Conventional Co-precipitation Technique Research Articles

Competition between Cubic and Tetragonal Phase Induced Unusual Vertical Magnetization Shift and Exchange Bias in CoxMn3−xO4 (1 ≤ x ≤ 2) Spinel Nanoparticles

CoxMn3−xO4 (1 ≤ x ≤ 2) spinel nanoparticles synthesized through conventional coprecipitation technique exhibit the coexistence of tetragonal and cubic phases in the range of 1 ≤ x ≤ 1.5, while a pure cubic phase is observed for 1.75 ≤ x ≤ 2 at room temperature. Reduction in tetragonal phase fraction from 92 % for x = 1 to 47% for x = 1.5 is attributed to diminution of Jahn–Teller (J–T) active Mn3+ ions occupying the octahedral site of spinel lattice. X‐ray photoelectron spectroscopy confirms both +2 and +3 oxidation states for Co and Mn. Surprisingly, cubic and tetragonal phases exhibit magnetic transition, Tc1 and Tc2, corresponding to a paramagnetic to a high and low temperature ferrimagnetic state, respectively. Tetragonal phase induces high spontaneous (HSEB) and conventional (HCEB) exchange bias with unusually high vertical magnetization shift (VMS) than that of the pure cubic phase, shows maximum HCEB of 4.062 kOe for x = 1.5 and a VMS of 2.5 emu g−1 for x = 1. Such dependence of VMS and exchange bias on tetragonal to cubic phase ratio in CoxMn3−xO4 is demonstrated for the first time and interpreted based on the interaction between different arrangement of spins in tetrahedral and octahedral sublattice.

Enhancing photocatalytic performance of iron-doped TiO2 nanoparticles: Effects of annealing temperature on anatase-rutile mixed phase structure

The photocatalytic activity of the methylene blue in metal oxide anatase-rutile mixed phase TiO2 nanoparticles doped with iron after annealing at various temperature has been investigated. The ratio Fe/Ti (wt 3 %) was prepared using the conventional co-precipitation technique with annealing treatment. X-ray Diffraction (XRD) analysis showed anatase (∼25 %) and rutile (∼75 %) phase structures, and the crystallite size increased with increasing temperature. The Fourier transform infrared (FTIR) transmittance band at 517 cm−1 for TiO2 stretching vibration mode was examined using Kramer-Kronig relation for determining the optical characteristic such as the refractive index (n), the extinction coefficient (k), the dielectric function, and the energy loss function. Further analysis of the optical properties of Fe-doped TiO2 NPs shows the Δ (LO−TO) is shrinker after annealing above 200oC that indicated more stable bonding. The field emission scanning electron microscopy (FESEM) micrographs show agglomerations formed into clusters like as edelweiss flowers and roses on the surface. UV–Vis measurement reveals that the optical energy gap decreased from 3.05 eV annealed at 200oC to 2.88 eV annealed at 500oC. The UV–Vis absorbance with varying the time from 30 to 120 min to MB as a pollutant is reduced as time irradiation increases with photocatalytic rates for annealing at 500oC is 0.0071/min. The predominant anatase phase alignment, stable bonding, and unique surface make iron doped TiO2 NPs a promising catalyst.

Polypyrrole Coating via Lemieux-von Rudloff Oxidation on Magnetite Nanoparticles for Highly Efficient Removal of Chromium(VI) from Wastewater.

An alternative way for the coating of polypyrrole (PPy) polymer on hydrophobic magnetite (Fe3O4) nanoparticles is reported here to capture toxic chromium ions, Cr (VI), present in water. Iron oxide magnetic nanoparticles (Fe3O4) were synthesized by the conventional coprecipitation technique using FeCl3·6H2O and FeSO4·7H2O iron precursors and subsequently modified with oleic acid (OA). Then OA-Fe3O4 hydrophobic nanoparticles were oxidized using the Lemieux-von Rudloff reaction to transfer OA into hydrophilic azelaic acid (AA) (HOOC(CH2)7COOH-modified magnetic nanoparticles (AA-Fe3O4). Finally, a PPy polymer coating was formed by a seeded polymerization of pyrrole, using AA-Fe3O4 as seeds. The average size of PPy/Fe3O4 nanocomposites is 12.33 nm and is almost spherical in shape. The surface composition is confirmed by FTIR and thermogravimetry analyses. An X-ray diffraction study confirmed the formation of highly crystalline Fe3O4 nanoparticles, and the crystallinity was retained after the surface modification. The adsorption study suggested that the Cr(VI) ion adsorption is highly pH-dependent and the maximum amount of adsorption is obtained at pH 2.0. The adsorption results revealed that the Langmuir model provided the best fit for the isotherm, with a maximum adsorption capacity reaching approximately 173.22 mg g-1 at 323 K. Spontaneous and endothermic adsorption processes were confirmed by evaluating the thermodynamic parameters obtained in this investigation. The kinetics study showed that the interaction between Cr(VI) ions and magnetic nanocomposites was directed by a pseudo-second-order rate process indicating chemisorption. The prepared PPy/Fe3O4 nanocomposites would be promising adsorbents to purify water by eliminating Cr(VI) metal ions from wastewater.

Microwave-Assisted Hydrothermal Synthesis of Space Fillers to Enhance Volumetric Energy Density of NMC811 Cathode Material for Li-Ion Batteries

Ni-rich layered transition metal (TM) oxides are considered to be the most promising cathode materials for lithium-ion batteries because of their high electrochemical capacity, high Li+ ion (de)intercalation potential, and low cobalt content. However, such materials possess several drawbacks including relatively low volumetric energy density caused by insufficient values of tap density. Herein, we demonstrate an exceptionally rapid and energy-saving synthesis of the mixed hydroxide precursor for the LiNi0.8Mn0.1Co0.1O2 (NMC811) positive electrode (cathode) material through a microwave-assisted hydrothermal technique. The obtained material further serves as a space-filler to fill the voids between spherical agglomerates in the cathode powder prepared via a conventional co-precipitation technique boosting the tap density of the resulting mixed NMC811 by 30% up to 2.9 g/cm3. Owing to increased tap density, the volumetric energy density of the composite cathode exceeds 2100 mWh/cm3 vs. 1690 mWh/cm3 for co-precipitated samples. The crystal structure of the obtained materials was scrutinized by powder X-ray diffraction and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM); the cation composition and homogeneity of TM spatial distribution were investigated using energy-dispersive X-ray spectroscopy in a STEM mode (STEM-EDX). Well-crystallized NMC811 with a relatively low degree of anti-site disorder and homogeneous TM distribution in a combination with the co-precipitated material delivers a reversible discharge capacity as high as ~200 mAh/g at 0.1C current density and capacity retention of 78% after 300 charge/discharge cycles (current density 1C) within the voltage region of 2.7–4.3 V vs. Li/Li+.

Synthesis and material characterization of TiO2 nanoparticles doped with iron (Fe)

Titanium dioxide (TiO2) doped with iron (Fe) atom are investigated using X-Ray diffraction, field emission scanning electron microscopy (FESEM), and photocatalysts measurements. Fe-TiO2 nanoparticles with different concentration of iron were formed using the conventional co-precipitation technique from two different chemical solutions. The precursors of TiO2 were prepared using titanium tetrachloride (TiCl4) of 50 ml, and iron trichloride (FeCl3) was used as a dopant source. X-ray diffraction results show that diffraction pattern have two phases structures anatase and rutile phase structures where the intensity of the rutile structures are superior to that the anatase phase intensities. The results from FESEM micrograph indicate that the agglomerations were taken place, forming into clusters. Irradiation of ultraviolet (UV) with varying the time from 30 minutes to 120 minutes to the Fe-doped TiO2 nanoparticles using methylene blue shows that the absorption intensity reduces as time irradiation increased. The results indicate that the TiO2 nanoparticles doped with iron are suitable as photocatalysts.

Insight into the positive effect of Cu0/Cu+ ratio on the stability of Cu-ZnO-CeO2 catalyst for syngas hydrogenation

Cu-ZnO based catalysts are of industrial importance for methanol synthesis. In this work, Cu-ZnO-CeO2 (CZCe) catalyst has been prepared via conventional co-precipitation technique and applied for syngas hydrogenation to methanol with the purpose to study the effect of reversible redox metal oxide (ceria) on the distribution of valence state of active Cu species. Herein, CZCe catalyst exhibited the outstanding catalytic performance with initial methanol yield as high as 0.665 g·g–1 cat.·h–1 and the STYMeOH could well be maintained with a high value (0.600 g·g–1 cat.·h–1) at 230 °C after 70 h of evaluation, which exceeded the reference Cu-ZnO-Al2O3 (CZAl) catalyst prepared by the same method. The excellent performance could be attributed to ceria doping tended to dynamically tune the distributions and/or concentrations of Cu+ and Cu° species on the catalyst surfaces and retard the conversion of Cuδ+ (δ < 2) to Cu2+ in the process of reaction.

Cation distribution and magnetic properties of Zn-substituted CoCr2O4 nanoparticles

CoCr2O4 is a normal spinel where Co occupies the tetrahedral (A) site and Cr occupies the octahedral (B) site; it is important to examine the cation distribution and magnetic properties by substituting a non-magnetic ion like Zn. In this context, we have synthesized pure phase ZnxCo1-xCr2O4 (x = 0.05, 0.1) of crystallite size 10 nm through conventional co-precipitation technique. Fourier transform of Co, Zn, and Cr K-edge spectra obtained from extended X-ray absorption fine structure demonstrates that while Co and Zn prefer the A site, Cr strongly occupies the B site. The paramagnetic to long range ferrimagnetic transition, TC, decreases from 97 K in CoCr2O4 (bulk) to 87.4 K at x = 0.1 with an intermediate TC of 90 K at x = 0.05. The decrease in TC is ascribed to decrease in A-B exchange interaction confirming the preferential occupation of Zn2+ ions towards the A site. The spin-spiral transition, TS, decreases from 27 K in bulk (CoCr2O4) to 24 K at x = 0.1 followed by a spin lock-in transition, TL, observed at 10 K which remains unchanged with increase in Zn concentration. The diffuse neutron scattering in both compositions shows the evidence of long range spiral ordering in contrast to the simultaneous formation of long and short range order in single crystals of CoCr2O4. The decrease in maximum magnetization from 9 to 8 emu/g and an increase in coercivity from 3.2 to 5.2 kOe at 2 K with an increasing Zn concentration from 0.05 to 0.1 have been explained by considering the Yafet-Kittel model.

Evolution of structure and magnetic properties of stoichiometry and oxygen rich LaMnO3 nanoparticles

In this report, the evolution of structure and magnetic properties in stoichiometry and oxygen rich LaMnO3 samples synthesized by a simple, cost effective, conventional co-precipitation technique are systematically studied. While X-ray powder diffraction reveals a monoclinic, I2/a structure in both samples, Reitveld refinement demonstrates higher John-Teller (J-T) distortion in the former one. Higher J-T distortion is accompanied with a large deviation in MnO bond length. FESEM (Field Emission Scanning Electron Microscopy) analysis combined with crystallite size calculated from XRD peak profile suggest that the particles are of 50–60nm and are polycrystalline in nature. The antiferromagnetism observed in bulk LaMnO3 with TN=140K evolves towards a ferromagnetic order in both stoichiometry and oxygen rich samples. However, Curie temperature, TC, is found to be higher in oxygen rich sample due to higher MnOMn bond angle. The large effective magnetic moment calculated from Curie-Weiss plot is found to be higher in stoichiometry sample. Higher moment is ascribed to high oxygen vacancies evidenced from XPS analysis. Dispersion behavior observed in frequency dependent ac susceptibility (χ) indicates the spin-glass, cluster-glass and interacting superparamagnetic behavior. Fitting the susceptibility data with phenomenological models such as Neel-Arrhenius, Vogel-Fulcher and Power law, while canonical spin-glass, cluster-glass and interacting superparamagnetism is ruled out, the spin-glass behavior with a higher relaxation time in oxygen rich sample is confirmed.

Effect of fatty acid chain length and concentration on the structural properties of the coated CoFe2O4 nanoparticles

The present study investigates the effect of various synthesis parameters including chain length of fatty acids, concentration ratio of precursor to fatty acid, reaction temperature and aging time on the structural as well as magnetic properties of the CoFe2O4 nanoparticles. The synthesis of nanoparticles was achieved successfully in aqueous solution by the conventional Co-precipitation technique using Fe3+ and Co2+ ions by the addition of a strong base NaOH. Herein, the Oleic acid and Lauric acid was used as the stabilizing agent during the nucleation stage of the nanoparticles. The structural as well as morphological properties were characterized by XRD, FTIR and FESEM techniques and the magnetic intensity was investigated by vibrational sample magnetometer (VSM). The XRD analysis of the coated nanoparticles confirmed that the cubic spinel phase of the CoFe2O4 nanoparticles were retained after coating and the crystallite size reduced as the concentration of fatty acid increased. FESEM analysis revealed that the synthesized nanoparticles were of spherical shape and the extent of nanoparticle aggregation reduced gradually as the ratio of precursor to oleic acid was decreased from 4 to 1. Further, the hysteresis loop confirmed the ferromagnetic nature of the coated nanoparticles with high coercivity.

Comparative study of structural features and thermal behavior of mixed silica-titania xerogels prepared via the peroxo method and the conventional co-precipitation technique

Detailed investigation of thermal and structural properties of mixed SiO2/TiO2 xerogels prepared via the method based on application of a precursor containing peroxo titanic acid and oligomeric silica and by the conventional co-precipitation technique has been presented. Formation of oxide phases from the xerogels prepared via the peroxo method and the co-precipitation of inorganic salts has been studied by TG/DSC, FTIR and in situ powder XRD techniques. The co-precipitation method provides higher degree of molecular homogeneity of the composite oxide, while in the case of the peroxo route segregation of the oxides takes place. The silica–titania samples prepared by the co-precipitation method include anatase phase, which is stable up to 1000°C, while TiO2 in the mixed oxide synthesized by the peroxo method transits to rutile at temperatures near 800°C. The presented data give no evidence for formation of SiOOTi peroxo bridges in the xerogels prepared via the peroxo method. Peroxo groups in the silica–titania xerogels synthesized via the peroxo-method have been found to be more stable in silica–rich samples, compared to pure titania. Thus, these materials hold promise for application as catalysts in oxidation reactions and photocatalysis.

Tuning of magnetic transition temperatures in nanoparticles of CoCr2O4 multiferroic by B-site mixing

Pure CoCr2−xFexO4 nanoparticles synthesized through conventional coprecipitation technique show particle size distribution in the range of 16–20 and 6–10nm for x=0.1 and 0.2 respectively. Magnetic and specific heat measurements show an enhancement of paramagnetic to collinear ferrimagnetic transition temperature, Tc from 100 to 110K and to a short range non-collinear spiral ordering, Ts from 18 to 36K with increasing x from 0.1 to 0.2 respectively. In addition, a strong disagreement between the paramagnetic moment obtained from the fitting of χ−1=T/C+1/χ0–b/(T−θ) and ferrimagnetic moment measured from the M vs. H loop at 10K corroborates the nonsaturation behavior of magnetization at 50–100kOe field and an order of magnitude higher coercivity (Hc). The enhancement of Tc and Ts with increasing Fe concentration is attributed to an intrinsic change in non-collinear to collinear spin structure and strong JA–B interaction.

Study of the preparation, properties and kinetics of anion release in drug intercalated magnetic nanohybrids

We report a new magnetic nanohybrid material to make layered double hydroxides (LDHs) as a targeted drug carrier. The magnetite prepared using a modified conventional coprecipitation technique was embedded in to the fluvastatin intercalated hydrophobic anionic clay through one step process. XRD analysis shows a decrease in lattice parameter of magnetite which is due to generation of stress by the LDHs. Filtered HRTEM image indicates that the magnetic nanohybrid consists of well-defined composite structure and the diameter is around 13nm. Further, it is shown through magnetisation and ESR study that the exchange interaction between magnetite and drug intercalated LDHs layers shifted the TB of Fe3O4 in magnetic nanohybrid to lower temperatures. In vitro release study of nanohybrid particles at pH 7.4 in PBS and at 37°C show a faster release for magnetic nanohybrids. The mechanism is probably due to combined effect of interparticle and heterogeneous diffusion via anionic exchange.

Photocatalytic performance of nano-photocatalyst from TiO 2 and Fe 2O 3 by mechanochemical synthesis

Nano-particles of homogeneous solid solution between TiO 2 and Fe 2O 3 (up to 10 mol%) have been prepared by mechanochemical milling of TiO 2 and yellow Fe 2O 3/red Fe 2O 3/precipitated Fe (OH) 3 using a planetary ball mill. Such novel solid solution cannot be prepared by conventional co-precipitation technique. A preliminary investigation of photocatalytic activity of mixed oxide (TiO 2/Fe 2O 3) on photo-oxidation of different organic dyes like Rhodamine B (RB), Methyl orange (MO), Thymol blue (TB) and Bromocresol green (BG) under visible light (300-W Xe lamp; λ > 420 nm) showed that TiO 2 having 5 mol% of Fe 2O 3 (YFT1) is 3–5 times higher photoactive than that of P25 TiO 2. The XRD result did not show the peaks assigned to the Fe components (for example Fe 2O 3, Fe 3O 4, FeO 3, and Fe metal) on the external surface of the anatase structure in the Fe 2O 3/TiO 2 attained through mechanochemical treatment. This meant that Fe components were well incorporated into the TiO 2 anatase structure. The average crystallite size and particle size of YFT1 were found to be 12 nm and 30 ± 5 nm respectively measured from XRD and TEM conforming to nanodimensions. Together with the Fe component, they absorbed wavelength of above 387 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe 2O 3/TiO 2 particle attained through mechanochemical method. This meant that Fe components were well inserted into the framework of the TiO 2 anatase structure. EPR and magnetic susceptibility show that Fe 3+ is in low spin state corresponding to μ B = 1.8 BM. The temperature variation of μ B shows that Fe 3+ is well separated from each other and does not have any antiferromagnetic or ferromagnetic interaction. The evidence of Fe 3+ in TiO 2/Fe 2O 3 alloy is also proved by a new method that is redox titration which is again support by the XPS spectrum.

Optimization of the MnCeOx system for the catalytic wet oxidation of phenol with oxygen (CWAO)

A class of MnCeOx catalysts has been synthesized via the new redox-precipitation route in alternative to the conventional co-precipitation technique. The effects of preparation method, composition and calcination temperature on catalyst texture, dispersion and reduction pattern properties have been addressed. Redox-precipitated systems exhibit high surface area (SA, 120–170m2/g), large pore volume (PV, 0.4–0.5cm3/g) and a “narrow” pore size distribution (PSD) in a wide range of the Mn/Ce ratio (1/3–3/1). A quasi-molecular dispersion markedly improves oxide-support interactions and reducibility of the active phase. Redox-precipitated systems show a superior performance in the catalytic wet oxidation of phenol with oxygen (CWAO) at 373K in terms of substrate and total organic carbon (TOC) elimination and mineralization (i.e., CO2 formation) selectivity. Carbon mass-balance from TG-DSC data of used catalysts and CO2 selectivity values signal that the CWAO of phenol proceeds via a L–H reaction path, the oxidation of C-containing species being the rate limiting step (r.l.s.). Then, an optimum average pore diameter (APD, 10–15nm) enhances the rate of the adsorption step, while a straight relation between CO2 selectivity and reducibility prove that dispersion and redox properties of the active phase control the mineralization activity of the MnCeOx system.

Synthesis of layered double hydroxides in W/O micro-emulsion: Influence of method of preparation on the physico-chemical and adsorption characteristics

ABSTRACTZn/Al layered double hydroxide was synthesized in micro-emulsion system with the oil phase comprising of cyclohexane + TX100 (surfactant) + n-hexanol (co-surfactant). Aqueous NaOH solution was used as the precipitating agent. The XRD pattern showed Zincite as the primary and hydrotalcite as the secondary phase. The d003 diffraction peak corresponded to interlayer hydroxide ion. There was no interlayer NO3- ion. The synthesized LDH showed much higher BET surface area (116.3 m2/g) than similar LDH synthesized by conventional co-precipitation technique (4.2 m2/g). Well defined flaky nano-crystals having an average dimension of 5-20 nm were observed by HRTEM.

Synthesis of highly dispersed MnCeO x catalysts via a novel “redox-precipitation” route

A new synthesis route driving redox-precipitation reactions among Mn VII, Ce III and Mn II precursors in basic aqueous solution yields MnCeO x catalysts (Mn loading, 9–33 wt%) with improved textural and structural properties in comparison to the conventional co-precipitation technique. Irrespective of the Mn loading, BET, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) findings prove that the new method ensures a very high reproducibility in all the main physico-chemical properties of MnCeO x catalysts. Enabling a monolayer dispersion of the active phase, the “redox-precipitation” method greatly promotes the reducibility and the surface affinity of the MnCeO x system towards gas-phase oxygen.

Unagglomerated powders for transformation-toughened structural ceramics

Results of a study of the characteristics of ZrO2 powders stabilized by 3 mol% Y2O3 and fabricated by the method of ultrasound spray pyrolysis from aerosols of aqueous solutions of mineral salts are presented. Unlike powders of the same composition obtained by the conventional coprecipitation technique, aerosol powders have coarser particles with a narrower size distribution and do not contain agglomerates. The temperature of sintering coarse aerosol powders to a maximum density is not high (1450°C). Despite the larger grain size in ceramics sintered from aerosol powders, their strength is much higher than that of ceramics obtained from ultradisperse coprecipitated powders of a similar composition.