Conventional Hydrothermal Technique Research Articles

Structural, morphological & optical studies of Hydroxyapatite microplates synthesized using hydrothermal technique

Hydroxyapatite or Penta-calcium hydroxide triphosphate (Ca10(PO4)6(OH)2 - HA) is biologically as well as naturally occurring mineral of Calcium. It has a vast range of applications in curing bone and teeth related issues as well as in solving environmental problems. In the present study, an attempt was made to synthesize HA using the conventional hydrothermal technique. Calcium and Phosphate precursors (namely Calcium nitrate tetrahydrate and Di-potassium Hydrogen Phosphate) were mixed in a certain proportion via drop wise addition with a stoichiometric Ca/P molar ratio of 1.67. Around 1 ml solution of Potassium Hydroxide (KOH) was used to set the pH of the solution to 4.0 – 5.0 (acidic medium). The resultant solution was given hydrothermal treatment at 160 ˚C for 24 h. Obtained precipitates were air-dried and calcinated at 600 ˚C for 2 h. X-ray Diffraction (XRD) analysis was carried out for the structural study of the synthesized sample. XRD analysis shows that HA is present as a major phase (JCPDS Card no. – 09–0432) along with secondary phases, namely Calcium Hydrogen Phosphate, Calcium Phosphate and Calcium Carbonate. Sharp peaks attributed to HA having (h k l) plane (002), (102), (210), (211) and (112) can be observed that confirm the formation of HA. Average Crystallite size was about 40 nm calculated using Debey-Scherrer’s equation. A morphological study was carried out using Scanning Electron Microscopy (SEM). SEM micrographs show well-defined plate-like particles (similar to bone apatite) with non-similar size distribution. At higher magnification, agglomerated smaller size particles can be observed. UV–vis spectroscopy was utilized to study the optical property. UV–vis transmittance spectrum was taken in the range of 200 nm to 1000 nm. It was found that HA exhibits strong absorption in the UV region and the approximate optical band gap of as-synthesized material was about 4.5 eV.

Luminescent carbon dots obtained from different precursors and methods and their applications as sensors for metal ions

Carbon dots (CDs) represent a rising class of nanomaterials with numerous optical and physicochemical properties that make them useful for a variety of applications. In this work, three different methods, conventional hydrothermal carbonization (CHC), microwave-assisted irradiation and heating reflux reaction technique, were used as different bottom-up approaches to obtain different CDs. The carbon nanoparticles were prepared using three different carbon precursors (maleic, fumaric and adipic acids) and one nitrogen source (ethylenediamine). The CDs were characterized using different techniques including Fourier transform infrared spectroscopy, Transmission electron microscopy, Ultraviolet-visible, Fluorescence and Zeta potential measurements. Both, the experimental method used to obtain the CDs and the different precursors, presented a considerable influence on the quantum yield values (QY), and also on the fluorescence emission curves. The molar proportion between the carbon and nitrogen source was varied to improve the QY, and one of the samples prepared by CHC method reached QY = 25.4%. The carbon nanoparticles obtained by CHC were used as nanoprobes for metal ions and exhibited great selectivity and sensitivity for Fe3+ ions, reaching a limit of detection of 35 nM, which is lower than most reported values for CD-based PL method used as probes for Fe3+ ions.

Comparison of three different structures of zeolites prepared by template-free hydrothermal method and its CO2 adsorption properties

In this study, zeolite sodalite SOD (50NaO2:Al2O3:5SiO2), zeolite LTA (2NaO2:Al2O3:1.926SiO2) and zeolite FAU (16NaO2:Al2O3:4SiO2) of different structures were synthesized successfully through simple conventional hydrothermal crystallization technique without using any template agent. Morphological analysis of three different types of zeolites revealed that the samples exhibit three different shapes such as the “Raspberry-like”, “Dice” cube like and “Octahedral” shaped morphology respectively. The thermal stability was found to be about 4.8%, 14.6% and 20.5% for the synthesized zeolites SOD, LTA and FAU respectively. From the N2 adsorption-desorption studies, it was observed that adsorption types IV and I correspond to the synthesized samples. CO2 adsorption by the synthesized zeolite SOD, LTA and FAU were examined in the pressure range from 0 to 101.325 kPa at a constant temperature of 297.15 K. The highest adsorption capacity of 3.7 mmol/g was obtained for zeolite FAU. The synthesized zeolite was studied using a nonlinear regression curve fit to determine the adsorption isotherm model using Langmuir and Freundlich isotherm model. It has been found that the synthesized zeolites have a large electric field gradient due to which they can strongly adsorb quadrupole of CO2 molecules.

Optimizing Rice Husk Silica Mass and Sonication Time for a More Efficient and Environmentally Friendly Synthesis of SBA-15

By optimizing rice husk silica mass and sonication time, SBA-15 was successfully synthesized in a more efficient and environmentally friendly way. The solution of Pluronic P-123 was mixed with the solution containing NaOH and various masses of rice husk silica (4–12 g), followed by sonication for a certain time (30–150 min). The mixture was filtered and washed with distilled water and ethanol until neutral, then dried at 110 °C for 2 h and calcined at 500 °C for 6 h. The results showed that the optimal mass of rice husk silica was 8 g, while the optimal sonication time was 30 min. The product has a cylindrical pore shape with good crystallinity and pore structure regularity. The specific surface area (SBET), the pore diameter (DBJH), the specific pore volume (VBJH), and the wall thickness (WT) of the product were 601 m2 g–1, 4.76 nm, 0.88 mL g–1, and 5.02 nm, respectively. These results are not considerably different from the porosity of SBA-15, synthesized previously using conventional hydrothermal techniques from various silica sources. In addition, it is also comparable to the porosity of SBA-15 produced from TEOS by sonochemical methods as well as with commercial SBA-15.

Electrochemical performance of mixed-phase 1T/2H MoS2 synthesized by conventional hydrothermal v/s microwave-assisted hydrothermal method for supercapacitor applications

Mixed-phase 1T/2H MoS2 has been receiving immense attention as an electrode material for supercapacitors due to the synergistic effects of both the phases. Herein, we synthesized mixed-phase 1T/2H MoS2 via two different techniques: conventional hydrothermal (HT) and microwave-assisted hydrothermal (MHT) technique. The formation of MoS2 is confirmed through X-ray diffraction pattern, scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman-spectra, and X-ray photoelectron spectra. The electrochemical performance of the two samples is investigated using cyclic voltammetry (CV), Gravimetric charging-discharging (GCD) and electrochemical impedance spectroscopy (EIS). MoS2 synthesized via MHT method (MS-MW) and HT method (MS-HT) deliver capacitances of 421 F g−1 and 742 F g−1 at 5 mV s−1, respectively. The energy density of MS-HT (57 Wh kg−1) is almost double than that of MS-MW (30 Wh kg−1). MS-HT also exhibited remarkable capacitance retention of 91% over 1200 cycles, compared with MS-MW. The results demonstrate that MoS2 synthesized by the hydrothermal method delivers superior electrochemical performance.

Anion-Controlled Synthesis of Enantiomeric Twofold Interpenetrated 3D Zinc(II) Coordination Polymer with Ligand Substitution-Induced Single-Crystal-to-Single-Crystal Transformation and Photocatalysis

An anion-controlled synthesis of a new three-dimensional (3D) “racemate”, an enantiomorphic twofold interpenetrated 3D zinc(II) coordination polymer containing bridging glutarate (glu) and 4,4′-bipyridine (4,4′-bipy) ligands, {[Zn4(H2O)2(4,4′-bipy)4(glu)3](NO3)2}n, 1 (P21/c), with ligand substitution-induced single-crystal-to-single-crystal (SCSC) transformation and photocatalysis for dye degradation was studied. The influence of a counteranion in zinc(II) starting materials and synthetic techniques upon the phase formation were explored. The complex 1 was successfully synthesized from zinc(II) nitrate salt via microwave-assisted techniques as well as the conventional hydrothermal technique, whereas the employment of zinc(II) acetate or sulfate salt yielded a two-dimensional coordination polymer, [Zn(4,4′-bipy)(glu)]n, 2 (P1̅), and the use of zinc(II) chloride led to a one-dimensional (1D) zigzag chain, [Zn(4,4′-bipy)Cl2]n 3 (C2/c). The synthetic-method-dependent formation was illustrated as the microwave-assisted techniques and conventional hydrothermal technique enabled the formation of crystalline-phase pure 1, while the sonochemical synthesis provided mixed crystalline-phases of 1 and 2. In the structure of 1, the 4,4′-bipy ligand links dinuclear Zn(II) building units into 1D chains along the [1̅01] direction. The glu2– ligand acts as tethering linkers expanding the structure into a cationic 3D coordination polymer that interpenetrates with its enantiomer to give a 3D solid-state “racemate”. Powder X-ray diffraction revealed that the ligand substitution-induced SCSC transformation of the twofold interpenetrated 3D framework, 1 (P21/c), which was triggered by chloride, led to a 1D zigzag chain, 3 (C2/c), whereas the bromide-triggered reaction led to a mixed crystalline phase between the isostructural 1D zigzag chain, [Zn(4,4′-bipy)Br2]n, 4 (C2/c), and its polymorph, [Zn(4,4′-bipy)Br2]n, 5 (P212121). The photocatalysis for the methyl orange degradation of 1 was studied.

Synthesis of Zeolite A from Iraqi Natural Kaolin Using a Conventional Hydrothermal Synthesis Technique

The synthesis of zeolite materials by hydrothermal transformation of kaolin using a conventional hydrothermal method was investigated. Different analytical techniques were used to characterize the starting kaolin and produced zeolite A samples, including scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), x-ray diffraction (XRD), x-ray fluorescence (XRF), thermogravimetric analysis (TGA), and Fourier transform infrared (FT-IR) spectroscopy. The synthetic zeolite type A was obtained after activation of kaolin and metakaolin followed by different thermal and chemical treatments. The metakaolinization phase was achieved by calcining the kaolin in air at 600°C for 3 hours, a much lower temperature than previously reported in the literature. Metakaolin was treated with 3 M sodium hydroxide solution at a ratio of 1:5 and, using stainless steel autoclaves with teflon liners, heated the mixture to 200°C in a microwave for 24 hours. The results from this synthesis route showed that zeolite A with a cubic crystal habit has been successfully synthesized.

Flower-like carbon doped MoS2/Activated carbon composite electrode for superior performance of supercapacitors and hydrogen evolution reactions

Abstract Polyethylene tetraphthalate (PET) bottles, a major environmental pollutant from the food industry, has been used as an activated carbon source in the current work. The specific surface area of the activated carbon has been analyzed using N2 adsorption/desorption isotherms, at different sonication time periods. A high surface area of 899 m2 g-1 with microporosity has been achieved for 20 h sonication followed by activation at 800 °C. To further enhance the material performance, carbon doped MoS2 (MoS2–C), using conventional hydrothermal technique has been synthesized. Different composite ratios of activated carbon and MoS2-C have been tested using electrochemical impedance spectroscopy and the best ratio owing to lesser charge-transfer resistance has been chosen for supercapacitor and HER analysis. The porous network of the plastic derived activated carbon (PAC) with a few layers of MoS2–C contributes significantly to the increase in the power density (469 W kg-1). By inducing defects on the material surface, there has been a significant enhancement in the electrocatalytic activity on PAC and this facilitates HER on its surface. Subsequently, the HER activity of the PDAC/MoS2–C composite has also been reported. Here, the PDAC defective sites along with the hexagonal MoS2–C’s largely exposed reactive edges indicate a reduction in the overpotential and Tafel values of −195 mV and −82 mVdec−1, suggesting that the material under investigation is a good catalyst for electrochemical HER. Also, this article reports for the first-time, HER activity of defect induced plastic derived activated carbon and its excellent catalytic activity.

Synthesis and solid solution in “rubidium richterite”, Rb(NaCa)Mg5Si8O22(OH,F)2

The OH–F substitution in “synthetic Rb-richterite” has been investigated along the join Rb(NaCa)Mg5Si8O22(OH)2–Rb(NaCa)Mg5Si8O22(F)2. Syntheses were done by conventional hydrothermal techniques (Tuttle-type vessels) at 800 °C, 1 kbar P(H2O). SEM microscopy showed very high yields of acicular to prismatic amphibole crystals up to XF = F/(F + OH) = 0.6. Beyond this value, a micaceous phase and a very fine-grained granular phase were present. Powder X-ray diffraction patterns show a single amphibole phase below XF = 0.6; above XF = 0.6, a distinct peak at d = 12.18 A indicates the presence of a mica and there is a broad hump starting at ~ 20o 2θ and ~ 15o wide, both features increasing in intensity with increasing XF. Cell dimensions at XF = 0 are compatible with an ideal amphibole composition Rb(NaCa)Mg5Si8O22(OH)2 and evolve with increasing XF up to XF = 0.6, where there is a sharp discontinuity in a, β and V. The infrared OH-stretching spectrum of the OH end-member shows a main band at 3732 cm−1 which is assigned to the local MgMgMg–OH→ Rb arrangement, and a minor band at 3670 cm−1 assigned to the local MgMgMg–OH→ □ arrangement. This latter band indicates a slight departure toward tremolite. Intermediate OH–F compositions show the appearance of a second band at 3718 cm−1, whose intensity is proportional to the F content in the system, in accord with OH−OH and OH–F arrangements across the filled A-site. For XF > 0.6, the OH-stretching spectra are complicated by the appearance of two more peaks at 3705 and 3685 cm−1. Additional bands at lower wavenumbers, centered around 3595, 3540 and 3475 cm−1, respectively, are better resolved by collecting the spectra on disks heated at 250 °C to remove the adsorbed moisture in the pellet. Combining the behavior of unit-cell dimensions and the infrared spectra with mass-balance arguments indicates that at high XF values, Na replaces part of the Rb at the A-site in the amphibole and the tremolite component of the amphibole increases, while “Rb tetrasilicic magnesium mica” crystallizes, along with semi-amorphous nanophases. The variation in band intensities as a function of XF indicates that OH and F randomly occupy local pairs of O(3) sites across a (filled) A-site, and that there is no short-range order of OH and F.

Tunable Optical Behaviour and Room Temperature Ferromagnetism of Cobalt-Doped BaSnO3 Nanostructures

In this work, the effect of Co doping on the structural, vibrational, morphological, optical and magnetic behaviour of BaSnO3 nanostructures is reported. Pure and Co (1,3, and 5%)-doped barium stannate (BSO) nanostructures were prepared by conventional hydrothermal technique followed by calcination at 900 °C for 5 h. The single crystalline cubic phase was identified by XRD analysis and structural distortions associated with Co doping were evidenced by variation in microstarin and crystallite size. FTIR and Raman studies further confirm the structural quality of the prepared samples. FESEM analysis revealed the mixed morphology of prepared samples, and the chemical compositions of all the samples were analysed using EDAX studies. The absorption studies revealed the incorporation of dopant ions and their effect on the bandgap subsequently in samples. The presence of defects and paramagnetic centres in the samples were confirmed by PL and EPR analyses. Magnetization studies demonstrated that pure BSO exhibits characteristic diamagnetism at room temperature and the addition of Co into Ba–Sn–O lattice drives the F-centre exchange interactions which results in the ferromagnetic behaviour. Hence, the occurrence of diamagnetic to ferromagnetic transition at room temperature with addition of Co as a dopant was identified.

Micro-wave sintered nickel doped cobalt ferrite nanoparticles prepared by hydrothermal method

The present paper report a study of the nickel doped cobalt ferrite Co0.9Ni0.1Fe2O4 have been synthesized by conventional hydrothermal technique followed by microwave sintering. The Co0.9Ni0.1Fe2O4 nanoparticles are characterized by X-ray diffraction (XRD), transmission electron microscopy, field emission scanning electron microscopy, particle size analyzer and vibrating sample magnetometer. The XRD spectra show a high degree of crystallinity and also indicates that the diffraction peaks correspond to the cubic spinel structure. Transmission electron microscopy indicating that, the crystallite size of Co0.9Ni0.1Fe2O4 nanoparticles was in the range of 40–75 nm. The nanoparticles show relatively high saturation magnetization of 32.540 emu/g.

Highly efficient visible light mediated azo dye degradation through barium titanate decorated reduced graphene oxide sheets

This study investigates BaTiO3 decorated reduced graphene oxide sheets as a potential visible light active catalyst for dye degradation (Rhodamine B). The composites were prepared through conventional hydrothermal synthesis technique using hydrazine as a reducing agent. A number of techniques have been employed to affirm the morphology, composition and photocatalytic properties of the composites; these include UV-visible spectrophotoscopy that assisted in quantifying the concentration difference of Rhodamine B. The phase homogeneity of the composites was examined through x-ray powder diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) was employed to confirm the orientation of the BaTiO3 particles over the reduced graphene oxide sheets. Photoluminescence (PL) emission spectra assisted in determining the surface structure and excited state of the catalyst. Fourier transformed-infrared (FTIR) spectra investigated the vibrations and adsorption peak of the composites, thereby ascertaining the formation of reduced graphene oxide. In addition, diffuse reflectance spectroscopy (DRS) demonstrated an enhanced absorption in the visible region. The experimental investigations revealed that graphene oxide acted as charge collector and simultaneously facilitated surface adsorption and photo-sensitization. It could be deduced that BaTiO3-reduced graphene oxide composites are of significant interest the field of water purification through solar photocatalysis.

A microfluidic device with integrated ZnO nanowires for photodegradation studies of methylene blue under different conditions

A microfluidic device with integrated ZnO nanowires (NWs) has been used for photodegradation studies of organic dye. By using conventional photolithography and hydrothermal growth techniques, high density and well-aligned ZnO NWs were grown on a patterned area over a glass substrate, allowing easy integration into a microfluidic reaction chamber for photodegradation under continuous-flow conditions. Cyclic photodegradation experiments are shown to demonstrate the variation of the photocatalytic efficiency during the first cycles. Accordingly, the device pretreatments such as ZnO NWs annealing and flushing with dye solution were performed in order to determine the optimal photocatalytic conditions. As expected, the microfluidics based approach exhibited a much improved photodegradation efficiency comparing to the conventional method using dispersed ZnO NWs.

Effect of synthesis technique on electrochemical performance of bismuth selenide

In this work we propose a novel idea of using thermoelectric material in lithium ion batteries. The reason behind this idea is to improve the efficiency of batteries especially when heat dissipation and exothermic reaction of cathode and anode with the electrolyte at higher temperatures restricts their continuous operation due to thermal runaway. In order to execute this idea we develop a new synthetic technique for fabrication of Bi2Se3 (thermoelectric material) and also compare it's efficiency by preparing this material by existing synthetic technique. Charge/discharge comparison of both the samples indicate that the synthesis technique has a profound effect on electrochemical performance. Bismuth selenide (Bi2Se3) is intentionally selected for this purpose. Bi2Se3 rectangular nanosheets (BRNS) with thicknesses of 200–500 nm are synthesized by a simple thermochemical method in which we use bismuth and selenium powders as precursors. Self assembled nanosheets (SANS) in spherical shape are prepared by conventional hydrothermal technique. Charge discharge experiments show that BRNS synthesized with this technique have reasonable performance as compared to nanosheets synthesized by conventional hydrothermal technique. It shows that first discharge capacity is up to 725.6 mAh g−1 for BRNS and 419.6 mAh g−1 for SANS.

The Microwave Synthesis and Photocatalytic Activity of Silver Vanadate

Using one simple microwave synthesis method, take silver nitrate and vanadium(V) oxide as raw meterial to synthesize Silver Vanadate. The photocatalytic degradation of methyl orange under visible light irradation showed that the photocatalytic activities of microwave synthetic samples were better than those of samples produced by conventional hydrothermal technique. This experiment is to discuss the impact of these factors upon the catalyst performance through the control of the calcine temperature, the quantity of hydrogen peroxide, pH, the concentration of methyl orange and the quantity of catalyst. When the catalyst was calcined at 500 °C ,0.1 g, and 0.5 mL hydrogen peroxide joinded as well as pH was 2.0, the degradation ratio of Ag3VO4 for methyl orange of 100 mL 5 mg/L reached 91.49％ in 40 min.

Preparation of Visible-Light-Driven Silver Vanadates by a Microwave-Assisted Hydrothermal Method for the Photodegradation of Volatile Organic Vapors

A variety of visible-light-driven silver vanadates, including α-AgVO3, β-AgVO3, and α-Ag3VO4, were synthesized using a microwave-assisted hydrothermal synthesis method. UV−vis spectroscopy indicated that each of the silver vanadate particles obtained in the study had strong visible-light absorption with associated band gaps in the range of 2.2−2.5 eV. The α-Ag3VO4 crystalline sample with rich hydroxyl functional groups on the surface exhibited the highest degree of photocatalytic activity. The reaction rates of the photodegradation of isopropanol (IPA) and benzene vapors were approximately 8 times higher than those of P25 under visible-light irradiation. Furthermore, the active sites at which catalysts play a role as proton donors (Brønsted acidity) in the photodegradation of VOC were characterized by the temperature-programmed desorption (TPD) method in conjunction with the diffuse reflectance infrared Fourier transform (DRIFT) technique. In addition, the photocatalytic activities of microwave-assisted hydrothermal samples were higher than those of samples produced by conventional hydrothermal techniques. This was due to an increase in the specific surface area and additional hydroxyl functional groups on the surface. These results demonstrate that the microwave-assisted hydrothermal method is an efficient technique for the fabrication of visible-light-responsive silver vanadates with outstanding performance in the photocatalysis of VOCs.

Surfactant-Assisted Solvothermal Synthesis of Ba(CoTi)xFe12−2xO19 Nanoparticles and Enhancement in Microwave Absorption Properties of Polyaniline

Barium ferrite (BaFe12O19) nanoparticles have been successfully synthesized from solvothermal route with the assistance of surfactant P123 (EO20PO70EO20), which has been proven to be a better method for barium-ferrite synthesis as compared to conventional hydrothermal technique, and the resultant product shows high-purity crystalline phase, small particle size, excellent magnetic properties, and characteristic of single magnetic domains. A series of Co−Ti-doped barium-ferrite nanoparticles [Ba(CoTi)xFe12−2xO19, 0.25 ≤ x ≤ 1.0] were also prepared by this method, indicating that this route is versatile for barium-ferrite nanoparticles with different chemical compositions. With increasing heteroatoms content, saturation magnetization and coercivity drastically decreased because of the selective substitution of Fe3+ sites by Co2+ and Ti4+ in the magnetoplumbite structure. By supplying these inorganic nanoparticles as nucleation sites, polyaniline/ferrite composites were prepared through in situ polymerization technique. Compared with pure polyaniline, these composites exhibited essentially enhanced reflection loss properties because of the synergetic behavior between organic and inorganic materials, and proper heteroatom substitution can even improve the reflection loss. More importantly, well reflection loss over a wide frequency range can be simply achieved by manipulating the absorber thickness, suggesting these composites may be used as lightweight and highly effective microwave absorbers.

Novel hydrothermal solution routes of advanced high melting nanomaterials processing

Novel hydrothermal solution processing routes covering conventional hydrothermal, solvothermal and supercritical hydrothermal techniques are becoming the most efficient routes for advanced nanomaterials processing including the high melting compounds. The importance of these novel hydrothermal solution routes has been discussed with appropriate examples. The current trends in the hydrothermal solution processing of materials, the importance of solubility study, thermodynamic calculations and the role of surfactants and chelates have been discussed in detail. The multi-energy processing of materials, instant hydrothermal system and the new concept in materials processing, viz. Chemistry at the speed of light have been highlighted here. The hydrothermal synthesis of nanomaterials of carbon polymorphs, rare earth vanadates, metal oxides and their nanocomposites have been discussed with an emphasis on the control of size and morphology.

Rapid Microwave–Hydrothermal Synthesis of Anatase Form of Titanium Dioxide

Pure anatase titanium dioxide was synthesized by a microwave (MW)‐assisted hydrolysis of diluted acidic solutions of titanium tetrachloride. MW irradiation combined with hydrothermal process has proved to be a very efficient and fast alternative to conventional hydrothermal technique, as an almost complete crystallization of anatase occurred in reaction times as short as 30 min. The addition of small amounts of sulfuric acid was necessary to obtain a pure anatase phase, as the presence of sulfate prevented the crystallization of trace amounts of brookite. Transmission electron micrographs showed nanoparticles arranged in spherical aggregates with 1% sulfuric acid, while less aggregated nanoparticles were obtained with 0.1% sulfuric acid.

Synthesis and characterization of praseodymium-doped ceria powders by a microwave-assisted hydrothermal (MH) route

Nanocrystalline Pr-doped ceria powders were prepared for the first time by a microwave-assisted hydrothermal route. The effect of the microwave treatment in relation to the conventional hydrothermal technique was evaluated. The samples prepared were characterized in terms of composition, crystalline structure, particle shape and size distribution by X-ray diffraction, transmission electron microscopy (TEM) and specific surface area analysis (BET). The color properties of these solid solutions were also evaluated as a function of synthesis conditions and composition. Finally the oxidation state of the Pr cations and the relative quantities of Pr(IV) and Pr(III) were investigated by X-ray absorption at the M4,5 Pr absorption edge.