and Fuels Changzhi Li,† Xiaochen Zhao,† Aiqin Wang,† George W. Huber,†,‡ and Tao Zhang*,† †State Key Laborotary of Catalysis, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China ‡Department of Chemical and Biological Engineering, University of WisconsinMadison, Madison, Wisconsin 53706, United States

Catalytic Transformation of Lignin for the Production of Chemicals and Fuels

Quantitative aspects of microbial crystalline iron(III) oxide reduction were examined using a dissimilatory iron(III) oxide-reducing bacterium (Shewanella alga strain BrY). The initial rate and lon...

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Microbial Reduction of Crystalline Iron(III) Oxides: Influence of Oxide Surface Area and Potential for Cell Growth

https://hal-upec-upem.archives-ouvertes.fr/hal-01721053/document

An overview on the removal of synthetic dyes from water by electrochemical advanced oxidation processes.

In most soils, FeIII oxides (group name) are the common source of Fe for plant nutrition. Since this Fe has to be supplied via solution, the solubility and the dissolution rate of the Fe oxides are essential for the Fe supply. Hydrolysis constants and solubility products (Ksp) describing the effect of pH on FeIII ion concentration in solution are available for the well-known Fe oxides occurring in soils such as goethite, hematite, ferrihydrite. Ksp values are usually extremely low ((Fe3+)·(OH)3=10−37−10−44). However, for each mineral type, Ksp may increase by several orders of magnitude with decreasing crystal size and it decreases with increasing Al substitution assuming ideal solid solution between the pure end-members. Based on such calculations a poorly crystalline goethite with a crystal size of 5 nm may well reach the solubility of ferrihydrite. The variations in Ksp are of relevance for soils because crystal size and Al substitution of soil Fe oxides vary considerably and can now be determined relatively easily. The concentration of Fe2+ in soil solutions is often much higher than that of Fe(III) ions. Therefore, redox potential strongly influences the activity of FeII. At a given pH and Eh, the activity of FeII is higher the higher Ksp of the FeIII oxide and thus also varies with the type of Fe oxide present. Besides the solubility, it is the dissolution rate which governs the supply of soluble Fe to the plant roots. Dissolution of Fe oxides takes place either by protonation, complexation or, most important, by reduction. Numerous dissolution rate studies with various FeIII oxides were conducted in strong mineral acids (protonation) and they have shown that besides the Fe oxide species, crystal size and/or crystal order and substitution are important determinative factors. For example, in soils, small amounts of a more highly soluble meta- or instable Fe oxide such as ferrihydrite with a large specific surface (several hundred m2g−1) may be essential for the Fe supply to the plant root. Its higher dissolution rate can also be used to quantify its amount in soils. Ferrihydrite can be an important component in soils with high amounts of organic matter and/or active redox dynamics, whereas highly aerated and strongly weathered soils are usually very low in ferrihydrite. On the other hand, dissolution rates of goethites decrease as their Al substitution increases. Much less information exists on the rate of reductive and chelative dissolution of Fe oxides which generally simulate soil conditions better than dissolution by protonation. Here again, type of oxide, crystal size and substitution are important factors. Organic anions such as oxalate, which are adsorbed at the surface, may weaken the Fe3+-O bonds and thereby increase reductive dissolution. As often observed in weathering, the dissolution features of the crystals appear to follow zones of weakness in the crystal.

Solubility and dissolution of iron oxides

Review on the application of modified iron oxides as heterogeneous catalysts in Fenton reactions

Simultaneous incorporation of Mn and Al in the goethite structure

An ATR-FTIR study of different phosphonic acids in aqueous solution.

The effect of pH in the adsorption of Alizarin and Eriochrome Blue Black R onto iron oxides.

Phenolic compounds removal is a very active research field due to occurrence and the toxicity of phenolic pollutants in industrial wastewaters. In order to make an a priori selection of the most efficient removal process for a target structure this contribution reviews and compares some of the mechanistic aspects of the oxidation in the presence of hydrogen peroxide and catalyzed by complexed iron which is the in-common element in Fenton systems, plant peroxidases and biomimetics. Different substrates were considered from the most basic phenol molecule to complex structures such as phenolic dyes and lignins. The reactivity of iron is related to its microenvironment generated by ligands and their electron withdrawing capacity thus conditioning the type of cleavage induced on hydrogen peroxide and the oxidation state change on iron upon reaction. The relative concentrations of organic to inorganic free radicals generated control the main catalytic action; i.e. from degradation up to mineralization in Fenton systems or oligomerization up to polymerization in plant peroxidases systems. Moreover, some reaction conditions as the peroxide concentration, the initial molar ratio of organic compounds to peroxide and the type of reaction solvent are identified as key factors to promote a desired action mechanism by peroxidases (and their biomimetics).

Elsa H. Rueda

Papers

Simultaneous incorporation of Mn and Al in the goethite structure

An ATR-FTIR study of different phosphonic acids in aqueous solution.

The effect of pH in the adsorption of Alizarin and Eriochrome Blue Black R onto iron oxides.

Mechanisms of radical generation in the removal of phenol derivatives and pigments using different Fe-based catalytic systems

Adsorption and dissolution in the system goethite/aqueous EDTA