Particle Size Of Hematite Research Articles

Effect of manganese(II) and magnesiumg(II) in zinc acid leaching solution on iron precipitation via the hematite process

Abstract Iron (Fe) removal is a critical step in the hydrometallurgical zinc (Zn) extraction process. Hematite, a stable Fe precipitate, offers an environmentally friendly option that complies with environmental protection standards. While existing research primarily focuses on hematite process technology, there is a lack of studies on how ions in ZnSO4 leaching solutions affect Fe removal efficiency and hematite particle size distribution. This study investigated the influence of manganese II (Mn(II)) and magnesium II (Mg(II)) concentrations and temperature on both Fe removal efficiency and hematite particle size distribution in ZnSO4 leaching solution. The results indicated that at various temperatures, the highest Fe removal efficiency occurred with an initial Mn(II) concentration of 10 g/L and an Mg(II) concentration of 15 g/L. As the concentrations of Mn(II) and Mg(II) as well as temperature increased, FeSO₄ crystallization also increased, which adversely affected hematite precipitation. The average particle size of hematite decreases from 300 to 100 nm, resulting in a more uniform particle size distribution, which correlated with the homogeneous solution saturation precipitation mechanism. However, the number of rod-shaped, regular small particles decreases, while the number of irregular, blocky particles increased.

Hydrothermal precipitation of hematite from the model solution of zinc hydrometallurgical extraction

Abstract The effect of temperature and silicon concentration on iron precipitation and morphology of hematite particles was discussed. The results showed that increase of initial silicon centration will lead to the decrease of iron removal efficiency, and the Fe content decreases and S content increases in hematite. Increasing temperature is beneficial to increase iron removal rate and Fe content in hematite, but increasing temperature can not decrease silicon content in hematite. The content of Si in precipitate is proportional to the concentration of silicon in solution. Silicon is adsorbed on the surface of hematite in the form of silicic acid. Hematite particle was agglomerated microsphere. Increasing concentration of silicon will increase the disorder degree of hematite crystallization. With the increase of silicon concentration, the agglomeration of hematite particle was more obvious, and the average particle size of hematite particles increased. At 175 °C, the morphology of iron precipitation particles are composed of flake particles and rhomboid massive particles, but when the temperature rises to 195 °C, the agglomeration phenomenon is obvious, small flake particles agglomerate into microspherical aggregates.

Controlled Morphology Direct Iron Reduction from an Alkaline Slurry of Hematite for a Low-Cost Energy Storage Technology

Iron-air batteries became a promising research direction for low-cost and long-duration energy storage. Moreover, extensive work on iron-related technologies can assist in the decarbonization of the steelmaking industry.1 To mitigate the issue of a parasitic hydrogen evolution reaction that significantly lowers the high theoretical specific capacity of the device, grafted Fe/C, as well as carbonyl-iron composite electrodes were studied.2 Despite the effectiveness of such methods and commercialization success, the complicated nature of a starting material makes it costly for plant-scale production. In this work, we are presenting the iron-plating method under alkaline conditions which is aimed to produce various morphology anodes for improved cycling in a pouch-cell with a perspective usage in the iron-air storage technology. This preparation approach of the battery component from abundant metal could replace the more emission-intensive technologies being used today. Additionally, a study on zinc monolithic anodes has proven to dramatically elevate the performance of the primary and secondary devices predicting a similar success for various metals.3 In the first cycle of the research, we discover how the faradaic efficiency and specific capacity of direct iron metal deposition from the iron (III) oxide slurry are impacted by varying temperatures of the process. Additionally, changes in the morphology and the porosity distribution are observed based on the initial controlled hematite particle size. The second cycle is dedicated to the cycling behavior of the prepared anodes. By performing a set of characterizations, we are able to account for the factors influencing the final performance of the prepared anodes. These findings allow us to better understand the feasibility of such a preparation method of the iron anode for an alternative energy storage scale-up. Woodford, W. H.; Burger, S.; Ferrara, M.; Chiang, Y.-M., The iron-energy nexus: A new paradigm for long-duration energy storage at scale and clean steelmaking. One Earth 2022, 5 (3), 212-215.Hang, B. T.; Eashira, M.; Watanabe, I.; Okada, S.; Yamaki, J.-I.; Yoon, S.-H.; Mochida, I., The effect of carbon species on the properties of Fe/C composite for metal–air battery anode. Journal of Power Sources 2005, 143 (1-2), 256-264.Joseph F. Parker, C. N. C., Irina R. Pala, Meinrad Machler, Michael F. Burz, Jeffrey W. Long, Debra R. Rolison, Rechargeable nickel–3D zinc batteries: An energy-dense, safer alternative to lithium-ion. Science 2017, 356, 415–418.

Growth behavior and kinetics of magnetite during magnetization roasting

The magnetization roasting of hematite with two particle sizes was performed to investigate the growth behavior and kinetics of magnetite. The magnetite exhibited comparable growth trends throughout the magnetization roasting process at different roasting temperatures, and enhancing the roasting temperature can facilitate the growth of magnetite. The nascent magnetite nuclei appeared acicular, predominantly developed along the edges and fissures of the hematite particles before progressively growing inward. Moreover, the temperature stress and magnetite formation led to the loose and porous structure of the nascent magnetite particles. The growth kinetics demonstrated that the growth process of magnetite could be divided into induction period and growth period based on the different growth rates. For the same hematite sample, the growth rate of magnetite in the induction period was lower than that in the growth period. The magnetization roasting of hematite with a smaller particle size may be completed in a shorter time, even if increasing the particle size of hematite can accelerate the growth rate of magnetite. The growth kinetic models were established based on the parabolic law, and the reliability of describing the growth process of magnetite was verified by comparing the predicted values with the experimental values.

Thermally-induced color transformation of hematite: insight into the prehistoric natural pigment preparation

Since the prehistoric era, hematite has been known as a reddish color pigment on rock art, body paint, and decorating substances for objects discovered almost worldwide. Recently, studies about purple hematite used in prehistoric pigment have been done vigorously to investigate the origin of the purple pigment itself. These previous studies indicate that the differentiation of crystallinity, crystal size, morphology, and electronic structure can cause the color shift, resulting in purple hematite. In this study, we conducted a detailed study of the sintering temperature effects on the formation of hematite minerals. This study aims to reveal the structural, crystallography, and electronic transformation in hematite due to heating treatment at various temperatures. The hematite was synthesized using precipitation to imitate the primary method of hematite formation in nature. The sintering process was carried out with temperature variations from 600 °C to 1100 °C and then characterized by crystallographic and structural properties (XRD, Raman Spectroscopy, FTIR), particle size (TEM), as well as electronic properties (DRS, XANES). The crystallinity and particle size of hematite tend to increase along with higher sintering temperatures. Moreover, we noted that the octahedral distortion underwent an intensification with the increase in sintering temperature, which affected the electronic structure of hematite. Specifically, the 1s → 3d transition exhibited lower energy for hematite produced at a higher temperature. This induced a shift in the absorbed energy of the polychromatic light that led to a color shift within hematite, from red to purple. Our finding emphasizes the importance of electronic structure in explaining hematite pigment’s color change rather than relying on simple reasons, such as particle size and crystallinity. In addition, this might strengthen the hypothesis that the prehistoric human created a purple hematite pigment through heating.

The flotation of fine hematite by selective flocculation using sodium polyacrylate

• Fine hematite was separated from fine quartz by PAAS flocculation flotation . • The hematite particle size increased by 52% due to PAAS selective flocculation. • The adsorption mechanism of PAAS on the hematite surface was discussed in detail. Fine hematite and quartz are particularly difficult to separate using classic flotation and magnetic separation methods because the particles were very small and readily reported to the wrong product. The effect of sodium polyacrylate (PAAS) on the flotation separation of fine hematite from quartz and its mechanism were investigated by micro-flotation experiments using NaOL as a collector, particle size analysis, zeta potential measurements, FT-IR, SEM analysis as well as XPS analyses. The flotation tests found that the flotation recovery of fine hematite increased observably to 94.51% from 68.69% by adding 4 mg/L PAAS before NaOL at pulp pH 7.3; in the separation of mixed hematite and quartz, the separation efficiencies of fine hematite with and without the addition of the PAAS are 85.71% and 68.84%, respectively. After treatment with the PAAS, the fine hematite was well flocculated so that the average hematite particle size increased to 26.73 μm from 17.69 μm, and the particle size distribution of hematite less than 17 μm decreased to 29.58% from 52.51%. Zeta potential variations indicate that the collector NaOL is able to adsorb on the hematite surface after flocculation by the flocculant PAAS whereas the adsorption of the PAAS on quartz plays an inhibitory role in the adsorption of collector NaOL on the quartz surface, considerably improving the floatability of fine hematite, and thus realizing the effective separation of fine hematite from fine quartz. Furthermore, FT-IR, SEM, and XPS analyses suggest that the flocculant PAAS adsorbs on the hematite surface in a scattered punctiform morphology via a chemical bond in which the Fe 3+ of the hematite surface reacts with the –COO – of PAAS to form dimers, including (RCOO) 2 2– or RCOOH-RCOO - .

Study the hematite reduction kinetics by the magnetic method

This study is devoted to the reduction of Fe2O3 supported on silica gel in H2 in the temperature range of 290–600 °C. A continuous magnetization measurement method was used to obtain the temperature programmed reduction (TPR) profile. The influence of the external magnetic field on the dynamics of the process is investigated. It was shown that the TPR profile depends both on the magnitude of the applied field and on the particle size of hematite.

Enhancing the capacity of large-scale ball mill through process and equipment optimization: An industrial test verification

The production capacity of the large-scale ball mill in the concentrator is a crucial factor affecting the subsequent separation and the economic benefits of the operation. The main aim of this study is to improve the processing capacity of the large-scale ball mill. Taking a Φ5.49 × 8.83 m ball mill as the research object, the reason for the low processing capacity of the ball mill was explored via process mineralogy, physicochemical analysis, workshop process investigation, and the power consumption method. Based on this framework, a series of laboratory grinding optimization tests were conducted and verified via industrial tests. The results show that the ore primarily contained hematite and magnetite, the disseminated particle size of magnetite was primarily a coarse-grained inlay that was easy to separate from gangue, while the disseminated particle size of hematite was primarily an uneven and medium-sized inlay, which increased the grinding difficulty. Under optimum conditions of +6.0 mm material suitable for a 100 mm ball diameter, −6.0 + 2.0 mm material suitable for an 80 mm ball diameter, −2.0 mm material suitable for a 70 mm ball diameter; medium ratio of Φ90 mm 34.62%, Φ70 mm 26.92%, Φ60 mm 23.08%, Φ40 mm 15.38%; filling ratio of 32%; material ball ratio of 1.0; rotation speed rate of 80%; and grinding concentration of 78%, the −0.074 mm content in the grinding product increased from 55.10% to 58.86% and the processing capacity of the ball mill increased from 310 to 320 t/h to 350 t/h. Scanning electron microscopy/energy dispersive X-ray spectrometry (SEM-EDS) micrograph analysis shows that the fineness of the ore and dissociation degree of useful minerals were apparently improved by optimizing the process and equipment.

Iron isotope exchange and fractionation between hematite (α-Fe2O3) and aqueous Fe(II): A combined three-isotope and reversal-approach to equilibrium study

Hematite is the most thermodynamically stable Fe oxide at the Earth’s surface and its isotopic composition may record past biogeochemical Fe cycling and paleo-environmental conditions. Proper interpretation of its isotopic values requires an understanding of the equilibrium Fe isotope fractionation factor between hematite and other Fe-bearing minerals and aqueous species. Here, we use the three-isotope method (54Fe-56Fe-57Fe, with 56Fe/54Fe and 57Fe/56Fe ratios expressed in delta notation relative to the IRMM-014 isotope standard) to simultaneously determine Fe isotope exchange, via tracking an enriched tracer-isotope (i.e. 57Fe), and measure mass-dependent isotope fractionation between aqueous Fe(II) (Fe(II)aq) with structural-Fe(III) in hematite, as determined from variations in 56Fe/54Fe ratios. Specifically, we used a reversal-approach to equilibrium by reacting three hematite samples of varying particle size and reactivity with two Fe(II)aq solutions that had initial 56Fe/54Fe ratios above and below the presumed equilibrium value. We confirm that Fe(II)aq readily exchanges with hematite at low temperature, and that the extent of exchange depends on hematite particle size. In three-isotope plots, δ56Fe values of Fe(II)aq exhibit unique trajectories depending on the initial hematite particle size. Rapid exchange occurring between Fe(II)aq and small hematite particles are affected by an apparent mixing reaction, which results in the δ56Fe value of Fe(II)aq to approach the isotopic composition of hematite. These trajectories exhibit inflections to more negative δ56Fe values during continued exchange. The location of these inflections depend on particle size and are interpreted to represent a change in the recrystallization mechanism from rapid “heterogeneous” recrystallization, which is limited to surface exchange, to “homogeneous” recrystallization involving the bulk hematite. Slow isotopic exchange occurring at longer reaction times appears to approximate equilibrium for all particle sizes with measured Fe(II)aq-hematite Fe isotope fractionation factors at 22 °C ranging from −2.61 ‰ (±0.26‰, 2σ) to −3.14 ‰ (±0.34‰, 2σ) in δ56Fe, and an average value of −2.8‰. This value is consistent with estimated fractionation factors measured during microbial Fe reduction experiments and with calculated and spectroscopically derived reduced partition function ratios. The three-isotope method provides a robust measure of equilibrium fractionation if proper constrains are utilized to eliminate extrapolation from partial exchange. Furthermore, it can provide insight into the mechanism of mineral-fluid exchange which is necessary for accurate quantification of the extent of mineral recrystallization when using isotopic tracers.

Synthesis, photoluminescence and Magnetic properties of iron oxide (α-Fe2O3) nanoparticles through precipitation or hydrothermal methods

In this work the iron oxide (α-Fe2O3) nanoparticles are synthesized using two different methods: precipitation and hydrothermal. Size, structural, optical and magnetic properties were determined and compared using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FT-IR), Raman spectroscopy, Differential Thermal Analysis (DTA), Thermogravimetric Analysis (TGA), Ultraviolet–Visible (UV–Vis) analysis, Superconducting QUantum Interference Device (SQUID) magnetometer and Photoluminescence (PL). XRD data further revealed a rhombohedral (hexagonal) structure with the space group (R-3c) and showed an average size of 21 nm for hydrothermal samples and 33 nm for precipitation samples which concorded with TEM and SEM images. FT-IR confirms the phase purity of the nanoparticles synthesized. The Raman spectroscopy was used not only to prove that we have synthesized pure α-Fe2O3 but also to identify their phonon modes. The TGA showed three mass losses, whereas DTA resulted in three endothermic peaks. The decrease in the particle size of hematite of 33 nm for precipitation samples to 21 nm for hydrothermal samples is responsible for increasing the optical band gap of 1.94–2.10 eV where, the relation between them is inverse relationship. The products exhibited the attractive magnetic properties with good saturation magnetization, which were examined by a SQUID magnetometer. Photoluminescence measurements showed a strong emission band at 450 nm. Pure hematite prepared by hydrothermal method has smallest size, best crystallinity, highest band gap and best value of saturation magnetization compared to the hematite elaborated by the precipitation method.

The nature of hematite depression with corn starch in the reverse flotation of iron ore

The function of corn starch and the significance of the order of addition of corn starch and mono ether amine in the reverse flotation of iron ore has been investigated. Understanding hematite depression with starch and the corresponding hydrophilic state involves consideration of adsorption with amine as well as flocculation of fine hematite. Captive bubble contact angle and micro-flotation experiments indicated that amine has an affinity towards both hematite and quartz, and that the role of starch is to hinder the adsorption of amine at the hematite surface so that flotation is inhibited. Micro-flotation results confirmed that quartz does not have affinity towards starch at pH 10.5. In addition to competitive adsorption, flocculation of fine hematite occurs and images from high resolution X-ray computed tomography (HRXCT) and cryo-SEM reveal further detail regarding floc structure. These results provide substantial evidence that the fine hematite particles are flocculated in the presence of corn starch, and flocculation is dependent on the particle size of hematite, with greater flocculation for finer particles. Thus, starch is playing a dual role in the reverse flotation of iron ore, acting as a depressant by hindering amine adsorption at the hematite surface in order to maintain the hydrophilic surface state of hematite, and acting as a flocculant to aggregate fine hematite particles, which if not flocculated, could diminish the flotation separation efficiency by being transported to the froth phase during reverse flotation.

Synthesis and magnetic properties of magnetite prepared by chemical reduction from hematite of various particle sizes

In the process of beneficiating iron ores by the magnetic separation, particles of hematite and quartz accumulate, forming tailings that occupy large areas of agricultural lands. Such man-made deposits are quite common and contain large quantities of iron oxides such as hematite. Therefore the tailings can be used as raw material for the production of magnetite. In this work, magnetite was synthesized by hematite reduction at a temperature of 500 °C in an atmosphere of carbon monoxide. The source hematite was separated initially into ten particle size categories ranging from 0.05 to 2.5 mm. The reduction was carried out with carbon monoxide, which was synthesized by reaction of air and activated carbon at 750 °C. It was determined by X-ray diffraction analysis and magnetometry that, after reduction, samples of each particle size consisted mainly of magnetite. In addition, the magnetic properties of the resulting magnetite were noted to be somewhat different from those of natural magnetite. In particular, remanence and coercivity are higher for synthetic magnetite than for natural magnetite. The saturation magnetization of transformed samples increases to 60–80 Am2/kg, while the source hematite does not have strong magnetic properties. Hematite with a particle size from 0.05 to 0.25 mm is completely converted into magnetite, but if the size of hematite particles increases to from 0.25 to 2.5 mm, incomplete conversion of hematite to magnetite is observed. The obtained results are important for the development of technology for converting hematite to magnetite, which can, in turn, be used to beneficiate iron ores.

Experimental investigation of fluidized bed chemical looping combustion of Victorian brown coal using hematite

An experimental investigation on chemical looping combustion (CLC) of Victorian brown coal is carried out in a fluidized bed of hematite. The aim of this study is to understand the feasibility of Victorian brown coal CLC as very little technical information is currently available on the process using these coals. The in situ CLC experiments are first performed using a thermogravimetric analyzer (TGA). The TGA results show good performance of hematite as oxygen carrier over five multiple re-dox cycles under CO2 gasification environment. Therefore, further investigation is performed using a bench-scale fluidized bed that operates in a batch mode cyclically with reduction in CO2 environment, and oxidation in air. Several tests have been conducted to assess the impact of different temperatures, particle size of hematite and CO2 concentration in a flowing fluidizing gas medium. It is observed that the hematite particles of 100–150μm performed best with respect to carbon conversions that show an increasing trend with increasing temperature and CO2 concentration in the fluidizing gas.

Enhanced photocatalytic activity and stability of alumina supported hematite for azo-dye degradation in aerated aqueous suspension

Silica supported hematite (Fe2O3/silica) that is more active but less stable than the supported hematite for organic photodegradation in aqueous solution has been reported. In this work, we report on alumina supported hematite (Fe2O3/alumina) with significantly improved activity and stability. The catalysts were prepared by mixing alumina with a pre-made colloidal iron oxide at various loading (0–100wt %), followed by sintering at different temperatures (200–900°C). Solid characterization with X-ray diffraction and N2 adsorption showed that hematite particles were small in size, and large in surface area, as compared with the unsupported hematite prepared in parallel. The catalyst activity was evaluated with anionic Orange II as a model substrate, and the reaction was carried out in aerated aqueous suspension under light irradiation at wavelengths longer than 320nm. As the Fe2O3 loading on alumina or the catalyst sintering temperature increased, the apparent rate constant of dye degradation increased, and then decreased. The maximum rate of dye degradation was obtained with 25wt % Fe2O3/alumina, sintered at 400°C. Moreover, five consecutive experiments for dye photodegradation showed that Fe2O3/alumina was much more stable than Fe2O3/silica, due to alumina that has a positively charged surface and thus facilitates the dissolved iron species back onto iron oxide. The higher activity of Fe2O3/alumina than Fe2O3/silica and bare hematite is ascribed to the combined effect between the reduced particle size of hematite and the enhanced surface adsorption of dye on the catalyst.

Quantifying the Role of Grain Lining Hematite Cement in Controlling Permeability in a Relatively Tight Gas Sandstone Reservoir From the North Sea

Summary Recent work has shown the potential usefulness of both magnetic-susceptibility and magnetic hysteresis techniques in assessing the effect of fine-grained hematite on permeability, where the hematite was dispersed in the matrix of relatively tight gas red sandstone samples. The present study demonstrates that grain lining hematite cement is also a major controlling factor on permeability in a relatively tight gas sandstone reservoir in the North Sea. Magnetic susceptibility measurements on core plugs in this reservoir showed a strong correlation with probe permeability. Moreover, samples with a higher content of hematite exhibited lower permeability values. Thin-section analysis revealed the presence of a thin (approximately 10 to 15 μm) rim of hematite cement surrounding quartz grains, which block pore connections and reduce permeability. Magnetic hysteresis measurements on representative samples indicated a similar paramagnetic clay content in both the low and high permeability samples, suggesting that the clay (mainly illite) is not the dominant controlling factor that produces the variations in permeability that we observed. Because samples with higher hematite content exhibit lower permeability, it appears that hematite is a major control on the permeability variations seen in this reservoir. Although the paramagnetic clays undoubtedly have an influence on the absolute permeability values (increasing paramagnetic clay content has previously been shown to correlate with decreasing permeability), small amounts of grain lining hematite cement can reduce the permeability significantly further. Analysis of the magnetic hysteresis parameters on a Day plot indicated that the permeability was essentially independent of the hematite particle size for the fine particle sizes observed in this study.

Hematite nanoparticle monolayers on mica: Characterization by colloid deposition

Colloid particle deposition (also referred to as colloid enhancement, CE) was applied to characterize hematite nanoparticle monolayers on mica. The average size of hematite particles (determined by AFM and dynamic light scattering) was 22nm. The monolayers were produced under diffusion-controlled transport from suspensions of various bulk concentration at pH 3.5, I=10−2M, where the particles exhibited a positive zeta potential of 39mV. The monolayer coverage, quantitatively determined by AFM and SEM, was regulated within broad limits by adjusting the deposition time. The electrokinetic properties of hematite monolayers produced in this way were studied using the streaming potential method. The dependencies of the monolayer zeta potential on the coverage, pH and ionic strength were determined. Hematite monolayers were used as heterogeneous substrates for colloid particle deposition studies involving negatively charged polystyrene latex particles (800nm in diameter). An anomalous deposition of latex particles on substrates exhibiting a mean negative zeta potential was observed for higher ionic strength. These deviations from the classical DLVO theory were quantitatively interpreted in terms of the heterogeneous nanoparticle coverage distribution governed by fluctuation theory. However, for low ionic strength of 10−4M latex particle deposition proceeded in accordance with the DLVO theory. These data obtained for hematite can be used as useful reference states for analyzing particle or bacteria adhesion to heterogeneous surfaces covered by macromolecules and proteins.

Study the effect of HLB of surfactant on particle size distribution of hematite nanoparticles prepared via the reverse microemulsion

Hematite nanoparticles have been synthesized via reverse microemulsion route at room temperature. The microemulsion system, contained water, chloroform, 1-butanol, and surfactant, was combined with iron nitrate solution to result iron oxide nanoparticles precipitation. Three technical surfactants, with different structures and HLB (hydrophile–lipophile balance) values were employed and the effects of the HLB values on the hematite particle size were investigated. The prepared particles were evaluated by BET, XRD and TEM techniques. These results showed that the iron oxide particle size and particle size distribution increased with increasing surfactant HLB values.

Enhancing the photoelectrochemical performance of hematite (α-Fe2O3) electrodes by cadmium incorporation

Photoelectrochemical (PEC) water oxidation using hematite (α-Fe2O3) is of great interest in terms of solar fuels and artificial photosynthesis. In this study, Cd-incorporated nanocrystalline hematite films (Cd–Fe2O3) supported on conducting glass have been prepared via co-electrodeposition of aqueous Fe(III) and Cd(II) with varying Cd:Fe atomic ratios (up to 3.2at.%) and optimized for their PEC performances under a simulated solar light (AM 1.5-irradiation). Surface analysis indicates that the Cd co-deposition increases the hematite particle size from ca. 50nm to 70–100nm due to interparticle agglomeration and decreases the overall UV–Vis absorbance of hematite. X-ray photoelectron spectroscopic study also indicates that Cd incorporation shifts the binding energy of oxygen atoms to lower energy direction whereas it does not affect the binding energy of Fe 3d. This suggests that Cd exists mainly as CdO and/or Cd(OH)2 in the hematite surface. When an optimal level of Cd content (∼1at.%) is electrodeposited, the photocurrent of hematite film is significantly enhanced by a factor of ca. four at E=1.23VRHE under AM 1.5-irradiation and the photoactive spectral region is red-shifted. Electrochemical impedance spectroscopic analysis further reveals that the flat band potential of hematite is shifted by ca. −30mV to negative potential direction and the charge transfer resistance (Rct) is significantly reduced by Cd incorporation. Detailed surface analyses, optimization for preparation condition of hematite films, and discussion for PEC behaviors were described.

Preparation and characterization of pseudocubic hematite particles by utilizing polyethylene amine nonionic surfactants in forced hydrolysis reaction

The shape and porosity of hematite particles, produced from a forced hydrolysis reaction of acidic FeCl3 solution, were controlled by using polyethylene amine nonionic surfactants (Surfonamine®; 0∼10 wt.%). Surfonamine® possesses a nominal formula of CH3-(PEO)x-(PPO)y-NH2. Surfonamine with the highest total amine content (PEO contents were over 76 mol%, L-100) gave spherical particles, but those with lower total amine contents (L-200, L-207 and L-300) produced pseudocubic hematite particles. The pH value of the system with 10 wt.% of L-100 rose up to 8.49. With this pH rise, the diameter of the spherical particles was dramatically decreased. This fast particle formation was explained by the aggregation of very fine 6-line ferrihydrite particles produced at their high pH conditions. The uniformity of pseudocubic hematite particles produced with L-200, L-207 and L-300 were improved by increasing their concentrations. Since the pH values of these systems before aging were controlled between 2.03 and 2.35, it was presumed that the Surfonamine molecules acts as a buffer agent and attained pseudocubic particles. From the calculation of crystallite size, all the pseudocubic hematite particles were regarded as a polycrystal as well as the large spherical hematite particles produced without Surfonamine (control system). This polycrystallinity of the particles provided evidence that the particles are grown by aggregation of polynuclear (PN) primary particles. Not only the morphology but also the pore size of hematite particles was controlled from nonporous to microporous by using Surfonamines. The N2 adsorption experiment and t-plot curve analysis revealed that the pseudocubic hematite particles have uniform micropores. The XRD, transmission electron microscope, inductively coupled plasma atomic emission spectroscopy and total organic carbon analysis measurements employed on the systems produced for pseudocubic particles elucidated that the pseudocubic crystal habit was formed by the specific adsorption of chloride ions and/or chloroferric complexes to the {012} faces, restraining the growth process through stacking of ultrafine PN particles in the direction of normal to the {012} faces but strictly restricting the growth and mutual fusion of PN ones. The uniform micropores could be produced between the PN particles. The uniform pseudocubic particles were found to be an effective photocatalytic material than the spherical particles due to their large size with uniform flat crystal faces.

Effects of Pluronics surfactants on morphology and porosity of hematite particles produced from forced hydrolysis reaction

The shape and porosity of hematite particles, produced from a forced hydrolysis reaction of acidic FeCl3 solution, were controlled by using Pluronics as nonionic surfactants (0–4 wt.%). Pluronics possess a nominal formula of (PEO)x–(PPO)y–(PEO)x. The effect of Pluronics with low hydrophilicity (PEO contents were less than 50 mol%) was small and provided spherical particles the same as that of the system without Pluronics (control system). However, Pluronics with higher hydrophilicity (PEO contents were over 50 mol%) gave ellipsoidal hematite particles. This effect on the particle morphology was enhanced by an increase in their molecular weight. On the other hand, the Pluronics possessing an opposite nominal formula [(PPO)x–(PEO)y–(PPO)x] exhibited no effect on the particle shape; it only depressed phase transformation from ⎕-FeOOH to hematite. Not only the morphology but also the pore size of hematite particles was controlled from nonporous to mesoporous by using Pluronics. The N2 adsorption experiment and t-plot curve analysis revealed that the hematite particles changed from mesoporous to microporous by an increase in the concentration of Pluronics. On the other hand, in the presence of very low amounts of Pluronics molecules (0.1 wt.%), nonporous hematite particles were produced via strong aggregation of PN particles by their hydrogen bonding between hydroxyl and PEO or PPO groups. The dynamic light scattering measurement for the system with Pluronics clarified the existence of polynuclear (PN) particles with a hydrodynamic particle diameter (Da) of ca. 40 nm after these were aged for 6 h. The size of PN particles remained constant at ca. 40 nm during aging time of 12 h∼3 days, but the scattering intensity was decreased. This decrease in the scattering intensity reveals that the number of PN particles is reduced by aggregation. The transmission electron microscope, inductively coupled plasma atomic emission spectroscopy, and total organic carbon analysis measurements employed on the systems produced for ellipsoidal particles elucidated that the formation of ellipsoidal hematite particles is attributed to the adsorption of Pluronics on the surfaces of PN and growing hematite particles.