Poly(catechol) modified Fe3O4 magnetic nanocomposites with continuous high Fenton activity for organic degradation at neutral pH

Fe3O4 magnetic nanoparticles (MNPs) have been widely used as a recyclable catalyst in Fenton reaction for organic degradation. However, the pristine MNPs suffer from the drawbacks of iron leaching in acidic conditions as well as the decreasing catalytic activity of organic degradation at a pH higher than 3.0. To solve the problems, Fe3O4 MNPs were modified by poly(catechol) (Fe3O4/PCC MNPs) using a facile chemical co-precipitation method. The poly(catechol) modification improved both the dispersity and the surface negative charges of Fe3O4/PCC MNPs, which are beneficial to the catalytic activity of MNPs for organics degradation. Moreover, the poly(catechol) modification enhanced the efficiency of Fe(II) regeneration during Fenton reaction due to the acceleration of Fe(III) reduction by the phenolic/quinonoid redox pair. As a result, the Fenton reaction with Fe3O4/PCC MNPs could efficiently degrade organic molecules, exampled by methylene blue (MB), in an expanded pH range between 3.0 and 10.0. In addition, Fe3O4/PCC MNPs could be reused up to 8 cycles for the MB degradation with negligible iron leaching of lower than 1.5 mg L-1. This study demonstrated Fe3O4/PCC MNPs are a promising heterogeneous Fenton catalysts for organic degradation.

Utilization of Crystalline and Amorphous Silica as a Sintering Inhibitor in Iron/Iron Oxide Thermochemical Water Splitting Cycle

Hydrogen as a chemical fuel and energy carrier can provide the path to solar energy storage to overcome the intermittency issues. Hydrogen can be produced by various methods; among them is the thermochemical water splitting of metal/metal oxide reduction oxidization (redox) reactions. Many redox cycles were identified, including the non-volatile redox pair, such as the iron/iron oxide. This redox pair has the capability to produce Hydrogen with rapid reaction rates especially when it is used in powder form due to the high specific reactive surface area. Yet, this pair suffers from sintering at temperatures exceeding 500°C. Sintering adversely affects the Hydrogen production process and inhibits the recycling of the powder. To overcome sintering, experimental investigations using elemental iron and silica were conducted as detailed in this paper. The oxidation of elemental iron (Fe) powder by steam to produce Hydrogen was carried out using a fluidized bed reactor. The investigations aimed at developing a practical sintering inhibition technique that can allow repeated redox cycles, stabilize the powder reactivity, and maintain Hydrogen production. The experimental investigations involved varying the fluidized bed temperature between 630–968°C. The steam mass flow rate was set to 2 g/min. To inhibit sintering, solid-state mixing of crystalline, or amorphous silica with porous iron powder was used at various iron/silica volume fractions. The investigations showed that mixing iron with silica hinders the sintering but reduces the Hydrogen yield. Mixing iron with crystalline silica with 0.5, 0.67, and 0.75 apparent volume fraction reduces the Hydrogen yield compared to pure iron by 20, 30, and 45%, respectively. Mixing iron with amorphous silica reduces the Hydrogen yield by 35 and 45%, as compared to pure iron, for iron 0–250 and 125–355 µm particle size distribution, respectively. The Hydrogen production rate for iron/amorphous silica mixtures surpassed that of the iron/crystalline silica. Mixing iron with amorphous silica prevented sintering at elevated bed temperatures in the range of 850°C, and only clumping occurred. The clumped samples restored their original powder condition with minimum agitation. Thus, solid-state mixing of amorphous silica with iron powder can be a promising technique to retard iron/iron oxide particles sintering.

Exploring the Potential of Cytochrome P450 CYP109B1 Catalyzed Regio—and Stereoselective Steroid Hydroxylation

Cytochrome P450 enzyme CYP109B1 is a versatile biocatalyst exhibiting hydroxylation activities toward various substrates. However, the regio- and stereoselective steroid hydroxylation by CYP109B1 is far less explored. In this study, the oxidizing activity of CYP109B1 is reconstituted by coupling redox pairs from different sources, or by fusing it to the reductase domain of two self-sufficient P450 enzymes P450RhF and P450BM3 to generate the fused enzyme. The recombinant Escherichia coli expressing necessary proteins are individually constructed and compared in steroid hydroxylation. The ferredoxin reductase (Fdr_0978) and ferredoxin (Fdx_1499) from Synechococcus elongates is found to be the best redox pair for CYP109B1, which gives above 99% conversion with 73% 15β selectivity for testosterone. By contrast, the rest ones and the fused enzymes show much less or negligible activity. With the aid of redox pair of Fdr_0978/Fdx_1499, CYP109B1 is used for hydroxylating different steroids. The results show that CYP109B1 displayed good to excellent activity and selectivity toward four testosterone derivatives, giving all 15β-hydroxylated steroids as main products except for 9 (10)-dehydronandrolone, for which the selectivity is shifted to 16β. While for substrates bearing bulky substitutions at C17 position, the activity is essentially lost. Finally, the origin of activity and selectivity for CYP109B1 catalyzed steroid hydroxylation is revealed by computational analysis, thus providing theoretical basis for directed evolution to further improve its catalytic properties.

Cyclic oxygen exchange capacity of Ce-doped V2O5 materials for syngas production via high-temperature thermochemical-looping reforming of methane

Cerium doping into the V2O5 lattice forms a reversible V2O3/VO redox pair after sequential methane partial oxidation and CO2/H2O splitting reactions and produces syngas (H2, CO) with fast rates and high oxygen exchange capacity.

Nematic Ordering Driven by Atomic-scale Multipoles

We found a beautiful empirical rule (α ∝ <em>η</em>^-0.4) between the electrochemical Seebeck coefficient <em>α</em> for Fe²⁺/Fe³⁺ redox pair and viscosity coefficient <em>η</em> of the organic solvent.

A Solvent Viscosity-dependent Thermoelectric Conversion Efficiency

We found a beautiful empirical rule (α ∝ <em>η</em>^-0.4) between the electrochemical Seebeck coefficient <em>α</em> for Fe²⁺/Fe³⁺ redox pair and viscosity coefficient <em>η</em> of the organic solvent.