Physical and chemical properties of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles prepared by combustion and ultrasonic bath methods

The combustion and ultrasonic bath methods have been utilized to generate nickel spinel ferrite nanoparticles. Physical and chemical properties of generated nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). Between the nanoparticles generated by mentioned methods, there were differences in size, oxygen-metal bonding, and magnetic properties which have been investigated in the work.     

Characterization of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles synthesized by various methods

Microwave-induced combustion with glycine, CTAB-assisted hydrothermal process with NaOH and NH3, EDTA assisted-hydrothermal methods have been applied to prepare NiFe₂O₄ nanoparticles for the first time. Structural and magnetic properties of the products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmison electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and electron spin resonance spectrometry (EPR). TEM measurements showed that morphology of the product depends on the synthesis method employed. The average cystallite size of NiFe₂O₄ nanoparticles was in the range of 14–59 nm as measured by XRD. The uncoated sample (Method A) had an EPR linewidth of 1973 Oe, the coated samples reached lower values. The magnetic dipolar interactions existing among the Ni ferrite nanoparticles are reduced by the coatings, which could cause the decrease in the linewidth of the EPR signals. Additionally, the linewidth increases with an increase in the size and the size distribution of nanoparticles.     

Synthesis and characterization of chitosan coating of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles for biomedical applications

Nickel ferrite nanoparticle is a soft magnetic material whose appealing properties as well as various technical applications have rendered it as one of the most attractive class of materials; its technical applications range from its utility as a sensor and catalyst to its utility in biomedical processes. The present paper focuses first on the synthesis of NiFe₂O₄ nanoparticles through co-precipitation method resulting in calcined nanoparticles that were achieved at different times and at a constant temperature (773 k). Afterward, they were dispersed in water that was mixed by chitosan. Chitosan was bonded on the surface of nanoparticles by controlling the pH of media. In order to assess the structural and magnetic properties of nanoparticles, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) analyses were conducted at room temperature. As per the results of XRD analysis, the pure NiFe₂O₄ was synthesized. Additionally, nanoparticles grew in size by extending the calcination process duration. TEM micrographs were used to determine the size and shape of particle; the obtained results indicate that the particle size was in a range of 17–30 nm and of a circular shape. The proper chitosan covering was also indicated by FTIR results. The VSM analysis also revealed that the saturated magnetization of NiFe₂O₄ nanoparticles stood in a range of 29 emu/g and 45 Q_e. A stable maximum temperature ranging from 30 to 42 was successfully achieved within 10 min. Also, a specific absorption rate of up to 8.4 W/g was achieved. The study results revealed that the SAR parameter of the coated nickel ferrite nanoparticle is more than that of pure nickel ferrite or cobalt ferrite nanoparticles.     

Preparation and Application of Magnetically Recoverable Cationic Exchanger Support on Monodisperse Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles

A magnetically recoverable cationic exchanger has been effectively prepared through immobilized chloroacetic acid (CA) onto the Fe₃O₄ nanoparticles. The magnetic nanoparticles (MNPs) were synthesized by a coprecipitation method in an aqueous system. The MNPs were modified with sodium silicate and chloroacetic acid (CA), thus endowed these nanoparticles with strong magnetism and good dispersion. The physicochemical properties of the cationic exchange materials were characterized with Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). The magnetic properties of the cationic exchange materials were analyzed by a vibrating sample magnetometer (VSM). The content of ions was measured by atomic absorption spectrophotometric method. The prepared cationic exchange nanoparticles display an excellent magnetic property with a saturation magnetization value of 26.58 emu/g and the prepared exchanger possess considerable thermal stability, which indicating a great potential application in heavy metal ion wastewater treatment. In this experiment, the exchange capacity of lead ion was 3.4 mmol g^–1, And the maximum lead removal rate is up to 73.85%.     

Effect of different conductive additives on charge/discharge properties of LiCoPO<Subscript>4</Subscript>/Li batteries

Single-phase LiCoPO₄ nanoparticles were synthesized by solid-state reaction method and subsequent high-energy ball milling. The electrochemical properties of LiCoPO₄/Li batteries were analyzed by ac impedance experiments, cyclic voltammetry (CV), and charge/discharge tests. The structural and morphological performance of LiCoPO₄ nanoparticles was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The XRD result demonstrated that LiCoPO₄ nanoparticles had an orthorhombic olivine-type structure with a space group of Pmnb. Different conductive additives including acetylene black and carbon black (SP270) were used to fabricate electrodes. The morphologies of the electrodes and different conductive additives were observed by field emission-scanning electron microscopy (FE-SEM). LiCoPO₄/Li battery with acetylene black showed the best electrochemical properties, and exhibited a discharge plateau at around 4.7 V with an initial discharge capacity of 110 mAh g⁻¹ at a discharge current density of 0.05 mA cm⁻² at 25 °C.     

Synthesis,Phase Transition of La<Subscript>0.69</Subscript>Sr<Subscript>0.31</Subscript>MnO<Subscript>3</Subscript> Nanoperovskites Toward Its Versatile Structural,Electrical and Mechanical Properties Employing Ultrasonic Measurements

The present investigation correlates the propagation of ultrasonic waves with various micro structural features of nano La_0.69Sr_0.31MnO₃ (LSMO) perovskites with different grain sizes. A solid state reaction followed by the ball milling technique was used to synthesize the nano LSMO perovskite samples with various grain sizes. The occurrence of ferro-paramagnetic transition temperature (T_c) was explored through the observed anomalous behaviour in ultrasonic velocities, attenuations and elastic moduli. As the particle size gets reduced, lower T_c and broader transitions are observed due to the distribution of grain boundaries. The diffusion of the FM–PM phase transition along with decrease in T_c is correlated due to the effect of particle size. Furthermore structural, vibrational and electrical properties of nanosized LSMO perovskite samples with different grain sizes were studied by XRD, FTIR, BET surface area measurement, HRSEM, TEM and four probe conductivity studies. The phase of the synthesized nano LSMO perovskite samples are perfectly indexed to pure rhombohedral perovskite type crystal structure. The conductivity study proves the semiconductor nature of the nano LSMO perovskite samples. In addition to this, the peak broadening in ultrasonic studies at phase transition is in line with the observation made from the XRD pattern for the prepared nano LSMO perovskite samples.     

The Effect of Particle Size on the Processes of Charging and Discharging of the LiFe<Subscript>0.97</Subscript>Ni<Subscript>0.03</Subscript>PO<Subscript>4</Subscript>/C/Ag Cathode Material

Olivine-structured LiFe_0.97Ni_0.03PO₄/C/Ag nanomaterials of varying dispersibility are prepared by using sol–gel synthesis with subsequent milling. The materials are certified using X-ray diffraction analysis, scanning electron microscopy, low-temperature nitrogen adsorption, and electrochemical testing under the lithium-ion battery operating conditions. The LiFe_0.97Ni_0.03PO₄/C/Ag cathode material primary particles’ size was shown to decrease, under the intensifying of ball-milling, from 42 to 31 nm, while the material’s specific surface area increased from 48 to 65 m²/g. The discharge capacity, under slow charging–discharging (C/8), approached a theoretical one for all materials under study. It was found that under fast charging–discharging (6 C and 30 C) the discharge capacity is inversely proportional to the particles’ mean size. The discharge capacity under the 6 С current came to 75, 94, 97, and 106 mA h/g for the initial material and that milled at a rotation velocity of 300, 500, and 700 rpm, respectively. An increase in the lithium diffusion coefficient upon the samples’ intense milling is noted.     

Synthesis and characterization of Co<Subscript>0.8</Subscript>Zn<Subscript>0.2</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Cobalt zinc ferrite, Co_0.8Zn_0.2Fe₂O₄, nanoparticles have been synthesized via autocatalytic decomposition of the precursor, cobalt zinc ferrous fumarato hydrazinate. The X-ray powder diffraction of the ‘as prepared’ oxide confirms the formation of single phase nanocrystalline cobalt zinc ferrite nanoparticles. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential thermal analysis. The precursor has also been characterized by FTIR, and chemical analysis and its chemical composition has been determined as Co_0.8Zn_0.2Fe₂(C₄H₂O₄)₃·6N₂H_4. The Curie temperature of the ‘as-prepared oxide’ was determined by AC susceptibility measurements.     

Li<Subscript>0.99</Subscript>Ti<Subscript>0.01</Subscript>FePO<Subscript>4</Subscript>/C composite as cathode material for lithium ion battery

Three kinds of LiFePO₄ materials, mixed with carbon (as LiFePO₄/C), doped with Ti (as Li_0.99Ti_0.01FePO₄), and treated both ways (as Li_0.99Ti_0.01FePO₄/C composite), were synthesized via ball milling by solid-state reaction method. The crystal structure and electrochemical behavior of the materials were investigated using X-ray diffraction, SEM, TEM, cyclic voltammetry, and charge/discharge cycle measurements. It was found that the electrochemical behavior of LiFePO₄ could be increased by carbon coating and Ti-doping methods. Among the materials, Li_0.99Ti_0.01FePO₄/C composite presents the best electrochemical behavior, with an initial discharge capacity of 154.5 mAh/g at a discharge rate of 0.2 C, and long charge/discharge cycle life. After 120 cycles, its capacity remains at 92% of the initial capacity. The Li_0.99Ti_0.01FePO₄/C composite developed here can be used as the cathode material for lithium ion batteries.     

Chelation-assisted method for the preparation of cathode material LiFePO<Subscript>4</Subscript>

LiFePO₄/C composite cathode material is prepared by ball milling with the assistance of EDTA chelation with using water as the media of ball mill procedure. FePO₄ and LiOH are used as starting materials; a certain amount of glucose is used as carbon sources and reduction agent. The structure and morphology of the composite are characterized by X-ray diffraction and scanning electron microscopy. Cyclic voltammetry, AC impedance measurements, and galvanostatic charge–discharge and cycling performances are used to characterize its electrochemical properties. The results indicate that the performances of composites prepared by chelation-assisted method are much better than common ball milling method which using alcohol or acetone as the media of ball mill procedure. The stable discharge capacity of the prepared composite is 150 and 105 mAh g⁻¹ at 1 and 10 C rate, respectively.     

2-pyrrolidone - capped Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals

Water-soluble Mn₃O₄ nanocrystals have been prepared through thermal decomposition in a high temperature boiling solvent, 2-pyrrolidone. The final product was characterized with XRD, SEM, TEM, FTIR and Zeta Potential measurements. Average crystallite size was calculated as ∼15 nm using XRD peak broadening. TEM analysis revealed spherical nanoparticles with an average diameter of 14±0.4 nm. FTIR analysis indicated that 2-pyrrolidone coordinates with the Mn₃O₄ nanocrystals only via O from the carbonyl group, thus confining their growth and protecting their surfaces from interaction with neighboring particles.      

Obtaining of Ni<Subscript>0.65</Subscript>Zn<Subscript>0.35</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposites by thermal decomposition of complex compounds embedded in silica matrix

This article presents the results of our investigation on the obtaining of Ni_0.65Zn_0.35Fe₂O₄ ferrite nanoparticles embedded in a SiO₂ matrix using a modified sol–gel synthesis method, starting from tetraethylorthosilicate (TEOS), metal (Fe^III,Ni^II,Zn^II) nitrates and ethylene glycol (EG). This method consists in the formation of carboxylate type complexes, inside the silica matrix, used as forerunners for the ferrite/silica nanocomposites. We prepared gels with different compositions, in order to obtain, through a suitable thermal treatment, the nanocomposites (Ni_0.65Zn_0.35Fe₂O₄)_x–(SiO₂)_100–x (where x=10, 20, 30, 40, 50, 60 mass%). The synthesized gels were studied by differential thermal analysis (DTA), thermogravimetry (TG) and FTIR spectroscopy. The formation of Ni–Zn ferrite in the silica matrix and the behavior in an external magnetic field were studied by X-ray diffraction (XRD) and quasi-static magnetic measurements (50 Hz).     

Coordination mechanism,characterization, and photoluminescence properties of spinel ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles prepared by a modified polyacrylamide gel route

Single-phase ZnAl₂O₄ nanoparticles with the spinel structure were successfully synthesized using a modified polyacrylamide gel method according to the atomic ratio of Zn to Al = 1: 1.8. The as-prepared samples were characterized by means of X-ray powder diffraction (XRD), thermogravimetric analysis (TG), differential scanning calorimetry analysis (DSC), field-emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL) spectra. XRD patterns show that the pure phase of ZnAl₂O₄ is obtained after heating the xerogel at 900°C for 5 h in air. The SEM images reveal that the ZnAl₂O₄ nanoparticles have a narrow particle size distribution and the average particle size is around 45 nm. Photoluminescence (PL) spectra demonstrate the single phase ZnAl₂O₄ nanoparticles have an emission peak located at 469 nm when excited by 350 nm light. The phase structure, coordination mechanism, and luminescence properties have been discussed on the basis of the experimental results.     

Synthesis of La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> by thermal treatment of mechanically activated salt mixture

A lanthanum zirconate La₂Zr₂O₇ was synthesized by soft mechanochemical method using zirconium oxynitrate ZrO(NO₃)₂·6H₂O and lanthanum carbonate La₂(CO₃)₃·8H₂O as reagents. Mechanical activation of the reagents was carried out in a centrifugal planetary ball mill. The processes occurring during calcination of the jointly and the separately mechanically activated salt mixture were studied using DSC, TG coupled with mass spectrometry, XRD analysis, and FTIR spectroscopy. It was shown that in the course of joint mechanical activation in the mill alongside with intimate mixing of the reagents and their amorphization exchange reaction occurred, producing lanthanum nitrate, basic lanthanum nitrate, basic zirconium carbonate, and hydrated zirconium oxide. The DSC curve of the jointly mechanically activated salt mixture showed a strong exothermic peak at 878 °C which was not associated with mass loss. This peak was attributed to La₂Zr₂O₇ crystallization in agreement with XRD data. Nanocrystalline lanthanum zirconate synthesized by annealing of the jointly mechanically activated salt mixture was characterized using XRD analysis, scanning, and transmission electron microscopy.     

Sol–gel nanocoating on commercial TiO<Subscript>2</Subscript> nanopowder using ultrasound

The surface of commercial titania particles was coated by a layer of silica by a two-step process which involved a power ultrasound initiated sol–gel reaction. In the first step of this solution process, aminosilane, i.e. organosilane with amino functional group, was used to modify the surface of pristine nanoparticles. Subsequent silica nanocoating was initiated and sustained under power ultrasound agitation in a mixture of surface modified particles and epoxysilane. As a result, a homogenous coverage of silica on the nanoparticles’ surface, with thickness controllable from one to several nanometers, was obtained. Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and particle surface zeta potential measurements were employed to follow steps in the process and to confirm the reaction mechanism.     

Nanosized TiO<Subscript>2</Subscript> particles decorated on SiO<Subscript>2</Subscript> spheres (TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>): synthesis and photocatalytic activities

Nanosized TiO₂ and nano-anatase TiO₂ decorated on SiO₂ spherical core shells were synthesized by using a sol–gel method. The synthesized pure TiO₂ nano particle and TiO₂ grafted on SiO₂ sphere with various ratios have been characterized for their structure and morphologies by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrophotometry (FTIR) and transmission electron microscopy (TEM). Their surface areas were measured using the BET method. The photocatalytic activity of all nanocomposites was investigated using methylene blue as a model pollutant. The synthesized TiO₂/SiO₂ particles appeared to be more efficient in the degradation of methylene blue pollutant, as compared to pure TiO₂ particles.     

Synthesis of novel magnetic sulfur-doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles for efficient removal of Pb(II)

In this work, we report the synthesis of magnetic sulfur-doped Fe₃O₄ nanoparticles (Fe₃O₄:S NPs) with a novel simple strategy, which includes low temperature multicomponent mixing and high temperature sintering. The prepared Fe₃O₄:S NPs exhibit a much better adsorption performance towards Pb(II) than bare Fe₃O₄ nanoparticles. FTIR, XPS, and XRD analyses suggested that the removal mechanisms of Pb(II) by Fe₃O₄:S NPs were associated with the process of precipitation (formation of PbS), hydrolysis, and surface adsorption. The kinetic studies showed that the adsorption data were described well by a pseudo second-order kinetic model, and the adsorption isotherms could be presented by Freundlich isotherm model. Moreover, the adsorption was not significantly affected by the coexisting ions, and the adsorbent could be easily separated from water by an external magnetic field after Pb(II) adsorption. Thus, Fe₃O₄:S NPs are supposed to be a good adsorbents for Pb(II) ions in environmental remediation.     

Surface chemistry of nanoscale Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> dispersed in magnetic fluids

The interaction between stabilizers and nanoparticles is one of the important factors to prepare stable magnetic fluids. The magnetic nano-size Fe₃O₄ core with single domain and the average grain size around 8–12 nm were prepared by chemical precipitation method. The O/Fe molar ratio of the particle surface was measured by X-ray photoelectron spectroscopy (XPS). The heat effects of stabilizers adsorption on nanoparticles were measured by solution calorimetry. The excess amount of oxygen was possibly the result of the hydroxygen formed on the surface of the nanoparticles. The heat effects showed that compounds containing carboxyl groups can be adsorbed chemically on magnetite by forming chemical bonds. The other stabilizers involving NH-groups, such as polyethylene-imine, can be adsorbed physically. The exothermic value is about half of the former case. Supported by the National Natural Science Foundation of China (Grant No. 50476039), and Guangdong Provincial Department of Science and Technology (Grant No. 2004A10-703001)     

Electrochemical behavior of α-Keggin-type nanoparticles,Co(en)<Subscript>3</Subscript>(PMo<Subscript>12</Subscript>O<Subscript>40</Subscript>), in polyethylene glycol

The electrochemical behavior of α-Keggin-type nanoparticles, Co(en)₃(PMo₁₂O₄₀) (abbreviated as PMo₁₂-Co), have been studied in poly(ethylene glycol) for four different molecular weights (PEG, average MW 400, 600, 1000, and 2000 g mol^–1) and containing LiClO₄ (O/Li=100/1) supporting electrolyte. The diffusion coefficients of the PMo₁₂-Co nanoparticles were determined using a microelectrode by chronoamperometry for PEG of different molecular weights that were used to describe the diffusion behavior of PMo₁₂-Co nanoparticles in different phase states. Moreover, the conductivity of the composite system increases upon addition of PMo₁₂-Co nanoparticles, which was measured by an a.c. impedance technique. FT-IR spectra and DSC were used to follow the interactions of PEG-LiClO₄-PMo₁₂-Co, and well described the reason that the PMo₁₂-Co nanoparticles could promote the conductivity of the PEG-LiClO₄-PMo₁₂-Co system. Electronic Publication     

Phase diagram of the system KF-K<Subscript>2</Subscript>TaF<Subscript>7</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>

As an asymmetric organic molecular crystal, p-N,N-dimethylaminobenzaldehyde (DAB) exhibits peculiar optical property. It was first grown by solution technique adopting slow evaporation method at room temperature using CCl₄ as growth medium. The solubility of DAB increases with temperature. Good quality transparent crystals of p-N,N-dimethylaminobenzaldehyde were carefully collected and subjected various characterization studies such as UV, FTIR, ¹H and ¹³CNMR spectral studies and thermal (TG-DTG) studies to determine the purity and application oriented properties of the grown crystals.