Iron silicate perovskite and postperovskite in the deep lower mantle.

Ferromagnesian silicates are the dominant constituents of the Earth's mantle, which comprise more than 80% of our planet by volume. To interpret the low shear-velocity anomalies in the lower mantle, we need to construct a reliable transformation diagram of ferromagnesian silicates over a wide pressure-temperature (P-T) range. While MgSiO3 in the perovskite structure has been extensively studied due to its dominance on Earth, phase transformations of iron silicates under the lower mantle conditions remain unresolved. In this study, we have obtained an iron silicate phase in the perovskite (Pv) structure using synthetic fayalite (Fe2SiO4) as the starting material under P-T conditions of the lower mantle. Chemical analyses revealed an unexpectedly high Fe/Si ratio of 1.72(3) for the Pv phase in coexistence with metallic iron particles, indicating incorporation of about 25 mol% Fe2O3 in the Pv phase with an approximate chemical formula (Fe2+0.75Fe3+0.25)(Fe3+0.25Si0.75)O3. We further obtained an iron silicate phase in the postperovskite (PPv) structure above 95 GPa. The calculated curves of compressional (VP) and shear velocity (VS) of iron silicate Pv and PPv as a function of pressure are nearly parallel to those of MgSiO3, respectively. To the best of our knowledge, the iron silicate Pv and PPv are the densest phases among all the reported silicates stable at P-T conditions of the lower mantle. The high ferric iron content in the silicate phase and the spin-crossover of ferric iron at the Si-site above ~55 GPa should be taken into account in order to interpret the seismic observations. Our results would provide crucial information for constraining the geophysical and geochemical models of the lower mantle.

Inhibition of acid rock drainage with iron-silicate or phosphate film: in rainy and submerged environments.

Iron phosphate-based coating and iron silicate-based coating were used to inhibit the oxidation of sulfide minerals in rainy and submerged environments. The inhibiting effectiveness of coating agents on the oxidation of iron sulfide minerals was investigated using pyrite and rock samples resulting from acid drainage. The film formed with both surface-coating agents was identified by pyrite surface analysis. It was also confirmed that the formation of coatings varies depending on the crystallographic orientation. The inhibitory effects under rainy and submerged conditions were investigated using column experiments. Submerged conditions accelerated deterioration compared to that under rainy conditions. Iron phosphate coating had a significantly better oxidation-inhibitory effect (84.86-98.70%) than iron silicate coating (56.80-92.36%), and at a concentration of 300 mM, H+ elution was inhibited by more than 90% throughout the experiment. Furthermore, methods for effective film formation were investigated in terms of producing Fe3+; (1) application of coating agents mixed with oxidant (H2O2), (2) application of coating agent after the use of the oxidant. In a rainy environment, applying iron phosphate-based coating using the sequential method showed oxidation inhibition effects for cycles 1-9, whereas applying the mixed material showed effects for cycles 9-13. The use of a surface-coating agent after applying an oxidant did not inhibit oxidation. The surface coating agent and the oxidizing agent should be applied as a mixture to form a film.

Enhanced silicate remediation in cadmium-contaminated alkaline soil: Amorphous structure improves adsorption performance.

Silicates have been used as soil heavy metal passivators, but low remediation efficiency limited their development. In order to solve this problem, in this paper, an economical and environmentally friendly amorphous iron silicate was prepared by a simple co-precipitation method. It could be proved from the passivation experiments that the remediation efficiency of amorphous iron silicate (AIS) on Cd-contaminated soil was better than that of natural silicates (montmorillonite and diatomite), which reflected the superiority of amorphous materials. Plant experiments showed that AIS could effectively inhibit the absorption and accumulation of Cd2+ in the edible parts of garlic. In addition, it may effectively reduce the potential ecological risk assessment of soil, and its immobilization mechanism of Cd2+ includes electrostatic adsorption, co-precipitation, ion exchange, and complexation of surface functional groups. This study demonstrates the advantages of amorphous iron silicate as a new functional material in the remediation of Cd-contaminated soil and provides a reference for the development and application of environment-friendly passivators.

Construction of TiO2-x Confined by Layered Iron Silicate toward Efficient Visible-Light-Driven Photocatalysis-Fenton Synergistic Removal of Organic Pollutants.

The photocatalysis-Fenton synergistic reaction has great potential for water purification but generally suffers from unsatisfactory electron transfer due to an undesirable interface structure. Herein, we developed a novel heterojunction of oxygen vacancy-rich TiO2-x confined in the layer space of a synthetic montmorillonite-like iron silicate (denoted as TiO2-x/FeMMT) that addresses the issue mentioned above. Two-dimensional layered montmorillonite-like silicates in heterojunctions as a support not only provided more active sites for the reaction but also induced oxygen vacancies in TiO2-x through interfacial effects to enhance the visible-light harvesting ability. Notably, such loading TiO2-x as an electron donor accelerated the Fe(III)/Fe(II) redox cycling and facilitated the effective activation of H2O2, while Fe(III) in the montmorillonite-like silicate as electron trap sites greatly improved the separation of photogenerated electron-hole pairs. More interestingly, the internal electric field and oxygen vacancies (Vo) existing at the interface realized the directional migration of photogenerated electrons and improved the energy band structure of the heterojunction, respectively. Eventually, the TiO2-x/FeMMT composites exhibited superior photocatalysis-Fenton performance toward degradation removal of phenol, dinotefuran (DIN), and sulfamethoxazole (SMX) under visible-light irradiation. This paves the way for the rational design of high-efficiency heterojunction catalysts based on layered silicates for environment-related applications.

The silicon active sites driven by oxygen vacancies in iron silicate for activating peroxymonosulfate.

Most metal sites and some non-metallic sites such as carbon and nitrogen are usually considered to be traditional active sites during peroxymonosulfate (PMS) activation. However, as an important non-metallic element, the actual role of silicon (Si) in PMS activation still remains unclear. In this work, taking iron silicate (FeSi) as an example, the role of the Si region in PMS activation was clearly revealed. The experiments and density functional theory (DFT) calculation results showed that besides the traditional Fe sites, the Si also played a non-negligible role during PMS activation. In FeSi containing oxygen vacancies (Ovac), Fe-Si was the active site instead of Fe-Fe. The Bard charge results implied that the presence of Ovac tuned the electronic properties of FeSi, making the Si participate in PMS activation. This work deepened understanding of the role of Si in silicates for PMS activation and provided a theoretical basis for the development of excellent Si-based catalysts.

Comparison of nanowire pellicles for plasma membrane enrichment: coating nanowires on cell.

A study is reported on the effect of nanowire density on the ease of pellicle formation and the enrichment of plasma membrane proteins for analysis by mass spectrometry. An optimized synthesis is reported for iron silicate nanowires with a narrow size range of 900 ±400 nm in length and 200 nm diameter. The nanowires were coated with Al2O3 and used to form pellicles around suspended multiple myeloma cells, which acted as a model for cells recovered from tissue samples. Lighter alumina-coated silica nanowires were also synthesized (Kim et al. 2013), which allowed a comparison of the construction of the two pellicles and of the effect of nanowire density on plasma membrane enrichment. Evidence is offered that the dense nanowire pellicle does not crush or distort these mammalian cells. Finally, the pellicles were incorporated into a mass-spectrometry-based proteomic workflow to analyze transmembrane proteins in the plasma membrane. In contrast to a prior comparison of the effect of density with nanoparticles pellicles (Choksawangkarn et al. 2013), nanowire density was not found to significantly affect the enrichment of the plasma membrane. However, nanowires with a favorable aspect for pellicle formation are more easily and reliably produced with iron silicate than with silica. Additionally, the method for pellicle formation was optimized through the use of iron silicate nanowires (ISNW), which is crucial to the improvement of PM protein enrichment and analysis.