Forced Hydrolysis Research Articles

Ferromagnetic resonance in Ni–Zn ferrite nanoparticles in different aggregation states

Ferrite nanoparticles of composition Zn0.5Ni0.5Fe2O4 were synthesized by forced hydrolysis in polyol from the corresponding zinc, nickel and iron acetates. By varying the preparation conditions, different aggregation states were obtained, ranging from isolated nanoparticles with average diameter of 5nm, to clusters of some 20nm, formed as well by nanoparticles with average diameter in the 5nm range, as confirmed by X-ray diffraction and high resolution transmission electron microscopy. Ferromagnetic resonance measurements exhibited a ferrimagnetic behavior for both aggregation states at 77K; at 300K, however, isolated nanoparticles showed a superparamagnetic behavior while clustered ones remained ferrimagnetic with a broad linewidth. These results are interpreted on the basis of interactions between nanoparticles.

Versatile ferrofluids based on polyethylene glycol coated iron oxide nanoparticles

Versatile ferrofluids based on polyethylene glycol coated iron oxide nanoparticles were obtained by a facile protocol and thoroughly characterized. Superparamagnetic iron oxide nanoparticles synthesized using a modified forced hydrolysis method were functionalized with polyethylene glycol silane (PEG silane), precipitated and dried. These functionalized particles are dispersable in a range of solvents and concentrations depending on the desired properties. Examples of tunable properties are magnetic behavior, optical and magneto-optical response, thermal features and rheological behavior. As such, PEG silane functionalized particles represent a platform for the development of new materials that have broad applicability in e.g. biomedical, industrial or photonic environments. Magnetic, optical, magneto-optical, thermal and rheological properties of several ferrofluids based on PEG coated particles with different concentrations of particles dispersed in low molecular mass polyethylene glycol were investigated, establishing the applicability of such materials.

Size-dependent magnetic properties of CoFe2O4 nanoparticles prepared in polyol

Highly crystalline CoFe2O4 nanoparticles with different diameters ranging from 2.4 to 6.1 nm have been synthesized by forced hydrolysis in polyol. The size can be controlled through adjusting the nominal water/metal molar ratio. X-ray diffraction, transmission electron microscopy, x-ray absorption spectroscopy and 57Fe Mössbauer spectrometry were employed to investigate the structure and the microstructure of the particles produced. Magnetic measurements performed on these particles show that they are superparamagnetic with a size-dependent blocking temperature. At 5 K, high saturation magnetization (∼85 emu g−1) approaching that of the bulk was found for the larger particles, whereas a very large coercivity (14.5 kOe) is observed for the 3.5 nm sized particles.

Facile synthesis and magnetic properties of cross α -Fe 2 O 3 nanorods

Novel cross α-Fe 2 O 3 nanorods were obtained by forced hydrolysis of ferric chloride in the water solution system. The as-obtained products were characterised by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectrum, Brunauer-Emmett-Teller and vibrating sample magnetometry. XRD results revealed that the product exhibited α-Fe 2 O 3 phase. A comprehensive TEM analysis revealed that the cross structures consisted of α-Fe 2 O 3 nanorods with an average length of 400 nm and diameter of about 75 nm. Magnetic hysteresis measurement reveals that the novel cross α-Fe 2 O 3 nanorods display weak ferromagnetic behaviour with a remanence of 0.115 emu/g and a coercivity of 491.5 Oe at room temperature.

Comparative Study of Ni- and Co-Substituted ZnO Nanoparticles: Synthesis, Optical, and Magnetic Properties

Ni- and Co-substituted ZnO nanoparticles were synthesized using forced hydrolysis of acetate metallic salts in a polyol medium. The X-ray diffraction patterns show a hexagonal wurtzite structure (space group P63mc). The characteristic absorption bands of UV–vis-IR spectra are correlated with the d–d transitions of tetrahedrally coordinated Co2+ and Ni2+ ions in octahedral and tetrahedral sites. The photoluminescence spectra exhibited a typical ZnO UV-exitonic emission band around 380 nm and a broad band between 400 and 500 nm that might be ascribed to the intrinsic defects in the ZnO material. The transmission electron microscopy displays spherical particles with a diameter between 20 and 30 nm. The magnetic measurements reveal that Zn1–xNixO and Zn1–xCoxO nanoparticles show, respectively, ferromagnetic and paramagnetic behavior at 5 K. Homogeneous distributions of Co and Ni ions in the particles observed by filter imaging analysis indicates that there is no evidence of Co or Ni metal throughout the powders.

Bottom-up and new compaction processes: A way to tunable properties of nanostructured cobalt ferrite ceramics

In this work we describe a novel bottom-up strategy to process cobalt ferrite CoFe 2O 4 nanostructured bulk material. This strategy offers the possibility to drive their magnetic and mechanical properties in a wide range of different behaviors. In particular, we show how to tune the blocking temperature along with optimized mechanical strength. This method combines forced hydrolysis in polyol, a soft chemistry route, and Spark Plasma Sintering (SPS) for consolidation. To highlight this method, we also performed compaction by a standard Hot Isostatic Pressing (HIP) process. Thus we compare the nanostructured bulk microstructures (for both compaction techniques) and magnetic static properties to those of several CoFe 2O 4 nanopowder samples showing particle size and annealing temperatures comparable to those of the nanostructured bulk samples. Microstructure, radio-crystallographic and magnetic studies have been carried out in order to show the optimization of the processing strategy in this work.

Effect of a compact ZnO interlayer on the performance of ZnO-based dye-sensitized solar cells

ZnO is a promising material for application in dye-sensitized solar cells, related to its attractive electrical properties and the facile preparation of nanomaterials, with excellent control over the structure and morphology. In this work ZnO-based dye-sensitized solar cells were prepared, and the effect of the presence of a compact ZnO interlayer between the transparent conducting oxide (TCO) electrode and the nanostructured, mesoporous ZnO film on the performance of the solar cell is reported. The compact interlayer was deposited using planar rf magnetron sputtering, and the ZnO nanomaterial was prepared by forced hydrolysis from zinc acetate in ethanol solution. The presence of the compact interlayer has a positive effect on the overall characteristics of the solar cell and decreases the recombination rate from the TCO substrate, resulting in a higher open circuit voltage under low light conditions. The best efficiency of non-optimized solar cells at 1 sun was 4.0%.

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.

Ferromagnetic resonance behavior of spark plasma sintered Ni–Zn ferrite nanoparticles produced by a chemical route

Ferrite nanoparticles of composition Zn0.5Ni0.5Fe2O4 were prepared by forced hydrolysis in a polyol (polyol process) from the corresponding iron, nickel, and zinc acetates. Synthesis conditions allowed for obtaining polycrystalline epitaxial clusters of about 22 nm in size with an average crystal size of about 5 nm. These powders were subsequently consolidated by spark plasma sintering (SPS) technique under a pressure of 80 MPa and temperatures in the 350 to 500 °C range for short periods (5 to 10 min). Densities reached 92% to 94% of the theoretical density. Particle size remained smaller than 61 nm, even for the highest temperature. Ferromagnetic resonance experiments at 77 K showed broadened resonance lines. In contrast with powdered nanoparticles, these high-density bodies can be used in many high-frequency applications.

Characterization and dissolution properties of ruthenium oxides

Ruthenium oxides (RuO2·1·10H2O and RuO2) have been synthesized by forced hydrolysis and oxidation of ruthenium chloride. The resulting materials were extensively characterized to determine the crystallinity, surface area, and ruthenium oxidation state. Surface charging experiments indicate a large quantity of reactive functional groups for both materials and a decrease in the acidity of the surface functional groups with crystallization of the hydrous oxide. Dissolution studies conducted in acidic and basic pH environments indicate Ru-oxides are insoluble in 0.1M HCl and slightly soluble in 0.1M NaOH. Oxalate and ascorbate (5mM) promoted dissolution of RuO2·1·10H2O demonstrated an increase in dissolution rates with decreasing pH and increasing ligand surface coverage. XPS analysis of the RuO2·1·10H2O surface after ligand promoted dissolution revealed the reduction of Ru(IV) to Ru(III) indicating that both ascorbate and oxalate reductively dissolve RuO2·1·10H2O. Dissolution experiments with RuO2 resulted in dissolution only for 5mM oxalate at pH 3. Dissolution rates calculated for RuO2·1·10H2O and RuO2 are compared with previously published dissolution rates for iron oxides, demonstrating an order of magnitude decrease in the oxalate and ascorbate promoted dissolution.

Magnetism of ZnO nanoparticles: Dependence on crystallite size and surfactant coating

Many recent reports on magnetism in otherwise nonmagnetic oxides have demonstrated that nanoparticle size, surfactant coating, or doping with magnetic ions produces room-temperature ferromagnetism. Specifically, ZnO has been argued to be a room-temperature ferromagnet through all three of these methods in various experimental studies. For this reason, we have prepared a series of 1% Fe doped ZnO nanoparticle samples using a single forced hydrolysis coprecipitation synthesis method from the same precursors, while varying size (6–15 nm) and surface coating concentration to study the combined effects of these two parameters. Size was controlled by modifying the water concentration. Surfactant coating was adjusted by varying the concentration of polyacrylic acid in solution. Samples were characterized by x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, optical absorbance spectroscopy, and magnetometry. No clear systematic effect on magnetization was observed as a function of surfactant coating, while evidence for a direct dependence of magnetization on the crystallite size is apparent.

Goethite hierarchical nanostructures: Glucose-assisted synthesis, chemical conversion into hematite with excellent photocatalytic properties

This paper describes an original and facile method for preparing goethite (α-FeOOH) hierarchical nanostructures (HNSs), as well as chemically converting into hematite (α-Fe 2O 3) under the preservation of α-FeOOH complex morphology. This method was based on a forced hydrolysis–oxidation of iron (II) salts in the presence of d-(+)-glucose as structure-directing agents, where control over the concentration and feeding way of d-(+)-glucose can considerably modulate the morphologies of the α-FeOOH HNSs from 1D unique architecture composed of arrayed nanoplates to 3D sea urchin-like superstructures. Moreover, using the sea urchin-like α-FeOOH nanostructures as precursors, the α-Fe 2O 3 HNSs with the same morphology but tailored crystallization and texture characteristics are robustly achieved only by adjusting annealing temperature. The formation mechanism of the α-FeOOH HNSs is proposed to be the synergistic effects of polar interaction and magnetic interaction between the building blocks of the nanoparticles. Due to the high BET specific surface area and favorable crystallization, the α-Fe 2O 3 HNSs obtained at 300 °C show excellent photocatalytic efficiency. Taking advantages of environmental benign biocompatibility, chemical stability and potential for mass generation, the α-Fe 2O 3 HNSs described in this work are believed to have a wide range of applications including catalysis, gas sensing.

Design of ZnO nanostructured films: Characterization and ecotoxicological studies

The potential ecotoxicological impact of ZnO nanostructured films was investigated using common Anabaena flos-aquae, Calothrix pulvinata cyanobacteria and Euglena gracilis euglenoid microalgae. The pre-formed ZnO nanoparticles were synthesized in di(ethylene glycol) medium by forced hydrolysis of ionic Zn 2+ salts. Particle size and shape were controlled by addition of protective agents such as tri- n-octylphosphine oxide and polyoxyethylene stearyl ether. ZnO nanostructured films were directly prepared by spray deposition of pre-formed polyol-based ZnO nanoparticles (ZnO, ZnO-TOPO and ZnO-Brij-76) at 250 °C heated glass substrate. Another sample was prepared from zinc acetate in di(ethylene glycol) diluted in ethanol medium without nanoparticles (ZnO-SOL). In this case, ZnO nanostructured film was formed directly on the glass substrate at the same temperature. Water contact angle on ZnO-based films showed that nanostructured ZnO films containing ZnO nanoparticles prepared without protective agent or with tri- n-octylphosphine oxide present a hydrophobic character while the ones containing nanoparticles prepared using polyoxyethylene stearyl ether or the control sample are hydrophilic. Here we showed that (i) the use of protective agents, (ii) the surface properties of the films and (iii) the nature of the biological system can strongly influence the ecotoxicological studies. Epifluorescence microscopy analyses and Live/Dead tests showed that all films are toxic for Euglena gracilis. In the case of Anabaena flos-aquae and Calothrix pulvinata, tri- n-octylphosphine oxide and polyoxyethylene stearyl ether molecules can prevent ZnO nanoparticle toxicity.

Preparation and characterization of spindle-like Fe3O4 mesoporous nanoparticles.

Magnetic spindle-like Fe3O4 mesoporous nanoparticles with a length of 200 nm and diameter of 60 nm were successfully synthesized by reducing the spindle-like α-Fe2O3 NPs which were prepared by forced hydrolysis method. The obtained samples were characterized by transmission electron microscopy, powder X-ray diffraction, attenuated total reflection fourier transform infrared spectroscopy, field emission scanning electron microscopy, vibrating sample magnetometer, and nitrogen adsorption-desorption analysis techniques. The results show that α-Fe2O3 phase transformed into Fe3O4 phase after annealing in hydrogen atmosphere at 350°C. The as-prepared spindle-like Fe3O4 mesoporous NPs possess high Brunauer-Emmett-Teller (BET) surface area up to ca. 7.9 m2 g-1. In addition, the Fe3O4 NPs present higher saturation magnetization (85.2 emu g-1) and excellent magnetic response behaviors, which have great potential applications in magnetic separation technology.

Iron oxyhydroxide nanoparticles formed by forced hydrolysis: dependence of phase composition on solution concentration

Nanoparticles of single-phase lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) have been synthesized by forced hydrolysis of ferric nitrate with no other additives, and the particles have been characterized by XRD, FT-IR and TEM. At low Fe(NO(3))(3) concentrations the hydrolysis product is predominantly γ-FeOOH, while at high concentrations it is α-FeOOH. These particles are nanometers in size and fall within narrow particle size distributions. The dependence of the oxyhydoxide phase on ferric nitrate concentration is attributed to two thermodynamic factors, the enthalpy of formation and the surface enthalpy of hydration at the oxide-water interface (which is a function of surface area). Two potential mechanisms for the phase-specific growth are proposed that explain the solution concentration dependence of the phase formed. Three other common nanoscale particles (α-Fe(2)O(3), Fe(3)O(4) and γ-Fe(2)O(3)) have also been prepared by relatively simple thermal/chemical treatment of the γ-FeOOH nanoparticles.

Size-controlled synthesis of monodispersed mesoporous α-Alumina spheres by a template-free forced hydrolysis method

We demonstrated the formation of monodispersed spherical aluminum hydrous oxide precursors with tunable sizes by controlling the variables of a forced hydrolysis method. The particle sizes of aluminum hydrous oxide precursors were strongly dependent on the molar ratio of the Al(3+) reactants (sulfates and nitrates). In addition, the systematic phase and morphological evolutions from aluminum hydrous oxide to γ-alumina (Al(2)O(3)) and finally to α-Al(2)O(3) through thermal dehydrogenation were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). After annealing the amorphous aluminum hydrous oxide in air at 900 °C and 1100 °C for 1 h, we observed complete conversion to phase-pure γ- and α-Al(2)O(3), respectively, while maintaining monodispersity (125 nm, 195 nm, 320 nm, and 430 nm diameters were observed). Furthermore, both γ- and α-Al(2)O(3) were found to be mesoporous in structure, providing enhanced specific surface areas of 102 and 76 m(2) g(-1), respectively, based on the Brunauer-Emmett-Teller (BET) measurement.

New Fe-immobilized natural bentonite plate used as photo-Fenton catalyst for organic pollutant degradation

Novel photo-Fenton catalysts were prepared by immobilizing iron species on commercial bentonite plates via two methods: (1) ion exchange reaction (Fe 3+ vs. Na +) by aqueous suspension powder-clay/FeCl 3 followed by plate preparation, and (2) forced hydrolysis of Fe(NO 3) 3 onto a prefabricated clay plate. The last method led to a more photo-active Fe-oxide/bentonite plate. This material allowed, at a non-adjusted initial pH of 5.5 and in the presence of H 2O 2, the total degradation of resorcinol and 55% mineralization in 80 and 100 min of irradiation, respectively. The reached degradation percentages were correlated to the presence of dissolved iron, demonstrating that in these processes, the homogeneous photo-Fenton reactions were mainly responsible for the resorcinol elimination. Likewise, in slurry system, where clay has normally an increased surface area, there was no increase in activity because of a reduced leached iron probably due to the diminished light penetration in the suspension. Despite the lower surface area, in comparison to that of the slurry, the clay plates have the advantage, as heterogeneous photo-catalysts, that separation of the reaction media after treatment is not needed, and thus, a potential use for batch and continuous reaction systems is proposed.

Crystallization Pathways of Multicomponent Oxide Nanocrystals: Critical Role of the Metal Cations Distribution in the Case Study of Metal Ferrites

Metal ferrite (MFe2O4, with M = Fe, Mn, Co, Ni, Cu, Zn) nanoparticles were synthesized by processing metal oxide sols in a coordinating environment. The sols were prepared by forced hydrolysis of t...

Photo-Fenton degradation of resorcinol mediated by catalysts based on iron species supported on polymers

Novel Fe supported catalysts were prepared by immobilizing iron species on commercial polyethylene via three different methods: (1) acidic pre-treatment of the polyethylene followed by impregnation in aqueous Fe(NO 3) 3, (2) TiO 2 photo-catalytic pre-treatment of the polyethylene followed by forced hydrolysis of Fe(NO 3) 3, and (3) direct photo-Fenton attack with concomitant iron deposition on the polyethylene surface. The last method required soft conditions and led to the most photo-active Fe–polyethylene film. With this material, at a non-adjusted initial pH of 5.6 in the presence of H 2O 2, total degradation and 50% of resorcinol mineralization were observed in 40 and 60 min, respectively. Photo-Fenton functionalization/Fe-deposition process was also applied to polypropylene, high-impact polystyrene, and polymethylmethacrylate films. The efficiencies of all the prepared heterogeneous photo-catalysts were similar to that of an homogeneous photo-Fenton system containing the same amount of Fe 3+/2+ that leached during “heterogeneous” processes. That demonstrated than in our systems mainly homogeneous photo-Fenton reactions were responsible for the resorcinol degradation. The photo-catalytic activity observed for the Fe/polymer was a function of the specific polymer capacity to release the initially deposited iron into the solution.

Cetyltrimethyl ammonium bromide assisted hydrothermal growth of hematite hollow cubes

Hematite hollow cubes have been prepared by forced hydrolysis of ferric chloride solutions under hydrothermal conditions. The effects of reaction time, reaction temperature and cetyltrimethyl ammonium bromide on the transformation process from akageneite to hematite were investigated in detail. The products were characterized by X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. It is found that cetyltrimethyl ammonium bromide was a critical factor influencing the phase transformation process of akageneite and the final morphology of the as-prepared products. With cetyltrimethyl ammonium bromide, hematite hollow cubes and porous spheres were obtained. Otherwise only dense cubes were observed even prolonging reaction time or increasing reaction temperature. The mechanism was proposed.