Preparation of silicon-doped ferrihydrite for adsorption of lead and cadmium: Property and mechanism

In this study, Si-doped ferrihydrite (Si-Fh) was successfully synthesized by a simple coprecipitation method for removal of heavy metals in water. Subsequently, the physicochemical properties of Si-Fh before and after adsorption were further studied using several techniques. The Si-Fh exhibited good adsorption capacity for heavy metal ions such as Pb(II) and Cd(II). The maximum adsorption capacities of lead and cadmium are respectively 105.807, 37.986 mg/g. The distribution coefficients of the materials for Pb(II) and Cd(II) also showed a great affinity (under optimal conditions). Moreover, it was found that the adsorption fit well with the Freundlich isotherm and pseudo-second-order kinetic model which means this was a chemical adsorption process. It can be conducted from both characterization and model results that adsorption of Pb(II) and Cd(II) was mainly through the complexation interaction of abundance oxygen functional groups on the surface of Si-Fh. Overall, the Si-Fh adsorbents with many superiorities have potential for future applications in the removal of Pb(II) and Cd(II) from wastewater.     

Selective Formation of Metastable Ferrihydrite in the Chiton Tooth

Metastable precursors are thought to play a major role in the ability of organisms to create mineralized tissues. Of particular interest are the hard and abrasion‐resistant teeth formed by chitons, a class of rock‐grazing mollusks. The formation of chiton teeth relies on the precipitation of metastable ferrihydrite (Fh) in an organic scaffold as a precursor to magnetite. In vitro synthesis of Fh under physiological conditions has been challenging. Using a combination of X‐ray absorption and electron paramagnetic resonance spectroscopy, we show that, prior to Fh formation in the chiton tooth, iron ions are complexed by the organic matrix. In vitro experiments demonstrate that such complexes facilitate the formation of Fh under physiological conditions. These results indicate that acidic molecules may be integral to controlling Fh formation in the chiton tooth. This biological approach to polymorph selection is not limited to specialized proteins and can be expropriated using simple chemistry.     

Fe–Mn–Al–C Alloys: a Study of Their Corrosion Behaviour in SO2 Environments

The corrosion reaction of four Fe–Mn–Al alloys exposed to a cycling, dry–humid, SO₂ (0.001% by volume) polluted atmosphere was studied. ICEMS, XPS, AES-SAM and transmission Mössbauer spectroscopy at different temperatures were employed to characterize the corrosion products. The analytical results indicate that (i) ferrihydrite is the main component of the rust; (ii) there is an abundant presence of Mn²⁺ and SO₃ ^2–/SO₄ ^2– on the top of the corrosion layer, the concentration of SO₄ ^2– increasing with the number of cycles; and (iii) the magnetic hyperfine pattern exhibited by the series of low-temperature spectra of the rust is quite different from that observed in the rust formed under similar corrosive environments on iron and weathering steel. This latter finding is correlated with a slow rate of transformation of the Fe³⁺ species formed at the early stages of corrosion into -FeOOH, the usual final product of this type of corrosion processes. The sulphate anions, abundant inside the electrolyte during the wet periods, could be incorporated to the ferrihydrite structure being responsible for the Mössbauer spectral pattern recorded from the corrosion products at low temperatures.     

Effect of Precipitation Temperature and Number of Iron Atoms per Molecule on the Structure of Hydrated Iron(III) Oxyhydroxide Ferritin Cores Synthesised in vitro

Hyperfine Interactions - Horse spleen apoferritin was reconstituted with varying numbers of iron atoms per protein shell at 25 and 50°C. Samples with mean particle sizes ranging from...     

Theoretical study on Si-doped hexagonal boron nitride (h-BN) sheet: Electronic,magnetic properties,and reactivity

The properties and reactivity of Si-doped hexagonal boron nitride (h-BN) sheets were studied using density functional theory (DFT) methods. We find that Si impurity is more likely to substitute the boron site (Si_B) due to the low formation energy. Si-doping severely deforms h-BN sheet, resulting in the local curvature changes of h-BN sheet. Moreover, Si-doping introduces two spin localized states within the band gap of h-BN sheet, thus rendering the two doped systems exhibit acceptor properties. The band gap of h  -BN sheet is reduced from ∼4.70 eV$\sim 4.70\text{eV}$ to 1.24 (for Si_B) and 0.84 eV (for Si_N), respectively. In addition, Si-doped one exhibits higher activity than pristine one, endowing them wider application potential.     

Mössbauer and X-Ray Diffraction Investigations of a Series of B-Doped Ferrihydrites

X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy are used to characterize the influence of borate on two-line ferrihydrite's structure and develop likely models for its attachment. Particle sizes were in the 2–4 nm range, and as borate sorption increased, the ferrihydrite particle size decreased. The d-spacings of two-line ferrihydrite increased with increased borate adsorption. Isomer shift and quadrupole splitting exhibit slight increasing trends as well. Also, the phase transformation temperature of ferrihydrite to hematite is significantly raised due to borate coating of the surface. We suggest borate is sorbed onto the surface by attachment to the oxygen corners of the iron octahedra that are on the surface of the nanoparticles, placing boron in a tetrahedral molecular geometry.     

低温下Fe(II)对Ferrihydrite相转化的催化作用研究

研究了在低温、近中性条件下,在微量Fe(II)离子存在下Ferrihydrite(又称为水合氧化铁hydrousironoxide)的相转化过程.结果表明,微量Fe(II)离子的存在不仅可以加速Ferrihydrite的相转化过程,而且其相转化产物的组成也与没有Fe(II)离子存在时产物的组成有所不同,即除了α-FeOOH和α-Fe2O3外,还形成了γ-FeOOH;相转化过程既与阴离子的种类、反应温度、反应时间等因素有关,也与Fe(II)离子存在状态有关;Fe(II)离子通过催化Ferrihydrite的溶解过程,从而加速整个相转化过程.对该过程的深入研究将对认识和了解自然条件下铁氧化物的形成与相互转化具有重要意义.     

Application of the diffusive gradients in thin films technique for available potassium measurement in agricultural soils: Effects of competing cations on potassium uptake by the resin gel

The utilization of Amberlite (IRP-69 ion-exchange resin, 100–500 wet mesh) as the binding phase in the diffusive gradients in thin films (DGT) technique has shown potential to improve the assessment of plant-available K in soils. The binding phase has recently been optimized by using a mixed Amberlite and ferrihydrite (MAF) gel which results in linear K uptake over extended deployment periods and in solutions with higher K concentrations. As restriction of K uptake by Ca on the Amberlite based resin gel has been previously proposed, potential competing effects of Ca²⁺, Mg²⁺ and NH₄⁺ on K uptake by the MAF gel were investigated. These cations had no effect on K elution efficiency which was 85%. However, K uptake by the MAF gel was restricted in the presence of competing cations in solution. Consequently, the diffusion coefficient of K decreased in the presence of cations compared to previous studies but was stable at 1.12 × 10⁻⁵ cm² s⁻¹ at 25 °C regardless of cation concentrations. Uptake of K by the DGT device was affected by the presence of excessive Ca in more than 30% of twenty typical Australian agricultural soils. However, this problem could be circumvented by using a shorter deployment time than the normal 24 h. Moderate correlation of concentrations of K extracted by DGT with Colwell K (extracted by NaHCO₃, R² = 0.69) and NH₄OAc K (R² = 0.61) indicates that DGT measures a different pool of K in soils than that measured by the standard extractants used. In addition, the MAF gel has the ability to measure Ca and Mg simultaneously.     

热辅助存储磁盘硅掺杂非晶碳薄膜氧化的ReaxFF反应力场分子动力学模拟

Heat-assisted magnetic recording (HAMR) is one of the promising ways to extend the magnetic recording area density to 1 Tb·in^-2 in hard disk drives (HDDs).High temperature induced by laser heating can cause carbon overcoat (COC) oxidation.Reactive molecular dynamics (MD) simulations are performed to investigate the oxidation process of silicon-doped amorphous carbon (a-C:Si) films for HAMR application.The atomic details of the structure evolution and oxidation process are investigated, and, the oxidation mechanism of the a-C:Si film is clarified.The effect of the duration of laser irradiation on the oxidation of the a-C:Si film is investigated.The oxidation occurs during heating and the beginning of cooling process.Both volume expansion during heating process and cluster of carbon atoms during cooling process increase the rate of sp² carbon.Because of the decrease in the amount of unsaturated silicon atoms and low diffusion coefficient of atomic oxygen, the oxidation rate of the a-C:Si film decreases with laser irradiation cycles.The molecular oxygen is the oxidant due to surface defect of a-C:Si film.The atomic strains break the O-O bonds in Si-O-O-Si linkages and rearrange the surface oxide layers, and process the oxidation of the a-C:Si film.