Floating synthesis with enhanced catalytic performance via acoustic levitation processing

Acoustic levitation supplies a containerless state to eliminate natural convection and heterogeneous crystal nucleation and thus provides a highly uniform and ultra clean condition in the confined levitating area. Herein, we attempt to make full use of these advantages to fabricate well dispersed metal nanoparticles. The gold nanoparticles, synthesized in an acoustically levitated droplet, exhibited a smaller size and improved catalytic performance in 4-nitrophenol reduction were synthesized in an acoustically levitated droplet. The sound field was simulated to understand the impact of acoustic levitation on gold nanoparticle growth with the aid of crystal growth theory. Chemical reducing reactions in the acoustic levitated space trend to occur in a better dispersed state because the sound field supplies continuous vibration energy. The bubble movement and the cavitation effect accelerate the nucleation, decrease the size, and the internal flow inside levitated droplet probably inhibit the particle fusion in the growth stage. These factors lead to a reduction in particle size compared with the normal wet chemical synthetic condition. The resultant higher surface area and more numerous active catalytic sites contribute to the improvement of the catalytic performance.

A Facile Route for the Preparation of Monodisperse Iron nitride at Silica Core/shell Nanostructures

Uniform-sized iron oxide nanoparticles obtained from the solution phase thermal decomposition of the iron-oleate complex were encapsulated inside the silica shell by the reverse microemulsion technique, and then thermal treatment under NH₃ to transfer the iron oxide to iron nitride. The transmission electron microscopy images distinctly demonstrated that the as-prepared iron nitride at silica core/shell nanostructures were highly uniform in particle-size distribution. By using iron oxide nanoparticles of 6.1, 10.3, 16.2, and 21.8 nm as starting materials, iron nitride nanoparticles with average diameters of 5.6, 9.3, 11.6, and 16.7 nm were produced, respectively. The acid-resistant properties of the iron nitride at silica core/shell nanostructures were found to be much higher than the starting iron oxide at silica. A superconducting quantum interference device was used for the magnetic characterization of the nanostructure. Besides, magnetic resonance imaging (MRI) studies using iron nitride at silica nanocomposites as contrast agents demonstrated T ₂ enhanced effects that were dependent on the concentration. These core/shell nanostructures have enormous potential in magnetic nanodevice and biomedical applications. The current process is expected to be easy for large-scale and transfer other metal oxide nanoparticles.

A power-triggered preparation strategy of nano-structured inorganics: sonosynthesis

Ultrasound irradiation covers many chemical reactions crucially aiming to design and synthesize various structured materials as an enduring trend in frontier research studies. Here, we focus on the latest progress of ultrasound-assisted synthesis and present the basic principles or mechanisms of sonosynthesis (or sonochemical synthesis) from ultrasound irradiation in a brand new way, including primary sonosynthesis, secondary sonosynthesis, and synergetic sonosynthesis. This current review describes in detail the various sonochemical synthesis strategies for nano-structured inorganic materials and the unique aspects of products including the size, morphology, structure, and properties. In addition, the review points out the probable challenges and technological potential for future advancement. We hope that such a review can provide a comprehensive understanding of sonosynthesis and emphasize the great significance of structured materials synthesis as a power-induced strategy broadening the updated applications of ultrasound.

Sonochemical fabrication of inorganic nanoparticles for applications in catalysis

Catalysis covers almost all the chemical reactions or processes aiming for many applications. Sonochemistry has emerged in designing and developing the synthesis of nano-structured materials, and the latest progress mainly focuses on the synthetic strategies, product properties as well as catalytic applications. This current review simply presents the sonochemical effects under ultrasound irradiation, roughly describes the ultrasound-synthesized inorganic nano-materials, and highlights the sonochemistry applications in the inorganics-based catalysis processes including reduction, oxidation, degradation, polymerization, etc. Or all in all, the review hopes to provide an integrated understanding of sonochemistry, emphasize the great significance of ultrasound-assisted synthesis in structured materials as a unique strategy, and broaden the updated applications of ultrasound irradiation in the catalysis fields.

Sonochemical catalysis as a unique strategy for the fabrication of nano-/micro-structured inorganics

Ultrasound-assisted approaches, as an important trend in material synthesis, have emerged for designing and creating nano-/micro-structures. This review simply presents the basic principles of ultrasound irradiation including acoustic cavitation, sonochemical effects, physical and/or mechanical effects, and on the basis of the latest progress, it newly summarizes sonochemical catalysis for the fabrication of nano-structured or micro-structured inorganic materials such as metals, alloys, metal compounds, non-metal materials, and inorganic composites, where the theories or mechanisms of catalytic synthetic routes, and the morphologies, structures, sizes, properties and applications of products are described in detail. In the review, a few technological potentials and probable challenges of sonochemical catalysis are also highlighted for the future advance of synthesis methods. Therefore, sonochemical catalysis or ultrasound-assisted synthesis will serve as a unique strategy to reveal its great significance in material fabrication.

Enhanced magnetic properties and thermal stability of highly ordered ε-Fe3N1+x (-0.12 ≤ x ≤ -0.01) nanoparticles

ε-Iron nitrides with the general formula ε-Fe3N1+x (-0.40 < x < 0.48) have been widely studied due to their interesting magnetism. However, the phase diagram of the Fe-N binary system indicates the absence of monophasic ε-Fe3N1+x (x < 0) compounds that are stable below their synthetic temperatures. Here, ε-Fe3N1+x (-0.12 ≤ x ≤ -0.01) nanoparticles with excellent thermal stability and magnetic properties were synthesized by a simple chemical solution method. The ε-Fe3N1+x nanoparticles with space group P6322 have excellent oxidation resistance due to a carbon shell with a thickness of 2-3 nm. NPD refinements suggest that the ε-Fe3N1+x nanoparticles possess a highly ordered arrangement of N atoms and their magnetic moments align parallel to the c axis. The Curie temperature (TC) and room temperature saturation magnetization (MS) increase with decreasing N content, which results in record-high TC (632 K) and MS (169.2 emu g-1) at x = -0.12, much higher than the magnetic properties of the corresponding bulk materials. The significant enhancements in the intrinsic magnetic properties and thermal stability of ε-Fe3N1+x are ascribed to chemically engineering the stoichiometry and N occupancy from the disordered to the ordered site.

Recent developments in the sonoelectrochemical synthesis of nanomaterials

In recent years, the synthesis and use of nanoparticles have been of special interest among the scientific communities due to their unique properties and applications in various advanced technologies. The production of these materials at industrial scale can be difficult to achieve due to high cost, intense labour and use of hazardous solvents that are often required by traditional chemical synthetic methods. Sonoelectrochemistry is a hybrid technique that combines ultrasound and electrochemistry in a specially designed electrochemical setup. This technique can be used to produce nanomaterials with controlled sizes and shapes. The production of nanoparticles by sonoelectrochemistry as a technique offers many advantages: (i) a great enhancement in mass transport near the electrode, thereby altering the rate, and sometimes the mechanism of the electrochemical reactions, (ii) a modification of surface morphology through cavitation jets at the electrode-electrolyte interface, usually causing an increase of the surface area and (iii) a thinning of the electrode diffusion layer thickness and therefore ion depletion. The scalability of sonoelectrochemistry for producing nanomaterials at industrial scale is also very plausible due to its "one-pot" synthetic approach. Recent advancements in sonoelectrochemistry for producing various types of nanomaterials are briefly reviewed in this article. It is with hope that the presentation of these studies therein can generate more interest in the field to "catalyze" future investigations in novel nanomaterial development and industrial scale-up studies.

Iron Carbides and Nitrides: Ancient Materials with Novel Prospects

Iron carbides and nitrides have aroused great interest in researchers, due to their excellent magnetic properties, good machinability and the particular catalytic activity. Based on these advantages, iron carbides and nitrides can be applied in various areas such as magnetic materials, biomedical, photo- and electrocatalysis. In contrast to their simple elemental composition, the synthesis of iron carbides and nitrides still has great challenges, particularly at the nanoscale, but it is usually beneficial to improve performance in corresponding applications. In this review, we introduce the investigations about iron carbides and nitrides, concerning their structure, synthesis strategy and various applications from magnetism to the catalysis. Furthermore, the future prospects are also discussed briefly.

The impact of carbon coating on the synthesis and properties of α''-Fe16N2 powders

This paper presents the preparation of carbon composite Fe16N2 powders, and the influence of a protective carbon coating on the yield and magnetic properties of Fe16N2. Nanoparticle precursors with and without carbon were reacted under ammonia gas flow to produce Fe16N2. Neutron and X-ray powder diffraction indicate that the powders contain typically 40-60% Fe16N2, with the remaining phases being unreacted iron, Fe4N or Fe3N. Transmission electron microscopy demonstrates that the carbon coating is effective at reducing the level of sintering of Fe nanoparticles during the reduction stage prior to ammonolysis. XPS results support the retention of a carbon coating on the surface after ammonolysis, and that there is Fe-C bonding present at the particle surface. In situ TEM was used to observe loss of ordering in the nitrogen sublattice of carbon composite Fe16N2 powders in the range of 168 °C to 200 °C. Magnetic susceptibility measurements show maximum values for saturation magnetization in the range of 232 emu g(-1), and for coercivity near 930 Oe, for different samples measured up to 2 T applied field at 300 K.

Insights into the nitridation of zero-valent iron nanoparticles for the facile synthesis of iron nitride nanoparticles

The process of nitridation of zero-valent iron nanoparticles (ZVINPs) is investigated by employing two different synthesis strategies such as solvothermal method and gas diffusion using N₂ and NH₃.

Sonochemical synthesis of nanomaterials

High intensity ultrasound can be used for the production of novel materials and provides an unusual route to known materials without bulk high temperatures, high pressures, or long reaction times. Several phenomena are responsible for sonochemistry and specifically the production or modification of nanomaterials during ultrasonic irradiation. The most notable effects are consequences of acoustic cavitation (the formation, growth, and implosive collapse of bubbles), and can be categorized as primary sonochemistry (gas-phase chemistry occurring inside collapsing bubbles), secondary sonochemistry (solution-phase chemistry occurring outside the bubbles), and physical modifications (caused by high-speed jets or shock waves derived from bubble collapse). This tutorial review provides examples of how the chemical and physical effects of high intensity ultrasound can be exploited for the preparation or modification of a wide range of nanostructured materials.

Solvothermal metal azide decomposition routes to nanocrystalline metastable nickel, iron, and manganese nitrides

This paper describes the use of solvothermally moderated metal azide decomposition as a route to nanocrystalline mid to late transition metal nitrides. This method utilizes exothermic solid-state metathesis reaction precursor pairs, namely, metal halides (NiBr(2), FeCl(3), MnCl(2)) and sodium azide, but conducts the metathesis reaction and azide decomposition in superheated toluene. The reaction temperatures are relatively low (<300 degrees C) and yield thermally metastable nanocrystalline hexagonal Ni(3)N and Fe(2)N, and tetragonal MnN. These solvothermally moderated metal nitride metathesis reactions require several days to produce high yields of the intended nitrides. The products are aggregated nanoparticulates with room temperature magnetic properties consistent with their known bulk structures, for example, Fe(2)N and Ni(3)N are known ferromagnets. The stirred reactions with dispersed fine reagent powders benefit from solvothermal moderation more effectively than submerged pressed reagent pellets. Pellet reactions produced manganese nitrides with lower nitrogen content and higher aggregation than loose powder reactions, consistent with the occurrence of significant local exothermic heating in the pellet metathesis reactions.

Interfacial assembly of partially hydrophobic silica nanoparticles induced by ultrasonic treatment

A sonochemical approach has effectively been applied to prepare aqueous dispersions of air-filled nanostructured quartz silica shells from surface-engineered amorphous silica nanoparticles. The non-equilibrium nature of the cavitation process and high temperature and pressure in the cavitation microbubble can lead to partial crystallization of the amorphous silica nanoparticles producing the quartz phase and a high degree of interconnection between the silica nanoparticles in the microsphere shells. The very high stability of the silica shells against collapse and aggregation is determined by the hydrophobic nature of the silica nanoparticles. Because of the shell thickness and its high density caused by sintering of the silica nanoparticles, the gas (liquid) permeability through the shell is limited thus prolonging the life time of the air-filled nanostructured silica shells.

A sonochemical method for the selective synthesis of alpha-HgS and beta-HgS nanoparticles

A novel sonochemical method for the selective synthesis of alpha-HgS (cinnabar) and beta-HgS (metacinnabar) nanoparticles in aqueous solutions is reported in this paper. alpha-HgS and beta-HgS nanoparticles have been selectively prepared by choosing sodium thiosulfate and thiourea as the sulfur source respectively. To study the crystalline structure, size, morphology and composition of the products, characterization techniques including X-ray powder diffraction, transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis are employed. The optical properties of the nanoparticles are investigated by UV-visible absorption spectroscopic measurements. The direct band gap of the as-prepared alpha-HgS nanoparticles with an average size of 12 nm is calculated to be 2.8 eV according to the absorption spectrum. In the case of the beta-HgS nanoparticles with an average size of 13 nm, a broad absorption peak is observed in the UV-visible absorption spectrum, which can be ascribed to the special surface state of this sample. Probable mechanisms for the sonochemical formation of alpha-HgS and beta-HgS nanoparticles in aqueous solutions are presented. The optimum pH value of the stock solutions and the effect of sonication time on the particle size are also investigated.

Sonochemical Fabrication and Characterization of Stibnite Nanorods

Regular stibnite (Sb(2)S(3)) nanorods with diameters of 20-40 nm and lengths of 220-350 nm have been successfully synthesized by a sonochemical method under ambient air from an ethanolic solution containing antimony trichloride and thioacetamide. The as-prepared Sb(2)S(3) nanorods are characterized by employing techniques including X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, and optical diffuse reflection spectroscopy. Microstructural analysis reveals that the Sb(2)S(3) nanorods crystallize in an orthorhombic structure and predominantly grow along the (001) crystalline plane. High-intensity ultrasound irradiation plays an important role in the formation of these Sb(2)S(3) nanorods. The experimental results show that the sonochemical formation of stibnite nanorods can be divided into four steps in sequence: (1) ultrasound-induced decomposition of the precursor, which leads to the formation of amorphous Sb(2)S(3) nanospheres; (2) ultrasound-induced crystallization of these amorphous nanospheres and generation of nanocrystalline irregular short rods; (3) a crystal growth process, giving rise to the formation of regular needle-shaped nanowhiskers; (4) surface corrosion and fragmentation of the nanowhiskers by ultrasound irradiation, resulting in the formation of regular nanorods. The optical properties of the Sb(2)S(3) amorphous nanospheres, irregular short nanorods, needle-shaped nanowhiskers, and regular nanorods are investigated by diffuse reflection spectroscopic measurements, and the band gaps are measured to be 2.45, 1.99, 1.85, and 1.94 eV, respectively.