Review of iron-free Fenton-like systems for activating H2O2 in advanced oxidation processes

Synthesis, properties, and applications of magnetic iron oxide nanoparticles

The hydroxyl radical (•OH) is one of the most powerful oxidizing agents, able to react unselectively and instantaneously with the surrounding chemicals, including organic pollutants and inhibitors. The •OH radicals are omnipresent in the environment (natural waters, atmosphere, interstellar space, etc.), including biological systems where •OH has an important role in immunity metabolism. We provide an extensive view on the role of hydroxyl radical in different environmental compartments and in laboratory systems, with the aim of drawing more attention to this emerging issue. Further research on processes related to the hydroxyl radical chemistry in the environmental compartments is highly demanded. A comprehensive understanding of the sources and sinks of •OH radicals including their implications in the natural waters and in the atmosphere is of crucial importance, including the way irradiated chromophoric dissolved organic matter in surface waters yields •OH through the H2O2-independent pathway, and the ...

Environmental Implications of Hydroxyl Radicals ((•)OH).

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Government Printing Office expands database access

This study presents a critical review on the application of magnetite-based catalysts to industrial wastewater decontamination by heterogeneous Fenton oxidation. The use of magnetic materials in this field started only around 2008 and continues growing increasingly year by year. The potential of these materials derives from their higher ability for degradation of recalcitrant pollutants compared to the conventional iron-supported catalysts due to the presence of both Fe(II) and Fe(III) species. In addition, their magnetic properties allow their easy, fast and inexpensive separation from the reaction medium. The magnetic materials applied up to now can be classified in three general groups: magnetic natural minerals, in-situ-produced magnetic materials and ferromagnetic nanoparticles. A survey of the catalysts investigated so far is presented paying attention to their nature and competitive features in terms of activity and durability.

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Preparation of magnetite-based catalysts and their application in heterogeneous Fenton oxidation – A review

Iron is the fourth most common element by mass in the Earth’s crust and forms compounds in several oxidation states. Iron (hydr)oxides, some of which form inherently and exclusively in the nanometre-size range, are ubiquitous in nature and readily synthesized. These facts add up to render many Fe (hydr)oxides suitable as catalysts, and it is hardly surprising that numerous studies on the applications of Fe (hydr)oxides in catalysis have been published. Moreover, the abundant availability of a natural Fe source from rocks and soils at minimal cost makes the potential use of these as heterogeneous catalyst attractive.

Besides those Fe (hydr)oxides that are inherently nanocrystalline (ferrihydrite, Fe5HO8·4H2O, and feroxyhyte, δ′-FeOOH), magnetite (Fe3O4) is often used as a catalyst because it has a permanent magnetization and contains Fe in both the divalent and trivalent states. Hematite, goethite and lepidocrocite have also been used as catalysts in their pure forms, doped with other cations, and as composites with carbon, alumina and zeolites among others.

In this review we report on the use of synthetic and natural Fe (hydr)oxides as catalysts in environmental remediation procedures using an advanced oxidation process, more specifically the Fenton-like system, which is highly efficient in generating reactive species such as hydroxyl radicals, even at room temperature and under atmospheric pressure. The catalytic efficiency of Fe (hydr)oxides is strongly affected by factors such as the Fe oxidation state, surface area, isomorphic substitution of Fe by other cations, pH and temperature.

Iron oxide catalysts: Fenton and Fenton-like reactions - a review

-Introduction. List of Contents. Symbols and Abbreviations. Foreword. Acknowledgments. -1: Theory and Characteristics of the Mossbauer Effect. Theory of the Mossbauer Effect. Magnetism. Hyperfine Interactions. Relaxation Effects. Line Intensities. Diffusional Broadening. Mossbauer Spectroscopy in Mineralogy and Minerals Processing. Summary. -2: Mossbauer Instrumentation. General Considerations. Source and Reference Absorber. Conventional Spectrometers. Other Spectrometers. Sample Environment. Sample preparation. Summary. -3: Data Analysis and Interpretation. Fitting using Simple Lorentzians. Tests of Goodness of Fit. Convolution and Deconvolution. Thickness Effects and Recoilless Fraction. Fitting of Thickness Broadened Lines. Fitting of Lines Broadened by a Hyperfine Parameter Distribution. Magnetic Relaxation and Superparamagnetism. The Non Uniqueness Problem. Problems in Fitting and Interpretation. Presentation of Results. Summary. -4: Bulk and Clay Sized Phyllosilicates. 1:1 Minerals: Kaolinite. 2:1 Minerals: Illite. Montmorillonite. Nontronite. Summary. - 5: Iron Oxides and Oxyhydroxides. Anhydrous Oxides: Hematite. Magnetite. Maghemite. Oxyhydroxides: Goethite. Ferrihydrite. Summary. -6: Sediments. Terrestrial Sediments. Freshwater Sediments. Marine Sediments. Airborne Particles. Summary. -7: Soils and Clays. Soils. Clays. Summary. -8: Weathering. Silicate Weathering. Sulfide Weathering and Acid Mine Drainage. Summary. -9: Metastable Materials. Green Rusts. Fine Particle Magnetite. Anoxic Sediments. Fe2+ Sulfates Produced by Acid Mine Drainage. Summary. -10: Coal. Coal Characterization. Heat and Chemical Treatment. Hydroliquefaction. Summary. -11: ClayFiring. Individual Minerals: Kaolinite. Illite. Montmorillonite. Nontronite. Samples of Complex Mineralogy. Summary. -12: Mineral processing. Introduction. Iron Ores. Titanium Ores. Other Processing Operations Involving Iron. Gold. Summary. References. Index.

Mössbauer Spectroscopy of Environmental Materials and Their Industrial Utilization

Mossbauer spectroscopy is a powerful technique for the characterization of materials formed in the weathering environment. Mossbauer studies of clay-sized phyllosilicates, however, are burdened with several problems: the samples are rarely monomineralic, they may be poor in iron, and only few iron-rich species order magnetically above 4.2 K. Site occupancies are difficult to determine, and cis and trans octahedral-OH site assignments are normally not possible. Unequivocal information that can be gained from such work thus is often restricted to the determination of the oxidation state of iron and average structural site distortions. Mossbauer data on iron oxides are generally more straightforward to interpret because these can be studied in the magnetically ordered state. A further asset of Mossbauer spectroscopy when studying iron oxides lies in its high sensitivity for magnetically ordered phases. Adverse effects ensuing from small particle size, interparticle interactions, non-stoichiometry and foreign-element substitution that often affect the Mossbauer parameters of iron oxides occurring in clays and soils can be at least partly offset by taking spectra at low temperatures.

Clays and clay minerals: What can Mössbauer spectroscopy do to help understand them?

Potential application of highly reactive Fe(0)/Fe3O4 composites for the reduction of Cr(VI) environmental contaminants.

57Fe Mossbauer spectroscopy reveals changes in iron valence and iron site geometry when clays and clay minerals are heated, and allows a distinction to be made between paramagnetic and magnetically ordered phases. Mossbauer spectra can thus reveal the extent of iron retention in silicate structures upon heating, the identity of iron oxides initially present or formed during the heating process and their transformations, and the character of the atmosphere under which heating was carried out. This makes Mossbauer spectroscopy the most effective tool for the characterization of changes induced by heating phyllosilicates and iron oxides.

Enver Murad

Papers

Iron oxide catalysts: Fenton and Fenton-like reactions - a review

Mössbauer Spectroscopy of Environmental Materials and Their Industrial Utilization

Clays and clay minerals: What can Mössbauer spectroscopy do to help understand them?

Potential application of highly reactive Fe(0)/Fe3O4 composites for the reduction of Cr(VI) environmental contaminants.

Clays and clay minerals: The firing process