Energy filtered transmission electron microscopy for the physico-chemical characterization of aquatic submicron colloids

A combination of energy filtered transmission electron microscopic (EF-TEM) procedures is proposed for the non-perturbing physico-chemical characterization of submicron mineral and organic colloids in aquatic systems. Synthetic hematite microparticles and xanthan polysaccharides were used as well-characterized model colloids in order to determine the optimum EF-TEM analysis conditions. In this paper, it is demonstrated that (i) our model colloids are morphologically representative of naturally occurring mineral/organic associations, (ii) EF-TEM allows the detection of fine xanthan ultrastructures without artefacts of conventional staining methods and (iii) submicron hematite particles can be specifically visualized and spectrometrically measured by EF-TEM within a hematite/xanthan mixture. This EF-TEM procedure appears to be appropriate for the characterization of real aquatic samples.     

Complexes of Fulvic Acid on Hematite Interfaces: Characterization and Photochemical Properties

Fourier transform infrared spectroscopy (FTIR), combined with ultraviolet-visible spectroscopy (UV-Vis) and transmission electron micrograph (TEM), has been used to observe the interaction between fulvic acid (FA) and hematite. The FTIR data have shown that the interaction mechanism corresponds mainly to the ligand-exchange involving carboxylic functional groups of the FA and hematite surface sites. The general trends included an increase in the content of Fe(III)-humate complexes on hematite surfaces accompanied by a decrease in pH and an increasing in the ionic strength. Both UV-Vis spectroscopy and TEM images have shown that hematite can interplay with FA under acidic conditions. In particular, the TEM images have shown that the presence of FA can significantly alter the characteristics of the hematite surfaces. Photochemical experiments have shown that hematite promotes the phototransformation of lindane (-HCH), whereas the presence of FA adversely affects the phototransformation of the target pollutant. The hematite coated with FA displayed a somewhat better catalyzing capability compared to the hematite only.     

Brownian dynamics simulations with spin Brownian motion on the negative magneto-rheological effect of a rod-like hematite particle suspension

We have investigated the behaviour of a suspension of magnetic rod-like hematite particles in a simple shear flow with the addition of an applied magnetic field. A significant feature of the present hematite particle suspension is the fact that the magnetic moment of the hematite particle lies normal to the particle-axis direction. From simulations, we have attempted to clarify the dependence of the negative magneto-rheological effect on the particle aggregation and orientational distribution of particles. The present Brownian dynamics method has a significant advantage in that it takes into account the spin rotational Brownian motion about the particle axis in addition to the ordinary translational and rotational Brownian motion. The net viscosity is decomposed into three components and discussed at a deeper level and in detail: these three viscosity components arise from (1) the torque due to the magnetic particle–field interaction, (2) the torque and (3) the force due to the interaction between particles. It is found that a slight change in the orientational distribution has a significant influence on the negative magneto-rheological effect. In a relatively dense suspension, the viscosity components arising from an applied magnetic field and the interaction between particles come to change rapidly for a certain strength of the magnetic particle–particle interaction, which is due to the onset of the formation of raft-like clusters.     

Raman Microspectroscopic study of Iberian pottery from the La Vispesa archaeological site,Spain

Raman microspectroscopy has been employed for the characterization of 16 samples of ancient Iberian pottery. These sherds of vessels were found in the archaeological site of La Vispesa in Tamarite de Litera (Huesca, Spain) and correspond to the Iberian time. The composition of certain mineral phases such as non‐plastic inclusions has been particularly considered with a view to obtaining information on the source materials and their provenance, as well as the technological conditions of ceramic production. Typical minerals such as calcite and quartz were found in most of the samples. The presence of anatase in a group of the samples suggested the use of different clays in the production of the vessels. Furthermore, the absence of rutile in these samples, together with the identification of calcite, is indicative of a mild firing temperature. Hematite was identified in all samples, both in the ceramic body and in the decoration. Differences in the position of the bands and relative intensities characterized hematite in terms of crystallinity and origin. An attempt to assign the samples to different production centers was made according to their chemical composition and morphology. Copyright © 2011 John Wiley & Sons, Ltd.     

The Role of Surface States in the Oxygen Evolution Reaction on Hematite

Hematite (α‐Fe₂O₃) is an extensively investigated semiconductor for photoelectrochemical (PEC) water splitting. The nature and role of surface states on the oxygen evolution reaction (OER) remain however elusive. First‐principles calculations were used to investigate surface states on hematite under photoelectrochemical conditions. The density of states for two relevant hematite terminations was calculated, and in both cases the presence and the role of surface states was rationalized. Calculations also predicted a Nerstian dependence on the OER onset potential on pH, which was to a very good extent confirmed by PEC measurements on hematite model photoanodes. Impedance spectroscopy characterization confirmed that the OER takes place via the same surface states irrespective of pH. These results provide a framework for a deeper understanding of the OER when it takes place via surface states.     

Negative magneto-rheological effect of a dispersion composed of spindle-like hematite particles

We have experimentally investigated the negative magneto-rheological effect that is theoretically predicted to appear in a dispersion composed of spindle-like hematite (α-Fe₂O₃) particles. The spindle-like hematite particles were synthesized by aging a solution of FeCl₃ and KH₂PO₄ for 72?h at 373?K. The particle size distribution was determined by digital image analysis from electronic microscope observation of the particles. In the present study we considered a glycerol–water-based dispersion in order to clarify the influence of the shear rate and the magnetic field strength on the negative magneto-rheological effect. Measurement of the viscosity was carried out using a rotational-type rheometer in an external magnetic field generated by Helmholtz coils. The main results obtained can be summarized as follows. The viscosity of a hematite/glycerol–water dispersion relative to that with no applied magnetic field decreases with increasing magnetic field strength: that is, we observed the negative viscosity effect that has previously been predicted from theoretical considerations. Moreover, the negative magneto-rheological effect is observed to decrease with increasing shear rate, which also agrees qualitatively with the theoretical prediction.     

基于镍基修饰的铁矿石载氧体煤化学链燃烧实验

使用1 kW_th串行流化床反应器,研究了以铁矿石为载氧体以及对铁矿石进行镍基修饰情况下煤化学链燃烧特性,对两种修饰方法(机械混合和浸渍)进行了对比评价。结果表明,铁矿石载氧体具有良好的反应性能和稳定性,是实现煤化学链燃烧的一种比较理想的载氧体。向矿石中机械添加少量NiO/Al₂O₃载氧体,能够有效改善其反应活性,提高系统CO₂捕集率;采用浸渍法修饰的铁矿石载氧体煅烧后,总体微观孔隙结构变差,导致煤气化产物与载氧体间的反应无法充分进行,系统CO₂捕集率显著下降。浸渍修饰的方法和过程需要进一步的研究和改善。     

Controllable fabrication and growth mechanism of hematite cubes

Monodispersed and single‐crystalline hematite (α‐Fe₂O₃) cubes have been successfully prepared by a template‐free hydrothermal synthetic route with FeCl₃ and CH₃COONH₄. The influences of the reactant concentration, reaction temperature, and reaction time on the crystal growth were systematically investigated. The results show that the monodisperse hematite cubes with high crystalline and narrow size distribution could be fabricated at the hydrothermal temperature of 160 °C for 24 h while the concentrations of FeCl₃ and CH₃COONH₄ were in the range of 0.03‐0.5 M and 0.05‐0.1 M, respectively. In addition, the formation mechanism of hematite cube is also proposed, where the CH₃COONH₄ plays a role of shape controller in the formation of cube hematite structure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical surface charge and potential of hematite/yttrium oxide core–shell colloidal particles

Interest in the synthesis of composite colloidal particles consisting of a core and shell with different compositions stems from the fact that such particles can be useful in processes where the properties of both core (e.g., size and shape homogeneity, ease of preparation in large amounts, magnetic characteristics, etc.) and shell (interfacial properties, porosity, chemical stability, etc.) might be of interest. However, the applicability must be based on a proper characterization of those properties. In this work, colloidal spheres of hematite (α-Fe₂O₃) were used as nuclei of mixed particles where the shell is yttrium oxide. The electrical properties of the aqueous interface are compared to those of the pure oxides by means of potentiometric titration of their surface charge and potential against pH, as a function of indifferent electrolyte concentration. It is found that the mixed particles efficiently mimic yttrium oxide, since the behavior of their surface electrical characteristics closely resembles that of the latter compound. Differences are found, however, that can be ascribed to an incomplete or porous coverage, but such divergences are of little significance when an overall comparison is carried out. Received: 30 January 2001 Accepted: 11 July 2001