Copper-doped akaganeite: Application in catalytic Cupro-Fenton reactions for oxidation of methylene blue

Highly active Fenton-like catalyst derived from solid waste-iron ore tailings using wheat straw pyrolysis

The pollutants degradation rate of iron ore tailings-based heterogeneous catalysts is the main factor limiting its application. Herein, an iron ore tailings-based Fenton-like catalyst (I/W(3:1)-900-60) with a relatively fast catalysis rate was constructed by co-pyrolysis (900°C, 60 min holding time) of iron ore tailings and wheat straw with a mass ratio of 3:1. With wheat straw blending, the generated I/W(3:1)-900-60 presented a larger surface area (24.53 m²/g), smaller pore size (3.76 nm), reduced iron species (Fe²⁺ from magnetic), and a higher catalytic activity (0.0229 min^-1) than I-900-60 (1.32 m²/g, 12.87 nm, 0.012 min^-1) pyrolyzed using single iron ore tailing under the same pyrolysis conditions. In addition, biochar and iron ore tailings in I/W(3:1)-900-60 were tightly combined through chemical bonding. The optimal catalyst remains active after three cycles, indicating its catalytic stability and recyclability. The good Fenton-like methylene blue degradation efficiency of I/W(3:1)-900-60 was ascribed to the sacrificial role of biochar, as well as the electron transfer between biochar and iron active sites or the redox cycles of ≡Fe³⁺/Fe²⁺. This finding provides a facile construction strategy for highly active iron ore tailings-based Fenton-like catalyst and thereby had a great potential application in wastewater treatment.

Green synthesis of akaganéite (β-FeOOH) nanocomposites as peroxidase-mimics and application for discoloration of methylene blue

This work reports an environmentally benign and readily scalable process for production of akaganéite (β-FeOOH) nanocomposites by using abundant gallic acid or grape seed tannins and urea. Influences from those phytochemicals on the properties of β-FeOOH nanocomposites were investigated by X-ray powder diffraction, Fourier transform infrared spectroscopy, Thermogravimetric analysis, Scanning electron microscopy, Transmission electron microscopy, UV-Vis spectroscopy and Photoluminescence. The addition of 0.1% (w/v) grape seed tannins or gallic acid (640 mg L^-1) solution yielded single-crystalline β-FeOOH nanocomposites with reduced dimensions, increased porosities and BET surface area, and no oxidized impurities such as hematite (Fe₂O₃) were formed. The added grape seed tannins (S_0.8) or gallic acid together with less urea (0.8 M) produced β-FeOOH nanocomposites with higher activities as peroxidase mimics compared to those prepared with only urea (C_0.8). Moreover, S_0.8 was more efficient in methylene blue (MB) discoloration compared to C_0.8 at all three pH values of 4, 7 and 11, and the S_0.8-mediated MB degradation pathways at pH 4 and 7 were different from those at pH 11 due to the generation of different predominant oxidants. The overall MB discoloration efficacies by S_0.8 at pH 4, 7 and 11 were combinative effects of both physical adsorption and chemical reactions. These β-FeOOH nanocomposites possess great potential as peroxidase mimics for facile monitoring of excess hydrogen peroxide and applications in environmental remediation.

Mineral characterization of the biogenic Fe(III)(hydr)oxides produced during Fe(II)-driven denitrification with Cu, Ni and Zn

The recovery of iron and other heavy metals by the formation of Fe(III) (hydr)oxides is an important application of microbially-driven processes. The mineral characterization of the precipitates formed during Fe(II)-mediated autotrophic denitrification with and without the addition of Cu, Ni, and Zn by four different microbial cultures was investigated by X-ray fluorescence (XRF), Raman spectroscopy, scanning electron microscopy equipped with energy dispersive X-Ray analyzer (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and X-ray Powder Diffraction (XRD) analyses. Fe(II)-mediated autotrophic denitrification resulted in the formation of a mixture of Fe(III) (hydr)oxides composed of amorphous phase, poorly crystalline (ferrihydrite) and crystalline phases (hematite, akaganeite and maghemite). The use of a Thiobacillus-dominated mixed culture enhanced the formation of akaganeite, while activated sludge enrichment and the two pure cultures of T. denitrificans and Pseudogulbenkiania strain 2002 mainly resulted in the formation of maghemite. The addition of Cu, Ni and Zn led to similar Fe(III) (hydr)oxides precipitates, probably due to the low metal concentrations. However, supplementing Ni and Zn slightly stimulated the formation of maghemite. A thermal post-treatment performed at 650 °C enhanced the crystallinity of the precipitates and favored the formation of hematite and some other crystalline forms of Fe associated with P, Na and Ca.

Use of an Environmental Pollutant From Hexavalent Chromium Removal as a Green Catalyst in The Fenton Process

The present study refers to the use of an environmental pollutant generated during the removal of hexavalent chromium from aqueous media. This pollutant is a material with catalytic properties suitable for application in the oxidative degradation of problematic organic compounds. The material, initially used as an adsorbent, is a composite prepared by modifying the crystalline phases of iron oxides together with the chitosan (CT-FeCr). Chemical and morphological characterizations of the materials were performed using SEM analysis coupled with EDS, XRD and DSC. The CT-FeCr beads were used in the degradation of methylene blue dye (MB) and showed excellent degradation potential (93.6%). The presence of Cr on the surface of the catalyst was responsible for the increase in catalytic activity compared to the CT-Fe and pure magnetite materials. The product of the effluent treatment and the presence of the catalyst itself in the environment do not pose toxic effects. In addition, the CT-FeCr beads showed catalytic stability for several consecutive reaction cycles with possible technical and economic viability. The concept of "industrial symbiosis" may be applied to this technology, with that term relating to the reuse of a byproduct generated in one particular industrial sector by another as a raw material.

Use of iron ore tailing from tailing dam as catalyst in a fenton-like process for methylene blue oxidation in continuous flow mode

The global demand for iron ore with high iron contents to supply the steel industry is associated, in most countries, with the generation of tailings from mineral processing. The chemical compositions of iron ore tailings (basically Fe₂O₃ and SiO₂) make them an excellent candidate as a catalyst for advanced oxidation processes (AOPs), especially the Fenton process and its derivatives. Therefore, this paper aimed to transform iron ore tailings from tailing dams into catalysts able to activate H₂O₂ for the purpose of treating, in a continuous flow, effluents contaminated with organic dyes, employing methylene blue as a model molecule. The mineralogical characteristics of in natura tailings, such as the associations between iron oxides and quartz and the particle sizes of iron oxides, are favourable points for their transformation into catalysts by Fenton-like processes. Different pellet geometries and binding agents were evaluated to optimize the dye removal. Pellet pretreatment in a CH₄ atmosphere at 550 °C for 2 h with 10% bentonite as a binding agent (RCSP sample) resulted in the removal of approximately 80% of dye. Kinetic removal data show the good stability of the catalyst in the flow system. Significant catalytic activity loss was not observed after four runs, and data from TG-MS indicate that there is a synergetic mechanism between the adsorption, radical attack and desorption processes of the substrate on the catalyst surface.

Pt supported on long-rod β-FeOOH as an efficient catalyst for HCHO oxidation at ambient temperature

A novel Pt/FeOOH catalyst containing highly active interface between Pt and β-FeOOH (010) plane have been developed for HCHO oxidation at ambient temperature.

Influences of As(v), Sb(iii), and Hg(ii) ions on the nucleation and growth of akaganeite

The physico-chemical properties of akaganeite are known to be modified when formed in the presence of ions, but there are no reports on these effects for arsenic, antimony and mercury.

Synthesis of different crystallographic FeOOH catalysts for peroxymonosulfate activation towards organic matter degradation

In this study, different crystalline structures of FeOOH have been prepared. α-FeOOH was synthesized through a hydrothermal method, whereas β-FeOOH was synthesized via a direct hydrolysis method. Moreover, γ- and δ-FeOOH were prepared by precipitation methods through slow and quick oxidation, respectively. On this basis, their crystal structure, morphology, and surface area were measured. Then, all the synthesized materials were applied to activate peroxymonosulfate (PMS) to generate sulfate radicals (SO4 -˙) for acid orange 7(AO7) degradation. Compared with α-FeOOH, β-FeOOH, and γ-FeOOH, δ-FeOOH showed more efficient decolorization of AO7 in the catalytic system because of its abundant surface area and crystalline structure. The effects of several parameters in the δ-FeOOH/PMS/AO7 system were investigated. The results show that the initial pH, which is related to the features of surface hydroxyl groups, is the decisive factor, and excellent catalytic activity is maintained in the pH range 5-8. The increase of catalyst dosage and appropriate increase of PMS concentration contributed to promote the degradation effect. However, self-quenching was observed in a high PMS concentration system. Moreover, δ-FeOOH was stable after six consecutive cycles, and the leaching of iron ions was negligible. According to the quenching test and electron spin resonance analysis, both SO4 -˙ and ˙OH were the dominant radicals for AO7 degradation.