Infrared spectroscopy of goethite dehydroxylation: III. FT-IR microscopy of in situ study of the thermal transformation of goethite to hematite

Reactive transport modeling to quantify the transformation of iron oxyhydroxides on the enrichment of iodine in groundwater of central Datong Basin

The enrichment of groundwater iodine is posing health risk for residents relying on groundwater for drinking. The transformation of iron oxyhydroxides plays the vital role in mobilizing sediment iodine into groundwater. However, few studies have provided sufficient knowledge of iodine adsorption on iron oxyhydroxides. In this study, we obtained thermodynamic parameters of iodate adsorption on magnetite and aluminum silicates through batch experiments. The extended three-layer model (ETLM) was developed to simulate the adsorption behavior under varying pH, ionic strength, and solid concentration. Using thermodynamic constants, a reactive transport model involving several scenarios was developed to explore the transformation of iron oxyhydroxides on the enrichment of iodine based on sediment profiles in the Datong Basin. Results indicate that the transformation from ferrihydrite to goethite within shallow aquifers reduces groundwater iodine concentrations by increasing the thermodynamic stability of the mineralogical system constituting the sediment, making iron oxyhydroxides less prone to reductive dissolution and release adsorbed iodine. In deep aquifers, newly formed secondary hematite and magnetite exhibit complementary surface properties, enhancing adsorption capacities of iodine compared to single-mineral systems. Overall, this study emphasizes the importance of minerals compositions and transformation on the mobilization of iodine in the groundwater system.

Autogenously Calcined Clays from Coal Tailings Dumps as Supplementary Cementitious Material: From Exploratory Investigations to an Industrial Trial

Autogenously calcined clays from tailings dumps, which are formed by the ignition of the contained residual coal, represent a huge resource of potentially pozzolanic material worldwide. This work presents preliminary studies of samples from the Western coal regions in Germany and investigations on the first industrially produced cement with autogenously calcined tailings concerning its suitability as supplementary cementitious material (SCM). Samples of the tailings materials and blended cements were thoroughly characterized physically, chemically and mineralogically. The reactivity was studied using the R3 test and mortar compressive strength testing. The influence on cement hydration was studied using X-ray diffractometry (XRD) and isothermal calorimetry. The preliminary investigations showed that the material is basically suitable as SCM, as it consists mainly of SiO2 and Al2O3, which partially occurs in X-ray amorphous form and has a low content of impurities, which can impair cement properties such as carbon or sulfur. The R3 reactivity and the relative compressive strength differed significantly depending on the sample. For the industrial cement production trial, low-processed material was used which still contained inert fractions. The average sample showed a relatively low R3 reactivity but still significantly higher than mostly inert materials such as limestone or quartz powder. Calorimetry and XRD investigations on cement pastes showed that the clinker reactions remain basically unaffected by the tailings. Mortar tests showed that the material contributes to strength development at a late age. It can be concluded that the tailings are basically suitable as SCM and, in appropriate blends, the clinker factor and, thus, the CO2 footprint of cement can be reduced.

Reusable Magnetite Nanoparticle (Fe3O4 NP) Catalyst for Selective Oxidation of Alcohols under Microwave Irradiation

Iron oxide nanoparticles (NPs) are nontoxic and abundant materials which have long been investigated as reusable catalysts in oxidation reactions, but their use so far has been hampered by a low selectivity. Here, unsupported iron oxide NPs have been found to successfully catalyze the microwave-assisted oxidation of primary and secondary alcohols to their respective aldehydes and ketones with a high selectivity when N-methylmorpholine N-oxide was used as the terminal oxidant. The crystalline phase and size of the iron-based catalyst have a drastic effect on its activity, with small magnetite (Fe3O4) NPs being the optimal catalyst for this reaction. The nanocatalyst could be easily recovered by magnetoseparation and successfully recycled four times without any need for special pretreatment or reactivation step and with a minimal loss of activity. The subsequent loss of activity was attributed to the transition from magnetite (Fe3O4) to maghemite (γ-Fe2O3), as confirmed by X-ray diffraction, Fourier transform infrared, and X-ray absorption near-edge spectroscopy. The nanocatalyst could then be reactivated by the high-temperature microwave treatment and used again for the microwave-assisted oxidation reaction.

Effective degradation of tetracycline in aqueous solution by an electro-Fenton process using chemically modified carbon/α-FeOOH as catalyst

This study applied an electro-Fenton process using chemically modified activated carbon derived from rubber seed shells loaded with α-FeOOH (RSCF) as catalyst to remove tetracycline residues from aquatic environment. Catalyst characteristics were evaluated using SEM, EDS, XRD, and XPS, showing successful insertion of iron onto the activated carbon. The effects of the parameters were investigated, and the highest treatment efficiency was achieved at pH of 3, Fe: H2O2 ratio (w/w) of 500:1, catalyst dose of 1 g/L, initial TCH concentration of 100 mg/L, and electric current of 150 mA, with more than 90% of TCH being eliminated within 30 min. Furthermore, even after five cycles of use, the treatment efficiency remains above 90%. The rate constant is calculated to be 0.218 min-1, with high regression coefficients (R 2 = 0.93). The activation energy (Ea) was found to be 32.2 kJ/mol, indicating that the degradation of TCH was a simple reaction with a low activation energy. These findings showed that the RSCF is a highly efficient and cost-effective catalyst for TCH degradation. Moreover, the use of e-Fenton process has the advantage of high efficiency, low cost thanks to the recyclability of the catalyst, and environmental friendliness thanks to less use of H2O2.

Ochre-based compound adhesives at the Mousterian type-site document complex cognition and high investment

Ancient adhesives used in multicomponent tools may be among our best material evidences of cultural evolution and cognitive processes in early humans. African Homo sapiens is known to have made compound adhesives from naturally sticky substances and ochre, a technical behavior proposed to mark the advent of elaborate cognitive processes in our species. Foragers of the European Middle Paleolithic also used glues, but evidence of ochre-based compound adhesives is unknown. Here, we present evidence of this kind. Bitumen was mixed with high loads of goethite ochre to make compound adhesives at the type-site of the Mousterian, Le Moustier (France). Ochre loads were so high that they lowered the adhesive's performance in classical hafting situations where stone implements are glued to handles. However, when used as handheld grips on cutting or scraping tools, a behavior known from Neanderthals, high-ochre adhesives present a real benefit, improving their solidity and rigidity. Our findings help understand the implications of Pleistocene adhesive making.

Synthesis and characterization of iron oxide-commercial activated carbon nanocomposite for removal of hexavalent chromium (Cr6+) ions and Mordant Violet 40 (MV40) dye

Iron Oxide-commercial activated carbon nanocomposite (CAC-IO) was prepared from commercial activated carbon (CAC) by the co-precipitation method, and the resulting nanocomposite was used as an adsorbent to remove hexavalent chromium (Cr6+) ions and Mordant Violet 40 (MV40) dye from wastewater. The produced materials (CAC, CAC after oxidation, and CAC-IO) were comparatively characterized using FTIR, BET, SEM, EDX TEM, VSM, and XRD techniques. The adsorption mechanism of Cr6+ ions and MV40 dye on CAC-IO was examined using Langmuir and Freundlich isotherm models.. Different models were applied to know the adsorption mechanism and it was obtained that Pseudo-second order fits the experimental data better. This means that the adsorption of the adsorbate on the nanocomposite was chemisorption. The maximum removal percent of Cr6+ ions by CAC-IO nanocomposite was 98.6% determined as 2 g L-1 adsorbent concentration, 100 mg L-1 initial pollutant concentration, solution pH = 1.6, the contact time was 3 h and the temperature was room temperature. The maximum removal percentage of Mordant Violet 40 dye (C.I. 14,745) from its solutions by CAC-IO nanocomposite was 99.92% in 100 mg L-1 of initial dye concentrations, 1.0 g L-1 of adsorbent concentration, solution pH = 2.07, the contact time was 3 h. The MV40 dye adsorption on CAC-IO was the most fitted to the Freundlich isotherm model. The maximum adsorption capacity was calculated according to the Langmuir model as 833.3 mg g-1 at 2 g L-1 of adsorbent concentration and 400 mg L-1 of initial MV40 dye concentration. The Cr6+ ions adsorption on CAC-IO was more fitted to the Freundlich model with Qmax, equal to 312.50 mg g-1 at 1 g L-1 adsorbent concentration and 400 mg L-1 of Cr6+ ions initial concentrations.

Simultaneous stabilization of arsenic and antimony co-contaminated mining soil by Fe(Ⅱ) activated-Fenton sludge: Behavior and mechanisms

Fenton sludge (FS) with high iron contents that discharged from the Fenton process was rarely studied for soil remediation. Herein, a novel Fe(Ⅱ) activated-Fenton sludge (FS-FeSO4) was proposed to stabilize arsenic (As) and antimony (Sb) co-contaminated soil meanwhile disposing FS. Multiple characteristic analyses revealed that the porous structures and rich functional groups of FS-FeSO4 involved in As and Sb adsorption. Meanwhile, Fe (hydro)oxides played a key role in As and Sb stabilization. Under the optimal application parameters (stabilizers dosage: 5%, incubation time: 60 days), the available As and Sb content decreased by 88.6% and 83.3%, respectively, and the leachability of As and Sb was reduced by 100% and 72.6% for FS-FeSO4 stabilized soil. Moreover, the mobile As and Sb fractions (F1 and F2) were transformed into the most stable fraction (F5). The adsorption of As and Sb on FS-FeSO4 was well fitted by pseudo-second-order kinetic and Langmuir models, while FS-FeSO4 exhibited a better affinity for As than Sb under competition conditions. Poorly crystalline α-FeOOH and amorphous Fe (hydro)oxides provided sufficient active sites for As and Sb, and the generation of Fe-As/Sb and Ca-Sb chemical bonds promoted the stability of As and Sb. This study demonstrated that FS-FeSO4 was a potentially effective stabilizer for As and Sb co-contaminated soil remediation.

In-situ synthesis of magnetic iron-chitosan-derived biochar as an efficient persulfate activator for phenol degradation

Persulfate activation is a forceful method for eliminating organic pollutants from coal chemical wastewater. In this study, an in-situ synthesis method was used to fabricate an iron-chitosan-derived biochar (Fe-CS@BC) nanocomposite catalyst using chitosan as a template. Fe was successfully imprinted into the newly synthesized catalyst. The Fe-CS@BC can activate persulfate to effectively degrade phenol. This point was confirmed by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The impact of various parameters on the removal rate was investigated in a single factor experiment. In Fe-CS@BC/PDS system, 95.96% of phenol (significantly higher than the original biochar of 34.33%) was removed within 45 min and 54.39% TOC within 2 h. The system showed superior efficiency over a broad pH value band from 3 to 9 and has a high degradation rate at ambient temperature. Free radical quenching experiment, EPR experiment and LSV experiment confirmed that multiple free radicals (including 1O2, SO4•-, O2•- and •OH) and electron transfer pathway combined to enhance phenol decomposition. Finally, the activation mechanism of persulfate by Fe-CS@BC was proposed to provide logical guidance on the treatment of organic pollutants in coal chemical wastewater.

Heterogeneous photo-Fenton catalyst α-Fe2O3@g-C3N4@NH2-MIL-101(Fe) with dual Z-Scheme heterojunction for degradation of tetracycline

A novel photo-Fenton catalyst α-Fe2O3@g-C3N4@NH2-MIL-101(Fe) (FGN) with dual Z-scheme heterojunction was successfully prepared by hydrothermal method to degrade tetracycline (TC). The preparation conditions were optimized by orthogonal test, and the successful synthesis was confirmed by characterization analyses. The prepared FGN showed better light absorption performance, higher photoelectrons-holes separation efficiency, lower photoelectrons transfer resistance, and higher specific surface area and pore capacity compared with α-Fe2O3@g-C3N4 and α-Fe2O3. The effects of experimental conditions on the catalytic degradation of TC were investigated. The degradation rate of 10 mg/L TC could reach 98.33% within 2 h when the dosage of FGN was 200 mg/L, and the degradation rate could remain 92.27% after 5 times of reuse. Furthermore, the XRD spectra and XPS spectra of FGN before and after reuse were compared to explore the structural stability and catalytic active sites of FGN, respectively. According to the identification of oxidation intermediates, three degradation pathways of TC were proposed. Through H2O2 consumption experiment, radical-scavenging experiments, EPR results, the mechanism of the dual Z-scheme heterojunction was proved. The improved performance of FGN was attributed to the dual Z-Scheme heterojunction effectively promoting the separation of photogenerated electrons from the holes and accelerating the electrons transfer, and the increase of the specific surface area.

Effect of dewatering conditioners on phosphorus removal efficiency of sludge biochar

Based on the best dehydration effect, this study compared the adsorption phosphorus effect of sludge biochar after sludge conditioning with FeCl3, KMnO4, and cationic polyacrylamide (CPAM). This provided insights into the effects of chemical conditioning during the sludge dewatering stage on the overall phosphate adsorption of the dewatered sludge biochar. The phosphorus adsorption mechanism of the dewatering sludge biochar was analysed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. Under the optimal pyrolysis temperature (300°C), the phosphate adsorption capacity of FeCl3-conditioned sludge biochar (SB-FeCl3) was increased 77 times of the unconditioned sludge biochar. In different solution environments (e.g. pH and coexisting anions), Phosphate adsorption of SB-FeCl3 was srtrongest when the pH of 9 and contained CO32-. Through the analysis of surface elements and functional groups, it was explained that the phosphorus removal effect of SB-FeCl3 comes from abundant active sites containing iron. Phosphorus release occurred in sludge biochar (SB) during the study. SB-FeCl3 solved SB the release of phosphorus, and improved the adsorption capacity of phosphorus.

Uranium surface processes with sandstone and volcanic rocks in acidic and alkaline solutions

Understanding the behaviour of uranium waste, for disposal purposes, is crucial due to the correlation between pH values and the disposal of distinct types of waste, with low level waste typically associated with acidic pH values, and higher and intermediate level waste commonly related to alkaline pH values. We studied the adsorption of U(VI) on sandstone and volcanic rock surfaces at pH 5.5 and 11.5 in aqueous solutions with and without bicarbonate (2 mM HCO₃^-) using XAS and FTIR. In the sandstone system, U(VI) adsorbs as a bidentate complex to Si at pH 5.5 without bicarbonate and as uranyl carbonate species with bicarbonate. At pH 11.5 without bicarbonate, U(VI) adsorbs as monodentate complexes to Si and precipitates as uranophane. With bicarbonate at pH 11.5, U(VI) precipitated as a Na-clarkeite mineral or remained as a uranyl carbonate surface species. In the volcanic rock system, U(VI) adsorbed to Si as an outer sphere complex at pH 5.5, regardless of the presence of bicarbonate. At pH 11.5 without bicarbonate, U(VI) adsorbed as a monodentate complex to one Si atom and precipitated as a Na-clarkeite mineral. With bicarbonate at pH 11.5, U(VI) sorbed as a bidentate carbonate complex to one Si atom. These results provide insight into the behaviour of U(VI) in heterogeneous, real-world systems related to the disposal of radioactive waste.

Magnetic Zinc Oxide/Manganese Ferrite Composite for Photodegradation of the Antibiotic Rifampicin

In this study, a composite of zinc oxide and manganese ferrite was synthesized using co-precipitation and hydrothermal routes, to be used as photocatalysts in reactions with UV/Vis light source. The synthesized materials were characterized by FTIR, XRD, and SEM, where it was possible to verify the efficiency of the syntheses performed, through the identification of the resulting phases, the evaluation of the structural morphology of the particles, and the analysis of the detachments of the main vibration bonds present in these materials. The composite ZnO/MnFe₂O₄ was used in photodegradation reactions of the antibiotic rifampicin, with catalyst dosage of 0.20; 0.40, and 0.60 g and 10 ppm of rifampicin, reactions using pure ZnO as a catalyst were also performed as a comparative parameter of the influence of MnFe₂O₄ in this system. The composite ZnO/MnFe₂O₄ showed a maximum percentage of rifampicin decontamination of 94.72% and ZnO, 74.20%using 0.20 g of photocatalyst after 90 min, which indicates a positive influence on this process. The solution treated with ZnO/MnFe₂O₄ was subjected to magnetic field induction for attraction and consequently accelerated removal of the solids present, successfully, compacting for the application of ZnO/MnFe₂O₄ to be presented as a promising material for decontamination of emerging pollutants through photocatalytic reactions.

Biochar modification with hematite and goethite as efficient persulfate activation catalysts for sulfamethoxazole degradation: one-step biochar synthesis method and solution matrix effect on sulfamethoxazole removal kinetics

Using biochar to adsorb and degrade organic contaminants has attracted increasing attention due to its relatively low cost and high efficiency. In this work, two magnetic biochars were synthesized by pyrolyzing a mixture of naturally occurring hematite or goethite mineral and pine needle biomass. The biochar composite was characterized with X-ray diffraction, scanning electron microscopy, and surface area analyzer. The result demonstrated iron minerals have been deposited on carbon surfaces and been reduced to magnetite or wustite minerals. In comparison to the unmodified biochar, the iron mineral-modified biochar had better sorption ability, likely because the iron mineral particles on the carbon surface served as additional sorption sites for sulfamethoxazole (SMX) removal. After modification, the biochar also showed higher persulfate activation capacity with radical generation: at 4 h, neutral pH, 67.5 and 77.9% of persulfate is activated with hematite and goethite modified biochar, where only 11.7% persulfate is activated by unmodified biochar. With persulfate, goethite-modified biochar showed better SMX removal capacity than hematite-modified biochar with about 79% of SMX removed in 4 h. Solution chemistry such as pH and co-exist humic acid can affect SMX removal by affecting iron minerals. Because the magnetized biochar can be easily isolated and removed with external magnets, it can be used in various contaminant removal applications.

Preparation of Iron Salt-Modified Sludge Biochar and Its Uptake Behavior for Phosphate

Residual sludge is a significant waste resource, and the preparation of biochar achieves sludge disposal. Biochar has a high uptake capacity for phosphate. To prepare a sludge biochar adsorbent for phosphate, sludge was chemically and anaerobically treated in the presence of iron salts and pyrolyzed. We investigated the effects of the pyrolysis temperature and iron salt on the phosphate uptake capacity, finding that the pretreatment of the sludge with iron salts removed intrinsic phosphate, thus improving the uptake ability. The optimal adsorbent, denoted SB-B-Fe, was prepared by pyrolysis at 700 °C and subsequently modified with a 20 g/L iron-containing solution, yielding a phosphate uptake capacity of 0.5 mg/g. Further, the performance of SB-B-Fe remains high at pH 5–9 and is less affected by interfering anions. The sorption kinetics are consistent with the pseudo-second-order kinetic model, suggesting uptake by chemisorption, and the Langmuir model has a saturation capacity of 0.85 mg/g for uptake and prefers monolayer molecular uptake. The characterization showed that the adsorbent surface provided many uptake sites for phosphate and a high specific surface area. We hope that these findings will encourage the development of other value-added waste-based materials for environmental remediation.

Effects of Iron Minerals on the Compressive Strengths and Microstructural Properties of Metakaolin-Based Geopolymer Materials

The current study aims to investigate the influence of iron minerals on the amorphous phase content, compressive strengths and the microstructural properties of the geopolymer materials. Geopolymer materials were prepared by the substitution of metakaolin by 10 and 20 wt.% of each iron mineral sample. Sodium waterglass from rice husk ash was used as a hardener, and metakaolin was used as an aluminosilicate source. The X-ray patterns show that the iron minerals denoted FR and FB are associated with hematite and magnetite, respectively. FY contains goethite together with a significant content of kaolinite and quartz. It is observed in the XRD patterns and FTIR absorption spectra that the additions of hematite, magnetite and goethite remain largely unreacted in the geopolymer binder. The compressive strengths of the related geopolymer composites show some significant variations indicating certain effects for mechanical stability obtained: 10 wt.% replacement of metakaolin by hematite increased the compressive strength from 51.1 to 55.5 MPa, while 20 wt.% hematite caused a decrease to 44.9 MPa. Furthermore, 10 and 20 wt.% replacement with FB revealed decreased values 47.0 and 40.3 MPa, respectively. It was also found that 10 and 20 wt.% of FY caused lower values of 30.9 and 39.1 MPa, respectively. The micrographs of geopolymer materials present some voids and cracks. The denser matrix is related to a superior gel formation producing a better glue between the crystalline additions. The unsubstituted geopolymer sample provides with about 50% the highest X-ray-amorphous content, whereas the substituted samples range between 35 and 45%, indicating systematically smaller gel contents without any clear trend with the compressive strength variation, however. The strength dependencies reveal more complex interaction between the gel and crystalline additions.

Synthesis and Characterization of Hematite-Based Nanocomposites as Promising Catalysts for Indigo Carmine Oxidation

The hematite-based nanomaterials are involved in several catalytic organic and inorganic processes, including water decontamination from organic pollutants. In order to develop such species, a series of bimetallic hematite-based nanocomposites were obtained by some goethite composites-controlled calcination. Their composition consists of various phases such as α-FeOOH, α-Fe₂O₃ or γ-Fe₂O₃ combined with amorphous (Mn₂O₃, Co₃O₄, NiO, ZnO) or crystalline (CuO) oxides of the second transition ion from the structure. The component dimensions, either in the 10–30 or in the 100–200 nm range, together with the quasi-spherical or nanorod-like shapes, were provided by Mössbauer spectroscopy and powder X-ray diffraction as well as transmission electron microscopy data. The textural characterization showed a decrease in the specific area of the hematite-based nanocomposites compared with corresponding goethites, with the pore volume ranging between 0.219 and 0.278 cm³g⁻¹. The best catalytic activity concerning indigo carmine removal from water in hydrogen peroxide presence was exhibited by a copper-containing hematite-based nanocomposite sample that reached a dye removal extent of over 99%, which correlates with both the base/acid site ratio and pore size. Moreover, Cu-hbnc preserves its catalytic activity even after four recyclings, when it still reached a dye removal extent higher than 90%.

Top-Down Formulation of Goethite Nanosuspensions for the Production of Transparent, Inorganic Glass Coatings

This study presents a simple but effective process route for the production of transparent coatings on glass substrates from inorganic pigment goethite. For this purpose, coating suspensions were prepared by wet milling with a stirred media mill. A water/ethanol mixture was used as the liquid medium to take advantage of the resulting low surface tension for the coating process. In this manner, stable suspensions with particles of down to 50 nm in size were obtained, which already showed a significant increase in transparency. With regard to grinding characteristics, particularly low stress energies proved to be energetically reasonable. The coating step was performed by wet film deposition, achieving coating thicknesses in a range of 0.5–2.5 µm via dip coating. Highly transparent coatings were obtained by applying small particles of 50 nm, which exhibited a significantly lower scattering loss of light (≈3%) in comparison to particles of around 300 nm (70–80%). Additionally, the film color could be adjusted through a variation of the drying temperature due to a conversion of goethite to hematite by dehydration. Since transparency was not affected, this provides an easy-to-implement process adaptation for controlling coating colors.

Effects of Al substitution on sorption of diclofenac to Fe(III) (hydr)oxides: roles of phase transition and sorption mechanisms

Fe(III) (hydr)oxides commonly contained many metal impurities such as Al. The incorporation of Al might change the properties of minerals and consequently affect sorption behaviors of pollutants with polar functional groups (e.g., diclofenac (DCF)). In this study, batch experiments and microscale characterization were conducted to investigate the DCF sorption mechanisms to goethite and Al-substituted minerals. Goethite and Al-substituted products (including Al-goethite, Al-goethite-hematite, and Al-hematite) were synthesized with different Al contents (i.e., 0%, 5%, 10%, and 15% (in mol)) by co-precipitation method. Due to difference of ionic radius between Al and Fe and formation of excessive -OH, Al substitution resulted in deviation of cell parameters from the Vegard line. Al substitution caused increasing -OH in Al-goethite and phase transformation caused decreasing -OH in Al-hematite. The total -OH in minerals was positively related to DCF sorption capacity. In the lower initial concentration range (0.4-9 mg/L), the sorption distribution coefficient (Kd) values of goethite, Al-goethite, and Al-hematite were 21.98, 22.25, and 21.18 L/kg, respectively. Desorption characteristics and ion strength effects indicated that DCF sorption to minerals occurred mainly through outer-sphere complexation. Fourier transform infrared analyses revealed that H-bonds could be formed through -OH of minerals and -COOH of DCF, and the H-bond strength on Al-hematite was stronger than that on goethite/Al-goethite. In the normal environmental pH (e.g., 6.0 to 8.0), Kd values of DCF decreased linearly with increasing pH. These findings are helpful for understanding of DCF migration in environment involving Al-substituted minerals.

Mine tailings in a redox-active environment: Iron geochemistry and potential environmental consequences

Iron (Fe) oxyhydroxides provide many functions in soils, mainly owing to their large surface area and high surface charge density. The reactivity of Fe oxyhydroxides is function of their mineralogical characteristics (e.g., crystallinity degree and crystal size). Detailed studies of these features are essential for predicting the stability and reactivity of these minerals within soil and sediments. The present study aimed to evaluate geochemical changes in Fe-rich tailings after the world's largest mining disaster in SE Brazil (in 2015) and to predict the potential environmental implications for the estuary. The mineralogical characteristics of the tailings were studied at three different times (2015, 2107, and 2019) to assess how an active redox environment affects Fe oxyhydroxides and to estimate the time frame within which significant changes occur. The study findings indicate a large decrease in the Fe oxyhydroxides crystallinity, which were initially composed (93%) of highly crystalline Fe oxyhydroxides (i.e., goethite and hematite) and 6.7% of poorly crystalline Fe oxyhydroxides (i.e., lepidocrocite and ferrihydrite). Within 4 years the mineralogical features of Fe oxyhydroxides had shifted, and in 2019 poorly crystalline Fe oxyhydroxides represented 47% of the Fe forms. Scanning electron microscope micrographs and the mean crystal size evidenced a decrease in particle size from 109 nm to 49 nm for goethite in the d₁₁₁ direction. The changes in mean crystal size increased the reactivity of Fe oxyhydroxides, resulting in a greater number of interactions with cationic and anionic species. The decreased crystallinity and increased reactivity led to the compounds being more susceptible to reductive dissolution. Overall, the findings show that the decrease in crystallinity along with higher susceptibility to reductive dissolution of Fe oxyhydroxides can affect the fate of environmentally detrimental elements (e.g., phosphorus and trace metals) thereby increasing the concentration of these pollutants in estuarine soils and waters.

The Effect of High Selenite and Selenate Concentrations on Ferric Oxyhydroxides Transformation under Alkaline Conditions

Iron-based nanomaterials have high technological impacts on various pro-environmental applications, including wastewater treatment using the co-precipitation method. The purpose of this research was to identify the changes of iron nanomaterial's structure caused by the presence of selenium, a typical water contaminant, which might affect the removal when the iron co-precipitation method is used. Therefore, we have investigated the maturation of co-precipitated nanosized ferric oxyhydroxides under alkaline conditions and their thermal transformation into hematite in the presence of selenite and selenate with high concentrations. Since the association of selenium with precipitates surfaces has been proven to be weak, the mineralogy of the system was affected insignificantly, and the goethite was identified as an only ferric phase in all treatments. However, the morphology and the crystallinity of ferric oxyhydroxides was slightly altered. Selenium affected the structural order of precipitates, especially at the initial phase of co-precipitation. Still, the crystal integrity and homogeneity increased with time almost constantly, regardless of the treatment. The thermal transformation into well crystalized hematite was more pronounced in the presence of selenite, while selenate-treated and selenium-free samples indicated the presence of highly disordered fraction. This highlights that the aftermath of selenium release does not result in destabilization of ferric phases; however, since weak interactions of selenium are dominant at alkaline conditions with goethite's surfaces, it still poses a high risk for the environment. The findings of this study should be applicable in waters affected by mining and metallurgical operations.

Soft synthesis and characterization of goethite-based nanocomposites as promising cyclooctene oxidation catalysts

Goethite based nanocomposites with a different composition such as 6FeO(OH)·MnO(OH)·0.5H₂O (Mn-composite), xFeO(OH)·M(OH)₂·yH₂O (Co-composite (M: Co, x = 12, y = 3), Ni-composite (M: Ni, x = 7, y = 2)) and xFeO(OH)·MO·yH₂O (Cu-composite (M: Cu, x = 5.5, y = 3), Zn-composite (M: Zn, x = 6, y = 1.5)) have been prepared by a soft chemical synthesis consisting in acetate hydrolysis. The data provided by Fourier transform infrared (FTIR), ultraviolet-visible-near infrared (UV-Vis-NIR), electron paramagnetic resonance (EPR) and Mössbauer spectra account for a slight modification of all composites' physicochemical properties compared to the starting material. Powder X-ray diffraction and transmission electron microscopy (TEM) investigations revealed the secondary phase nature and presence along with that of goethite. The TEM data are also consistent with a nano rod-like morphology with a 5–10 nm width and an average length of 40 nm. The catalytic oxidation of cyclooctene with O₂ using isobutyraldehyde as reductant and acetonitrile as a solvent was performed in batch conditions for 5 h at room temperature. The selectivity for the epoxide was higher than 99% for all tested solids. The conversion of cyclooctene decreased from 55% to 4% following the same order of variance as the base/acid sites ratio: Mn-composite > Fe-composite > Co-composite > Ni-composite > Zn-composite > Cu-composite. The 6FeO(OH)·MnO(OH)·0.5H₂O (Mn-composite) exhibited the most promising catalytic activity in cyclooctene oxidation, which can be correlated with the redox ability of Mn(iii) combined with the increased base character of this solid. The catalytic activity of this sample decreases by 10% after several successive reaction cycles.

Goethite based nanocomposites with different compositions (6FeO(OH)·MnO(OH)·0.5H₂O, xFeO(OH)·M(OH)₂·yH₂O or xFeO(OH)·MO·yH₂O where M = Co, Ni, Cu or Zn) have been prepared by a soft chemical synthesis via acetate hydrolysis.

Pyrolysis of Carboxylic Acids in the Presence of Iron Oxides: Implications for Life Detection on Missions to Mars

The search for, and characterization of, organic matter on Mars is central to efforts in identifying habitable environments and detecting evidence of life in the martian surface and near surface. Iron oxides are ubiquitous in the martian regolith and are known to be associated with the deposition and preservation of organic matter in certain terrestrial environments, thus iron oxide-rich sediments are potential targets for life-detection missions. The most frequently used protocol for martian organic matter characterization (also planned for use on ExoMars) has been thermal extraction for the transfer of organic matter to gas chromatography-mass spectrometry (GC-MS) detectors. For the effective use of thermal extraction for martian samples, it is necessary to explore how potential biomarker organic molecules evolve during this process in the presence of iron oxides. We have thermally decomposed iron oxides simultaneously with (z)-octadec-9-enoic and n-octadecanoic acids and analyzed the products through pyrolysis-GC-MS. We found that the thermally driven dehydration, reduction, and recrystallization of iron oxides transformed fatty acids. Overall detectability of products greatly reduced, molecular diversity decreased, unsaturated products decreased, and aromatization increased. The severity of this effect increased as reduction potential of the iron oxide and inferred free radical formation increased. Of the iron oxides tested hematite showed the least transformative effects, followed by magnetite, goethite, then ferrihydrite. It was possible to identify the saturation state of the parent carboxylic acid at high (0.5 wt %) concentrations by the distribution of n-alkylbenzenes in the pyrolysis products. When selecting life-detection targets on Mars, localities where hematite is the dominant iron oxide could be targeted preferentially, otherwise thermal analysis of carboxylic acids, or similar biomarker molecules, will lead to enhanced polymerization, aromatization, and breakdown, which will in turn reduce the fidelity of the original biomarker, similar to changes normally observed during thermal maturation.

Field demonstration of solar-powered electrocoagulation water treatment system for purifying groundwater contaminated by both total coliforms and arsenic

People who drink groundwater in rural areas of Southeast Asia are exposed to pathogens and arsenic (As)-related health problems. A water treatment system consisting of electrocoagulation reactors, using iron (Fe) electrodes and a filtration tank, was designed to treat complex contaminated groundwater for drinking. Its applicability was demonstrated near the Red River in Vietnam. The water treatment system reduced 10.3 CFU/mL of total coliform and 376 μg/L of As(III) in the groundwater to 0 CFU/mL and 6.68 μg/L, respectively. Total coliforms were attenuated by Fe(II) infiltration or enmeshed during Fe precipitate formation. Of the total As, 43% formed As(III) complexation with the Fe precipitates and the other 57% was oxidized to As(V) then adsorbed to Fe precipitates. The Fe precipitates, containing total coliforms and As, were separated from the discharge water in the filtration tank. The system required 49 W of power to operate, which equates to 423 kWh/year, to continuously purify 0.5 t water/day. This requirement was powered by a 380-750 W solar panel, without external energy supply, making the water treatment system an appropriate option for addressing drinking water problems in rural areas.

The Role of Growth Directors in Controlling the Morphology of Hematite Nanorods

The control of the growth of hematite nanoparticles from iron chloride solutions under hydrothermal conditions in the presence of two different structure promoters has been studied using a range of both structural and spectroscopic techniques including the first report of photo induced force microscopy (PiFM) to map the topographic distribution of the structure-directing agents on the developing nanoparticles. We show that the shape of the nanoparticles can be controlled using the concentration of phosphate ions up to a limit determined to be ~6 × 10^-3 mol. Akaganéite (β-FeOOH) is a major component of the nanoparticles formed in the absence of structure directors but only present in the very early stages (< 8 h) of particle growth when phosphate is present. The PiFM data suggest a correlation between the areas in which phosphate ions are adsorbed and areas where akaganéite persists on the surface. In contrast, goethite (α-FeOOH) is a directly observed precursor of the hematite nanorods when 1,2-diamino propane is present. The PiFM data shows goethite in the center of the developing particles consistent with a mechanism in which the iron hydroxide re-dissolves and precipitates at the nanorod ends as hematite.

Graphene oxide-induced formation of a boron-doped iron oxide shell on the surface of NZVI for enhancing nitrate removal

The surface products have a significant influence on the reactivity of zero-valent iron-based materials. Although the enhancing effect of graphene on the reactivity of nanoscale zero-valent iron (NZVI)/graphene composites have been confirmed, the effect of graphene on the formation of surface products of NZVI is not well understood. In order to assess the effect of graphene on the structural of the outer iron oxide layers of NZVI, the NZVI was pre-oxidized by graphene oxide (ONZVI-GO). Compared with the NZVI oxidized by O₂ (ONZVI-O₂), ONZVI-GO was shown to be effective at NO₃^- removal with a high efficiency over a wide range of initial pH values. The results from characterization showed that GO could induce the formation of a tight iron oxide shell with dense spinel structures. The boron introduced during the preparation of NZVI was doped into iron oxides on the surface of ONZVI-GO. The B-O in adsorbed borate was transformed to B-B/B-Fe in the lattice structure of iron oxides, causing the formation of highly electron-deficient Lewis acid sites on the surface of ONZVI-GO, which could effectively gather NO₃^- and OH^-, leading to the higher efficiency removal of NO₃^- than ONZVI-O₂ over a wide range of initial pH values. This study provides new insight into the interaction between graphene and the surface species of NZVI.

Raman imaging to quantify the thermal transformation degree of Pompeian yellow ochre caused by the 79 AD Mount Vesuvius eruption

Most of the wall paintings from Pompeii are decorated with red and yellow colors but the thermal impact of 79 AD Mount Vesuvius eruption promoted the partial transformation of some yellow-painted areas into red. The aim of this research is to develop a quantitative Raman imaging methodology to relate the transformation percentage of yellow ochre (goethite, α-FeOOH) into red color (hematite, α-Fe₂O₃) depending on the temperature, in order to apply it and estimate the temperature at which the pyroclastic flow impacted the walls of Pompeii. To model the thermal impact that took place in the year 79 AD, nine wall painting fragments recovered in the archeological site of Pompeii and which include yellow ochre pigment were subjected to thermal ageing experiments (exposition to temperatures from 200 to 400 °C every 25 °C). Before the experiments, elemental information of the fragments was obtained by micro-energy dispersive X-ray fluorescence (μ-ED-XRF). The fragments were characterized before and after the exposition using Raman microscopy to monitor the transformation degree from yellow to red. The quantitative Raman imaging methodology was developed and validated using synthetic pellets of goethite and hematite standards. The results showed almost no transformation (0.5% ± 0.4) at 200 °C. However, at 225 °C, some color transformation (26.9% ± 2.8) was observed. The most remarkable color change was detected at temperatures between 250 °C (transformation of 46.7% ± 1.7) and 275 °C (transformation of 101.1% ± 1.2). At this last temperature, the transformation is totally completed since from 275 to 400 °C the transformation percentage remained constant.

Investigation of the Optical, Physical, and Chemical Interactions between Diammonium Hydrogen Phosphate (DAP) and Pigments

This research investigates and evaluates the optical, physical, and chemical interactions between a diammonium hydrogen phosphate (DAP) solution and seven pigments commonly encountered in archaeological and historic fresco and secco wall paintings and polychrome monuments. The pigments include cinnabar, French ochre, chalk, lapis lazuli, raw sienna, burnt umber, and red lead. The raw pigments were analyzed before and after the interaction with the DAP solution, and the reaction products resulting from the contact of the pigments with the DAP solution were evaluated to obtain a comprehensive understanding of the effects of diammonium phosphate on the color, morphology, and chemical composition of the pigments. The results indicated no significant changes of the color or of the chemistry of cinnabar, French ochre, and lapis lazuli. Carbonate-containing primary and secondary (found as impurities in earth pigments) pigments, such as chalk and calcium carbonate, were transformed into calcium phosphate, though without a significant change in color. Phase and strong color changes occurred only for the red lead pigment, associated with the transformation of red lead into hydroxypyromorphite. These data established the parameters and identified the risks of the direct application of DAP solutions on pigments. Further research will be undertaken to assess the potential use of DAP as a consolidant of wall paintings and other polychrome surfaces through testing on wall painting/polychromy mockups and on-site archaeological/historic painted surfaces.

A Mineralogical Context for the Organic Matter in the Paris Meteorite Determined by A Multi-Technique Analysis

This study is a multi-technique investigation of the Paris carbonaceous chondrite directly applied on two selected 500 × 500 µm² areas of a millimetric fragment, without any chemical extraction. By mapping the partial hydration of the amorphous silicate phase dominating the meteorite sample matrix, infrared spectroscopy gave an interesting glimpse into the way the fluid may have circulated into the sample and partially altered it. The TOF-SIMS in-situ analysis allowed the studying and mapping of the wide diversity of chemical moieties composing the meteorite organic content. The results of the combined techniques show that at the micron scale, the organic matter was always spatially associated with the fine-grained and partially-hydrated amorphous silicates and to the presence of iron in different chemical states. These systematic associations, illustrated in previous studies of other carbonaceous chondrites, were further supported by the identification by TOF-SIMS of cyanide and/or cyanate salts that could be direct remnants of precursor ices that accreted with dust during the parent body formation, and by the detection of different metal-containing large organic ions. Finally, the results obtained emphasized the importance of studying the specific interactions taking place between organic and mineral phases in the chondrite matrix, in order to investigate their role in the evolution story of primitive organic matter in meteorite parent bodies.

The effect of interaction between Bacillus subtilis DBM and soil minerals on Cu(II) and Pb(II) adsorption

The effects of interaction between Bacillus subtilis DBM and soil minerals on Cu(II) and Pb(II) adsorption were investigated. After combination with DBM, the Cu(II) and Pb(II) adsorption capacities of kaolinite and goethite improved compared with the application of the minerals independently. The modeling results of potentiometric titration data proved that the site concentrations of kaolinite and goethite increased by 80% and 30%, respectively after combination with DBM. However, the involvement of functional groups in the DBM/mineral combinations resulted in lower concentrations of observed sites than the theoretical values and led to the enhancement of desorption rates by NH₄NO₃ and EDTA-Na₂. The DBM-mineral complexes might also help to prevent heavy metals from entering DBM cells to improve the survivability of DBM in heavy metal-contaminated environments. During the combination process, the extracellular proteins of DBM provided more binding sites for the minerals to absorb Cu(II) and Pb(II). In particular, an especially stable complexation site was formed between goethite and phosphodiester bonds from EPS to enhance the Pb(II) adsorption capacity. So, we can conclude that the DBM-mineral complexes could improve the Cu(II) and Pb(II) adsorption capacities of minerals and protect DBM in heavy metal-contaminated environments.

Abiotic phosphorus recycling from adsorbed ribonucleotides on a ferrihydrite-type mineral: Probing solution and surface species

Iron (Fe) (oxyhydr)oxide minerals, which are amongst most reactive minerals in soils and sediments, are known to exhibit strong adsorption of inorganic phosphate (P_i) and organophosphate (P_o) compounds. Beyond synthetic P_o compounds, much still remains unknown about the reactivity of these minerals to transform naturally-occurring P_o compounds to P_i, particularly with respect to solution versus surface speciation of P_o hydrolysis. To investigate this reactivity with a ferrihydrite-type mineral and ribonucleotides, we employed high-resolution liquid chromatography-mass spectrometry (LC-MS), X-ray absorption near-edge structure (XANES), Fourier-transform infrared (FTIR) spectroscopy, and molecular modeling. Kinetic experiments were conducted with the mineral (1 g L^-1) reacted with adenosine monophosphate, diphosphate, or triphosphate (respectively AMP, ADP, ATP; 50 µM). Analysis of solution organic species by LC-MS implied that only adsorption occurred with AMP and ADP but both adsorption and dephosphorylation of ATP were evident. Maximum adsorption capacities per gram of mineral were 40.6 ± 0.8 µmol AMP, 35.7 ± 1.6 µmol ADP, and 10.9 ± 1.0 µmol ATP; solution dephosphorylated by-products accounted for 15% of initial ATP. Subsequent XANES analysis of the surface species revealed that 16% of adsorbed AMP and 30% of adsorbed ATP were subjected to dephosphorylation, which was not fully quantifiable from the solution measurements. Molecular simulations predicted that ADP and ATP were complexed mainly via the phosphate groups whereas AMP binding also involved multiple hydrogen bonds with the adenosine moiety; our FTIR data confirmed these binding confirmations. Our findings thus imply that specific adsorption mechanisms dictate the recycling and subsequent trapping of P_i from ribonucleotide-like biomolecules reacted with Fe (oxyhydr)oxide minerals.

New Fe₂O₃-Clay@C Nanocomposite Anodes for Li-Ion Batteries Obtained by Facile Hydrothermal Processes

New iron-oxide-based anodes are prepared by an environmentally-friendly and low-cost route. The analysis of the composition, structure, and microstructure of the samples reveals the presence of a major hematite phase, which is accompanied by a certain concentration of an oxyhydroxide phase, which can act as a "lithium-reservoir". By using sodium alginate as a binder, the synthesized anodes display superior electrochemical response, i.e., high specific capacity values and high stability, not only versus Li but also versus a high voltage cathode in a full cell. From these bare materials, clay-supported anodes are further obtained using sepiolite and bentonite natural silicates. The electrochemical performance of such composites is improved, especially for the sepiolite-containing one treated at 400 °C. The thermal treatment at this temperature provides the optimal conditions for a synergic nano-architecture to develop between the clay and the hematite nanoparticles. High capacity values of ~2500 mA h g-1 after 30 cycles at 1 A g-1 and retentions close to 92% are obtained. Moreover, after 450 cycles at 2 A g-1 current rate, this composite electrode displays values as high as ~700 mA h g-1. These results are interpreted taking into account the interactions between the iron oxide nanoparticles and the sepiolite surface through hydrogen bonds. The electrochemical performance is not only dependent on the oxidation state and particle morphology, but the composition is revealed as a key feature.

Phosphorus saturation and superficial fertilizer application as key parameters to assess the risk of diffuse phosphorus losses from agricultural soils in Brazil

In Brazil, a steady increase in phosphorus (P) fertilizer application and agricultural intensification has been reported for recent decades. The concomitant P accumulation in soils potentially threatens surface water bodies with eutrophication through diffuse P losses. Here, we demonstrated the applicability of a soil type-independent approach for estimating the degree of P saturation (DPS; a risk parameter of P loss) by a standard method of water-soluble phosphorus (WSP) for two major soil types (Oxisols, Entisols) of the São Francisco catchment in Brazil. Subsequently, soil Mehlich-1P (M1P) levels recommended by Brazilian agricultural institutions were transformed into DPS values. Recommended M1P values for optimal agronomic production corresponded to DPS values below critical thresholds of high risks of P losses (DPS=80%) for major crops of the catchment. Higher risks of reaching critical DPS values due to P accumulation were found for Entisols due to their total sorption capacities being only half those of Oxisols. For complementary information on soil mineralogy and its influence on P sorption and P binding forms, Fourier transformation infrared (FTIR) spectroscopic analyses were executed. FTIR analyses suggested the occurrence of the clay minerals palygorskite and sepiolite in some of the analyzed Entisols and the formation of crandallite as the soil specific P binding form in the investigated Oxisols. Palygorskite and sepiolite can enhance P solubility and hence the risk of P losses. In contrast, the reshaping of superphosphate grains into crandallite may explain the chemical processes leading to previously observed low dissolved P concentrations in surface runoff from Oxisols. To prevent high risk of P losses, we recommend avoiding superficial fertilizer application and establishing environmental thresholds for soil M1P based on DPS. These measures could help to prevent eutrophication of naturally oligotrophic surface waters, and subsequent adverse effects on biodiversity and ecosystem function.

High-Resolution Analysis of Critical Minerals and Elements in Fe–Mn Crusts from the Canary Island Seamount Province (Atlantic Ocean)

Two Fe–Mn crusts among 35 samples, from six seamounts in the Canary Island Seamount Province, were selected as representatives of the endpoint members of two distinct types of genetic processes, i.e., mixed diagenetic/hydrogenetic and purely hydrogenetic. High-resolution analyses pursued the main aim of distinguishing the critical elements and their association with mineral phases and genetic processes forming a long-lived Fe–Mn crust. The Fe–Mn crust collected on the Tropic Seamount is composed of dense laminations of Fe-vernadite (>90%) and goethite group minerals, reflecting the predominance of the hydrogenetic process during their formation. Based on high-resolution age calculation, this purely hydrogenetic crust yielded an age of 99 Ma. The Fe–Mn crust collected on the Paps Seamount shows a typical botryoidal surface yielding an age of 30 Ma. electron probe microanalyzer (EPMA) spot analyses show two main types of manganese oxides, indicating their origin: (i) hydrogenetic Fe-vernadite, the main Mn oxide, and (ii) laminations of interlayered buserite and asbolane. Additionally, the occurrence of calcite, authigenic carbonate fluor-apatite (CFA) and palygorskite suggests early diagenesis and pervasive phosphatization events. Sequential leaching analysis indicated that Co, Ni, Cu, Ba and Ce are linked to Mn minerals. Therefore, Mn-oxides are enriched in Ni and Cu by diagenetic processes or in Co and Ce by hydrogenetic processes. On the other hand, Fe-oxides concentrate V, Zn, As and Pb. Moreover, the evidence of HREE enrichment related to Fe-hydroxides is confirmed in the mixed hydrogenetic/diagenetic crust.

Sorption of Hg(II) and Pb(II) Ions on Chitosan-Iron(III) from Aqueous Solutions: Single and Binary Systems

The present work describes the study of mercury Hg(II) and lead Pb(II) removal in single and binary component systems into easily prepared chitosan-iron(III) bio-composite beads. Scanning electron microscopy and energy-dispersive X-ray (SEM-EDX) analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and point of zero charge (pHpzc) analysis were carried out. The experimental set covered pH study, single and competitive equilibrium, kinetics, chloride and sulfate effects as well as sorption⁻desorption cycles. In single systems, the Langmuir nonlinear model fitted the experimental data better than the Freundlich and Sips equations. The sorbent material has more affinity to Hg(II) rather than Pb(II) ions, the maximum sorption capacities were 1.8 mmol·g-1 and 0.56 mmol·g-1 for Hg(II) and Pb(II), respectively. The binary systems data were adjusted with competitive Langmuir isotherm model. The presence of sulfate ions in the multicomponent system [Hg(II)-Pb(II)] had a lesser impact on the sorption efficiency than did chloride ions, however, the presence of chloride ions improves the selectivity towards Hg(II) ions. The bio-based material showed good recovery performance of metal ions along three sorption⁻desorption cycles.

Effectiveness and mechanisms of phosphate adsorption on iron-modified biochars derived from waste activated sludge

Excessive discharge of phosphate (P) into the surface water is the key factor to cause the eutrophication, so its removal has aroused much attention in recent years. In this study, different iron modification (chemical co-precipitation of Fe³⁺/Fe²⁺ or FeCl₃ impregnation) was used to improve the phosphate adsorption capacity of waste activated sludge (WAS)-based biochar. Comparative tests demonstrated that the FeCl₃-impregnated WAS-based biochar exhibited much superior phosphate adsorption capacity (111.0mg/g) in all as-prepared samples and performed well even under the interferences with pH and coexisting ions. X-ray diffraction (XRD) analyzes indicated that the iron in FeCl₃-impregnated WAS-based biochar existed mainly in amorphous phase, as hematite and amorphous hydroxides forms, which was of great benefit to the phosphate adsorption. Besides, ligand exchange plays important role in the adsorption of phosphate. The WAS-based biochar kept over 60% phosphate removal efficiency after five recycles.

Degradation of p-chloroaniline by FeO3−xH3−2x/Fe0 in the presence of persulfate in aqueous solution

Sulfate radical based advanced oxidation processes are promising techniques for the removal of organic compounds in aqueous solutions.

Rapid microwave assisted hydrothermal synthesis of porous α-Fe2O3 nanostructures as stable and high capacity negative electrode for lithium and sodium ion batteries

Porous α-Fe₂O₃ nanostructures were developed in the presence of a base catalyst by a rapid microwave assisted hydrothermal method.