Synthesis of polyvinyl alcohol hydrogel grafted by modified Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles: characterization and doxorubicin delivery studies

During the last two decades, serious efforts have been directed towards the synthesis and coating magnetic nanoparticles for biomedical applications. Among many different types of polymeric coating materials that have been utilized in previous studies, we have selected polyvinyl alcohol (PVA). In this study, we report a novel type of magnetite nanocomposite-based PVA hydrogel. For this purpose, first, Fe₃O₄ nanoparticles were modified through hexamethylene diisocyanate (HMDI) and then PVA was modified by bromoacetyl bromide to produce bromoacetylated PVA. The modified PVA was cross-linked through various diamines such as ethylene-diamine, propylene-diamine and hexamethylenediamine. The prepared weak tridimensional PVA hydrogels were further reacted through unreacted hydroxyl groups with Fe₃O₄, modified by HMDI to form magnetite hard tridimensional hydrogels. The swelling behavior of the prepared magnetite nanocomposites were investigated and showed a fast initial swelling followed by a mild increase until attaining equilibrium. The structural, morphological, thermal and magnetic properties of the synthesized magnetite nanocomposites were confirmed by FTIR, thermal gravimetric analysis, vibrating sample magnetometer and scanning electron microscopy. The doxorubicin anti-tumor drug was loaded on a selected synthesized magnetic hydrogel and in vitro drug release studies were done in phosphate buffer solution in 37 °C.     

One-Pot Green Synthesis and Bioapplication of<Emphasis Type="SmallCaps">l</Emphasis>-Arginine-Capped Superparamagnetic Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles

Water-soluble l-arginine-capped Fe₃O₄ nanoparticles were synthesized using a one-pot and green method. Nontoxic, renewable and inexpensive reagents including FeCl₃, l-arginine, glycerol and water were chosen as raw materials. Fe₃O₄ nanoparticles show different dispersive states in acidic and alkaline solutions for the two distinct forms of surface binding l-arginine. Powder X-ray diffraction and X-ray photoelectron spectroscopy were used to identify the structure of Fe₃O₄ nanocrystals. The products behave like superparamagnetism at room temperature with saturation magnetization of 49.9 emu g⁻¹ and negligible remanence or coercivity. In the presence of 1-ethyl-3-(dimethylaminopropyl) carbodiimide hydrochloride, the anti-chloramphenicol monoclonal antibodies were connected to the l-arginine-capped magnetite nanoparticles. The as-prepared conjugates could be used in immunomagnetic assay.     

NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> Nanoparticles Stabilized by Porous Silica Shells

Abstract  

NiFe₂O₄ nanoparticles stabilized by porous silica shells (NiFe₂O₄@SiO₂) were prepared using a one-pot synthesis and characterized for their physical and chemical stability in severe environments, representative of those encountered in industrial catalytic reactors. The SiO₂ shell is porous, allowing transport of gases to and from the metal core. The shell also stabilizes NiFe₂O₄ at the nanoparticle surface: NiFe₂O₄@SiO₂ annealed at temperatures through 973 K displays evidence of surface Ni, as verified by H₂ TPD analyses. At 1,173 K, hematite forms at the surface of the metallic cores of the NiFe₂O₄@SiO₂ nanoparticles and surface Ni is no longer observed. Without the silica shell, however, even mild reduction (at 773 K) can draw Fe to the surface and eliminate surface Ni sites.     

Effect of surface modification of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles on the preparation of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/polystyrene composite particles via miniemulsion polymerization

Fe₃O₄ nanoparticles were modified by n-octadecyltrimethoxysilane (C18TMS) and 3-trimethoxysilylpropylmethacrylate (MPS). The modified Fe₃O₄ nanoparticles were used to prepare Fe₃O₄/polystyrene composite particles by miniemulsion polymerization. The effect of surface modification of Fe₃O₄ on the preparation of Fe₃O₄/polystyrene composite particles was investigated by transmission electron microscopy, Fourier transform infrared spectrophotometer (FT-IR), contact angle, and vibrating sample magnetometer (VSM). It was found that C18TMS modified Fe₃O₄ nanoparticles with high hydrophobic property lead to the negative effect on the preparation of the Fe₃O₄/polystyrene composite particles. The obtained composite particles exhibited asymmetric phase-separated structure and wide size distribution. Furthermore, un-encapsulated Fe₃O₄ were found in composite particles solution. MPS modified Fe₃O₄ nanoparticles showed poor hydrophobic properties and resulted in the obtained Fe₃O₄/polystyrene composite particles with regular morphology and narrow size distribution because the ended C=C of MPS on the surface of Fe₃O₄ nanoparticles could copolymerize with styrene which weakened the phase separation distinctly.     

Reduced graphene oxide supported V<Subscript>2</Subscript>O<Subscript>5</Subscript>-WO<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> catalysts for selective catalytic reduction of NOx

We present a reduced-graphene-oxide (rGO)-supported V2O₅-WO₃-TiO₂ (VWTi) catalysts for the efficient selective catalytic reduction of NOx. The rGO support provides well-dispersed functional sites for the nucleation of nanoparticles, allowing the formation of VWTi catalysts with high specific surface areas. The dispersion of the nanoparticles, as observed by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), confirmed the uniform dispersion of the particles on the rGO surface. Detailed Fourier-transform infrared (FT-IR) and NH₃ temperature-programmed desorption (NH₃-TPD) analyses indicated that the high density of acidic sites provided by the rGO is key to the observed enhancement of NOx removal efficiency, and the rGO-supported catalysts exhibit improved NOx removal efficiencies with smaller amounts of V₂O₅ and WO₃ compared with the commercially available V₂O₅-WO₃-TiO₂ catalysts.     

Selective Synthesis of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanowires Via a Single Precursor: A General Method for Metal Oxide Nanowires

Hematite (α-Fe₂O₃) and magnetite (Fe₃O₄) nanowires with the diameter of about 100 nm and the length of tens of micrometers have been selectively synthesized by a microemulsion-based method in combination of the calcinations under different atmosphere. The effects of the precursors, annealing temperature, and atmosphere on the morphology and the structure of the products have been investigated. Moreover, Co₃O₄ nanowires have been fabricated to confirm the versatility of the method for metal oxide nanowires.     

Mercury ion adsorption on AC@Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-NH<Subscript>2</Subscript>-COOH from saline solutions: Experimental studies and artificial neural network modeling

An efficient, novel functionalized supported magnetic nanoparticle (AC@Fe₃O₄-NH₂-COOH) has been synthesized by co-precipitation method for removal of mercury ions from saline solutions. High dispersed supported magnetic nanoparticles with particle sizes less than 30 nm were formed over activated carbon derived from local walnut shell. Surface characterizations of supported magnetic nanoparticles were evaluated by Boehm test, Brunauer- Emmett-Teller (BET) surface area, X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and X-ray fluorescence (XRF). A three-layer artificial neural network (ANN) code was developed to predict the Hg (II) ions removal from aqueous solution by AC@Fe₃O₄-NH₂-COOH. The three-layer back-propagation (BP) is configured of tangent sigmoid transfer function (tansig) at hidden layer with eight neurons for AC@Fe₃O₄-NH₂-COOH, and linear transfer function (purelin) at output layer. According to the calculated MSEs, Levenberg-Marquardt algorithm (LMA) was the best training algorithm among others. The linear regressions between the predicted and experimental outputs were proven to be a good agreement with a correlation coefficient of about 0.9984 for five model variables. Maximum adsorption capacity was achieved 80mg/g by Langmuir isotherm at pH of 7 and salinity of 25,000 ppm. Kinetic studies illustrated that mercury adsorption follows pseudo-second-order.     

Chitosan- and dehydroascorbic acid-coated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles: preparation,characterization and their potential as draw solute in forward osmosis process

Forward osmosis (FO) is a natural osmosis process that has attracted a significant attention due to its many advantages. However, the development of FO process depends on the development of proper draw solutions. In this work, chitosan (CS)-coated Fe₃O₄ nanoparticles and dehydroascorbic acid (DHAA)-coated Fe₃O₄ nanoparticles were successfully synthesized by co-precipitation method and their performance as draw solutes was investigated for application in FO systems. CS and DHAA could improve the surface hydrophilicity of the Fe₃O₄ nanoparticles. The synthesized nanoparticles were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM) which the results presented a small size, crystalline morphology and high magnetization value for their structure as well as a good dispersion in water. Cellulose triacetate/cellulose acetate (CTA/CA)-based membranes were also prepared by immersion precipitation and used as FO membranes. The synthesized FO membranes were characterized by FESEM. The performance evaluation of synthesized nanoparticles revealed that the water flux of Fe₃O₄ nanoparticles capped with DHAA was higher than that of the chitosan-coated Fe₃O₄ nanoparticles. At the end of the process, the Fe₃O₄ nanoparticles were easily separated from the diluted draw solution by applying the magnetic field.     

Preparation and characterization of mesoporous TiO<Subscript>2</Subscript>-pillared titanate photocatalyst

Mesoporous anatase TiO₂-pillared titanate has been successfully prepared by the exfoliation-restacking route. The resulting nanocomposite was characterized by powder X-ray diffraction, scanning electron microscope, thermogravimetric analysis, IR and UV–Vis spectroscopy, specific surface area and porosity measurements. It was revealed that the present nanocomposite exhibits greatly expanded specific surface area (~200 m² g⁻¹) with 2.8- and 6.6-nm-in-diameter mesopore structure, and that there exists an electronic coupling between the host titanate sheets and the guest anatase TiO₂ nanoparticles in the pillared system. The results of degradation of methylene blue under ultraviolet and visible radiation show that the present nanocomposite exhibits much higher photocatalytic activities than that of TiO₂ nanoparticles or layered titanate alone, which are based on the bandgap excitation and the dye sensitization.     

Thermoelectric properties of Cu-dispersed bi<Subscript>0.5</Subscript>sb<Subscript>1.5</Subscript>te<Subscript>3</Subscript>

A novel and simple approach was used to disperse Cu nanoparticles uniformly in the Bi_0.5Sb_1.5Te₃ matrix, and the thermoelectric properties were evaluated for the Cu-dispersed Bi_0.5Sb_1.5Te₃. Polycrystalline Bi_0.5Sb_1.5Te₃ powder prepared by encapsulated melting and grinding was dry-mixed with Cu(OAc)₂ powder. After Cu(OAc)₂ decomposition, the Cu-dispersed Bi_0.5Sb_1.5Te₃ was hot-pressed. Cu nanoparticles were well-dispersed in the Bi_0.5Sb_1.5Te₃ matrix and acted as effective phonon scattering centers. The electrical conductivity increased systematically with increasing level of Cu nanoparticle dispersion. All specimens had a positive Seebeck coefficient, which confirmed that the electrical charge was transported mainly by holes. The thermoelectric figure of merit was enhanced remarkably over a wide temperature range of 323-523 K.     

Photocatalytic activity of metal-decorated SiO<Subscript>2</Subscript>@TiO<Subscript>2</Subscript> hybrid photocatalysts under water splitting

We report the fabrication of a metal-decorated hybrid nanocomposite with TiO₂ encapsulation (Metal/SiO₂@TiO₂, Metal=Pt or Ru) using a simple surface-modification chemical process. Metal nanoparticles capped with polyvinylpyrrolidone were successfully assembled on functionalized SiO₂ via electrostatic interactions, after which a thin layer of TiO₂ was coated on the surface by the sol-gel process to avoid agglomeration of the coated silica spheres. Transmission electron microscopy studies confirmed that the metal nanoparticles were uniformly distributed throughout the surface of the SiO₂ with a thin layer of TiO₂. In addition, X-ray diffraction was employed to ensure the crystal structure of the uniformly coated thin TiO₂ layer. Even after calcination at 500 °C, the structure remained intact, confirming high thermal stability. The photocatalytic activity of the metal-decorated SiO₂/TiO₂ nanocomposites was evaluated using the H₂ evolution reaction. The Metal/SiO₂@TiO₂ catalysts show the photocatalytic water splitting efficiency for H₂ generation (i.e., 0.14% for Pt/SiO₂@TiO₂ and 0.12% for Ru/SiO₂@TiO₂), while there is no generation of H₂ on the Metal/SiO₂ without a coating layer. These results indicate that the anatase crystalline coating layer has good thermal and chemical stability and plays a significant role in photocatalytic H₂ production.     

Synthesis of Heterogeneous Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> Nanostructured Anodes with Long-Term Cycle Stability

The 0D-1D Lithium titanate (Li₄Ti₅O₁₂) heterogeneous nanostructures were synthesized through the solvothermal reaction using lithium hydroxide monohydrate (Li(OH)·H₂O) and protonated trititanate (H₂Ti₃O₇) nanowires as the templates in an ethanol/water mixed solvent with subsequent heat treatment. A scanning electron microscope (SEM) and a high resolution transmission electron microscope (HRTEM) were used to reveal that the Li₄Ti₅O₁₂ powders had 0D-1D heterogeneous nanostructures with nanoparticles (0D) on the surface of wires (1D). The composition of the mixed solvents and the volume ratio of ethanol modulated the primary particle size of the Li₄Ti₅O₁₂ nanoparticles. The Li₄Ti₅O₁₂ heterogeneous nanostructures exhibited good capacity retention of 125 mAh/g after 500 cycles at 1C and a superior high-rate performance of 114 mAh/g at 20C.     

Thermochemical modification of Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> hydrosilicate nanotubes by silver nitrate solutions

The interaction of an aqueous solution of silver nitrate with Mg₃Si₂O₅(OH)₄ hydrosilicate nanotubes under atmospheric conditions at 50 and 80°C and under dynamic conditions with subsequent annealing at 300°C has been investigated. The intercalation of AgNO₃ solutions into the internal channel and interlayer spaces of the nanotube structure and the crystallization of the silver particles of the spherical shapes on the nanotube surface have been established.     

Preparation of hydrophobic SiO<Subscript>2</Subscript>@(TiO<Subscript>2</Subscript>/MoS<Subscript>2</Subscript>) composite film and its self-cleaning properties

TiO₂/MoS₂ composite was encapsulated by hydrophobic SiO₂ nanoparticles using a sol–gel hydrothermal method with methyltriethoxysilane (MTES), titanium tetrachloride (TiCl₄), and molybdenum disulfide (MoS₂) as raw materials. Then, a novel dual functional composite film with hydrophobicity and photocatalytic activity was fabricated on a glass substrates via the combination of polydimethylsiloxane adhesives and hydrophobic SiO₂@(TiO₂/MoS₂) composite particles. The influence of the mole ratios of MTES to TiO₂/MoS₂ (M:T) on the wettability and photocatalytic activity of the composite film was discussed. The surface morphology, chemical compositions, and hydrophobicity of the composite film on the glass substrate were investigated by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and water contact angle (water CA) measurements. The results indicated that the composite film exhibited stable superhydrophobicity and excellent photocatalytic activity for degradation of methyl orange (MO) even after five continuous cycles of photocatalytic reaction when M/T was 7:1. The water CA and degradation efficiency for MO remained at 154° and 94%, respectively. Further, the composite film showed a good non-sticking characteristic with the water sliding angle (SA) at about 4°. The SiO₂@(TiO₂/MoS₂) composite consisting of hydrophobic SiO₂ nanoparticles and TiO₂/MoS₂ heterostructure could provide synergistic effects for maintaining long-term self-cleaning performance.     

Wetting,surface tension,and work of adhesion of As<Subscript>2</Subscript>S<Subscript>3</Subscript> and As<Subscript>2</Subscript>Se<Subscript>3</Subscript> glass melts to quartz glass

The contact angles of the quartz glass surface by the As₂S₃ and As₂Se₃ glass melts and surface tension of these glass melts in the temperature range of 325–370°С have been experimentally measured. The polytherms are linear and possess negative slope in the mentioned temperature range. The work of the adhesion of As₂S₃ and As₂Se₃ glass melts to the quartz glass surface has been calculated and compared to the data on the adhesion strength of the As₂S₃–SiO₂ and As₂Se₃–SiO₂ boundaries of the solid phases.     

Some characteristics of heat-resisting concretes modified by SiO<Subscript>2</Subscript> and TiO<Subscript>2</Subscript> nanoparticles

Nanoparticles of SiO₂ or TiO₂ have been added in the preparation of heat-resisting concretes of two types. The major technical and chemical characteristics have been determined. Features have been found in some of the technological operations in making the concretes of both types, and also aspects of the physicomechanical properties. Higher chemical stability has been found for heat-resisting concrete containing TiO₂ nanoparticles in an NaOH solution.     

Catalytic properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles for rechargeable Li/air batteries

Three types of Co₃O₄ nanoparticles are synthesized and characterized as a catalyst for the air electrode of a Li/air battery. The shape and size of the nanoparticles are observed using scanning electron microscopy and transmission electron microscopy analyses. The formation of the Co₃O₄ phase is confirmed by X-ray diffraction. The electrochemical property of the air electrodes containing Co₃O₄ nanoparticles is significantly associated with the shape and size of the nanoparticles. It appears that the capacity of electrodes containing villiform-type Co₃O₄ nanoparticles is superior to that of electrodes containing cube- and flower-type Co₃O₄ nanoparticles. This is probably due to the sufficient pore spaces of the villiform-type Co₃O₄ nanoparticles.     

Thermal conductivity and viscosity measurements of ethylene glycol-based Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanofluids

The dispersion and stability of nanofluids obtained by dispersing Al₂O₃ nanoparticles in ethylene glycol have been analyzed at several concentrations up to 25% in mass fraction. The thermal conductivity and viscosity were experimentally determined at temperatures ranging from 283.15 K to 323.15 K using an apparatus based on the hot-wire method and a rotational viscometer, respectively. It has been found that both thermal conductivity and viscosity increase with the concentration of nanoparticles, whereas when the temperature increases the viscosity diminishes and the thermal conductivity rises. Measured enhancements on thermal conductivity (up to 19%) compare well with literature values when available. New viscosity experimental data yield values more than twice larger than the base fluid. The influence of particle size on viscosity has been also studied, finding large differences that must be taken into account for any practical application. These experimental results were compared with some theoretical models, as those of Maxwell-Hamilton and Crosser for thermal conductivity and Krieger and Dougherty for viscosity.     

Enhancement of UV-aging resistance of UV-curable polyurethane acrylate coatings via incorporation of hindered amine light stabilizers-functionalized TiO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> nanoparticles

In this study, polymeric hindered amine light stabilizers (HALS)-functionalized silica coated rutile titanium dioxide (TiO₂-SiO₂) nanoparticles were prepared by encapsulating commercially available TiO₂-SiO₂ nanoparticles with methyl methacrylate (MMA) and 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate (PMPM) copolymers via miniemulsion polymerization. The obtained functional (TiO₂-SiO₂/P(MMA-co-PMPM)) fillers have been added to polyurethane acrylate (PUA) oligomers to get UV-curable nanocomposite coatings. The functionalization of the TiO₂-SiO₂ nanoparticles with polymeric HALS has been confirmed by infrared spectra (IR), thermogravimetric (TG), and X-ray photoelectron spectroscopy (XPS) analyses. The scanning electron microscope (SEM) micrographs indicated that homogeneous dispersion of TiO₂-SiO₂/P(MMA-co-PMPM) composite nanoparticles resulted in improved transparency and mechanical properties of the UV-curable PUA coatings. Rhodamine B (Rh.B) photodegradation measurement confirmed the excellent UV-shielding performance of PUA nanocomposite coatings containing TiO₂-SiO₂/P(MMA-co-PMPM). The addition of TiO₂-SiO₂/P(MMA-co-PMPM) composite nanoparticles reduced the UV-curable PUA coatings degradation rate dramatically. The UV-aging resistance of PUA coatings was improved significantly. Over all, the combination of TiO₂-SiO₂ nanoparticles and polymeric HALS offers an attractive way to fabricate the multi-functional fillers, which can be used to improve the mechanical properties and UV-aging resistance of PUA coatings simultaneously.     

Electrical conductivity and structure of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>O<Subscript>5</Subscript> and Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>S<Subscript>5</Subscript> systems

The glasses, in which oxygen was partially replaced with sulfur, have been synthesized in the Na₂O-P₂O₅-Na₂S system. The chemical and chromatographic analyses of the glasses synthesized have been performed. The temperature-concentration dependences of electrical conductivity of the glasses have been studied over a wide temperature range; the glass transition temperatures and the nature of charge carriers have been determined. The IR spectra and Raman spectra have been recorded at room temperature; the density and microhardness of the glasses and ultrasound velocity have been measured. A comparison of the electrical conductivities of the investigated glasses with those of the earlier studied glasses in the Na₂O-P₂O₅ system has shown their fair coincidence. The introduction of sodium sulfide into the Na₂O-P₂O₅ system is accompanied by an approximately threefold increase in electrical conductivity, although the concentrations of charge carriers (sodium ions) in the glasses amount to ∼17 and ∼26 mmol/cm³, respectively. The rise in electrical conductivity has been assumed to be caused by the increase in the degree of dissociation of polar structural chemical units including sulfide ions and by the higher mobility of sodium ions in the oxygen-free matrix.