Synthesis of hybrid nanoparticles based on magnetic Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles and luminescent CdS nanoparticles

A new approach to the synthesis of hybrid nanoparticles based on magnetic Fe₃O₄ nanoparticles and CdS quantum dots, combining magnetic and luminescence properties, has been suggested. Conditions for preparation of their stable aqueous suspensions have been found, and their optical properties have been studied. Nanocomposites produced at the molar ratio Fe₃O₄: CdS = 5: 1, which exhibited the luminescence properties) and gave stable aqueous suspensions, have turned out to be most promising. The results are evidence that the synthesized nanoparticles can be used for the development of visualizing agents for in vitro biomedical research.     

Synthesis,characterization and stability of multicore-shell CdS-SiO<Subscript>2</Subscript> nanoparticles

Multicore-shell CdS-Si0₂ nanoparticles were synthesized in AOT/heptane/H₂O reverse micelles at room temperature. CdS-SiO₂ nanoparticles were characterized by UV-vis spectroscopy, TEM, and SEM methods. The results show that multicore-shell composites were formed. Fluorescence properties of composites were also investigated; the data imply that fluorescence properties of the silica-coated CdS nanoparticles were significantly improved when compared to those of the non-coated CdS nanoparticles. The stability of multicore-shell CdS-SiO₂ nanoparticles upon the UV irradiation was higher than that of non-coated CdS nanoparticles.     

Mechanism of the formation of photosensitive nanostructured TiO<Subscript>2</Subscript> with low content of CdS nanoparticles

A method for synthesizing a CdS/TiO₂ composite material, active in the visible region, was described. The CdS/TiO₂ composite was obtained by the sol–gel synthesis of nanostructured TiO₂ in a medium of a stable colloidal solution of CdS nanoparticles. The TiO₂ matrix produced by the sol–gel process is amorphous and contains a nanocrystalline anatase phase, the content of which depends on the Ti(OBu)₄ hydrolysis rate. The content of CdS nanoparticles forming in the colloidal solution and participating in the TiO₂ matrix sensitization is determined by the initial CdS: Ti(OBu)₄ ratio. Although the content of CdS nanoparticles in the composite is low (no more than 3 wt %), the composite demonstrates catalytic activity in the visible region, thus proving the possibility of reducing the content of toxic CdS nanoparticles in the TiO₂ matrix without decreasing the photosensitivity of the CdS/TiO₂ composite.     

Stability and optical properties of dispersions of CdS,ZnS, and Ag<Subscript>2</Subscript>S nanoparticles synthesized in microemulsion

CdS, ZnS, and Ag₂S nanoparticles have been synthesized in microemulsion. The synthesis of nanoparticles depend on the composition of the reaction medium and on the proportions of the precursors. The phase diagram for sedimentation stable dispersion of the nanoparticles synthesized in microemulsion has been determined. The region of the stable nanoparticle dispersion is much smaller than the region of the inverse microemulsion in the n-heptane-AOT-H₂O system. The UV-vis absorption and photoluminescence spectra of the CdS, ZnS, and Ag₂S nanoparticles have been investigated. The size of the nanoparticles increases with an increase in droplet size in the microemulsion, and this shifts the exciton peaks.     

In situ synthesis of plate-like Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in porous cellulose films with obvious magnetic anisotropy

Nanocomposite cellulose films with obvious magnetic anisotropy have been prepared by in situ synthesis of plate-like Fe₂O₃ nanoparticles in the cellulose matrix. The influence of the concentrations of FeCl₂ and FeCl₃ solutions on the morphology and particle size of the synthesized Fe₂O₃ nanoparticles as well as on the properties of the composite films has been investigated. The Fe₂O₃ nanoparticles synthesized in the cellulose matrix was γ-Fe₂O₃, and its morphology was plate-like with size about 48 nm and thickness about 9 nm, which was totally different from those reported works. The concentration of FeCl₂ and FeCl₃ solution has little influence on the particle size and morphology of the Fe₂O₃ nanoparticles, while the content of Fe₂O₃ nanoparticles increased with the increase of the concentration of the precursor solution, indicating that porous structured cellulose matrix could modulate the growth of inorganic nanoparticles. The unique morphology of the Fe₂O₃ nanoparticles endowed the composite films with obvious magnetic anisotropy, which would expand the applications of the cellulose based nanomaterials.     

Structure and spectral-optical characteristics of Se,Se/CdS,and Se/Cd<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>S nanoparticles,stabilized in polymer-containing media

A method was proposed for the production of colloidal nanoparticles of selenium stabilized by polymers and surfactants, and their structural and optical characteristics were studied. It was shown that during the deposition of CdS and Cd_0.5Zn_0.5S on the surface of the Se nanoparticles followed by dissolution of the selenium with sodium sulfite it is possible to obtain network “nanoframeworks” with size 30–50 nm, formed by CdS or Cd_0.5Zn_0.5S particles measuring 3–5 nm. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 24–29, January–February, 2007.     

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.     

Magnetic nanoparticles (Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> &amp; Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) and their applications in urea biosensing

Nanobiotechnology has opened a new and exciting opportunities for exploring urea biosensor based on magnetic nanoparticles (NPs) mainly Fe₃O₄ and Co₃O₄. These NPs have been extensively exploited to develop biosensors with stability, selectivity, reproducibility and fast response time. This review gives an overview of the development of urea biosensor based on Fe₃O₄ and Co₃O₄ for in vitro diagnostic applications along with significant improvements over the last few decades. Additionally, effort has been made to elaborate properties of magnetic nanoparticles (MNPs) in biosensing aspects. It also gives details of recent developments in hybrid nanobiocomposite based urea biosensor.     

Controllable incorporation of CdS nanoparticles into TiO<Subscript>2</Subscript> nanotubes for highly enhancing the photocatalytic response to visible light

A constant current electrochemical deposition was employed to incorporate CdS nanoparticles into the TiO₂ nanotube arrays (TiO₂NTs). The size and amount of CdS nanoparticles in TiO₂NTs (CdS@TiO₂NTs) were controllable via modulating current, deposition time and electrolyte concentration. It was revealed, from the scanning electron microscopy (SEM) images and X-ray photoelectron spectroscopy (XPS) in depth profile, that CdS nanoparticles were filled into TiO₂ nanotubes. A shift of the absorption edge toward the visible region under the optimal electrodeposition condition was observed with the diffuse reflectance spectroscopy (DRS). A 5-fold enhancement in the photocurrent spectrum for TiO₂NTs was observed and the photocurrent response range was significantly extended into the visible region because of the CdS incorporation. Compared with pure TiO₂NTs, under a visible light irradiation, CdS@TiO₂NTs exhibited a 3.5-fold improvement of photocatalytic activity, which was demonstrated by the photocatalytic decomposition of Rhodamine B (RhB).     

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.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Synthesis and Characterization of Al(OH)<Subscript>3</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanoparticles and Polymeric Nanocomposites

Applying of the most toxic halogenated and aromatic flame retardants is limited with respect to the environmental requirements. Nontoxic Al(OH)₃ nanoparticles were synthesized via a simple surfactant-free precipitation reaction at room temperature. The effect of various precipitation-agents on the morphology of the products was investigated. Al(OH)₃ nanoparticles were added to the polysulfone and poly styrene (PS) matrices. Electron microscope images show excellent dispersion of aluminium hydroxide in PS matrix. Nanoparticles appropriately enhanced both thermal stability and flame retardant property of the polymeric matrices. The enhancement of flame retardancy is due to endothermic decomposition of Al(OH)₃ that absorbs heat and simultaneously releases of water (makes combustible gases diluted and cold). Dispersed nanoparticles play the role of a barrier layer against flame, oxygen and polymer volatilization. Al(OH)₃ was converted to Al₂O₃ and its photo-catalyst property in degradation three different organic dyes as pollutants was investigated.     

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.     

Preparation and photocatalytic activity of TiO<Subscript>2</Subscript> films with Ni nanoparticles

Titania thin films were synthesized by sol–gel dip-coating method with metallic Ni nanoparticles synthesized separately from an organometallic precursor Ni(COD)₂ (COD = cycloocta-1,5-diene) in presence of 1,3-diaminopropane as a stabilizer. Titania was obtained from a titanium isopropoxide precursor solution in presence of acetic acid. A Ni/TiO₂ sol system was used to coat glass substrate spheres (6, 4 and 3 mm diameter sizes), and further heat treatment at 400 °C was carried out to promote the crystallization of titania. XRD analysis of the TiO₂ films revealed the crystallization of the anatase phase. Transmission Electron Microscopy (TEM) and High Resolution TEM studies of Ni nanoparticles before mixing with the TiO₂ solution revealed the formation of Ni nanostructures with an average size of 5–10 nm. High-angle annular dark-field images of the Ni/TiO₂ system revealed well-dispersed Ni nanoparticles supported on TiO₂ and confirmed by AFM analysis. The photocatalytic activity of the Ni/TiO₂ films was evaluated in hydrogen evolution from the decomposition of ethanol using a mercury lamp for UV light irradiation. Titania films in presence of Ni nanoparticles show higher efficiency in their photocatalytic properties in comparison with TiO₂.     

CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation using mixed matrix membrane-based polyurethane incorporated with ZIF-8 nanoparticles

This study presents using zeolitic imidazolate framework-8 (ZIF-8) as porous filler dispersed phase and polyurethane (PU) as continuous phase to synthesis mixed matrix membranes (MMMs). ZIF-8 nanoparticles were synthesized using centrifugal method. The synthesized nanoparticles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA). In order to investigate the effect of ZIF-8 loading on the membrane performance in CO₂/CH₄ separation, different membranes were prepared with various amounts of ZIF-8 (0–50 wt%). Membranes properties were characterized by SEM, XRD, TGA, differential scanning calorimetry (DSC), and tensile analysis. SEM images exhibit that the ZIF-8 is dispersed uniformly in cross section of membrane. Thermal stability of membranes increases with addition of the ZIF-8 nanoparticles into the polymer matrix. Both tensile strength and strain at break in the MMMs increase with the ZIF-8 loading. To study the effect of feed pressure on CO₂ and CH₄ transport properties of the membranes, single gas experiments were conducted at 4, 8, and 12 bar feed pressures. Incorporation of ZIF-8 crystals into continuous PU matrix resulted in high-performance gas separation membranes. Increasing feed pressure, significantly, increased separation performances in all the membranes.     

Effect of active impurities on the condensation of nanoparticles from supersaturated carbon vapor in the combined laser photolysis of C<Subscript>3</Subscript>O<Subscript>2</Subscript> and H<Subscript>2</Subscript>S

The effect of active H₂S, HS^·, and atomic hydrogen impurities on the condensation of highly supersaturated carbon vapor obtained in the combined laser photolysis of a mixture of C₃O₂ and H₂S diluted with argon was studied. The concentrations of carbon vapor, HS^·, and atomic hydrogen obtained in the laser photolysis of the mixture were determined using the absorption cross sections of C₃O₂ and H₂S molecules measured in this work and the measured amount of absorbed laser radiation. The time profiles of the sizes of growing nanoparticles synthesized in C₃O₂ + Ar and C₃O₂ + H₂S + Ar mixtures were measured using the laser-induced incandescence (LII) method. An improved LII model was developed, which simultaneously took into account the heating and cooling of nanoparticles and the temperature dependence of the thermophysical properties of nanoparticles, as well as the cooling of nanoparticles by evaporation and thermal emission. The size distributions of carbon nanoparticles formed in the presence and absence of active impurities were determined with the use of a transmission electron microscope. The final average size of carbon nanoparticles was found to decrease from 12 to 9 nm upon the addition of H₂S to the system, whereas the rate of nanoparticle growth decreased by a factor of 3, and the properties of nanoparticles changed. In particular, the translational energy accommodation coefficient for Ar molecules at the surface of carbon nanoparticles was found to decrease from 0.44 to 0.30. A comparison of the calculated total carbon balance at the early stage of nanoparticle formation with experimental data demonstrated that the reaction C + H₂S → HCS^· + H, which removes a portion of carbon vapor from the condensation process, has a determining effect on the carbon balance in the system. It was found that HS^· and atomic hydrogen affect the carbon balance in the system only slightly. Thus, the experimentally observed decrease in the rate of nanoparticle growth and in the sizes of nanoparticles can be explained by a decrease in the concentration of free carbon upon the addition of H₂S molecules to the system.     

Effect of heat treatment on magnetic MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

MgFe₂O₄ (Mg-ferrite) nanoparticles encapsulated in amorphous SiO₂ were prepared by the wet chemical method. The particle sizes were estimated, based on the X-ray diffraction peaks, to be between 3 and 8 nm, depending on the annealing temperature. The particle size increased as the annealing temperature increased. From the magnetization measurements, the blocking temperature, T _b, was found to be between 30 and 60 K. The magnetization values varied with the annealing or quenching conditions. To clarify the process of crystal growth, thermogravimetric and differential thermal analysis (TG-DTA) measurements were performed and the results were compared with the X-ray diffraction patterns.     

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.     

Fast removal and determination of doxycycline in water samples and honey by Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles

Adsorption characteristics and doxycycline (DC) removal efficiency of Fe₃O₄ magnetic nanoparticles as adsorbents have been determined by investigating the effects of pH, concentration of the DC, amount of adsorbents, contact time, ionic strength and temperature. The mechanism of adsorption was also studied. The adsorption of DC to the Fe₃O₄ magnetic nanoparticles could be described by Langmuir-type adsorption isotherms. Short contact time between the reagents, reusability of Fe₃O₄ for three times after recycling of the nanoparticles, good precision and accuracy, wide working pH range and high breakthrough volume are among the highlights of this procedure. The proposed extraction and determination procedure based on magnetic nanoparticles as adsorbent was successfully applied to the determination of DC spiked in honey and various water samples. The method presented here is fast, simple, cheap and robust, and it does not require the use of organic solvents. Also, the method needs only a magnet and can be performed in any laboratory without sophisticated equipment.     

Synthesis and photocatalytic activity of TiO<Subscript>2</Subscript> nanoparticles fluorine-modified with TiF<Subscript>4</Subscript>

Fluorine-modified TiO₂ nan oparticles were synthesized by introducing TiF₄ as a fluorine source either before or after the sufficient hydrolysis and condensation of Ti(OEt)₄. The photocatalytic activity of the fluorine-modified catalysts was found to be greatly affected by the fluorine position in TiO₂ nanoparticles. When TiF₄ and Ti(OEt)₄ hydrolyzed with synchronization, the fluorine tended to be doped in the lattice. The formation of Ti³⁺ defects could result in charge recombination in bulk and bring down the photocatalytic activity. In contrast, if TiF₄ was introduced after the sufficient hydrolysis and condensation of Ti(OEt)₄. Ti−F bonds could exist mainly on the TiO₂ particles surface, which not only prevented the growth of anatase crystals but also facilitated the transfer of organic compounds from solution to catalyst surface by reducing the hydrophilic properties.