E. and J.S.. All authors reviewed and edited the manuscript. All authors have given approval to the final version of the manuscript. Acknowledgement We thank Laurel Thomas Arrigo (Université de Neuchâtel) for synthesizing 6-line ferrihydrite and analyzing by XRD and Kerstin Hockmann (University Freiburg) for synthesizing 2-line ferrihydrite and analyzing by XRD. Data Availability The datasets used and/or analyzed during the current study is available from the corresponding author on reasonable request. References Barrón, V. & Torrent, J. Iron, manganese and aluminium oxides and oxyhydroxides. (2013). Navrotsky, A., Mazeina, L. & Majzlan, J. Size-driven structural and thermodynamic complexity in iron oxides. Science 319 , 1635–1638 (2008). Hiemstra, T. Ferrihydrite interaction with silicate and competing oxyanions: geometry and hydrogen bonding of surface species. Geochim. Cosmochim. Acta . 238 , 453–476 (2018). Sposito, G. The chemistry of soils (Oxford University Press, 2008). Blume, H. P. et al. Scheffer/Schachtschabel Lehrbuch der Bodenkunde 16 , 10.1007 (2010). Cornell, R. M. & Schwertmann, U. The iron oxides: structure, properties, reactions, occurrences and uses (Wiley, 2003). Michel, F. M. et al. The structure of ferrihydrite, a nanocrystalline material. Science 316 , 1726–1729 (2007). Wang, X. et al. Characteristics of phosphate adsorption-desorption onto ferrihydrite: comparison with well-crystalline Fe (hydr) oxides. Soil Sci. 178 , 1–11 (2013). Sassi, M., Chaka, A. M. & Rosso, K. M. Ab initio thermodynamics reveals the nanocomposite structure of ferrihydrite. Commun. Chem. 4 , 134 (2021). Yang, H., Lu, R., Downs, R. T., Costin, G. & Goethite α-FeO (OH), from single-crystal data. Struct. Rep. 62 , i250–i252 (2006). Cui, H., Ren, W., Lin, P. & Liu, Y. Structure control synthesis of iron oxide polymorph nanoparticles through an epoxide precipitation route. J. Exp. Nanosci. 8 , 869–875 (2013). Kappler, A. et al. An evolving view on biogeochemical cycling of iron. Nat. Rev. Microbiol. 19 , 360–374 (2021). Schwertmann, U., Friedl, J. & Kyek, A. Formation and properties of a continuous crystallinity series of synthetic ferrihydrites (2-to 6-line) and their relation to FeOOH forms. Clay Clay Min. 52 , 221–226 (2004). Jiang, Z. et al. A new model for transformation of ferrihydrite to hematite in soils and sediments. Geology 46 , 987–990 (2018). Ruan, H., Frost, R. & Kloprogge, J. T. The behavior of hydroxyl units of synthetic goethite and its dehydroxylated product hematite. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 57 , 2575–2586 (2001). Ona-Nguema, G., Morin, G., Juillot, F., Calas, G. & Brown, G. E. EXAFS analysis of arsenite adsorption onto two-line ferrihydrite, hematite, goethite, and lepidocrocite. Environ. Sci. Technol. 39 , 9147–9155 (2005). Santoro, V. et al. Inorganic and organic P retention by coprecipitation during ferrous iron oxidation. Geoderma 348 , 168–180 (2019). Swedlund, P. J., Miskelly, G. M. & McQuillan, A. J. An attenuated total reflectance IR study of silicic acid adsorbed onto a ferric oxyhydroxide surface. Geochim. Cosmochim. Acta . 73 , 4199–4214 (2009). Trivedi, P., Axe, L. & Tyson, T. A. An analysis of zinc sorption to amorphous versus crystalline iron oxides using XAS. J. Colloid Interface Sci. 244 , 230–238 (2001). Wang, K. & Xing, B. Mutual effects of cadmium and phosphate on their adsorption and desorption by goethite. Environ. Pollut . 127 , 13–20 (2004). Trivedi, P. & Axe, L. Ni and Zn sorption to amorphous versus crystalline iron oxides: macroscopic studies. J. Colloid Interface Sci. 244 , 221–229 (2001). Zhang, R., Liu, D. & Yang, P. Morphology control of α-Fe 2 O 3 towards super electrochemistry performance. RSC Adv. 9 , 21947–21955 (2019). Hu, L., Percheron, A., Chaumont, D. & Brachais, C. H. Microwave-assisted one-step hydrothermal synthesis of pure iron oxide nanoparticles: magnetite, maghemite and hematite. J. Solgel Sci. Technol. 60 , 198–205 (2011). Prasad, P. et al. In situ FTIR study on the dehydration of natural goethite. J. Asian Earth Sci. 27 , 503–511 (2006). Bikiaris, D. et al. Ochre-differentiation through micro-Raman and micro-FTIR spectroscopies: application on wall paintings at Meteora and Mount Athos, Greece. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 56 , 3–18 (2000). Čiuladienė, A., Luckutė, A., Kiuberis, J. & Kareiva, A. Investigation of the chemical composition of red pigments and binding media. Chemija 29 (2018). Cavalheri, A. S., Balan, A. M., Künzli, R. & Constantino, C. J. Vibrational spectroscopy applied to the study of archeological ceramic artifacts from Guarani culture in Brazil. Vib. Spectrosc. 54 , 164–168 (2010). Schwertmann, U. & Cornell, R. M. Iron oxides in the laboratory: preparation and characterization (Wiley, 2008). Khorshidi, N. & Azadmehr, A. R. Competitive adsorption of Cd (II) and Pb (II) ions from aqueous solution onto Iranian hematite (Sangan mine): optimum condition and adsorption isotherm study. Desalination Water Treat. 58 , 106–119 (2017). Ellerbrock, R., Stein, M. & Schaller, J. Comparing amorphous silica, short-range-ordered silicates and silicic acid species by FTIR. Sci. Rep. 12 , 11708 (2022). Ellerbrock, R. H., Stein, M. & Schaller, J. Comparing silicon mineral species of different crystallinity using Fourier transform infrared spectroscopy. Front. Environ. Chem. 5 , 1462678 (2024). Villacís-García, M. et al. Laboratory synthesis of goethite and ferrihydrite of controlled particle sizes. Boletín de la. Sociedad Geológica Mexicana . 67 , 433–446 (2015). Salimi, F., Rahimi, H. & Karami, C. Removal of methylene blue from water solution by modified nanogoethite by Cu. Desalination Water Treat. 137 , 334–344 (2019). Eusterhues, K. et al. Reduction of ferrihydrite with adsorbed and coprecipitated organic matter: microbial reduction by Geobacter bremensis vs. abiotic reduction by Na-dithionite. Biogeosciences 11 , 4953–4966 (2014). Amelingmeier, E. & Römpp, H. Römpp kompakt Basislexikon Chemie: M-Re. Bd. 3 Vol. 3 (Thieme, 1999). Atkinson, R., Posner, A. & Quirk, J. P. Adsorption of potential-determining ions at the ferric oxide-aqueous electrolyte interface. J. Phys. Chem. 71 , 550–558 (1967). Ellerbrock, R., Höhn, A. & Rogasik, J. Functional analysis of soil organic matter as affected by long-term manurial treatment. Eur. J. Soil. Sci. 50 , 65–71 (1999). Haberhauer, G. & Gerzabek, M. Drift and transmission FT-IR spectroscopy of forest soils: an approach to determine decomposition processes of forest litter. Vib. Spectrosc. 19 , 413–417 (1999). Farmer, V. C. The infrared spectra of minerals. Mineralogical Soc. Monogr. 4 , 331–363 (1974). Xiao, W., Jones, A. M., Collins, R. N., Bligh, M. W. & Waite, T. D. Use of fourier transform infrared spectroscopy to examine the Fe (II)-Catalyzed transformation of ferrihydrite. Talanta 175 , 30–37 (2017). Additional Declarations No competing interests reported. Supplementary Files SupportinginformationtoFeoxides.docx Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 27 Feb, 2026 Reviews received at journal 26 Feb, 2026 Reviews received at journal 18 Feb, 2026 Reviewers agreed at journal 11 Feb, 2026 Reviewers agreed at journal 11 Feb, 2026 Reviewers agreed at journal 05 Feb, 2026 Reviewers invited by journal 04 Feb, 2026 Editor invited by journal 04 Feb, 2026 Editor assigned by journal 31 Jan, 2026 Submission checks completed at journal 31 Jan, 2026 First submitted to journal 30 Jan, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8741763","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":586198678,"identity":"4dd4eb90-7b5a-43ef-97f8-510b3b2f11b1","order_by":0,"name":"Ruth H. Ellerbrock","email":"","orcid":"","institution":"Leibniz Centre for Agricultural Landscape Research (ZALF)","correspondingAuthor":false,"prefix":"","firstName":"Ruth","middleName":"H.","lastName":"Ellerbrock","suffix":""},{"id":586198679,"identity":"bf82591a-f8b0-4aaa-81b3-fd715825a786","order_by":1,"name":"Nisha Bhattarai","email":"","orcid":"","institution":"Leibniz Centre for Agricultural Landscape Research (ZALF)","correspondingAuthor":false,"prefix":"","firstName":"Nisha","middleName":"","lastName":"Bhattarai","suffix":""},{"id":586198680,"identity":"d650b987-b354-485b-acea-eca88b752bb4","order_by":2,"name":"Jörg Schaller","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABCElEQVRIie3QMWvCQBTA8Xc8aJZT6RZoab7CBYcupX4VJdBJ6OpQwpWALvkAgfohugoO7zhIl9Ksgkuk0Mmh0g4ZSumpuAg5HYXefzl4vB8PDsDlOsE8uXliEICPBHBjRqwEbiFsS7QhTBpyB4AojiG0I/oIMkry1TdQcO0pSatp0WklCLAcWEiaR0+XEIeTtCdV9jFHXyOw8auFZP02+oBdQT2pOc3PQLcIG0Mbuf/akmIh9Q+98cBcwcZvPTnP+sg+12RmrgCRLzZE1pMLnrcRhA6fZwupUopEaIga5/Wk6SXvrBrEgSgiVVZ027l6SVi5fKgn65CLvQnZgfmC6tCGy+Vy/e/+AO3ZVLpWXkWxAAAAAElFTkSuQmCC","orcid":"","institution":"Leibniz Centre for Agricultural Landscape Research (ZALF)","correspondingAuthor":true,"prefix":"","firstName":"Jörg","middleName":"","lastName":"Schaller","suffix":""}],"badges":[],"createdAt":"2026-01-30 13:39:51","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8741763/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8741763/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102309557,"identity":"7a6f717a-d2f1-43d6-992f-3f65e62d6d7c","added_by":"auto","created_at":"2026-02-10 11:51:03","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":115663,"visible":true,"origin":"","legend":"\u003cp\u003eOctahedral structure of a) iron oxides and b) iron oxyhydroxides, adopted from Blume, et al. \u003csup\u003e5\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8741763/v1/f41c50406bcb3300e1dd0c48.png"},{"id":102309850,"identity":"d221b281-2bb6-4517-a605-8e3f8be01e9c","added_by":"auto","created_at":"2026-02-10 11:51:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":328342,"visible":true,"origin":"","legend":"\u003cp\u003eSchemes of typical connections between octahedral units of iron(oxyhydr)-oxides \u003csup\u003e5\u003c/sup\u003e and their 3D-arangement within a) hematite, b) goethite, c) lepidocrocite, and d) ferrihydrite. The 3D structures are adopted from Sassi, et al. \u003csup\u003e9\u003c/sup\u003e and Yang, et al. \u003csup\u003e10\u003c/sup\u003e. The FTIR of lepidocrocite (black line) is adopted from Cui, et al. \u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8741763/v1/ee7c9980e0a2e2ebee99a404.png"},{"id":102309404,"identity":"918baaa2-b6a8-4513-ac4b-582ee44a9710","added_by":"auto","created_at":"2026-02-10 11:50:40","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":141074,"visible":true,"origin":"","legend":"\u003cp\u003eb) FTIR spectra of raw hematite adopted from\u0026nbsp; Khorshidi and Azadmehr \u003csup\u003e29\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eFTIR spectra (WN range 4000 to 400) of hematite samples\u003c/p\u003e\n\u003cp\u003ea)\u0026nbsp; from three replicate (2.V, 3.V and 4.V) synthesis routines, with the insert: FTIR spectra of hematite (WN range 2000 to 400 cm\u003csup\u003e-1\u003c/sup\u003e) adopted from Hu, et al. \u003csup\u003e23\u003c/sup\u003e shown in original in transmittance at WN range 2000 to 400 cm\u003csup\u003e-1 \u003c/sup\u003e(perpendicular red lines; the yellow arrow indicating absorption bands of silicate traces especially in the hematite 3.V sample), and b) FTIR spectra of raw hematite adopted from\u0026nbsp; Khorshidi and Azadmehr \u003csup\u003e29\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8741763/v1/b91a0754837bd5578d9183dd.png"},{"id":102309378,"identity":"ac84a1bb-ea47-48be-bab1-f4b89d601336","added_by":"auto","created_at":"2026-02-10 11:50:38","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":140566,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of goethite samples adopted from a) Prasad et al. (2006), b) Cui et al. (2013), and c) synthesized in this study (n=3).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8741763/v1/7bbca7eee5c6030cffc3968d.png"},{"id":102308417,"identity":"e65bbed0-8c02-4a9f-a35c-3ea95ee8e7da","added_by":"auto","created_at":"2026-02-10 11:48:49","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":151851,"visible":true,"origin":"","legend":"\u003cp\u003ea) FTIR spectra of ferrihydrite (WN 1800 to 400 cm-1) adopted from Eusterhues, et al. \u003csup\u003e34\u003c/sup\u003e as well as FTIR spectra (WN 4000 to 400 cm-1) of b) ferrihydrite line 2, c) sodium nitrate and d) ferrihydrite line 2 samples (n=4).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8741763/v1/c60157e02211e1170ae3b805.png"},{"id":102309545,"identity":"4ee4097c-6b45-46d5-8117-9708664f6242","added_by":"auto","created_at":"2026-02-10 11:50:55","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":186590,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of hematite, goethite, lepidocrocite (adopted from Cui, et al. \u003csup\u003e11\u003c/sup\u003e, and ferrihydrite. The differently colored blocks indicate the WN regions of the νO-H (bluish), the δ Fe-O-H (reddish), and ν Fe-O-Fe bands (greenish) characteristic for the respective iron(hydro) oxides (Goe-I, Goe-II, Hem-I).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8741763/v1/fa4ff543e1e8a321963a50d1.png"},{"id":102309292,"identity":"f12f965f-8b20-4a25-b91f-6c89d7ce66ff","added_by":"auto","created_at":"2026-02-10 11:50:24","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":242086,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra at the WN range from 1400 to 400 cm\u003csup\u003e-1\u003c/sup\u003e of hematite-goethite mixtures with increasing Goethite/Hematite (Goe/Hem) ratio normalized to show the same intensity at the Goe-I band maximum (yellowish Goe-I arrow). With the yellow arrows indicating band characteristic for goethite and the reddish ones indicating bands characteristic for hematite.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8741763/v1/87fa60fe50ee41f5f4b036f3.png"},{"id":102311212,"identity":"589ff834-e17a-4ef7-9067-2326299e532d","added_by":"auto","created_at":"2026-02-10 11:57:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2168222,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8741763/v1/fdf4e409-4c67-4ae6-a8bb-57e8295240e2.pdf"},{"id":102310276,"identity":"fa8b670b-8551-483e-841b-d8ad7c76d2a1","added_by":"auto","created_at":"2026-02-10 11:53:04","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":101896,"visible":true,"origin":"","legend":"","description":"","filename":"SupportinginformationtoFeoxides.docx","url":"https://assets-eu.researchsquare.com/files/rs-8741763/v1/7e8b0e1c1db7d7ec38436e94.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Comparing and quantifying goethite, hematite, lepidocrocite, and ferrihydrite by FTIR","fulltext":[{"header":"Introduction","content":"\u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003eImportance of crystallinity for iron (oxyhydr)-oxides\u003c/h2\u003e \u003cp\u003eIron-(oxyhydr)-oxides show relatively high specific surface areas. Since they also offer a significant amount of hydroxyl sites \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e they considerably contribute to the soil sorption properties \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. In soils the iron(III) (oxyhydr)-oxides are frequently present as ocre colored goethite (α-FeOOH) and red-colored hematite (α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e). Additionally, orange colored lepidocrocite (γ-FeOOH), redish-brown colored maghemite (γ-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), and the low crystalized water holding ferrihydrite (5Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e*H\u003csub\u003e2\u003c/sub\u003eO). These iron(III) (oxyhydr)-oxides are formed from octahedral units which have an iron in the center and at the corners either of 6 O atoms (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) or 3 O atom plus 3 OH groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn hematite the octahedral units are connected via the octahedral surfaces such the units are connected via three O atoms (turquoise circles; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea left): these arrangement results in a hexagonal dense packing of oxygens (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea right) with the cations distributed in the interstice-spaces of the octahedra \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. In goethite and lepidocrocite the octahedral units are connected via octahedral edges (connection via two O atoms; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec left). In goethite the octahedra form double chains are interconnected via H-bridges between octahedral corners \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb right). In lepidocrocite the double chains are formed via octahedral edges in zick-zack pattern. The structure of ferrihydrite is similar to the Baker-Figgis δ-Keggin clusters and the ferrihydrite particles are within the diameters of 2\u0026ndash;10 nm \u003csup\u003e1,7\u003c/sup\u003e resulting in a 3D arrangement that is isostructural to akdalaite) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed; \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.mindat.org/min-69.html\u003c/span\u003e\u003cspan address=\"https://www.mindat.org/min-69.html\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). The structures and morphologies of the minerals control the surface properties of iron (oxyhydr)-oxides. The specific surface area values decrease in the sequence: ferrihydrite (200\u0026ndash;600 m\u003csup\u003e2\u003c/sup\u003e /g) \u0026gt; goethite (30\u0026ndash;90 m\u003csup\u003e2\u003c/sup\u003e/g) \u0026gt; hematite (10\u0026ndash;90 m\u003csup\u003e2\u003c/sup\u003e/g). Their pH values of point of zero charge range from 7.5 to 9.5 \u003csup\u003e6,8\u003c/sup\u003e, indicating the surface of these minerals are (under environmental conditions) mostly positively charged.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eFormation of iron oxides in soil: dissolution \u0026ndash; precipitation\u003c/h2\u003e \u003cp\u003eIn case of fast Fe\u003csup\u003e3+\u003c/sup\u003e dissolution or fast Fe\u003csup\u003e2+\u003c/sup\u003e oxidation, high amounts of Fe\u003csup\u003e3+\u003c/sup\u003e were offered to the formation of iron-(oxydr)oxides which will cause a fast precipitation of iron hydroxides at relatively high pH resulting in ferrihydrite formation \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Such fast hydrolysis of Fe(III) or rapid oxidation of aqueous Fe(II) oxides will form poorly crystalline Fe(II) ferrihydrite with a grain size of 2\u0026ndash;10 nm \u003csup\u003e12\u003c/sup\u003e. Ferrihydrite can be found across a diversity of soil and aquatic environments on Earth \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. For such poorly ordered material a precise analysis of its structure remains difficult. However, the most common ferrihydrite types can be distinguished by the number of peaks present in the XRD pattern into 2- and 6-line ferrihydrites. Despite the XRD-based differentiation, the X-ray pair distribution function analyses suggest that there are no significant structural differences between 2- and 6-line ferrihydrites. The differences in XRD seem instead to reflect variations in the average size of coherent scattering domains \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Please note, dissolved silicates, phosphates and organics may be entrapped within the ferrihydrite because of its fast precipitation. The entrapped silicates etc. will mostly prohibit the restructuring of naturally formed ferrihydrite into goethite or hematite \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIf the Fe\u003csup\u003e3+\u003c/sup\u003e is dissolved slowly in low amounts, it becomes hydrolyzed, and in presence of hydroxyl anions a slow precipitation of iron hydroxides will start. Such slow processes will result in goethite (FeO(OH); Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) in soils in the temperate region in long-term. While at higher temperature hematite will be formed, since at higher temperature each pair of FeO(OH) will lose one water molecule resulting in a Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e unit of hematite. By slow processes of dissolution and precipitation at colder conditions mostly goethite will be formed, while at higher temperatures preferably hematite will be formed. In soils both hematite and goethite, are stable minerals distributed ubiquitously in soils. Through dissolution\u0026ndash;recrystallization under acid or alkaline conditions the iron hydroxides and ferrihydrite converts generally to goethite, and under neutral pH to hematite through internal rearrangement \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Hence, the distributions of iron (oxyhydr)-oxides can vary under different geological conditions. However, under laboratory conditions goethite can be transformed into hematite especially at higher temperature (e.g., Cornell and Schwertmann \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e and Ruan, et al. \u003csup\u003e15\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eIron (oxyhydr)-oxides\u003c/h3\u003e\n\u003cp\u003eAs the structure and properties of iron (oxyhydr)-oxides control their abilities in interacting with environmental chemicals, determining the exact surface reactivity of each iron (oxyhydr)-oxides is needed for understanding their roles in affecting the character of soils \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The adsorption processes of ions on iron (oxyhydr)-oxides determines the transport of the ions and the cycling of elements, which has been intensively studied \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan additionalcitationids=\"CR17 CR18 CR19 CR20 CR21\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe conditions during formation of the oxides affect the lattice structure and such the Fourier transform infrared spectroscopy (FTIR) spectra. Such it can be hypothesized that difference in the \u0026ldquo;crystal\u0026rdquo; structure (crystallinity) of the iron (oxyhydr)-oxides should be reflected in their FTIR spectra \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAssignment of WN ranges of absorption bands from 3800 to 400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in Fourier transform infrared spectroscopy (FTIR) spectra of iron (oxyhydr)-oxides towards defined stretching and bending modes. With the bold letters indicating the WN range of each band in total, and the normal letters indicating the WN of the band maxima specific to the respective oxide species (e.g. goethite).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWN region\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbbrev.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eVibration\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eWN of band maxima for the oxides synthesized here,\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ecm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003etype\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003egroup\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003ecm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eGoethite*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHematite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eFerrihydrite\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3400 to 3250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eν O-H\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eWater molecules at minerals surface\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003e3375s\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e3366\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e3357\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e3250 to 2900\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eν O-H\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOH in minerals\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e3108\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003e3151\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cem\u003e2951\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e930 to 850\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eGoe-I\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eδ Fe-\u003cb\u003eO-H\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFe-O goethite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e892\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e835 to 772\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eGoe-II\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eδ Fe-\u003cb\u003eO-H\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e795\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e660 to 620\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eGoe-III\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e636\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e607 to 546\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eHem-I\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e584\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cem\u003e577\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e511 to 400\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHem-II\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eν Fe-O\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e478\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e463\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e463\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThere are several studies that either (i) characterize mixtures of iron (oxyhdr)-oxides, (ii) analyze changes in goethite caused by heating using FTIR or (iii) investigate the adsorption behaviors / mechanisms of typical cations and oxyanions (i.e., cadmium and phosphate) on the omnipresent iron oxide minerals: Prasad, et al. \u003csup\u003e24\u003c/sup\u003e followed the hematite formation during dehydration of natural goethite by heating, while Ruan, et al. \u003csup\u003e15\u003c/sup\u003e followed the transformation from goethite to hematite during heating processes by using defined absorption bands in FTIR spectra of goethite characteristic for OH deformation modes (WN at 888 to 884 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e; 800 to 798 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e). Furthermore, in archeology FTIR was used to study nature and composition natural earth pigments used as Byzantine ochre\u0026acute;s palette \u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e or for rubrications / illustrations of ancient texts \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e and to identify the pigments in the manufacture of the ceramic artifacts \u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e, among others. However, the above given studies did not reflect on differences in the FTIR spectra with respect to differences in the 3D structure or crystallinity of the iron (oxyhydr)-oxides. Our aim was to compare spectra of laboratory synthesized hematite with those of naturally occurring minerals (raw hematite), and to find characteristic absorption bands in FTIR that allows to distinguish between hematite, goethite, lepidocrocite and ferrihydrite. Additionally, we tested if we could determine the amount of the different iron minerals in mixture.\u003c/p\u003e"},{"header":"Results \u0026 Discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eHematite\u003c/h2\u003e \u003cp\u003eThe samples collected during hematite samples from the 2nd, 3rd and 4th run of synthesis (2.V, 3.V and 4.V) did not show differences in FTIR spectra (Fig.\u0026nbsp;3a) suggesting that the samples are not different in their \u0026ldquo;crystalline\u0026rdquo; structure \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe FTIR spectra of the hematite samples show nearly identical FTIR pattern (Fig.\u0026nbsp;3b). All spectra of the hematite samples from the 2nd, 3rd and 4th run of synthesis (2.V, 3.V and 4.V) show two band maxima (at WN 567 and WN 478 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) which is in accordance with the data shown by Hu, et al. \u003csup\u003e23\u003c/sup\u003e. The broad band in FTIR of hematite with the maximum at WN 3426 cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e is related to O\u0026ndash;H stretching modes of water molecules within the crystal structure \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. Its broadness is caused by hydrogen bridges between the water molecules. The band with the maximum at 3111 to 3236 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is mostly caused by O\u0026ndash;H stretching modes of OH groups within the iron (oxyhydr)-oxide. This band also becomes broad in case hydrogen bridges are formed.\u003c/p\u003e \u003cp\u003eComparison with the spectra of raw hematite \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e indicate sample from the 3rd run of synthesis (3.V) to be contaminated with silicate traces (yellow arrow in Fig.\u0026nbsp;3b). During the 3rd run of synthesis (3.V) samples we used glass ware. From the surfaces of the glass ware some silicate may be partly dissolved in small amounts during the heating procedure. Such silicate traces may co-precipitate together with the iron oxide and which will be reflected by bands at WN of about 1080 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (yellow arrow, Fig.\u0026nbsp;3b) \u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. The WN of this band is in accordance with that of the silicate band detected in the FTIR spectrum of raw hematite (Fig.\u0026nbsp;3c, adopted from Khorshidi and Azadmehr \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eGoethite\u003c/h3\u003e\n\u003cp\u003eThe FTIR spectra of the goethite samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003ea) from synthesis \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e are mostly identical among each other. Additionally, these spectra are similar to the ones published by others for goethite synthesized by the same procedure \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e, for goethite nano particles \u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e(and goethite precipitated from pH regulated FeCl\u003csub\u003e2\u003c/sub\u003e propylenoxide mixtures by bubbling air through it \u003csup\u003e11\u003c/sup\u003e, despite the WN range 3800 to 2700 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Comparing the FTIR of the goethite samples synthesized here with goethite collected at an Indian site (natural 1 and 2) indicated the natural samples to contain significant amounts of silicate (Band at WN 1076/1082 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e) \u003csup\u003e24\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe lower intensity of the OH bands (WN range 3800 to 2700 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e) in the FTIR spectra of the goethite samples studied here compared to already published FTIR spectra \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e can be explained by the drying procedures since the bands at WN range 3800 to 2700 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e reflect to large extent the presence of water molecules at the surface and within the iron (oxyhydr)-oxides structures. The samples studied here were freeze-dried. Please note, the water content of freeze-dried samples is lower as compared to samples dried in an air ventilated oven at 60\u0026deg;C \u003csup\u003e32,33\u003c/sup\u003e or 80\u0026deg;C \u003csup\u003e11\u003c/sup\u003e. Such lower water content in the freeze-dried goethite samples studied here is reflected by relatively lower OH bands in the respective FTIR spectra compared to more intense OH bands in the FTIR of the goethite samples studied by Prasad, et al. \u003csup\u003e24\u003c/sup\u003e or Cui, et al. \u003csup\u003e11\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eFerrihydrite\u003c/h2\u003e \u003cp\u003eIn the spectra of the line 6 ferrihydrite (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003ed) compared to the spectra of ferrihydrite published by Eusterhues, et al. \u003csup\u003e34\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003ea) the sharp band at 1384 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e is missing. This band appears in the spectra of the ferrihydrite line 2 sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003eb) indicating line 2 and line 6 samples to be different in general. However, the band at 1384 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e may be caused by nitrate residues in the ferrihydrite line 2 sample which are missing in the ferrihydrite line 6 sample. For ferrihydrite line 2 synthesis an iron nitrate solution is used \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. An incomplete washing of the precipitates may have caused nitrate residues in the ferrihydrite samples, such that the ferrihydrite samples may show a sharp intense band of the nitrate at 1384 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (green arrow in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e). A similar sharp and intense band was found in FTIR of sodium nitrate (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003ec).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eComparing hematite, goethite, lepidocrocite and ferrihydrite\u003c/h3\u003e\n\u003cp\u003eComparing the FTIR spectra of the different iron (oxyhydr)oxides at WN range 1000 to 400 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e) indicates for (i) hematite samples two intense bands with maxima at WN of about 600 and 480 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (greenish), (ii) for goethite samples three intense bands at about 885, 702, 635 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, and a small one at WN 400 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, and (iii) for ferrihydrite samples three maxima located at WN 604, 563 and 442 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). For ferrihydrite these absorption bands are broader as compared to the ones in the FTIR of hematite and goethite samples and their maxima are more difficult to identify (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e, bottom). In comparison to the FTIR of goethite the one of lepidocrocite shows a sharp band at WN 1021 cm\u003csup\u003e-1 11\u003c/sup\u003e. Please note lepidocrocite is formed from octahedral units that are very similar to those of goethite (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, left hand side) but the 3D arrangement structures of these octahedral units are different (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, center) \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. Such differences in the 3D arrangement may cause an increase in the energy needed to cause deformation modes into the Fe-O-H groups which will result in a shift of the Fe-O-H band maximum towards higher WN.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eNote, differences in the bands at WN range 1200 to 400 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e are mostly related to difference in the content of Fe-OH groups within the iron (oxyhydr)-oxides since all iron (oxyhydr)-oxides studied here are formed by octahedral units, with an iron cation in the center and either O or OH at the edges. An OH group is located at the edge of the FTIR will show δFe-O-H bands in FTIR. In general, the Fe-O-H group shows two bending modes that result in two δ Fe-O-H bands: one at WN range 876 to 892 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, and the second at WN range 790 to 798 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, as it was found for goethite (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e). These δ Fe-O-H bands are present in the FTIR of goethite and ferrihydrite but missing in the FTIR of hematite (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e) and magnetite \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. This difference in FTIR spectra can be explained by the relatively lower OH and water content of hematite compared to goethite samples \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. The FTIR spectra of hematite samples show relatively strong ν Fe-O-Fe band at WN 561 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e) because the structure of hematite is dominated by a large number of Fe-O-Fe bonds (connecting the octahedral units; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Note, such ν Fe-O-Fe bands were also found in magnetite but at a different WN (WN 592 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e; \u003csup\u003e15\u003c/sup\u003e). However, magnetite was not studied here since it is formed from Fe\u003csup\u003e2+\u003c/sup\u003e instead of Fe\u003csup\u003e3+ 35\u003c/sup\u003e. In the FTIR spectra of goethite the ν Fe-O-Fe band is of much lower intensity compared to the one in the FTIR spectra of hematite, caused by the lower number of Fe-O-Fe bonds compared to hematite (see structures in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea to c). Additionally, in FTIR of goethite the ν Fe-O-Fe band is located at a different WN (621 to 674 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e). This is because goethite shows a less condensed 3D structure of the octahedral units inter-connected by Fe-O-Fe bonds (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) as compared to hematite (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Please note in FTIR spectra of raw hematite the ν Fe-O-Fe band is hard to identify because it is overlapped by Si-O-Si and OH bands \u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eComparing the spectra of the different iron (oxyhydr)-oxides (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e) indicate differences in the WN range from 3700 to 2900 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (blue oval in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e): The spectra of ferrihydrite shows the largest intensity of the OH bands, caused by the higher content of OH groups in the ferrihydrite (Fe\u003csub\u003e10\u003c/sub\u003eO\u003csub\u003e14\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e nH₂O compared to Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e for hematite) and the potentially higher water content within the minerals structure of ferrihydrite because of its higher surface area. Compared to the FTIR spectra of hematite, ferrihydrite and lepicrocite, the FTIR spectra of goethite shows a group of three distinct absorption bands (WN 889, 794 and 636 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e; Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003ea to \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, red circle). This is in accordance with findings of Xia et al. (2017) who used these absorption bands to determine the goethite concentration in different artificial goethite-ferrihydrite, or with findings of Prasad, et al. \u003csup\u003e24\u003c/sup\u003e and Ruan, et al. \u003csup\u003e15\u003c/sup\u003e who used these bands to study the formation of hematite when heating goethite samples.\u003c/p\u003e\n\u003ch3\u003eHematite-Goethite mixtures\u003c/h3\u003e\n\u003cp\u003eThe FTIR spectra of goethite hematite mixtures show bands at 892 and 795 characteristic for goethite (Goe-I and Goe-II; yellowish arrows Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e) and at 569 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e characteristic for hematite (Hem-I; reddish arrow Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e). When normalizing the FTIR spectra to the Goe-I band (All spectra show the same intensity of the Goe-I band) the intensity of the Hem-I band was found to increase with increasing Hem/Goe ratio (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e, reddish arrow). The intensity of the Hem-I band was linearly related to the Goethite/Hematite ratio (for ratios from 95/5 to 30/70) (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAdditionally, the ratio between the intensities of the Hem-I and the Goe-I band maxima (Hem-I/Goe-I) increases linearly with the Hem/Goe weight ratio (Fig. S2b) from 5/95 to 30/70 with an r\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.94 (Fig. S2b). While the ration between the intensities of the Goe-I to Hem-I band maxima increases linearly with increasing Goe/Hem ratio (r\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.99) (Fig. S2c) for the Goe/Hem weight ratios from 5/95 to 30/70. This finding suggests that the ratio between the intensities of the Hem-I and Goe-I band maxima can be used to estimate the Hem/Goe ratio.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe FTIR spectra of the different iron (oxyhydr)-oxides differ according to their OH and water content. For the minerals studied here the δ Fe-O-H bands at WN 900 and 794 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e characteristic for bending modes of the Fe-O-H group are only detectable in the FTIR spectra of goethite and ferrihydrite. While only in the FTIR spectra of the hematite samples a ν Fe-O-Fe band (WN 561 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was found. These differences suggest that FTIR analysis in general allows to distinguish between the iron (oxyhydr)-oxides studied here. Hence, FTIR is a suitable method to distinguish between different iron minerals and may allow a quantification of goethite in mixtures. Please note the spectra of hematite and ferrihydrite cannot be distinguished that easily. However, when applying the FTIR approach to soil derived samples one has to consider that several absorption bands characteristic for the iron (oxyhydr)-oxides may become overlapped with bands that are caused by vibration modes within silicates and soil organic matter.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eHematite (Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) synthesis\u003c/h2\u003e \u003cp\u003eHematite synthesis was done according to a procedure described by Schwertmann and Cornell \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e: Briefly 30.42 g of iron perchlorate (Fe(OCl\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e hydrate were mixed with 500 mL of deionized water in a beaker until the solid was completely dissolved. The beaker was put in an oven at 97\u0026deg;C for seven days (evaporation needs to be prohibited). After 24h of storage at 97\u0026deg;C the precipitation started. After seven days the mixture was centrifuged at 3600 min\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e for 20 minutes to separate the precipitate from the acidic supernatant. Afterwards, the precipitate was washed three times with distilled water to eliminate the acid as far as possible. Then the sample was frozen at -20\u0026deg;C and freeze-dried before FTIR analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eGoethite FeOOH synthesis\u003c/h2\u003e \u003cp\u003eGoethite was obtained according to Atkinson, et al. \u003csup\u003e36\u003c/sup\u003e as follows: 135 g of FeCl\u003csub\u003e3\u003c/sub\u003e * 6 H\u003csub\u003e2\u003c/sub\u003eO were dissolved in in a beaker within 1000 mL of deionized and degassed water (pH of obtained solution\u0026thinsp;\u0026lt;\u0026thinsp;1). The solution was cooled down to 0\u0026deg;C in an ice bath, then 150 ml of 10 M NaOH solution was added carefully until a pH value of 10 to 11. The pH was controlled automatically using a pH meter (Schott, Germany). The formation of a homogeneous dark brownish suspension (ferrihydrite) started, and temperature of the suspension increased. If temperature increases above 45\u0026deg;C, the dropwise addition of NaOH was slowed down until a pH of 12 is reached. The hot solution protected from evaporation was then stored for 24 h in an oven at 55\u0026deg;C to allow a crystallized of the precipitate into goethite. The color of suspension changed from reddish-brown to ochre. To allow for complete crystallisation the suspension was repeatedly mixed using a silicone spatula. The solid was separated by filtration and washed with distilled water until the pH of the filtrates shows a pH value of about 7.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eFerrihydrite Fe\u003csub\u003e10\u003c/sub\u003eO\u003csub\u003e14\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e synthesis\u003c/h2\u003e \u003cp\u003e6-Line ferrihydrite was prepared using the method described by Schwertmann and Cornell \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Specifically, 20 g of Fe(NO₃)₃\u0026middot;9H₂O were dissolved in 2 L of nanopure water preheated to 75\u0026deg;C in an oven. The solution was returned to the oven for another 10 minutes, then rapidly cooled in ice water. It was subsequently transferred to a dialysis bag (Spectrum Labs, 6\u0026ndash;8 kDa MWCO) and dialyzed with regular water changes for 7 days until a brown precipitate formed. The product was shock-frozen in liquid N₂ and freeze-dried.\u003c/p\u003e \u003cp\u003eFor comparison, 2-Line ferrihydrite was synthesized using a modified method of Schwertmann and Cornell \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Briefly, 40 g of Fe(NO₃)₃\u0026middot;9H₂O were dissolved in 500 mL of distilled water, followed by the addition of 330 mL of 1 M NaOH to adjust the pH to 7\u0026ndash;8. The resulting suspension was centrifuged, the supernatant was decanted, and the obtained solide were freeze-dried.\u003c/p\u003e \u003cp\u003eX-ray diffraction (XRD) analysis confirmed the successful formation of 2-Line and 6-Line ferrihydrite, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of goethite-hematite-mixtures\u003c/h2\u003e \u003cp\u003eThe freeze dried oxides were mixed in weight based ratios (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u003c/span\u003e) as follows: For preparing 500mg of a goethite to hematite mixture with a 5 to 95 weight % ratio 25 mg of goethite was mixed with 475 mg of hematite and carefully homogenized within an agate mortar. From this mixture 1mg was used for FTIR analysis. The same procedure was used to prepare the other goethite to hematite weight % ratios (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe weights of hematite (Hem) and goethite (Goe) used to produce the goethite hematite mixtures studied here as well as the mMol of Fe offered by hematite in the mixtures and the intensities of the Hem-I, Goe-I and Goe-I band maxima in FTIR spectra of the mixtures.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMixture\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGoethite\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHematite\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHematite-Fe in the mixture\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eBand intensities\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGoe/Hem\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003emg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003emMol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHem-I\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGoe-I\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eGoe-II\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5/95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e475\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e5.938\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.978\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.555\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.576\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10/90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e450\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e5.625\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.702\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.510\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.517\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15/85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e425\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e20/80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e5.000\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.365\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.507\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.503\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e30/70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e350\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e4.375\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.161\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.832\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.803\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e40/60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e3.750\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.474\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.837\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.782\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e50/50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e3.125\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.463\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.617\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.553\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e60/40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2.500\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.715\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.64\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e70/30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e350\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e1.875\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.133\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.906\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.791\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e80/20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e1.250\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.383\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.384\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.364\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e85/15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e425\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.938\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.959\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.088\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.962\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e90/10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e450\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.625\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.258899\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.792\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.623\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e95/5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e475\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.313\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.316\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.799\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.672\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003eFTIR analysis\u003c/b\u003e:\u003c/h2\u003e \u003cp\u003eKBr technique: 2 mg of finely ground samples (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u003c/span\u003e) were combined with 98 mg of KBr, finely ground in an agate mortar, dried for 12 h over silica gel in a desiccator to standardize the water content and were then pressed into pellets. Note for the goethite-hematite mixture we used 1mg of mixture diluted in 99 mg of KBr. The pellets were analyzed using a FTS135 (BioRad, Krefeld, Germany) \u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e in transmission mode. All spectra were recorded in 2 replicates at a resolution of 2 cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e and 16 scans (=\u0026thinsp;16 repetitions of a single spectra; Ellerbrock, et al. \u003csup\u003e37\u003c/sup\u003e) to obtain the absorption spectra in a range of wavenumbers between 4000 and 400 cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. All spectra were corrected for ambient air \u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e, and baseline-corrected (BioRad Winirez software). The baseline-corrected spectra (e.g., Ellerbrock, et al. \u003csup\u003e37\u003c/sup\u003e) were analyzed for the WN and the intensity of absorption bands characteristic for stretching and bending modes in the iron (oxyhydr)-oxide octahedra (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The characteristic absorption bands caused by (1) stretching vibrations of (1a) O-H groups at the particles surfaces able to interact with H\u003csub\u003e2\u003c/sub\u003eO appear at WN 3400 to 3250 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e(ν O-H\u003csub\u003eH2O\u003c/sub\u003e; \u003csup\u003e39\u003c/sup\u003e), (2) O-H groups within the matrix of the iron (oxyhydr)-oxides at WN 3250 to 2900 (ν O-H\u003csub\u003eOx\u003c/sub\u003e; \u003csup\u003e39\u003c/sup\u003e), those of (3) the Fe\u003cb\u003e-\u003c/b\u003eO-H bending at WN 930 to 850 and 835 to 772 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (δ Fe-O-H;) as well as (4) the Fe-O-Fe stretching vibrations at WN 720\u0026thinsp;\u0026minus;\u0026thinsp;583 and 511 to 400 (ν Fe-O-Fe) within the iron (oxyhydr)-oxides (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u003c/span\u003e; \u003csup\u003e11,23\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003eWhen interpreting the spectra, we focus on the δ Fe-OH, and the ν Fe-O-Fe bands within the iron (oxyhydr)-oxides which were assumed to mostly reflect potential differences in the structure of the studied iron (oxyhydr)-oxide species (\u003csup\u003e11,23,39\u003c/sup\u003e) compared to the hematite.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe iron (oxyhydr)-oxides studied here by FTIR spectroscopy, their origin and references for the FTIR spectra used for comparison.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFe- species\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOrigin / reference\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRef. for spectra\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGoethite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOwn synth.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCui, et al. \u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHematite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOwn synth.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHu, et al. \u003csup\u003e23,\u003c/sup\u003eKhorshidi and Azadmehr \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFerrihydrite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLine 2\u0026nbsp;: Own synth.\u003c/p\u003e \u003cp\u003eLine 6 Own synth.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eXiao, et al. \u003csup\u003e40\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLepidocrocite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCui, et al. \u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCui, et al. \u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe FTIR of the goethite-hematite mixture was interpreted for the intensity of the hematite (Hem)-I, goethite (Goe)-I and Goe-II bands. The maxima of the δ Fe-OH (Goe-I), and the ν Fe-O-Fe (Goe-II), and Hem-I bands were identified using an automated identification procedure of the BioRad WINIREZ Software (BioRad Corp, Krefeld, Germany) as follows: the left and right limits of the WN region characteristic for each band (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) were used to construct so called \u0026lsquo;\u0026lsquo;def\u0026rsquo;\u0026rsquo;-files (offered by WINIREZ) that were than applied within the automated BioRad WINIREZ procedure. Note, we focus the interpretation of the hematite content in the goethite-hematite mixtures on the Hem-I band located at WN region from 607 to 546 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) since the second band of hematite located at about 475 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is overlapping with a ν Fe-O band of goethite (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The band of the hydroxyl groups at WN 3700 to 3250 cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (νO\u0026ndash;H band) were only considered with respect to the water content of the studied iron (oxyhydr)-oxides.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eOpen Access funding enabled and organized by Projekt DEAL.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eJ.S. had the idea. Measurements were done by R.E. and N.B.. The manuscript was written by R.E. and J.S.. All authors reviewed and edited the manuscript. All authors have given approval to the final version of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe thank Laurel Thomas Arrigo (Universit\u0026eacute; de Neuch\u0026acirc;tel) for synthesizing 6-line ferrihydrite and analyzing by XRD and Kerstin Hockmann (University Freiburg) for synthesizing 2-line ferrihydrite and analyzing by XRD.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets used and/or analyzed during the current study is available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBarr\u0026oacute;n, V. \u0026amp; Torrent, J. Iron, manganese and aluminium oxides and oxyhydroxides. (2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNavrotsky, A., Mazeina, L. \u0026amp; Majzlan, J. Size-driven structural and thermodynamic complexity in iron oxides. \u003cem\u003eScience\u003c/em\u003e \u003cb\u003e319\u003c/b\u003e, 1635\u0026ndash;1638 (2008).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHiemstra, T. Ferrihydrite interaction with silicate and competing oxyanions: geometry and hydrogen bonding of surface species. \u003cem\u003eGeochim. Cosmochim. Acta\u003c/em\u003e. \u003cb\u003e238\u003c/b\u003e, 453\u0026ndash;476 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSposito, G. \u003cem\u003eThe chemistry of soils\u003c/em\u003e (Oxford University Press, 2008).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBlume, H. P. et al. \u003cem\u003eScheffer/Schachtschabel Lehrbuch der Bodenkunde\u003c/em\u003e \u003cb\u003e16\u003c/b\u003e, 10.1007 (2010).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCornell, R. M. \u0026amp; Schwertmann, U. \u003cem\u003eThe iron oxides: structure, properties, reactions, occurrences and uses\u003c/em\u003e (Wiley, 2003).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMichel, F. M. et al. The structure of ferrihydrite, a nanocrystalline material. \u003cem\u003eScience\u003c/em\u003e \u003cb\u003e316\u003c/b\u003e, 1726\u0026ndash;1729 (2007).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, X. et al. Characteristics of phosphate adsorption-desorption onto ferrihydrite: comparison with well-crystalline Fe (hydr) oxides. \u003cem\u003eSoil Sci.\u003c/em\u003e \u003cb\u003e178\u003c/b\u003e, 1\u0026ndash;11 (2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSassi, M., Chaka, A. M. \u0026amp; Rosso, K. M. Ab initio thermodynamics reveals the nanocomposite structure of ferrihydrite. \u003cem\u003eCommun. Chem.\u003c/em\u003e \u003cb\u003e4\u003c/b\u003e, 134 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang, H., Lu, R., Downs, R. T., Costin, G. \u0026amp; Goethite α-FeO (OH), from single-crystal data. \u003cem\u003eStruct. Rep.\u003c/em\u003e \u003cb\u003e62\u003c/b\u003e, i250\u0026ndash;i252 (2006).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCui, H., Ren, W., Lin, P. \u0026amp; Liu, Y. Structure control synthesis of iron oxide polymorph nanoparticles through an epoxide precipitation route. \u003cem\u003eJ. Exp. Nanosci.\u003c/em\u003e \u003cb\u003e8\u003c/b\u003e, 869\u0026ndash;875 (2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKappler, A. et al. An evolving view on biogeochemical cycling of iron. \u003cem\u003eNat. Rev. Microbiol.\u003c/em\u003e \u003cb\u003e19\u003c/b\u003e, 360\u0026ndash;374 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchwertmann, U., Friedl, J. \u0026amp; Kyek, A. Formation and properties of a continuous crystallinity series of synthetic ferrihydrites (2-to 6-line) and their relation to FeOOH forms. \u003cem\u003eClay Clay Min.\u003c/em\u003e \u003cb\u003e52\u003c/b\u003e, 221\u0026ndash;226 (2004).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJiang, Z. et al. A new model for transformation of ferrihydrite to hematite in soils and sediments. \u003cem\u003eGeology\u003c/em\u003e \u003cb\u003e46\u003c/b\u003e, 987\u0026ndash;990 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRuan, H., Frost, R. \u0026amp; Kloprogge, J. T. The behavior of hydroxyl units of synthetic goethite and its dehydroxylated product hematite. \u003cem\u003eSpectrochim. Acta Part A Mol. Biomol. Spectrosc.\u003c/em\u003e \u003cb\u003e57\u003c/b\u003e, 2575\u0026ndash;2586 (2001).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOna-Nguema, G., Morin, G., Juillot, F., Calas, G. \u0026amp; Brown, G. E. EXAFS analysis of arsenite adsorption onto two-line ferrihydrite, hematite, goethite, and lepidocrocite. \u003cem\u003eEnviron. Sci. Technol.\u003c/em\u003e \u003cb\u003e39\u003c/b\u003e, 9147\u0026ndash;9155 (2005).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSantoro, V. et al. Inorganic and organic P retention by coprecipitation during ferrous iron oxidation. \u003cem\u003eGeoderma\u003c/em\u003e \u003cb\u003e348\u003c/b\u003e, 168\u0026ndash;180 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSwedlund, P. J., Miskelly, G. M. \u0026amp; McQuillan, A. J. An attenuated total reflectance IR study of silicic acid adsorbed onto a ferric oxyhydroxide surface. \u003cem\u003eGeochim. Cosmochim. Acta\u003c/em\u003e. \u003cb\u003e73\u003c/b\u003e, 4199\u0026ndash;4214 (2009).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrivedi, P., Axe, L. \u0026amp; Tyson, T. A. An analysis of zinc sorption to amorphous versus crystalline iron oxides using XAS. \u003cem\u003eJ. Colloid Interface Sci.\u003c/em\u003e \u003cb\u003e244\u003c/b\u003e, 230\u0026ndash;238 (2001).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, K. \u0026amp; Xing, B. Mutual effects of cadmium and phosphate on their adsorption and desorption by goethite. \u003cem\u003eEnviron. Pollut\u003c/em\u003e. \u003cb\u003e127\u003c/b\u003e, 13\u0026ndash;20 (2004).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrivedi, P. \u0026amp; Axe, L. Ni and Zn sorption to amorphous versus crystalline iron oxides: macroscopic studies. \u003cem\u003eJ. Colloid Interface Sci.\u003c/em\u003e \u003cb\u003e244\u003c/b\u003e, 221\u0026ndash;229 (2001).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, R., Liu, D. \u0026amp; Yang, P. Morphology control of α-Fe 2 O 3 towards super electrochemistry performance. \u003cem\u003eRSC Adv.\u003c/em\u003e \u003cb\u003e9\u003c/b\u003e, 21947\u0026ndash;21955 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHu, L., Percheron, A., Chaumont, D. \u0026amp; Brachais, C. H. Microwave-assisted one-step hydrothermal synthesis of pure iron oxide nanoparticles: magnetite, maghemite and hematite. \u003cem\u003eJ. Solgel Sci. Technol.\u003c/em\u003e \u003cb\u003e60\u003c/b\u003e, 198\u0026ndash;205 (2011).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePrasad, P. et al. In situ FTIR study on the dehydration of natural goethite. \u003cem\u003eJ. Asian Earth Sci.\u003c/em\u003e \u003cb\u003e27\u003c/b\u003e, 503\u0026ndash;511 (2006).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBikiaris, D. et al. Ochre-differentiation through micro-Raman and micro-FTIR spectroscopies: application on wall paintings at Meteora and Mount Athos, Greece. \u003cem\u003eSpectrochim. Acta Part A Mol. Biomol. Spectrosc.\u003c/em\u003e \u003cb\u003e56\u003c/b\u003e, 3\u0026ndash;18 (2000).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eČiuladienė, A., Luckutė, A., Kiuberis, J. \u0026amp; Kareiva, A. Investigation of the chemical composition of red pigments and binding media. \u003cem\u003eChemija\u003c/em\u003e \u003cb\u003e29\u003c/b\u003e (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCavalheri, A. S., Balan, A. M., K\u0026uuml;nzli, R. \u0026amp; Constantino, C. J. Vibrational spectroscopy applied to the study of archeological ceramic artifacts from Guarani culture in Brazil. \u003cem\u003eVib. Spectrosc.\u003c/em\u003e \u003cb\u003e54\u003c/b\u003e, 164\u0026ndash;168 (2010).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchwertmann, U. \u0026amp; Cornell, R. M. \u003cem\u003eIron oxides in the laboratory: preparation and characterization\u003c/em\u003e (Wiley, 2008).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhorshidi, N. \u0026amp; Azadmehr, A. R. Competitive adsorption of Cd (II) and Pb (II) ions from aqueous solution onto Iranian hematite (Sangan mine): optimum condition and adsorption isotherm study. \u003cem\u003eDesalination Water Treat.\u003c/em\u003e \u003cb\u003e58\u003c/b\u003e, 106\u0026ndash;119 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEllerbrock, R., Stein, M. \u0026amp; Schaller, J. Comparing amorphous silica, short-range-ordered silicates and silicic acid species by FTIR. \u003cem\u003eSci. Rep.\u003c/em\u003e \u003cb\u003e12\u003c/b\u003e, 11708 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEllerbrock, R. H., Stein, M. \u0026amp; Schaller, J. Comparing silicon mineral species of different crystallinity using Fourier transform infrared spectroscopy. \u003cem\u003eFront. Environ. Chem.\u003c/em\u003e \u003cb\u003e5\u003c/b\u003e, 1462678 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVillac\u0026iacute;s-Garc\u0026iacute;a, M. et al. Laboratory synthesis of goethite and ferrihydrite of controlled particle sizes. \u003cem\u003eBolet\u0026iacute;n de la. Sociedad Geol\u0026oacute;gica Mexicana\u003c/em\u003e. \u003cb\u003e67\u003c/b\u003e, 433\u0026ndash;446 (2015).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSalimi, F., Rahimi, H. \u0026amp; Karami, C. Removal of methylene blue from water solution by modified nanogoethite by Cu. \u003cem\u003eDesalination Water Treat.\u003c/em\u003e \u003cb\u003e137\u003c/b\u003e, 334\u0026ndash;344 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEusterhues, K. et al. Reduction of ferrihydrite with adsorbed and coprecipitated organic matter: microbial reduction by Geobacter bremensis vs. abiotic reduction by Na-dithionite. \u003cem\u003eBiogeosciences\u003c/em\u003e \u003cb\u003e11\u003c/b\u003e, 4953\u0026ndash;4966 (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAmelingmeier, E. \u0026amp; R\u0026ouml;mpp, H. \u003cem\u003eR\u0026ouml;mpp kompakt Basislexikon Chemie: M-Re. Bd. 3\u003c/em\u003e Vol. 3 (Thieme, 1999).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAtkinson, R., Posner, A. \u0026amp; Quirk, J. P. Adsorption of potential-determining ions at the ferric oxide-aqueous electrolyte interface. \u003cem\u003eJ. Phys. Chem.\u003c/em\u003e \u003cb\u003e71\u003c/b\u003e, 550\u0026ndash;558 (1967).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEllerbrock, R., H\u0026ouml;hn, A. \u0026amp; Rogasik, J. Functional analysis of soil organic matter as affected by long-term manurial treatment. \u003cem\u003eEur. J. Soil. Sci.\u003c/em\u003e \u003cb\u003e50\u003c/b\u003e, 65\u0026ndash;71 (1999).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHaberhauer, G. \u0026amp; Gerzabek, M. Drift and transmission FT-IR spectroscopy of forest soils: an approach to determine decomposition processes of forest litter. \u003cem\u003eVib. Spectrosc.\u003c/em\u003e \u003cb\u003e19\u003c/b\u003e, 413\u0026ndash;417 (1999).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFarmer, V. C. The infrared spectra of minerals. \u003cem\u003eMineralogical Soc. Monogr.\u003c/em\u003e \u003cb\u003e4\u003c/b\u003e, 331\u0026ndash;363 (1974).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXiao, W., Jones, A. M., Collins, R. N., Bligh, M. W. \u0026amp; Waite, T. D. Use of fourier transform infrared spectroscopy to examine the Fe (II)-Catalyzed transformation of ferrihydrite. \u003cem\u003eTalanta\u003c/em\u003e \u003cb\u003e175\u003c/b\u003e, 30\u0026ndash;37 (2017).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"crystal structure, FTIR, ferrihydrite, goethite, hematite, crystallinity","lastPublishedDoi":"10.21203/rs.3.rs-8741763/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8741763/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIron-(oxyhydr)-oxides like goethite, hematite and ferrhydrite affect soil properties like sorption capacity and can be distinguished by their specific surface and spectroscopic data like XRD. During dissolution\u0026ndash;recrystallization the iron (oxyhydr)-oxide can convert from one into the other. Some studies used Fourier-transform infrared spectroscopy (FTIR) to analyze hematite and goethite. The objective of this study was to identify absorption bands in FTIR that allow to distinguish hematite, goethite, lepidocrocite, and ferrihydrite and to compare the FTIR of laboratory synthesized with those of natural iron (oxyhydr)-oxides. Comparing the FTIR spectra of the different iron minerals indicate that all studied iron (oxyhydr)-oxides show absorption band located at different WN in the WN region from 1180 to 400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e typical for each of them. Distinct differences allow to distinguish and quantify, especially goethite from the other oxides. Hence, FTIR is a suitable method to distinguish between the different iron (oxyhydr)-oxides.\u003c/p\u003e","manuscriptTitle":"Comparing and quantifying goethite, hematite, lepidocrocite, and ferrihydrite by FTIR","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-10 11:25:23","doi":"10.21203/rs.3.rs-8741763/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-02-27T06:35:55+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-26T10:23:06+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-18T15:58:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"77729581300993900114898587087423656424","date":"2026-02-11T11:56:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"106305453561136508379957340986578458761","date":"2026-02-11T07:41:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"195730316622317537381152755618038176016","date":"2026-02-05T08:33:14+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-04T14:14:54+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-02-04T07:56:56+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-31T12:56:48+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-31T12:55:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-01-30T13:15:48+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e054df64-c968-48de-8b16-9f2c06b23039","owner":[],"postedDate":"February 10th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[{"id":62368604,"name":"Physical sciences/Chemistry"},{"id":62368605,"name":"Earth and environmental sciences/Environmental sciences"},{"id":62368606,"name":"Physical sciences/Materials science"},{"id":62368607,"name":"Earth and environmental sciences/Solid earth sciences"}],"tags":[],"updatedAt":"2026-05-14T03:39:04+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-10 11:25:23","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8741763","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8741763","identity":"rs-8741763","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}