The role of the activity coefficients of surface groups in the formation of surface charge of oxides. Part II: Ion exchange and ζ potentials

A new method is developed to calculate the surface charge densities and potentials of oxides in contact with electrolyte solution as functions of pH and ionic strength. For low ionic strength and not too far from p.z.c. (up to 3 pH units for 10^–3 mol dm^–3 NaCl) the previous model (Kosmulski, 1992) neglecting the ion exchange can be used but farther from p.z.c., correction for the ion exchange is necessary for some systems. This correction leads to increase of the calculated titration charge (that is not necessarily equal to the surface charge), but does not affect the diffuse charge and potential.     

Effect of a weak magnetic field on hematite sol in stationary and flowing systems

The effect of a weak magnetic field on the aggregation state and electrophoretic mobility of hematite sol was studied in flowing (dynamic) systems as a function of time and electrolyte concentration (0–60 mmol/dm³ KCl) and compared with the effect of the field in stationary (static) systems and flow in the absence of the field. During the entire treatment period, the pH remained almost constant (4.06–4.24). Conductance varied with KCl concentration, but except for minor fluctuations appeared to be unaffected by any form of treatment. While aggregation of hematite was observed during dynamic magnetic treatment (change in turbidity, scattered light intensity, and photon correlation spectroscopy), little effect on aggregation state was observed for the static systems or for the flowing systems in the absence of the field. Mobility also increased during the first 30 min of static and dynamic magnetic treatment. After longer treatment periods (90–120 min), the mobility decreased, but in almost all cases remained larger than in the case of untreated systems. Changes in both mobility and particle aggregation state also showed a significant dependence on electrolyte concentration. These effects are discussed in terms of a magnetohydrodynamic interaction between the magnetic field and the charged colloidal particles, which results only when the particles are made to pass rapidly through the field.     

The influence of hematite nano-crystals on the thermal stability of polystyrene

A synthetic procedure based on thermal hydrolysis of iron(III) chloride solutions for the preparation of hematite (α-Fe₂O₃) sol consisting of nano-crystals (NCs) is described. The α-Fe₂O₃ NCs were characterized by transmission electron microscopy and X-ray diffraction measurements. Incorporation of α-Fe₂O₃ NCs into polystyrene (PS) was based on the transfer of α-Fe₂O₃ NCs from the aqueous phase to the organic solvent. A significant shift in the glass transition temperature of PS by 17 °C towards higher temperatures was observed after incorporation of α-Fe₂O₃ NCs. Also, the thermal stability of PS was improved by about 100 °C in the presence of 3.6 wt% of α-Fe₂O₃ NCs.     

Magneto-optical properties of α-Fe2O3@ZnO nanocomposites prepared by the high energy ball-milling technique

Magnetic–fluorescent nanocomposites (NCs) with 10 wt% of α-Fe₂O₃ in ZnO have been prepared by the high energy ball-milling. The crystallite sizes of α-Fe₂O₃ and ZnO in the NCs are found to vary from 65 nm to 20 nm and 47 nm to 15 nm respectively as milling time is increased from 2 to 30 h. XRD analysis confirms presence of α-Fe₂O₃ and ZnO in pure form in all the NCs. UV–vis study of the NCs shows a continuous blue-shift of the absorption peak and a steady increase of band gap of ZnO with increasing milling duration that are assigned to decreasing particle size of ZnO in the NCs. Photoluminescence (PL) spectra of the NCs reveal three weak emission bands in the visible region at 421, 445 and 485 nm along with the strong near band edge emission at 391 nm. These weak emission bands are attributed to different defect – related energy levels e.g. Zn-vacancy, Zn interstitial and oxygen vacancy. Dc and ac magnetization measurements show presence of weakly interacting superparamagnetic (SPM) α-Fe₂O₃ particles in the NCs. ⁵⁷Fe-Mössbauer study confirms presence of SPM hematite in the sample milled for 30 h. Positron annihilation lifetime measurements indicate presence of cation vacancies in ZnO nanostructures confirming results of PL studies.     

SO2在Fe2O3颗粒表面不同温度下非均相反应的实验模拟

使用漫反射Fourier变换红外光谱(DFTIRS)、离子色谱(IC)及透射电子显微镜(TEM)对不同温度条件下SO2在α-Fe2O3颗粒表面的非均相反应过程进行实验模拟和监测, 并分析了反应剧烈波段(8.7 μm)的产物硫酸盐以及颗粒吸收和后向散射光学系数的变化. 结果表明, 在15-45 ℃内, 硫酸盐生成量、生成速率以及吸收系数、后向散射系数都随反应温度的升高而呈现先增加后减少的趋势; 同一反应温度下, 硫酸盐生成速率随时间呈现先增大后减小, 最后逐渐趋于稳定的演变; 光学系数变化与硫酸盐生成量之间存在较好的指数关系. 在当前全球气候变暖背景下, 研究结果将对深入了解真实大气中SO2与矿尘非均相反应造成的气溶胶光学特性演变, 以及定量评估其辐射强迫影响具有一定意义.     

Insight into the influence of high temperature annealing on the onset potential of Ti-doped hematite photoanodes for solar water splitting

The unfavorable onset potential shift of Ti:Fe₂O₃ photoanode induced by high temperature post-annealing was studied. The underlying mechanism is the surface Ti/Fe atomic ratio increase, leading to adsorption capacity change of surface hydroxide ions and the positive shift of flatband potential (i.e., theoretical onset potential).     

α-Fe_2O_3光阳极光电化学分解水的研究进展与挑战

近年来,光电化学分解水制氢(PEC)技术为未来的能源需求提供了一个清洁、可再生的途径.赤铁矿(α-Fe_2O_3)因其带隙小(～2.1 eV)、无毒、存储量大以及光电化学稳定等优点而受到广泛关注.然而,导电性差、空穴扩散长度短(2～4 nm)、表面水氧化动力学缓慢、激发态寿命短(10×10~(-12) sec)等缺点,极大地限制了Fe_2O_3光阳极的光转换效率.我们回顾了赤铁矿光阳极用于PEC水氧化的研究进展,主要集中在促进Fe_2O_3光阳极表面的水氧化反应,体相的电荷分离和迁移以及提高光吸收能力.最后,对Fe_2O_3光阳极面临的挑战和未来的发展进行了展望.     

FT-IR, XPS and PEC characterization of spray deposited hematite thin films

Hematite thin films were prepared by spraying ethanolic solution of ferric trichloride and have been characterized by using Fourier transform infra-red (FT-IR) and X-ray photoelectron spectroscopic (XPS) techniques. The film prepared by spray consists of a single phase of α-Fe₂O₃. The XPS studies confirm that chemical states of Fe³⁺ and O²⁻ in the film; thereby confirming the formation of the hematite thin films. The photoelectrochemical (PEC) studies have been carried out by forming a three-electrode system using 1 M NaOH electrolyte. The junction is illuminated with white light to obtain I-V characteristics in chopped light. The studies indicate the films exhibit n-type conductivity.     

Synthesis of Monodisperse α-Fe2O3 Particles in Short Periods

Asanimportantmaterialusedformagnetic,pigment,catalysis,gas-sensitiveandmedicalimagingapplications,monodispersehematite(a-Fe2O3)particleshaveattractedmoreattentionsinrecentyears1,2.Althoughvariousmorphologica-Fe2O3particleshavebeensynthesizedbyforcedhydrolysisprocess3,4,inwhichthepropertiesofa-Fe2O3particlesvaryconsiderablywithalargenumberofsynthesisparameterssuchaspH,theconcentrationofreactants,thecoexistentanionsetc.,thereisalackofmethodforpreparingmonodispersea-Fe2O3particlesinshortperiod…