One-pot synthesis of α-Fe2O3 nanospheres by solvothermal method

We have successfully prepared α-Fe₂O₃ nanospheres by solvothermal method using 2-butanone and water mixture solvent for the first time, which were about 100 nm in diameter and composed of very small nanoparticles. The as-prepared samples were characterized using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results showed that the product was α-Fe₂O₃ nanosphere, and the temperature was an important factor on the formation of α-Fe₂O₃ nanospheres.     

Single-phase γ-Fe2O3 nanoparticles synthesized by green ionothermal method and their magnetic characterization

The γ-Fe₂O₃ nanoparticles were prepared by ionothermal method in ionic liquids. A wide range of maghemite particle sizes within the nanometer scale are obtained by this method. The structural and magnetic properties of these γ-Fe₂O₃ particles were studied by using XRD, SEM and IR. Magnetic properties of the prepared nanoparticles were evaluated on a vibrating sample magnometer (VSM). By changing the ionic liquids, particles with an average diameter from 5 to 10 nm were prepared. The size of the final particle decreases with the longer alkyl chain of ionic liquid in this method while the template is bounded to the particle surface. Also magnetic properties of the products change with different ionic liquids. A longer alkyl chain in ionic liquid causes an increase in the magnetic properties in this method.     

On modelling of surface tension of CMC-α-Fe2O3 nanoparticles by fuzzy-hybrid approach: A comparison study

Surface tension is one of the most important rheological parameters of nanoliquids. It influences the thermophysical and mass transfer properties of nanostructures. Accurate estimation of the surface tension from operating variables is critical for determining optimal production processes. However, the challenges of producing nanoparticles and measuring their properties introduce experimental errors in the data used for mathematical modelling. Crisp regression approaches provide adequate representation of the data, but they do not provide information about the experimental uncertainty. In this study, a fuzzy-hybrid approach is proposed for mathematical modelling of surface tension of carboxymethyl cellulose/chitosan-α-Fe₂O₃ nanoparticles. Then, the proposed model is compared with a crisp model from a previous study. Error analysis is conducted to validate the constructed fuzzy model. It is observed that the fuzzy-hybrid modelling approach has yielded significantly lower error values (a 60%–90% improvement in all error metrics on average), and thus, it is superior to the crisp approach. This study contributes to the subject of modelling rheological properties. It is shown that the fuzzy-hybrid approach has impressive potential to be utilized for modelling the rheological properties of nanostructures.     

Efficient removal of Congo red by magnetically separable mesoporous TiO2 modified with γ-Fe2O3

Magnetically separable mesoporous TiO₂ modified with γ-Fe₂O₃ was prepared and characterized by X–ray diffraction, N₂ adsorption–desorption measurements, scanning electron microscopy, UV–vis absorption and magnetic measurements. The adsorptive removal of Congo red using the binary system was performed under various experimental conditions to examine the effects of contact time, solution pH, and initial concentration of Congo red. The results show that the removal abilities and separability of mesoporous TiO₂ adsorbent for Congo red can be significantly improved by modification with γ-Fe₂O₃. The adsorption of Congo red on the γ-Fe₂O₃–TiO₂ reaches the maximum percentage removal of ca. 97 % within 60 min, showing that most of Congo red can be removed in a short time. When the pH of solution is varied from 3.4 to 10.3, the percentage removal of Congo red decreases from ca. 97 to ca. 15 %, showing that the adsorption is strongly dependent on solution pH. The adsorption kinetics of Congo red fit well with pseudo-second-order kinetic model, and the equilibrium data is best described by Langmuir adsorption model. The maximum adsorption capacity of the γ-Fe₂O₃–TiO₂ for Congo red is estimated to be 125.0 mg/g.     

Using modified Pechini method to synthesize α-Al2O3 nanoparticles of high surface area

A modified Pechini method for the preparation of a high surface area α-alumina is proposed. The synthesis of these nanoparticles was carried out using a polymer as a chelating agent. The polymer was prepared from citric acid and acrylic acid by the melt blending method. The resulting α-alumina (98.16%) after calcination at 900 °C consisted of cylindrical nanoparticles of 100–200 nm in length and <25 nm in diameter with a relatively high surface area (18 m² g^?1).     

Facile synthesis of α-Fe2O3 nanoparticles and their catalytic activity in oxidation of benzyl alcohols with periodic acid

α-Fe₂O₃ nanoparticles (NPs) were synthesized by homogeneous chemical precipitation followed by calcination. Size-tuning of NPs was achieved by using polyethylene glycol with a molecular weight of 400 and 4000 as surfactant. Synthesized α-Fe₂O₃ NPs were characterized by powder XRD, transmission electron microscopy, N₂ adsorption–desorption isotherm and vibrating sample magnetometry. These α-Fe₂O₃ NPs were used as magnetically recoverable catalyst in oxidation of benzyl alcohols to aldehydes with periodic acid. The catalyst showed higher efficiency with decrease in their sizes.     

Narrowing size distribution widths of small α-Al2O3 nanoparticles by addition of large nanoparticles in coagulation separation

α-Al₂O₃ nanoparticles separated by fractionated coagulation still have broad size distributions which limit their wider applications. By adding 20-time mass of large α-Al₂O₃ (40.5 nm) into α-Al₂O₃ nanoparticles to be separated in coagulation separation, the average size of separated α-Al₂O₃ nanoparticles decrease from 6.6 nm without addition of large α-Al₂O₃ NPs to 4.4 nm, and the size distribution changes from 3–10 nm without addition of large α-Al₂O₃ NPs to 3–6 nm. With increasing amount of large α-Al₂O₃ NPs added, separated α-Al₂O₃ NPs exhibit smaller average sizes and narrower size distribution widths at the same separation concentrations. This approach may be applied to narrow size distribution widths in large-scale size-selective separations of other nanoparticles.     

Template synthesis of SnO2/α-Fe2O3 nanotube array for 3D lithium ion battery anode with large areal capacity

Electrodes with three-dimensional (3D) nanostructure are expected to improve the energy and power densities per footprint area of lithium ion microbatteries. Herein, we report a large-scale synthesis of a SnO(2)/α-Fe(2)O(3) composite nanotube array on a stainless steel substrate via a ZnO nanowire array as an in situ sacrificial template without using any strong acid or alkali. Importantly, both SnO(2) and α-Fe(2)O(3) contribute to the lithium storage, and the hybridization of SnO(2) and α-Fe(2)O(3) into an integrated nanotube structure provides them with an elegant synergistic effect when participating in electrochemical reactions. Large areal capacities and good rate capability are demonstrated for such a composite nanotube array. Particularly noteworthy is that the areal capacities (e.g. 1.289 mAh cm(-2) at a current rate of 0.1 mA cm(-2)) are much larger than those of many previous thin-film/3D microbattery electrodes. Our work suggests the possibility of further improving the areal capacity/energy density of 3D microelectrodes by designing ordered hybrid nanostructure arrays.     

Pd/Fiber glass and Pd/5% γ-Al2O3/Fiber glass catalysts by surface self-propagating thermal synthesis

The technique of Surface Self-propagating Thermal Synthesis (SSTS) was used to prepare Pd/??-Al₂O₃/fiber glass (FG) catalysts for selective liquid-phase hydrogenation of acetylene in the presence of CO. The results of XRD SR analysis (in synchrotron radiation) in combination with the technique of arrested combustion shed new light on the dynamic of phase transformations in the systems under study and variation in the size of diffraction-active crystallites. The catalytic performance of synthesized catalysts was found to be close to that of similar conventionally prepared catalysts. The EXAFS and TEM data afforded to estimate the variation in relative amounts of Pd⁰ and PdO in synthesized catalysts. In the course of selective hydrogenation, PdO rapidly (<15 min) reduced to Pd⁰.     

Biotemplate synthesis of mesoporous α-Fe2O3 hierarchical structure with assisted pseudocapacitive as an anode for long-life lithium ion batteries

The oriented biotemplate synthesis of nanostructured metal oxides as anode materials for lithium-ion batteries (LIBs) has recently attracted widespread attentions. Herein, mesoporous α-Fe₂O₃ hierarchical tubes (named as Fe-400) were successfully prepared by facile iron salt impregnation and air calcination at 400 °C using waste poplar branch as biotemplate. The hierarchical structure of Fe-400 is constructed from cross-linked small nanoparticles (~29 nm), which then results in large specific surface area (37.7 m² g^?1) and uniform mesoporous size distribution (12.2 nm). As anode material for LIBs, Fe-400 displays reversible capacity of 880.7 mA h g^?1 after long-cycle of 800^th at 1 A g^?1, indicating that this material has high capacity retention and good long-cycle stability. The prominent electrochemical properties are mainly ascribed to the large specific surface area, unique homogeneous mesopores, and the assisted pseudocapacitive behaviors of Fe-400. In view of the low-cost, environment-friendly and easily large-scale synthesis of Fe-400 electrode material, the present biotemplate strategy can present useful reference for the synthesis of other transition metal oxide-based anode materials for LIBs.     

Separation of Arsenic from Aqueous Solutions by Amino-Functionalized γ-Fe2O3-β-Zeolite

In this research, γ-Fe₂O₃-β-zeolite nanocomposite was synthesized and functionalized by 3-amino propyl trimethoxysilane. The magnetic functionalized adsorbent was characterized by FTIR, X-ray diffraction, thermal analysis, vibrating sample magnetometry, scattering electron microscopy, and N₂ adsorption-desorption techniques. The adsorbent was then used for adsorption of arsenic from aqueous solutions. At optimized conditions the adsorption capacity of 30 mg.g^?1 was obtained, which was higher than the previously reported values. The loaded adsorbent was easily separated from the solution by applying an external magnetic field. Regeneration of the adsorbent by NaOH solution indicated that 97% of the initial capacity was remained after four adsorption-regeneration cycles.     

Fabrication of mesoporous Cr2O3 with highly distributed α-Fe2O3 and Pt nanoparticles for ultrafast H2 evolution rate

In the present contribution, p-n type heterojunction α-Fe₂O₃/Cr₂O₃ S-scheme system photocatalyst has been fabricated utilizing a sol-gel approach with assisted nonionic surfactant for a highly effective H₂ evolution rate under visible illumination. Pt NPs have been reduced by photodeposition during the photocatalytic reaction to collect Pt@α-Fe2O3/Cr2O3 finally. XRD analysis of Fe₂O₃/Cr₂O₃ nanocomposites verified the construction of Fe₂O₃ and Cr₂O₃ with rhombohedral phases. TEM images of Cr₂O₃ NPs were almost spherical and uniform in shape and size (20 ± 5 nm), and very small Fe₂O₃ NPs (3-5 nm) were distributed on the mesoporous Cr₂O₃ networks. The obtained α-Fe₂O₃/Cr₂O₃ photocatalyst exhibited noteworthy photocatalytic H₂ evolution with high efficiency and stability for 45 h. Interestingly, the photocatalytic H₂ evolution rate gradually boosted with the extent of Fe₂O₃ percentage up to 15% and its rate of 2215.4 μmol g^-1h^-1, which was fostered 7.25 folds larger than that of Cr₂O₃ NPs (305.7 μmol g^-1h^-1). The enhancement H₂ evolution rate of Fe₂O₃/Cr₂O₃ photocatalyst in comparison with bare Cr₂O₃ NPs was ascribed to facilitate the separation of photocarriers and existing considerable reactive sites. In addition, constructing n-type Fe₂O₃ and p-type Cr₂O₃ with close contact is essential in improving the H₂ evolution rate. The possible photocatalytic mechanism over Fe₂O₃/Cr₂O₃ nanocomposite was addressed based on electrochemical measurements. The construction of the S-scheme system of Fe₂O₃/Cr₂O₃ nanocomposite could be suggested to improve the separation of photocarriers through optimal transfer channels owing to the formation of synergistic characteristics. Our results provide avenues for constructing stable photocatalysts with high efficiency for H₂ evolution through visible exposure.     

Preparation of spherical α-Al2O3 nanoparticles by microwave hydrothermal synthesis and addition of nano-Al seeds

Due to their special appearance, spherical α-Al₂O₃ nanoparticles play an important role for obtaining high-performance structural and functional ceramics. However, there are still problems such as easily agglomerates to form worm-like structures at high temperatures and difficult availability of spherical nanoparticles. In this study, spherical α-Al₂O₃ nanoparticles with high dispersion were prepared by a combination of a microwave hydrothermal method and an addition of nano-Al particles as seeds. First, spherical amorphous alumina precursors were synthesized by the microwave hydrothermal method at 100°C for 30 min using Al₂(SO₄)₃·18H₂O, Al(NO₃)₃·9H₂O, and urea, as raw materials, and then spherical α-Al₂O₃ nanoparticles with a diameter of about 66 nm were acquired after calcined the precursor at 1050°C for 90 min by adding nano-Al seeds, which reduced the calcination temperature by 50°C and holding time by 30 min compared to that without seeds. Kinetic analysis shows that 5 wt.% nano-Al seeds can reduce the activation energy of crystalline transition of γ-Al₂O₃ to α-Al₂O₃ from 516.51 to 474.37 kJ/mol. Moreover, the microscopic mechanism of nano-Al particles as seeds was investigated. The characterizations of sintering properties show that spherical α-Al₂O₃ nanoparticles facilitate the acquisition of uniform microstructure for resulting ceramic and the fracture modes include both intergranular and transgranular fractures.     

A critical role of pH in the colloidal synthesis and phase transformation of nano size α-Al2O3 with high surface area

This paper demonstrates the critical role of pH in the colloidal (i.e. sol-gel) synthesis of nano size α-Al₂O₃. Investigation, based on X-ray diffraction pattern, indicates that the transformation of α-Al₂O₃ from gels obtained at high pH⩾7, undergoes via formation of boehmite (gel→AlOOH→γ-Al₂O₃→α-Al₂O₃). On the other hand, the transformation of α-Al₂O₃ at low pH (⩽6) follows the gel→γ-Al₂O₃ →α-Al₂O₃ sequence. The transmission electron microscopy reveals that the particle size of the α-Al₂O₃ decreases from ≈750 to ≈70 nm with decreasing pH from 12 to 2.5, respectively. The α-Al₂O₃ with large surface area (≈130 m²/g) is obtained when it is processed at low pH (2.5). The true powder density of the α-Al₂O₃ sample derived at pH=2.5 is observed to be 3.92 g/cm³ after sintering at 1450 °C, due to fine particles. The isoelectric point (iep) and ξ of the α-Al₂O₃ are found to be 8.7 and 9.2 when synthesized at pH 2.5 and 12, respectively.     

Designing of a β-Cyclodextrin-based supramolecular fluorescent sensor doped with superparamagnetic α-Fe2O3 nanoparticles with improved light fastness,thermal, and photoluminescent properties

1-Pyrene butyric acid (PBA), a carboxylic derivative of pyrene, which is a well-studied fluoroprobe, has been greatly used for fluorescent modification of macromolecules belonging to different classes. The present study aimed at the synthesis and characterization of fluorescently modified β-cyclodextrin (CD) by covalent immobilization of PBA onto supramolecular CD via Steglich esterification. Fluorescently modified CD-PBA conjugate was further encapsulated with iron (III) oxide nanoparticles (IONP), which belong to the α-Fe₂O₃ (hematite) phase. The three systems PBA, CD-PBA, and CD-PBA-IONP were well characterized and compared for their photoresponsive and thermal properties. Photo stability of the samples under study was investigated by exposing the samples to visible light upto 6 h and at regular intervals of time measuring their respective photodegradation by UV/visible spectrophotometry. Thermal properties were monitored using thermogravimetric (TG-DTG) analysis. Steady state fluorescent studies were performed for the photoluminescent properties. Also, time correlated single photon counting technique was used to measure the fluorescent lifetime of the samples in order to have a better understanding of the quenching mechanism prevailing.     

Easy synthesis of nitrogen-doped graphene–silver nanoparticle hybrids by thermal treatment of graphite oxide with glycine and silver nitrate

Nitrogen-doped graphene–silver nanoparticle hybrids were prepared by thermal treatment of graphite oxide (GO) with glycine and silver nitrate at 500 °C. Glycine was used to reduce the nitrate ions, resulting in the decomposition of a glycine–nitrate mixture near 200 °C. The products of decomposition act as sources for nitrogen doping. The thermal treatment of a mixture of GO, glycine and silver nitrate results in the formation of silver nanoparticles at 100 °C, promotes the reduction of GO near 200 °C, and generates pyrrolic and pyridinic type nitrogen doping in graphene at 300 and 500 °C, respectively. The atomic percentage of nitrogen in as-prepared sample is about 13.5%. This approach opens up a new possibility for the synthesis of nitrogen-doped graphene decorated with various metallic nanoparticles, which could find important applications in the fields of energy storage and conversion devices.     

The Preparation and Gas-sensing Property of Nanosize γ-Fe2O3／SiO2

Nanostructured γ-Fe2O3/SiO2 complex oxide was prepared by sol-gel method with tetraethoxysilane and iron nitrate as precursors. The particle size distribution, thermal and phase stabilities and gas sensing properties were systematically characterized by TEM, granularity distribution, TG-DTA, XRD and gas sensitivity measurements. The particle size is about 10 nm and size distribution is very narrow. The sensitivity of the sensing element to CO, H2, C2H4, C6H6 and the effects of calcination temperature on the sensitivity and conductance of gases were examined. The combination of excellent thermal stability and tunable gas sensing properties through careful control of the preparation and judicious selection of material compositions gives rise to novel nanocomposites, which is attractive for the sensitive and selective detection of reducing gases and some hydrocarbon gases.     

Mechanochemical synthesis of zinc ferrite from zinc oxide and α-Fe2O3

Mechanochemical synthesis of zinc ferrite (ZnFe₂O₄) from a powder mixture of zinc oxide (ZnO) and hematite (α-Fe₂O₃) by room temperature grinding using a planetary ball mill was investigated. The grinding enables us to obtain the amorphous mixture of the starting materials. Most of ZnO reacts with α-Fe₂O₃ to convert into insoluble amorphous zinc and iron compounds within 2h-grinding. Prolonged grinding enhances the crystallization of ZnFe₂O₄ from the amorphous compounds. ZnFe₂O₄ crystallized by the grinding for 3 h or more consists of nanocrystalline particles with high specific surface area.     

Novel synthesis and characterization of nanosized γ-Al2O3 from kaolin

This paper reports the synthesis of nanosized γ-Al₂O₃ from acid-leachates of calcined kaolin. Al (hydr)oxide was precipitated with ammonia from the leachate in the presence of polyethylene glycol. A white powder of nanosized γ-Al₂O₃ particles was obtained after calcination. X-ray diffraction (XRD), different scanning calorimetries and thermogravimetry (DSC-TG), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and magic angle spinning nuclear magnetic resonance (MAS NMR) were used to characterize the samples. Typical nanosized γ-Al₂O₃ particles showed rod-like morphology with width of about 7 nm and length of approximately 20 nm. A possible mechanism from kaolin to nanosized γ-Al₂O₃ is proposed.