Synthesis of superhydrophobic core–shell mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNPs) have been used in variety of applications due to their morphology and porous structure. This work reports the one-pot synthesis of ultrahydrophobic MSNPs using N-cetyl-n,n,n trimethyl ammonium bromide as a cationic surfactant template and ethanol (EtOH) as a cosolvent to form mesopores in the MSNPs. The effects of EtOH on the size and the pore structure of the MSNPs were studied by scanning electron microscopy and transmission electron microscopy. The results show that an addition of EtOH led to an enlargement of the MSNPs and a change in pore structure from a lamellar structure to a radially oriented structure. Co-condensation with two different types of fluoroalkyl silanes; trimethyl(fluoromethyl)silane, and trichloro(1H,1H,2H,2H-perfluorooctyl)silane provided low surface energy MSNPs with a core–shell structure. An assembly on the surface of these F-MSNPs generated nanostructure surface roughness rendering an improvement in surface wettability with water contact angle of 158.6°, which is a characteristic of oleophobic and ultrahydrophobic material.     

Synthesis and characterization of thermosensitive core–shell polymeric nanoparticles

Thermosensitive core–shell nanoparticles were synthesized by semicontinuous heterophase polymerization of styrene, followed by a seeded polymerization for forming a shell of poly(N-isopropyl acrylamide) (PNIPAM). Nanoparticles characterization by scanning transmission electronic microscopy showed core–shell morphology with average particle diameters around 40 nm. An inverse dependence of the particle size with temperature in the range 20–55 °C was identified by quasielastic light scattering measurements. As was expected for core–shell particles with PNIPAM as the shell, a volume phase transition near 32 °C was detected. In spite of thermosensitive properties of core–shell nanoparticles synthesized here, the volume percentage loss values were not so high, probably due to their relatively low content of PNIPAM.     

Viscoelasticity of shell-crosslinked core–shell nanoparticles filled polystyrene melt

Shell-crosslinked core–shell nanoparticles (SCCSN) of 63–104 nm in diameter and containing 79.1 wt% crosslinked polystyrene (PS) shell of 16.5–37.0 nm in thickness were prepared by miniemulsion polymerization of styrene in the presence of silane modified nanosilica. The PS shell was crosslinked using divinyl benzene in order to anchor the shell on the nanoparticle surface, to segregate the silica core from the matrix and to avoid entanglement between the shell PS and the matrix macromolecules in SCCSN filled PS composites. Steady and dynamic rheologies of SCCSN filled PS were compared with bare silica filled PS. The SCCSN filled PS composites exhibited exceedingly good rheological stability than silica filled ones during annealing. Both bare silica and SCCSN introduced a non-terminal dynamic rheology while they did not introduce additional mechanism responsible for origination of nonlinear steady flow except for macromolecular disentanglement of the PS matrix. The reinforcement of SCCSN to PS was related to the silica core even though the crosslinked shell could effectively eliminate filler aggregation as the case of silica filled PS.     

Combustion synthesis and characterization of spherical α-MnMoO4 nanoparticles

In this study, α-MnMoO₄ nanoparticles were prepared by combustion synthesis method. The structural, morphological and electrical characteristics of α-MnMoO₄ were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, transmission electron microscopy and impedance spectroscopy. The structural parameters were calculated from XRD pattern which confirmed the monoclinic structure of α-MnMoO₄. FT-IR and Raman spectroscopy results revealed the presence of MoO₄ surface functional groups. The TEM and HRTEM investigations evidenced the presence of homogeneous distribution of spherical nanoparticles and high crystallinity of α-MnMoO₄. Moreover, the SAED patterns clearly revealed the polycrystalline nature of the material. The conductivity measurements had inferred the semiconducting property of α-MnMoO₄ and the maximum conductivity of 1.94 × 10^? 6 S/cm was attained at 540 °C.     

α-Arylation of oxindoles using recyclable metal oxide ferrite nanoparticles: Comparison between the catalytic activities of nickel,cobalt and copper ferrite nanoparticles

Three different spinel metal oxide catalytic systems including NiFe₂O₄, CuFe₂O₄ and CoFe₂O₄ were synthesized using co-precipitation technique and their catalytic activities were compared to each other in α-arylation of oxindole derivatives under the optimized reaction conditions. Both nickel ferrite and copper ferrite magnetic nanoparticles show approximately the same behavior in these reactions but cobalt ferrite ones indicate slightly different properties and were not as good as the other two catalysts. These superparamagnetic catalysts allowed that α-arylation of different types of oxindoles will occur in high yields under mild conditions and at very short times.     

Ammonium fluoride-activated synthesis of cubic δ-TaN nanoparticles at low temperatures

Cubic delta-tantalum nitride (δ-TaN) nanoparticles were selectively prepared using a K₂TaF₇ + (5 + k) NaN₃ + kNH₄F reactive mixture (k being the number of moles of NH₄F) via a combustion process under a nitrogen pressure of 2.0 MPa. The combustion temperature, when plotted as a function of the number of moles of NH₄F used, was in the range of 850°C to 1,170°C. X-ray diffraction patterns revealed the formation of cubic δ-TaN nanoparticles at 850°C to 950°C when NH₄F is used in an amount of 2.0 mol (or greater) in the combustion experiment. Phase pure cubic δ-TaN synthesized at k = 4 exhibited a specific surface area of 30.59 m²/g and grain size of 5 to 10 nm, as estimated from the transmission electron microscopy micrograph. The role of NH₄F in the formation process of δ-TaN is discussed with regard to a hypothetical reaction mechanism.     

Thermally activated sintering–coarsening–coalescence-polymerization of amorphous silica nanoparticles

An onset sintering–coarsening–coalescence-polymerization (SCCP) event of amorphous SiO₂ nanoparticles (ca. 40–100 nm in size) by isothermal firing in the 1150–1300 °C range in air was characterized by an N₂ adsorption–desorption hysteresis isotherm coupled with X-ray diffraction and vibrational spectroscopy. The apparent activation energy of such a rapid SCCP process was estimated as 177±32 kJ/mol, based on 30% reduction of a specific surface area with an accompanied change of medium range orders, i.e. forming Si₂O₅ while retaining the Si–2ndO yet losing the Si–2ndSi without appreciable crystallization. The minimum temperature of the SCCP process, as of concern to industrial silica applications and sedimentary/metamorphosed sandstone formation, is 1120 °C based on the extrapolation of steady specific surface area reduction rates to null.     

The effect of ceramic nanoparticles on tribological properties of alumina sol–gel thin coatings

Thin alumina coatings containing zirconia or alumina nanoparticles having diameter of ～20–30 nm were deposited by the sol–gel dip-coating process on silicon wafers. The mass content of nanoparticles in the alumina coating was fixed at 15% in relation to the theoretical mass of alumina matrix resulted from the amount of the applied precursor. Atomic force microscopy (AFM) was used to image the surface topography of as-made coatings and find out the wear level after frictional tests. Tribological tests were performed with the use of a microtribometer operating in the load range of 30–100 mN. It was found that the presence of α-alumina (corundum) or zirconia nanoparticles enhances the tribological performance of alumina layers annealed at 100 °C by decreasing the average wear rate by 20% and 63% for zirconia and corundum nanoparticles, respectively. No wear was observed for samples containing both types of nanoparticles annealed at 500 °C.     

BIOTECHNOLOGY AND BIOENGINEERING Roles of biomolecules in the biosynthesis of silver nanoparticles: Case of gardenia jasminoides extract

Rapid development of biosynthesis of metal nanoparticles using plants has attracted extensive interests to further investigate this novel and eco-friendly method. In the biosynthesis process, the plant may act as reducing agent, capping agent or shape directing agent. However, identifying specific roles of various components in the plant is challenging. In this study, we use biosynthesis of silver nanoparticles with Gardenia jasminoides Ellis ex-tract to address this issue. The formation process of silver nanoparticles is investigated and the nanoparticles are characterized with the ultraviolet-visible spectroscopy, Fourier transform infrared spectra and scanning electron mi-croscopy. The results indicate that the Gardenia jasminoides Ellis extract can reduce silver ions to form silver nanoparticles, stabilize the nanoparticles, and affect the growth of silver nanocrystal to form silver nanowires. Only geniposide in the extract exhibits good shape-directing ability for silver nanowires. It is found that bovine albumin is a potential capping agent, whereas rutin, gallic acid and chlorogenic acid possess reducing and capping ability.     

Electrochemical investigation of high-performance silane sol–gel films containing clay nanoparticles

Silane sol–gel coatings are widely used as adhesion promoters between inorganic substrates, such as metals, and organic coatings. The aim of these pre-treatments is to enhance the corrosion protection performance of the organic coating improving the adhesion to the substrate and acting as a barrier against water and aggressive ions diffusion. It is a matter of fact that the silane sol–gel pre-treatments do not provide an active protection against corrosion processes except for the partial inhibition of the cathodic reaction. Inorganic pigments can improve the barrier properties of the silane sol–gel film, enhancing the resistance against corrosion. In this study, different amounts of montmorillonite nanoparticles were added to a water based silanes mixture in order to improve the barrier properties of the sol–gel coating. Hot dip galvanized steel was used as substrate. The sol–gel film consists of a combination of three different silanes, GPS, TEOS and MTES. The clay nanoparticles used in this study were mainly neat montmorillonite. The proper concentration of filler inside the sol–gel films was determined comparing the corrosion resistance of silane layers with different nanoparticles contents. Additionally, the effect of CeO₂ and Ce₂O₃ enriched montmorillonite particles. The EIS analysis and the polarization measurements demonstrated that the optimal amount of neat montmorillonite nanoparticles is about 1000 ppm. The same electrochemical techniques highlighted the limited effect of the cerium oxides grafted to the clay nanoparticles on the corrosion resistance of the silane sol–gel film. The TEM analysis proved the presence of a nano-crystalline structure inside the silane sol–gel film due to the formation of crystalline silica domains.     

Sintering kinetics of disperse ultrafine equiaxed α-Al2O3 nanoparticles

The sintering kinetics of ceramic nanoparticles is essential for preparing dense nanocrystalline ceramics with fine grains, but the sintering kinetics of disperse ultrafine α-Al₂O₃ nanoparticles has not been systematically explored so far. In this paper, the sintering kinetics of disperse ultrafine equiaxed α-Al₂O₃ nanoparticles with a mean particle size of 4.5 nm and a narrow size distribution of 2–8 nm without any agglomeration was studied systematically. Finally, α-Al₂O₃ nanocrystalline ceramic with a mean grain size of 36 nm and a relative density of 99.7% was sintered in air by two-step sintering (heated to 1100 °C without hold and then cooled down to 950 °C with a 40 h hold). The sintering temperature is the lowest for pressureless sintering of α-Al₂O₃ and almost fully dense α-Al₂O₃ nanocrystalline ceramic obtained also has the finest grain so far.     

Densification and properties of ZrO2 nanoparticles added magnesia–doloma refractories

In this work the effect of nano- and microZrO₂ addition on the densification and hydration resistance of MgO–CaO refractories was investigated. 0, 2, 4, 6 and 8 wt% ZrO₂ was added to MgO–CaO refractories that contain 35 wt% CaO. The crystalline phases and microstructure characteristics of specimens sintered at 1650 °C for 5 h in an electric furnace were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The physical properties are reported in terms of bulk density, apparent porosity and hydration resistance. Results show that with addition of ZrO₂ the bulk density and hydration resistance of the samples increased while apparent porosity decreased. Also the hydration resistance of the samples was appreciably improved by the addition of ZrO₂ due to its effect on decreasing the amount of free CaO in the refractories, promotion of densification as well as modification of the microstructure. Also it revealed that the nanoZrO₂ addition was more effective than microZrO₂ due to its higher activity.     

Structural and optical characterization of Zn0.95−xMg0.05AlxO nanoparticles

The structural and optical properties of ZnO nanoparticles doped simultaneously with Mg and Al were investigated. XRD results revealed the hexagonal wurtzite crystalline structure of ZnO. The FE-SEM study confirmed the formation of nano-sized homogeneous grains whose sizes decreased monotonously with increasing doping concentrations of Mg and Al. The absorption spectra showed that band gap increased from 3.20 to 3.31 eV with Mg doping. As the Al concentration changed from x=0.01 to x=0.06 mol% at constant Mg concentration the band gap observed to be decreased. Particle sizes estimated from effective mass approximation using absorption data and these values are in good agreement with the crystallite sizes calculated from XRD data. Raman spectra of ZnO showed a characteristic peak at 436 cm⁻¹ correspond to a non-polar optical phonon E₂ (high). With increase of the Al doping concentrations, E₂ (high) phonon frequency shifted to 439 cm⁻¹ from to 436 cm⁻¹. The origin of E₂ (high) peak shift in ZnO nanoparticles is attributed to optical phonon confinement effects or the presence of intrinsic defects on the nanoparticles. PL spectra indicated that with increase of Al co-doping along with Mg into ZnO, intensity of the peak positioned at 395 nm was initially increased at x=0 and then decreased with increase of the Al concentrations from x=0.01 to x=0.06 mol%.     

Effect of niobium valence on the mechanochemical activation of niobium oxides–hematite magnetic ceramic nanoparticles

Three types of nanostructured systems: xNbO·(1?x)α-Fe₂O₃, xNbO₂·(1?x)α-Fe₂O₃, and xNb₂O₅·(1?x)α-Fe₂O₃ were synthesized by ball milling at different molar concentrations (x=0.1, 0.3, 0.5, and 0.7). The effect of Nb valence and milling time on mechanochemical activation of these systems were studied by X-ray diffraction and the Mössbauer spectroscopy measurements. In general, Nb-substituted hematite was obtained at lower molar concentrations for all Nb oxides. For the NbO–Fe₂O₃ system the favorable substitution of Fe²⁺ for Nb²⁺ in the octahedral sites in the NbO lattice was observed after 12 h milling for x=0.7. In the case of the NbO₂–Fe₂O₃ and Nb₂O₅–Fe₂O₃ systems a formation of orthorhombic FeNbO₄ compound was observed, in which Fe³⁺ cations were detected. For the highest concentration of NbO₂ (x=0.7) iron was completely incorporated into the FeNbO₄ phase after 12 h milling. The molar concentrations of x=0.3 and 0.5 were the most favorable for the formation of ternary FeNbO₄ compound in the Nb₂O₅–Fe₂O₃ system. Influence of ball milling on thermal behavior of the powders was investigated by simultaneous DSC–TG measurements up to 800 °C.     

The biological properties of carbon nanofibers decorated with β-tricalcium phosphate nanoparticles

Carbon nanofibers decorated with β-tricalcium phosphate (β-TCP) nanoparticles (β-TCP/CNFs) have been prepared by sintering electrospun polyacrylonitrile fibers with calcium nitrate tetrahydrate as the calcium source and triethyl phosphate as the phosphorus source. Microstructure and phase composition analysis indicate that the resulting materials are composed of β-TCP nanoparticles and CNFs. And the long β-TCP/CNFs can be cut into organism-eliminable short CNFs gradually in hydrochloric acid solution due to the solubilization of β-TCP nanoparticles. The materials exhibit good biocompatibility, and have comparable effect on cell growth with pure CNFs, with their tuning ability in degradation.     

Methanol tolerant oxygen-reduction activity of carbon supported platinum–bismuth bimetallic nanoparticles

The oxygen reduction activity and methanol tolerance of Pt–Bi/C electrocatalysts were studied using electrochemical voltammetric techniques including rotating ring-disk electrode. The Pt–Bi/C catalyst was prepared via a polyol method and subjected to heat treatment to increase the degree of alloying. X-ray diffraction studies revealed the unalloyed character of the as-prepared catalyst and alloy formation upon heat treatment. The electrochemical behaviour of both catalysts showed different behaviour in dilute acid electrolytes, namely sulphuric and perchloric acids. In both electrolytes, the oxygen reduction reaction was found to occur via the four-electron process revealing that the mechanism of oxygen reduction is unaltered even in the presence of excess of methanol. Pt–Bi/C catalyst material showed dramatically different properties and reactivity with respect to oxygen reduction activity and methanol tolerance in perchloric and sulphuric acids. The onset potential for oxygen reduction reaction (ORR) significantly shifted by about 100 mV to more negative values and at the same time the current density was significantly enhanced. This type of non-ideal methanol-tolerant behaviour among Pt bimetallics and a “trade off” is common with all the known so-called methanol tolerant combinations of Pt. In general, the Pt–Bi surface appeared to have a negligibly lesser sensitivity towards methanol activity compared to pure platinum.     

Thermodynamic analysis and modification of Gibbs–Thomson equation for melting point depression of metal nanoparticles

Abnormal melting point depression of metal nanoparticles often occurs in heterogeneous catalytic reactions,which leads to a reduction in the stability of reactive nanoclusters.To study this abnormal phenomenon,the original and surface-energy modified Gibbs-Thomson equations were analyzed in this work and further modified by considering the effect of the substrate.The results revealed that the original Gibbs-Thomson equation was not suitable for the particles with radii smaller than 10 nm.Moreover,the performance of the surface-energy modified Gibbs-Thomson equation was improved,and the deviation was reduced to(-350-100) K,although further modification of the equation by considering the interfacial effect was necessary for the small particles(r 5 nm).The new model with the interfacial effect improved the model performance with a deviation of approximately-50 to 20 K,where the interfacial effect can be predicted quantitatively from the thermodynamic properties of the metal and substrate.Additionally,the micro-wetting parameter α_W can be used to qualitatively study the overall impact of the substrate on the melting point depression.     

Study of corrosion and friction reduction of electroless Ni–P coating with molybdenum disulfide nanoparticles

One composite coating of Ni–P alloys containing MoS₂ nanoparticles was prepared by electroless technique based on the better friction reduction ability of MoS₂ and better anticorrosion property of electroless Ni–P alloys on carbon steel surfaces. Electrochemical method—that is, using Tafel polarization curves—was carried out in order to study the corrosion performance of the coating. The results indicate that the anticorrosion ability of the composite coating was decreased because of the addition of nano-MoS₂ particles. The corrosional surfaces were studied and analyzed through scanning electron microscopy (SEM). The corrosion mechanism of the composite coatings was mainly ascribed to the formation of microcells around the nanosized MoS₂ particles, and the active ion-like Cl⁻ destroyed the surface film and induced the corrosion on the inside part of the coating. The friction coefficient of electroless composite coatings was measured by end-facing tribometer. It was found that the friction coefficient of the Ni–P–(nano-MoS₂) composite coating decreased greatly compared with those of Ni–P electroless coatings.     

Mechanical properties of sol–gel prepared nanocomposite coatings in the presence of titania and alumina-derived nanoparticles

Hybrid nanocomposite coatings were prepared by sol–gel method using silica, titania and alumina nanoparticles derived from their alkoxides precursors; in the presence of 3-glycidoxypropyl-trimethoxysilane (GPTMS) and bisphenol A (BPA) on 1050 aluminium alloy substrate. The effect of type and ratio of nanoparticles on mechanical behaviour of the coatings were investigated by dynamic mechanical thermal analysis (DMA) and nanoindentation experiments. DMA results demonstrated that the values of the glass transition temperature (T_g) and the temperature at maximum tan (δ), (T_t) as well as the storage modulus of the hybrid samples depend mainly on the silane content and titania to alumina molar ratio of nanoparticles in the coating composition. In addition, nanoindentaion experiments were performed to study the mechanical properties such as hardness, elastic modulus and E/H ratio for the nanocomposite hybrid coatings. Nanoindentation results indicate that the homogenous reinforced structure was formed in the surface of nanocomposite coating with incorporation of titania and alumina-derived nanoparticles. The incorporation of TiO₂ in comparison with AlOOH nanoparticles in the GPTMS-based coatings showed an improving effect on E/H ratio.     

Ionic liquid assisted one step green synthesis of Au–Ag bimetallic nanoparticles

Au–Ag bimetallic nanoparticles have been fabricated by one-step simple electrochemical deposition method using ionic liquid as green electrolyte (1-butyl-3-methylimidazolium tetrafluoro borate). Fabricated Au–Ag bimetallic nanoparticles have been characterized using cyclic voltammetry (CV), FE-SEM, UV–vis spectroscopy, and X-ray diffraction (XRD) studies. The electrodeposited Au–Ag bimetallic nanoparticles were found in the size range of 16–30 nm, respectively. This type of Au–Ag bimetallic nanoparticles could be directly applied for the optoelectronic and biosensing applications.