Improvement of dispersion stability and characterization of upconversion nanophosphors covalently modified with PEG as a fluorescence bioimaging probe

Upconverting (UC) phosphors (UCPs) are ceramic materials doped with rare earth ions. These materials can absorb and upconvert infrared (IR) radiation to emit visible light by the stepwise excitation among discrete energy levels of the rare earth ions. UCPs are potentially useful reagents for use in bioimaging since the use of low energy photons avoids photo-toxicity. The use of UCP nanoparticles as bioimaging probes requires surface modifications in an effort to improve dispersion stability in aqueous milieu. In this study, we covalently attached poly(ethylene glycol) (PEG) to the surface of Er-doped Y₂O₃ nanoparticles and firstly demonstrated that PEG covalently bound to the Y₂O₃ surface markedly improved dispersion stability in water. UC emission of PEG-modified Er–Y₂O₃ nanoparticles excited with IR light was successfully observed. We also showed that PEG-modified Er–Y₂O₃ nanoparticles exhibit no cell-toxicity. These observations lend strong support to the potential use of PEG-modified UCP nanoparticles as bioimaging tools.     

Influence of different materials on the microstructure and optical band gap of α-Fe2O3 nanoparticles

Composites of hematite (α-Fe₂O₃) nanoparticles with different materials (NiO, TiO₂, MnO₂ and Bi₂O₃) were synthesized. Effects of different materials on the microstructure and optical band gap of α-Fe₂O₃ nanoparticles were studied. Crystallite size and strain analysis indicated that the pure α-Fe₂O₃ nanoparticles were influenced by the presence of different materials in the composite sample. Crystallite size and strain estimated for all the samples followed opposite trends. However, the value of direct band gap decreased from ～2.67 eV for the pure α-Fe₂O₃ nanoparticles to ～2.5 eV for α-Fe₂O₃ composites with different materials. The value of indirect band gap, on the other hand, increased for all composite samples except for α-Fe₂O₃/Bi₂O₃.     

Luminescence properties of Eu3+ or Dy3+/Au co-doped SiO2 nanoparticles

Silica nanoparticles, prepared by the Stober method, have been doped with Eu³⁺, Dy³⁺, or processed to result in Au nanoparticles on the silica surface. The luminescence of the rare earth (RE)-doped SiO₂ particles has been studied as a function of the nature of the RE, their concentration and also of the presence of Au nanoparticles at the surface of the SiO₂ nanoparticles. We have shown that the Eu³⁺ emission is observable over the experimental conditions examined, whereas it was not possible to observe any emission for Dy³⁺ doped materials. No enhancement of the Eu³⁺ emission was observed following the adsorption of gold nanoparticles at the surface of the SiO₂ nanoparticle, however an excitation at 250 nm leads to both the emission of the matrix and Eu³⁺ showing an energy transfer from the SiO₂ matrix to Eu³⁺ ions.     

Surface engineered magnetic nanoparticles for removal of toxic metal ions and bacterial pathogens

Surface engineered magnetic nanoparticles (Fe₃O₄) were synthesized by facile soft-chemical approaches. XRD and TEM analyses reveal the formation of single-phase Fe₃O₄ inverse spinel nanostructures. The functionalization of Fe₃O₄ nanoparticles with carboxyl (succinic acid), amine (ethylenediamine) and thiol (2,3-dimercaptosuccinic acid) were evident from FTIR spectra, elemental analysis and zeta-potential measurements. From TEM micrographs, it has been observed that nanoparticles of average sizes about 10 and 6 nm are formed in carboxyl and thiol functionalized Fe₃O₄, respectively. However, each amine functionalized Fe₃O₄ is of size ∼40 nm comprising numerous nanoparticles of average diameter 6 nm. These nanoparticles show superparamagnetic behavior at room temperature with strong field dependent magnetic responsivity. We have explored the efficiency of these nanoparticles for removal of toxic metal ions (Cr³⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, Pb²⁺ and As³⁺) and bacterial pathogens (Escherichia coli) from water. Depending upon the surface functionality (COOH, NH₂ or SH), magnetic nanoadsorbents capture metal ions either by forming chelate complexes or ion exchange process or electrostatic interaction. It has been observed that the capture efficiency of bacteria is strongly dependent on the concentration of nanoadsorbents and their inoculation time. Furthermore, these nanoadsorbents can be used as highly efficient separable and reusable materials for removal of toxic metal ions.     

The effect of polysiloxane on the properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-NbC composite material produced by pyrolysis process

Recently, studies have been developed in order to obtain Al₂O₃-NbC composite materials. The reinforced materials have shown good potential to be used as cutting tool materials at high-speed cutting and high temperature as a substitute to WC-Co material. The main disadvantage to produce these alumina-reinforced materials is the necessity to use pressure assisted sintering or high sintering temperatures to produce dense bodies. Manufacturing of composite ceramic materials derived from polymer reactive filler has been intensively investigated. Polymer pyrolysis is a relatively new and very promising method for obtaining ceramic material in complex shapes and lower sintering temperatures. This work investigated a ceramic composite matrix based in SiC_xO_y and Al₂O₃ and reinforced with NbC obtained by means of the active fillers pyrolysis process. The results obtained in this work demonstrate that using a mixture of polysiloxanes produces a composite material with better properties when compared to others polymer materials.     

Chalcogenides by Design: Functionality through Metavalent Bonding and Confinement

A unified picture of different application areas for incipient metals is presented. This unconventional material class includes several main-group chalcogenides, such as GeTe, PbTe, Sb₂Te₃, Bi₂Se₃, AgSbTe₂ and Ge₂Sb₂Te₅. These compounds and related materials show a unique portfolio of physical properties. A novel map is discussed, which helps to explain these properties and separates the different fundamental bonding mechanisms (e.g., ionic, metallic, and covalent). The map also provides evidence for an unconventional, new bonding mechanism, coined metavalent bonding (MVB). Incipient metals, employing this bonding mechanism, also show a special bond breaking mechanism. MVB differs considerably from resonant bonding encountered in benzene or graphite. The concept of MVB is employed to explain the unique properties of materials utilizing it. Then, the link is made from fundamental insights to application-relevant properties, crucial for the use of these materials as thermoelectrics, phase change materials, topological insulators or as active photonic components. The close relationship of the materials' properties and their application potential provides optimization schemes for different applications. Finally, evidence will be presented that for metavalently bonded materials interesting effects arise in reduced dimensions. In particular, the consequences for the crystallization kinetics of thin films and nanoparticles will be discussed in detail.     

Effect of solid inorganic salts on the formation of cubic-like aggregates of ZnSnO3 nanoparticles in solventless,organic-free reactions and their gas sensing behaviors

The effect of added solid inorganic salts on the morphology of ZnSnO₃ nanoparticle aggregates has been investigated based on solventless and organic-free reactions at ambient temperature. Cubic-like aggregates of ZnSnO₃ nanoparticles can be synthesized successfully through direct reaction of solid MOH (M⁺ = K⁺, Na⁺) with a solid mixture of ZnCl₂ and SnCl₄·5H₂O in the presence of added inorganic salt, MCl (M⁺ = K⁺, Na⁺). In contrast, irregular spherical aggregates of ZnSnO₃ nanoparticles are produced in the reactions in absence of added solid inorganic salts. The added solid inorganic salts, which play a key role for producing the cubic-like aggregates of ZnSnO₃ nanoparticles with pores of ca. 2.8 nm, may act as a substrate-template for the growth of nanocrystals and the formation of their cubic-like aggregates. Gas sensors are further constructed with the aggregates of ZnSnO₃ nanoparticles as sensing materials. The sensors made with the cubic-like aggregates (C-sensors) exhibit much higher responses to the reducing gases tested, compared to those (S-sensors) from spherical aggregates synthesized without adding inorganic substrate-template into the reaction. The approach could open a new pathway for controlling the microstructure of materials with high gas sensing functionality.     

Samarium-doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles with improved magnetic and supercapacitive performance: a novel preparation strategy and characterization

Sm³⁺-doped magnetite (Fe₃O₄) nanoparticles were synthesized through a one-pot facile electrochemical method. In this method, products were electrodeposited on a stainless steel (316L) cathode from an additive-free 0.005 M Fe(NO₃)₃/FeCl₂/SmCl₃ aqueous electrolyte. The structural characterizations through X-ray diffraction, field-emission electron microscopy, and energy-dispersive X-ray indicated that the deposited material has Sm³⁺-doped magnetite particles with average size of 20 nm. Magnetic analysis by VSM revealed the superparamagnetic nature of the prepared nanoparticles (Ms = 41.89 emu g^?1, Mr = 0.12 emu g^?1, and H _Ci = 2.24 G). The supercapacitive capability evaluation of the prepared magnetite nanoparticles through cyclic voltammetry and galvanostat charge–discharge showed that these materials are capable to deliver specific capacitances as high as 207 F g^?1 (at 0.5 A g^?1) and 145 F g^?1 (at 2 A g^?1), and capacity retentions of 94.5 and 84.6% after 2000 cycling at 0.5 and 1 A g^?1, respectively. The results proved the suitability of the electrosynthesized nanoparticles for use in supercapacitors. Furthermore, this work provides a facile electrochemical route for the synthesis of lanthanide-doped magnetite nanoparticles.     

Poly(3-hydroxybutyrate)-based hybrid materials with photocatalytic and magnetic properties prepared by electrospinning and electrospraying

Several types of nanostructured hybrid fibrous materials containing poly(3-hydroxybutyrate), nanoparticles from iron oxide (Fe₃O₄) and titanium dioxide (TiO₂), and chitosan or chitosan oligosaccharides (COS) were prepared. The design of the surface of the materials and their magnetic properties were tailored purposefully by conjunction of electrospinning and electrospraying. The surface and bulk morphologies of the obtained nanostructured materials were examined by SEM. Further, the distribution of Fe₃O₄ and TiO₂ nanoparticles was estimated by TEM analyses, as well as their surface chemical composition was determined by XPS. It was found that the simultaneous electrospinning and electrospraying of Fe₃O₄/chitosan or TiO₂/COS dispersions resulted in uniform distribution of the nanoparticles along the length of the fibers, while electrospraying of the mixed Fe₃O₄/TiO₂/chitosan dispersion led to agglomerate formation. Furthermore, the nanostructured hybrid materials preserved the magnetic properties of Fe₃O₄ embedded therein. It was demonstrated that the hybrid materials of different designs displayed excellent photocatalytic activity under UV light irradiation against a model organic contaminant—methylene blue, even after threefold use of the materials.     

Hydrothermal synthesis of Fe3O4 and α-Fe2O3 nanocrystals as anode electrode materials for rechargeable Li-ion batteries

This paper describes a facile, economical and environment-friendly hydrothermal method of fabricating Fe₃O₄ and α-Fe₂O₃ nanoparticles at 180 °C for 12 h, respectively. The as-obtained products were characterized in detail. X-ray powder diffraction and transmission electron microscopy were used to investigate the products’ properties of crystal form, size, and morphology. The results showed the Fe₃O₄ and α-Fe₂O₃ nanocrystals’ diameter were about 5 and 20 nm, respectively. Moreover, the electrochemical performances of the Fe₃O₄ and α-Fe₂O₃ nanoparticles as anode materials for Li-ion batteries were also evaluated. The first-discharge capacities of Fe₃O₄ and α-Fe₂O₃ nanocrystals were 1,380 and 1,280 mAh g^?1, and stabled about 96 and 75 mAh g^?1 after 20 cycles, respectively. These materials offer substantial promise for developing alternative, high capacity negative electrodes for safer lithium batteries as energy storage and conversion materials.     

Electrochemical performance of CdS nanomaterials synthesized by microemulsion techniques

Precursor cadmium compounds influence the electro-catalytic performance of CdS nanomaterials for sulphide/polysulphide redox couple reaction. CdS nanorods and nanoparticles were synthesized from different raw materials, namely Cd(NO₃)₂, CdCl₂ or CdO, by a room temperature microemulsion approach using CS₂ as a sulphur source. Cadmium salts (i.e. CdCl₂, Cd(NO₃)₂) result in single phase CdS crystals with hexagonal structure while CdO gives two crystal phases with majority of cubic structure. Nanorods, produced from CdCl₂, demonstrated the best catalytic performance for the enhancement of the polysulphide reaction.     

Properties of magnesium alloys reinforced with nanoparticles and carbon nanotubes: a review

Magnesium alloys suffer from only moderate high-temperature strength and creep resistance. Aluminium-free magnesium alloys for sand casting or alloys containing aluminium with expensive additional alloying elements may be in use, but only microparticle or microfibre-reinforced magnesium alloys really exhibit satisfactory creep strengths at temperatures up to 250 °C. Reinforcing magnesium alloys with ceramic nanoparticles could be a solution for preserving a low density while increasing the high-temperature performance. When produced using melting processes, nanoparticle-reinforced magnesium composites are expected to enjoy strengthening due to the grain refinement described in the Hall–Petch relation. When an isotropic distribution of nanoparticles is achieved, the composites are additionally expected to be Orowan-strengthened. In this review, a variety of ceramic materials, such as SiC, Al₂O₃, Y₂O₃, SiO₂ and carbon nanotubes were investigated for reinforcement. Pure magnesium and various magnesium alloys were chosen as the matrix material and both powder metallurgical (PM) and melting processes were used for production of the composites. The mechanical properties of the composites were generally enhanced, compared to an unreinforced alloy; not only at room temperature, but also at elevated temperatures. In some cases an increase in strength in combination with increased ductility was also identified.     

AlN-(TiCr)B2 ion-plasma coating for cutting tools of cBN-based polycrystalline superhard material

The microstructure and oxidation kinetics of the surface layers of AlN-(TiCr)B₂ coating produced by magnetron RF sputtering have been studied in the course of the coating formation and use in tools of cBN-based polycrystalline superhard materials in machining ShKh 15 hardened steel. The coating is formed with the liquid phase present. After cutting the formation of two-layer tribofilm with a nanosized external layer has been revealed on the surface of the cutting insert. The tribofilm phase composition has been defined by a layer-by-layer Auger analysis. The film external nanosized layer is a glassy phase as solid solutions of Fe₂O₃-Al₂O₃ oxides that acts as a solid lubricant. As the cutting speed increases, the wear rate of a tool with a coating has been found to decrease as compared with tools without a coating.     

Synthesis and blue to near-infrared quantum cutting of Pr/Yb co-doped Li2TeO4 phosphors

Near-infrared (NIR) quantum cutting luminescent materials Li₂TeO₄ doped with Pr³⁺ and Yb³⁺ were synthesized by solid-state reaction method. The dependence of Yb³⁺ doping concentration on the visible- and NIR-emissions, decay lifetime, and quantum efficiencies of the phosphors are investigated. Quantum cutting down-conversion involving 647 nm red emission and 960-1050 nm broadband near-infrared emission for each 487 nm blue photon absorbed is realized successfully in the resulting phosphors, of which the process of near-infrared quantum cutting could be expressed as ³P₀(Pr³⁺) → ²F_5/2(Yb³⁺) + ²F_5/2(Yb³⁺). The maximum quantum cutting efficiency approaches up to 166.4% in Li₂TeO₄: 0.3 mol%Pr³⁺, 1.8 mol%Yb³⁺ sample corresponding to the 66.4% value of energy transfer efficiency.     

Influence of nanofluids application on contact length during hard turning

The length of tool–chip contact area (L_c) is considered as a considerable parameter in metal cutting process. Mechanical stresses and high temperature at this region may easily lead to abrasion or even breakage of cutting tool. Up to now, several solutions have been presented to overcome these limitations. Using cutting fluids is one of the solutions to reduce friction, stresses, and temperature over this area. This paper presents experimental investigation and finite element simulation of tool–chip interface in hard turning AISI 4140 using TiO₂ nanofluids. Nanofluids are newly class of engineering fluids developed by distributing nanometer solid particles in a base fluid. The main reason to use nanofluids in cutting process is to increase heat transfer capabilities and also its tribological attributes. At first, the effects of cutting speed, nanoparticles’ size, and nanofluid concentration on L_c have been experimentally investigated. Then, a numerical model has been developed to simulate the contact area length in case of nanofluids application. Comparing the results with that of the experimental tests shows that TiO₂ nanofluids are able to decrease L_c, about 35%, in feed rate of 0.11 mm/rev, nanoparticle size equal to 10 nm, and nanofluid concentration equal to 3.0 wt%.     

Functional nanostructured materials: Aerosol,aerogel, and de novo synthesis to emerging energy and environmental applications

In this review, we introduce advanced synthetic methods for functional nanostructured materials (in powder form) bridging to the development in emerging energy and environmental applications. Three types of synthetic methods (aerosol-based, aerogel-based, and de novo methods) are introduced, all of which have shown to be extensively investigated as novel routes to create nanostructured materials with designed material properties (i.e., controlled size, shape, porosity, and chemical composition are to be achievable). The typical experimental setup and the general experimental procedure for material preparation via the above three synthesis routes are discussed. Complementary characterization approaches are employed to study material properties of the synthesized nanostructured materials via the three synthesis routes. Here we investigate: (1) Cu_xO-CeO₂, Ni-CeO₂, and Cu_xO nanoparticle-encapsulating metal–organic framework (MOF) hybrid nanoparticles synthesized via the aerosol-based method; (2) Cr-encapsulating MOF (Cr-MOF-199), Au-encapsulating MOF (Au@ZIF-8), and MOF-derived nanocomposites (CuO/CuCr₂O₄) produced via the de novo route; (3) a variety of aerogels (carbon, metal oxide, polymer) with high porosity created by the aerogel-based approach. Finally, several examples of emerging energy and environmental applications are introduced using these functional nanostructured materials, including (1) catalytic transformation to chemicals by using precious metal nanoparticles-embedded MOFs and the MOF-derived nanocomposites as the catalysts; (2) methane combustion using Cu_xO-CeO₂ hybrid nanoparticles as catalyst, (3) methane dry reforming with CO₂ using Ni-CeO₂ hybrid nanoparticles as catalyst; (4) CO₂ capture by fluoroalkyl silane-modified mesoporous silica and polymethylsilsesquioxane (PMSQ) aerogel membranes; (5) adsorption of organic solvent, dye, and oil by cetyltrimethylammonium bromide-modified PMSQ aerogel.     

Design of Multifunctional Fluorescent Hybrid Materials Based on SiO2 Materials and Core–Shell Fe3O4@SiO2 Nanoparticles for Metal Ion Sensing

Hybrid fluorescent materials constructed from organic chelating fluorescent probes and inorganic solid supports by covalent interactions are a special type of hybrid sensing platform that has gained much interest in the context of metal ion sensing applications owing to their excellent advantages, recyclability, and solubility/dispersibility in particular, as compared with single organic fluorescent molecules. In recent decades, SiO₂ materials and core–shell Fe₃O₄@SiO₂ nanoparticles have become important inorganic solid materials and have been used as inorganic solid supports to hybridize with organic fluorescent receptors, resulting in multifunctional fluorescent hybrid systems for potential applications in sensing and related research fields. Therefore, recent progress in various fluorescent‐group‐functionalized SiO₂ materials is reviewed, with a focus on mesoporous silica nanoparticles and core–shell Fe₃O₄@SiO₂ nanoparticles, as interesting fluorescent organic–inorganic hybrid materials for sensing applications toward essential and toxic metal ions. Selective examples of other types of silica/silicon materials, such as periodic mesoporous organosilicas, solid SiO₂ nanoparticles, fibrous silica spheres, silica nanowires, silica nanotubes, and silica hollow microspheres, are also mentioned. Finally, relevant perspectives of metal‐ion‐sensing‐oriented silica‐fluorescent probe hybrid materials are provided.     

Preparation and characterization of carbon-encapsulated iron nanoparticles and their catalytic activity in the hydrogenation of levulinic acid

This study describes the synthesis of carbon-encapsulated iron nanoparticles using an ultrasonic method and also investigates their catalytic activity. These nanoparticles have been prepared using ultrasonic irradiation followed by annealing at various temperatures. As the annealing temperature of as-prepared α-Fe₂O₃ nanoparticles increased, the sample transformed into γ-Fe₂O₃, Fe₃O₄, and Fe nanoparticles via the reduction process without requiring any additional reducing agents such as H₂ gas, thus, creating a carbon shell surrounding the nanoparticles. By controlling the experimental conditions, Fe nanoparticles of various sizes can be formed with diameters in the range 100–800 nm; these nanoparticles are tightly encapsulated by 20-nm-thick carbon shells. Because of their high saturation magnetization 212 emu g^?1, the carbon-encapsulated Fe nanoparticles can be used for magnetic resonance imaging with a dramatically enhanced efficiency compared to commercially available T ₂ contrast agents. Moreover, the carbon-encapsulated Fe nanoparticles showed its superior catalytic activity and reusability for the hydrogenation of biomass-derived levulinic acid to GVL (99.6 %) in liquid phase.     

Beneficial influence of copper and manganese alloying elements on the mechanical properties of metallic composite materials based on the eutectic Al-5.7% Ni alloy

We have developed a new type of metallic composite material based on the binary eutectic Al-5.7 wt% Ni alloy. The structure of the initial alloys prepared by simple casting consists of strong, fine fibres of the Al₃Ni phase and a ductile aluminium matrix. These alloys are then transformed into dispersion-hardened materials by isostatic extrusion in which the Al₃Ni fibres are broken and dispersed in the ductile matrix. The materials thus prepared present a mechanical strength of the same order as the unidirectionally solidifed eutectic alloy: the tensile strength is nearly 300 MPa at room temperature. We observed in this work that the mechanical strength is remarkably increased by the addition of a small amount of copper or manganese: it attains about 400 MPa by the addition of 2 to 3wt% Cu, and more than 500 MPa by the addition of 3wt% Mn. These alloying elements also produce beneficial effects on the mechanical properties at high temperature.     

Optimized solvent-thermal preparation of NaYF4 :Yb3+, Er3+ up-conversion nanoparticles for application in solar cells

用溶剂热法合成Yb³⁺、Er³⁺共掺的NaYF₄ 纳米上转换材料, 研究了去离子水、乙醇两种反应溶剂对材料性能的影响. 用X射线衍射光谱、扫描电镜和荧光光谱等测试手段对材料性能进行了对比分析. 结果表明: 以乙醇为溶剂并加入一定比例的EDTA, 所制备的上转换材料能发射较强的、可被太阳电池吸收的可见光.