Preparation of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles by mechanical alloying and annealing for sensitizing C-modified TiO<Subscript>2</Subscript> and acquirement of efficient photocatalyst

ZnFe₂O₄ nanoparticles sensitized by C-modified TiO₂ hybrids (ZnFe₂O₄–TiO₂/C) were successfully prepared by a feasible method. The ZnFe₂O₄ nanoparticles were prepared by mechanical alloying and annealing. The residual organic compounds in the synthetic process of TiO₂ were selected as the carbon source. The as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray fluorescence, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible light diffuse reflectance spectroscopy (UV–Vis) and N₂ adsorption–desorption analysis. The photocatalytic activity of the photocatalysts was measured by degradation of methyl orange under ultraviolet (UV) light and simulated solar irradiation, respectively. The results show that the carbon did not enter the TiO₂ lattice but adhered to the surface of TiO₂. The photocatalytic activity of the as-prepared C-modified TiO₂ (TiO₂/C) improved both under UV and simulated solar light irradiation, but the improvement was not dramatic. Introduction of ZnFe₂O₄ into the TiO₂/C could enhance the absorption spectrum range. The ZnFe₂O₄–TiO₂/C hybrids exhibited a higher photocatalytic activity both than that of the pure TiO₂ and TiO₂/C under either UV or simulated solar light irradiation. The complex synergistic effect plays an important role in improving the photocatalytic performance of ZnFe₂O₄–TiO₂/C composites. The optimum photocatalytic performance was obtained from the ZnFe₂O₄(0.8 wt%)–TiO₂/C sample.     

MnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles with excellent catalytic activity in thermal decomposition of ammonium perchlorate

MnCo₂O₄ spinel nanoparticles (NPs) have been prepared using Aloe vera gel solution. The characterization of prepared spinel was performed applying Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron spectroscope, scanning electron microscope and dynamic light scattering. The results manifested that the prepared nanoparticles were mainly spherical plus minor agglomeration with average size distribution between 35 and 60 nm. The catalytic activity of the prepared nanoparticles upon thermal degradation of ammonium perchlorate (AP) was evaluated applying differential scanning calorimetry and thermogravimetry instruments. MnCo₂O₄ nanoparticles increased the released heat of AP from 450 to 1480 J g^?1 and decreased the decomposition temperature from 420 to 293 °C. The kinetic parameters obtained from Kissinger methods showed that the activation energy of AP thermal decomposition in the presence of MnCo₂O₄ NPs considerably decreased. Also, a mechanism has been proposed in the presence of catalyst for the process of thermal decomposition of AP.     

Ca- and Al-doped ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles as possible anode materials

Spinel ferrites are an amazing class of materials that can find application in different fields, from sensors and lithium-ion batteries to the intriguing biomedical field. For the use as anode in lithium-ion batteries, ZnFe₂O₄ is rather competitive due to low price, abundance, environmental benignity, working voltage of ~1.5 V, and, most importantly, a high theoretical specific capacity (~1072 mA h g^?1). For its practical application, however, some issues must be overcome, in particular its fast capacity fading and poor rate capability resulting from an inherent low electronic conductivity. Possible strategies are represented by ferrite carbon coating/embedding, peculiar synthesis routes, and doping. In this frame, we synthesized Ca- and Al-doped ZnFe₂O₄ nanoparticles by using microwave-assisted combustion synthesis, followed by a classical carbon coating (determined as about 5 wt% by thermogravimetry). A good solubility of Ca and Al up to 25 atom% on both Zn and Fe sites was obtained. Cyclic voltammetries evidenced redox reactions involving Zn and Fe ions, but also the Al intervention could be supposed. Galvanostatic charge–discharge cycles proved that particularly Al ions were useful to improve the anode structural stability at high C rate (up to 3C), thanks to the stronger Al–O bonds with respect to Fe–O ones. A further improvement of capacities comes from the use of sodium alginate as binder to substitute polyvinylidene fluoride in the anode preparation.     

The Role of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgO Additives on the Photoluminescence Properties of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Nanoparticles

The current research addressed synthesizing and studying photoluminescence studies of β-Si₃N₄ nanoparticles. The effect of MgO and Y₂O₃ as the typical additives on photoluminescence behaviour was evaluated. The β-Si₃N₄ with MgO and Y₂O₃ additive specimens were fabricated by a solid state technique (ball-milled method). The as-prepared products were characterized by X-ray diffraction technique, transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman analysis. The results showed that after ball-milled process, hexagonal β-Si₃N₄ with MgO or Y₂O₃ as the additives with the size distribution of 45–50 nm was obtained. The optical properties of the as-synthesized product were also investigated by photoluminescence and diffuse reflection spectroscopy. The obtained results confirmed that employing MgO as an additive, in comparison to the Y₂O₃, could enhance emission properties in the synthesized silicon nitride nanoparticles. The obtained results also showed that MgO–Si₃N₄ pair acted as FRET system to enhance the emission intensity of β-Si₃N₄ nanoparticles.     

Comparison of the Solubility of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> in High Temperature Water

As the solubility is a direct measure of stability, this study compares the solubilities of ZnFe₂O₄, Fe₃O₄ and Fe₂O₃ in high temperature water. Through literature analysis and formula derivation, it is shown that it is reasonable to assume ZnFe₂O₄ and Fe(OH)₃ coexist when ZnFe₂O₄ is dissolved in water. Results indicated that the solubility of ZnFe₂O₄ is much lower than that of Fe₂O₃ or Fe₃O₄. The low solubility of ZnFe₂O₄ indicates that it is more protectively stable as an anticorrosion phase. Moreover, the gap between the solubility of ZnFe₂O₄ and that of Fe₃O₄ or Fe₂O₃ was enlarged with an increase of temperature. This means that ZnFe₂O₄ is more protective at higher temperatures. Further analysis indicated that with the increase of temperature, the solubility of ZnFe₂O₄ changed little while those of Fe₂O₃ or Fe₃O₄ changed a lot. Little change of the solubility of ZnFe₂O₄ with increase of temperature showed that ZnFe₂O₄ is stable. The very low and constant solubility of ZnFe₂O₄ suggests that it is more protective than Fe₂O₃ and Fe₃O₄, especially in water at higher temperature.     

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.     

Facile Synthesis of Fe<Subscript>x</Subscript>O<Subscript>y</Subscript>/Ag Nanocomposites for Multifunctional and Efficient Catalytic Applications

In this study, the iron oxide/silver (Fe_xO_y/Ag) nanocomposite has been successfully prepared by a facile one-step method using goethite (α-FeOOH) rods as support. The diameter of the as-synthesized goethite rods was between 250 and 500 nm and the silver nanoparticles sizes were about 10–50 nm. By varying the concentrations, the Fe_xO_y/Ag nanocomposite with different Ag contents are successfully obtained. The Fe_xO_y/Ag nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and energy dispersive spectroscopy, respectively. Due to the unique nanostructure, these nanocomposites can catalyze degradation of both aromatic nitro compounds and organic dyes only within a few minutes, which show high catalytic performance.     

Nonstoichiometric Zn Ferrite and ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Composite Spheres: Preparation,Magnetic Properties,and Chromium Removal

Monodisperse and porous nonstoichiometric Zn ferrite can be prepared by a solvothermal method. Such non-Zn ferrite was used to be the precursor for synthesis of ZnFe₂O₄/Fe₂O₃ composite via calcination at 600°C for 3 h in air. X-ray powder diffractometer (XRD) and Energy Dispersive Spectrometer (EDS) proved the nonstoichiometry of Zn ferrite synthesized by solvothermal method and the formation of ZnFe₂O₄/Fe₂O₃ composite via calcination. TEM image showed that non-Zn ferrite spheres with wormlike nanopore structure were made of primary nanocrystals. BET surface area of non-Zn ferrite was much higher than that of ZnFe₂O₄/Fe₂O₃ composite. Saturation magnetization of non-Zn ferrites was significantly higher than that of ZnFe₂O₄/Fe₂O₃ composites. Calcination of non-Zn ferrite resulted in the formation of large amount of non-magnetic Fe₂O₃,which caused a low magnetization of composite. Because of higher BET surface area and higher saturation magnetization, non-Zn ferrite presented better Cr⁶⁺ adsorption property than ZnFe₂O₄/Fe₂O₃ composites.     

Supercapacitive performance of homogeneous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> nanotube arrays enhanced by carbon layer and oxygen vacancies

Self-supported and binder-free electrodes based on homogeneous Co₃O₄/TiO₂ nanotube arrays enhanced by carbon layer and oxygen vacancies (Co₃O₄/co-modified TiO₂ nanotube arrays (m-TNAs)) are prepared via a simple and cost-effective method in this paper. The highly ordered TNAs offer direct pathways for electron and ion transport and can be used as 3D substrate for the decoration of electroactive materials without any binders. Then, by a facile one-step calcination process, the electrochemical performance of the as-obtained carbon layer and oxygen vacancy m-TNAs is approximately 83 times higher than that of pristine TNAs. In addition, Co₃O₄ nanoparticles are uniformly deposited onto the m-TNAs by a universal chemical bath deposition (CBD) process to further improve the supercapacitive performance. Due to the synergistic effect of m-TNAs and Co₃O₄ nanoparticles, a maximum specific capacitance of 662.7 F g^?1 can be achieved, which is much higher than that of Co₃O₄ decorated on pristine TNAs (Co₃O₄/TNAs; 166.2 F g^?1). Furthermore, the specific capacitance retains 86.0 % of the initial capacitance after 4000 cycles under a high current density of 10 A g^?1, revealing the excellent long-term electrochemical cycling stability of Co₃O₄/m-TNAs. Thus, this kind of heterostructured Co₃O₄/m-TNAs could be considered as promising candidates for high-performance supercapacitor electrodes.     

Synthesis and Characterization of the Superparamagnetic Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag Nanocomposites

The study of superparamagnetic Fe₃O₄/Ag nanocomposites have received great research attention due to their wide range of potential applications in biomedicine. In this report, an easy microemulsion reaction was employed to synthesis Fe₃O₄/Ag nanocomposites with self-aggregated branch like nanostructures. The Fe₃O₄ nanoparticles were initially prepared and subsequently AgNO₃ was reduced as Ag by chemical reduction method. The results showed that the average size of the Fe₃O₄/Ag nanocomposites were in the range of 10 ± 2 nm. These nanoparticles were self-aggregated as a branch like nanostructure. The optical properties of Fe₃O₄ nanoparticles were modified with surface plasmon resonance of Ag nanoparticles. The observed saturation magnetization of superparamagnetic Fe₃O₄/Ag nanocomposites were 40 emu/g.     

Ni<Subscript>0.37</Subscript>Co<Subscript>0.63</Subscript>S<Subscript>2</Subscript>-reduced graphene oxide nanocomposites for highly efficient electrocatalytic oxygen evolution and photocatalytic pollutant degradation

A series of Ni_0.37Co_0.63S₂-reduced graphene oxide nanocomposites with different graphene contents (NCS@rGO-x) has been successfully prepared via a facile one-step hydrothermal method and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The XRD and FESEM analyses revealed that the phase structure and morphology of NCS nanoparticles were substantially influenced by the graphene contents. The phase structure of NCS nanoparticles gradually transformed from primary NiCo₂S₄ to Ni_0.37Co_0.63S₂ and the morphology and size of NCS nanoparticles were found to become more regular and homogeneous with the increase of graphene concentration. On the NCS@rGO-x nanocomposites, the NCS@rGO-2 sample demonstrated the best catalytic activity toward the OER, which delivers a stable current density of 10 mA cm^?2 at a small overpotential of ～276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec^?1. Furthermore, the NCS@rGO-2 sample showed the remarkable photocatalytic activity for degradation of methylene blue (MB), which may be attributed to the increased reaction sites and high separation efficiency of photogenerated charge carries due to the electronic interaction between NCS nanoparticles and rGO. All these impressive performances indicate that the NCS@rGO-2 nanocomposite is a promising catalyst in energy and environmental fields.

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Graphical abstract A series of Ni_0.37Co_0.63S₂-reduced graphene oxide nanocomposites with different graphene contents has been successfully prepared and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The NCS@rGO-2 catalyst-modified stainless steel wire mesh (SSWM) electrode delivers a stable current density of 10 mA cm^?2 at a small overpotential of ～276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec^?1. At the same time, the NCS@rGO-2 catalyst is also first investigated as an efficient photocatalyst for degradation of MB.

     

Ag nanoparticles decorated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/chitosan nanocomposite: synthesis,characterization and application toward electrochemical sensing of hydrogen peroxide

We studied a rapid, sensitive and selective amperometric sensor for determination of hydrogen peroxide by electrodeposited Ag NPs on a modified glassy carbon electrode (GCE). The modified GCE was constructed through a step by step modification of magnetic chitosan functional composite (Fe₃O₄–CH) and high-dispersed silver nanoparticles on the surface. The resulted Ag@Fe₃O₄–CH was characterized by various analytical methods including Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and cyclic voltammetry. The proposed sensor employed Ag@Fe₃O₄–CH/GCE as the working electrode with a linear current response to the hydrogen peroxide concentration in a wide range from 0.01 to 400 µM with a low limit of detection (LOD = 0.0038 µM, S/N = 3). The proposed sensor showed superior reproductivity, sensitivity and selectivity for the detection of hydrogen peroxide in environmental and clinical samples.     

Novel Visible-Light-Driven Photocatalyst Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/FeWO<Subscript>4</Subscript> for Efficient Decomposition of Organic Pollutants

A highly efficient and visible light (λ ≥ 420 nm) responsive composite photocatalyst, Co₃O₄/FeWO₄ was prepared by simple impregnation method. The heterojunction semiconductors Co₃O₄/FeWO₄ demonstrated notably high photocatalytic activity over a wide range of composition than the individual component Co₃O₄ or FeWO₄ for the complete degradation of 1,4-dichlorobenzene (DCB) in aqueous phase under visible light irradiation. The photocatalytic activity of composite was optimized at 1/99 Co₃O₄/FeWO₄ composition. After 2 h of visible light irradiation 51% decomposition of 1,4-dichlorobenzene (DCB) was observed utilizing 1/99 Co₃O₄/FeWO₄ photocatalyst while the end members demonstrated a negligible degradation under the same experimental condition. The valence band (VB) and conduction band (CB) of Co₃O₄ is located above the VB and CB of FeWO₄, respectively. Both the semiconductors Co₃O₄ and FeWO₄ exhibit strong absorption over the wide range of visible light. The obviously enhanced photocatalytic performance of Co₃O₄/FeWO₄ composite has been discussed on the hole (h⁺) as well as electron (e^?) transfer mechanism between the VB and CB of individual semiconductors.     

Enhanced electrochemical properties of Li<Subscript>2</Subscript>ZnTi<Subscript>3</Subscript>O<Subscript>8</Subscript>/C nanocomposite synthesized with phenolic resin as carbon source

Li₂ZnTi₃O₈/C nanocomposite has been synthesized using phenolic resin as carbon source in this work. The structure, morphology, and electrochemical properties of the as-prepared Li₂ZnTi₃O₈ samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), Raman spectroscopy (RS), galvanostatic charge–discharge, and AC impedance spectroscopy. SEM images show that Li₂ZnTi₃O₈/C was agglomerated with a primary particle size of ca. 40 nm. TEM images reveal that a homogeneous carbon layer (ca. 5 nm) formed on the surface of Li₂ZnTi₃O₈ particles which is favorable to improve the electronic conductivity and inhibit the growth of Li₂ZnTi₃O₈ during annealing process. The as-prepared Li₂ZnTi₃O₈/C composite with 6.0 wt.% carbon exhibited a high initial discharge capacity of 425 and 159 mAh g^?1 at 0.05 and 5 A g^?1, respectively. At a high current density of 1 A g^?1, 95.5 % of its initial value is obtained after 100 cycles.     

One pot facile hydrothermal synthesis of superparamagnetic ZnFe2O4 nanoparticles and their properties

Superparamagnetic ZnFe₂O₄ nanoparticles were synthesized by facile hydrothermal method using different amount of diethylamine (DEA) as a precipitating agent. The phase formation, morphological and magnetic properties were investigated using X-ray diffraction, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy and vibrating sample magnetometer. The amount of DEA required for forming single phase ZnFe₂O₄ was optimized. For 2 ml of DEA, a mixed phase of α-Fe₂O₃ and ZnFe₂O₄ was formed whereas single phase of ZnFe₂O₄ was formed with high crystalline quality for 4, 6, 8 and 10 ml of DEA. FE-SEM results indicated that all the synthesized products were in spherical shape with small aggregations. Particle size of 9 nm was obtained from TEM image for sample synthesized using 10 ml of DEA. Superparamagnetic property was observed for the samples synthesized using 4, 6, 8, and 10 ml of DEA.     

Particle size,morphology, and properties of transition metal ferrospinels of the MFe<Subscript>2</Subscript>O<Subscript>4</Subscript> (M = Co,Ni, Zn) type,produced by glycine-nitrate combustion

Ferrites-spinels of the MFe₂O₄ type (M = Co, Ni, Zn), produced by glycine-nitrate combustion were studied. A physicochemical study of ferrite samples was performed by X-ray fluorescence analysis, scanning electron microscopy, X-ray phase analysis, and X-ray spectroscopy. The average size of the coherent scanning region was found to be (nm): 28 ± 2 for CoFe₂O₄, 32 ± 2 for NiFe₂O₄, and 26 ± 2 for ZnFe₂O₄. Magnetic characteristics were determined by the NMR method. The specific residual magnetization, specific saturation magnetization, and coercive force were, respectively, 14.1 A m² kg^?1, 20.1 A m² kg^?1, 31800 A m^?1 for CoFe₂O₄; 4.4 A m² kg^?1, 23.1 A m² kg^?1, 6550 A m^?1 for NiFe₂O₄; and 5.1 A m² kg^?1, 18.3 A m² kg^?1, 3200 A m^?1 for ZnFe₂O₄. Their magnetic properties show that the resulting ferrospinel powders can be used in the following fields of technology: CoFe₂O₄ in those areas where heat transfer is necessary (hyperthermia) and in development of data storage media; NiFe₂O₄ and ZnFe₂O₄ in those areas where low heat exchange is necessary, ZnFe₂O₄ for fast remagnetization and NiFe₂O₄ as a core or shell for transportation of other substances. The ferrospinel samples compare well in magnetic properties with their foreign commercial analogs, which makes these compounds commercially viable.     

NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript>/rGO hybrid nanostructures for efficient electrocatalytic oxygen evolution

We report the synthesis of NiCo₂O₄/reduced graphene oxide (NiCo₂O₄/rGO) hybrid hierarchical structures with unique nanonet and microsphere morphologies by organic polar solvent-assisted solvothermal method. The electrocatalytic oxygen evolution reaction (OER) activity of these materials is studied by cyclic voltammetry, linear sweep voltammetry and chronoamperometry methods in O₂-saturated 0.1 M KOH solution. The NiCo₂O₄/rGO hybrid nanocomposite materials are found to be highly active electrocatalysts for OER at lower overpotentials. The nanonet and microsphere-like NiCo₂O₄/rGO catalysts require overpotentials of 0.450 and 0.530 V at a current density of 10 mA cm^?2, and their corresponding Tafel slopes are 53 and 62 mV dec^?1, which are much lower than values reported for non-precious electrocatalysts. Further, both NiCo₂O₄/rGO catalysts show good catalytic stability with current retention more than 92 % over long period of 15,000 s determined by chronoampirometry and at the end of 1000th cycle determined by linear sweep voltammetry. The enhanced OER activity of nanostructured NiCo₂O₄/rGO hybrid catalysts is attributed to synergistic interaction between rGO and NiCo₂O₄, which seems to be essential for maintaining the large contact area at the electrode-electrolyte interface, better mass, and charge transport and to minimize the aggregation of NiCo₂O₄ nanoparticles.     

Assessment of operating parameters for photocatalytic degradation of a textile dye by Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/clinoptilolite nanocatalyst using Taguchi experimental design

In the current study, a nanophotocatalyst doped with of TiO₂ and Fe₂O₃ nanoparticles supported on Iranian clinoptilolite was synthesized and characterized by XRD, XRF, SEM, and EDX analyses. The results suggested the successful loading of TiO₂ and Fe₂O₃ nanoparticles onto the surface of clinoptilolite. The SEM images confirmed the average size of nanoparticles deposited on zeolite, which was about 20–40 nm. Furthermore, application of the synthesized photocatalyst in photocatalytic degradation of Acid Black 172 dye was studied using the Taguchi method and the chosen parameters were as follows: pH (2–7), dye concentration (50–200 mg/l), irradiation time (30–120 min), and catalyst dosage (0.5–1.5 g/l). The results indicate that dye concentration, pH, and irradiation time are respectively the most effective factors in these experiments while with the minimum dosage of the catalyst (0.5 g/l), up to 90 % removal efficiency could be achieved. The optimum value for each parameter was pH = 2, dye concentration = 50 mg/l, catalyst dosage = 1 g/l and irradiation time = 60 min, and the dye removal efficiency reached up to 100 % at these optimal conditions. Furthermore, after five-times recycling and reusing the catalyst, the efficiency of the photocatalytic degradation was reduced from 91.5 to 65.9 %, which is still an acceptable value.     

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.     

Charge separation by tetrahexahedron-SrTiO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> heterojunction as an efficient photocatalyst

Charge separation plays a key role in the conversion of solar energy into chemical energy for use in the redox reaction and as well as in the photocatalytic activity. In this study, SrTiO₃ particles with different morphologies including irregular, tetrahexahedron, and cube were synthesized by an in situ solvothermal method. The photocatalytic activity of the synthesized nanoparticles was investigated in the photocatalytic decomposition of methylene blue under UV light irradiation. Tetrahexahedron SrTiO₃ particles exhibited high decomposition activity (70 %), which is about two times higher than those of the irregular and cubic SrTiO₃ particles. The high decomposition activity of tetrahexahedron SrTiO₃ particles could be attributed to the improvement of charge separation achieved on different crystal facets. To reach a good charge separation, tetrahexahedron SrTiO₃/TiO₂ coupled nanoparticles were fabricated by impregnation method. Results showed that coupling tetrahexahedron SrTiO₃ with TiO₂ could produce efficient charge separation between tetrahexahedron SrTiO₃ and TiO₂ due to their matched band edges. In order to achieve better charge separation, the tetrahexahedron SrTiO₃/90 %TiO₂ sample was calcined at different temperatures in the 450–750 °C range. Tetrahexahedron SrTiO₃/90 %TiO₂ coupled nanoparticles calcined at 650 °C show high photocatalytic activity compared with other samples. The prepared samples were characterized by using various techniques such as X-ray diffraction, scanning electron microscopy, photoluminescence emission spectra, and UV–Vis diffuse reflectance spectroscopy.