Modelling of nanoparticle formation during spray pyrolysis

Preparation and Characterization of Multielement Composite Oxide Nanomaterials Containing Ce, Zr, Y, and Yb via Continuous Hydrothermal Flow Synthesis

The synthesis of multielement composite oxide nanomaterials containing Ce, Zr, Y, and Yb was investigated using a micro confined jet mixer reactor operated in continuous mode under supercritical water conditions. The obtained nanoparticles were characterized using ICP-AES, SEM-EDS, FTIR, Raman spectroscopy, XRD, and TEM. All samples exhibited a uniform particle shape and a narrow particle size distribution. An analysis of the d-spacing results using selected electron area diffraction (SAED) patterns confirmed the production of cubic-phase crystals. A BET test was employed to determine the specific surface area of the prepared nanoparticles. OSC and TPR techniques were utilized to characterize the oxygen storage capacity and reduction performance of the obtained samples, with an analysis conducted to determine how the different proportions of elements affected the performance of multielement mixed oxides. The ionic conductivity of multielement composite oxide was measured using alternating current impedance spectroscopy (EIS), and the impact of Y, Ce, and Yb on the electrolyte material's ionic conductivity was analyzed.

Synthesis of porous C/Fe3O4 microspheres by spray pyrolysis with NaNO3 additive for lithium-ion battery applications

In this work, we successfully synthesized porous C/Fe3O4 microspheres by spray pyrolysis at 700ºC with a sodium nitrate (NaNO3) additive in the precursor solution. Furthermore, we studied their electrochemical properties as anode material for Li-ion batteries. The systematic studies by various characterization techniques show that NaNO3 catalyzes the carbonization of sucrose and enhances the crystallization of Fe3O4. Moreover, an aqueous etching can easily remove sodium compounds to produce porous C/Fe3O4 microspheres with large surface areas and pore volumes. The porous C/Fe3O4 microspheres exhibit a reversible capacity of ~780 mAh g–1 in the initial cycles and ~520 mAh g–1 after 30 cycles at a current density of 50 mA g–1. Moreover, a reversible capacity of ~400 mAh g–1 is attainable after 200 cycles, even at a high current density of 500 mA g–1. The wide range of pores produced from the removal of sodium compounds might enable easy electrolyte penetration and facilitate fast Li-ion diffusion, while the N-doping can promote the electronic conductivity of the carbon. These features of porous C/Fe3O4 microspheres led to the improved electrochemical properties of this sample.

Graphical Abstract

Titanium Oxynitride Spheres with Broad Plasmon Resonance for Solar Seawater Desalination

The facile production of hollow and solid nitridized submicrometer titania spheres has been successfully realized, with potential for mass production. The nitridation process gives submicrometer titanium oxynitride spheres, which possess a strong and broadband light absorption property. Interband-transition-induced resonance and plasmon resonance have been found to coexist in titanium oxynitride spheres through single-particle dark-field scattering measurements. Theoretical modeling has further confirmed that the excellent light absorption properties of the oxynitride spheres originate from the supported dual-mode optical resonance. A highly efficient, easy-to-build, and self-sustainable device is rationally designed for solar-driven seawater desalination, where the titanium oxynitride spheres function as photothermal transducers. The hollow spheres possess a higher water evaporation rate than the solid ones as the inner surface of the hollow spheres also provides surface sites for interaction with water molecules. Given the outstanding light absorption capability and the unique morphology of the hollow spheres, a water evaporation rate of ∼1.49 kg m^-2 h^-1 with a solar-to-thermal conversion efficiency of ∼89.1% has been achieved under the illumination of simulated solar light (1 sun, 1 kW m^-2). This marks the record performance among reported plasmon-based solar seawater desalination systems.

Continuous Hydrothermal Flow Synthesis and Characterization of ZrO2 Nanoparticles Doped with CeO2 in Supercritical Water

A confined jet mixing reactor operated in continuous hydrothermal flow synthesis was investigated for the synthesis of CeO₂-ZrO₂ (CZ) nanoparticles. The obtained ultrafine powders were characterized using scanning electron microscopy–energy dispersive spectrometry (SEM-EDS), inductively coupled plasma–atomic emission spectroscopy (ICP-AES), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED), a BET (Brunauer-Emmett-Teller)-specific surface area test and pore analysis, oxygen storage capacity (OSC) test, and a H₂ temperature programmed reduction (H₂-TPR) test. The XRD results show that all samples were composed of high-purity cubic CZ nanoparticles. High resolution transmission electron microscope (HR-TEM) analysis showed that CZ nanoparticles with uniform size and shape distributions were obtained in this investigation. The d-spacing values, determined based on the TEM-selected area electron diffraction (SAED) patterns, were in good agreements with the reference data. BET results showed that the prepared CZ samples had large specific surface areas. Pore volume and size distribution were obtained by pore analysis. Oxygen pulse adsorption technology was used to test the oxygen storage capacity of the sample. The redox capacity of the CZ material was determined by a H₂ temperature-programmed reduction test.

A Comprehensive Updated Review on Magnetic Nanoparticles in Diagnostics

Magnetic nanoparticles (MNPs) have been studied for diagnostic purposes for decades. Their high surface-to-volume ratio, dispersibility, ability to interact with various molecules and superparamagnetic properties are at the core of what makes MNPs so promising. They have been applied in a multitude of areas in medicine, particularly Magnetic Resonance Imaging (MRI). Iron oxide nanoparticles (IONPs) are the most well-accepted based on their excellent superparamagnetic properties and low toxicity. Nevertheless, IONPs are facing many challenges that make their entry into the market difficult. To overcome these challenges, research has focused on developing MNPs with better safety profiles and enhanced magnetic properties. One particularly important strategy includes doping MNPs (particularly IONPs) with other metallic elements, such as cobalt (Co) and manganese (Mn), to reduce the iron (Fe) content released into the body resulting in the creation of multimodal nanoparticles with unique properties. Another approach includes the development of MNPs using other metals besides Fe, that possess great magnetic or other imaging properties. The future of this field seems to be the production of MNPs which can be used as multipurpose platforms that can combine different uses of MRI or different imaging techniques to design more effective and complete diagnostic tests.

Water evaporation from solute-containing aerosol droplets: Effects of internal concentration and diffusivity profiles and onset of crust formation

The evaporation of droplets is an important process not only in industrial and scientific applications, but also in the airborne transmission of viruses and other infectious agents. We derive analytical and semi-analytical solutions of the coupled heat and mass diffusion equations within a spherical droplet and in the ambient vapor phase that describe the evaporation process of aqueous free droplets containing nonvolatile solutes. Our results demonstrate that the solute-induced water vapor-pressure reduction considerably slows down the evaporation process and dominates the solute-concentration dependence of the droplet evaporation time. The evaporation-induced enhanced solute concentration near the droplet surface, which is accounted for using a two-stage evaporation description, is found to further slow-down the drying process. On the other hand, the presence of solutes is found to produce a lower limit for the droplet size that can be reached by evaporation and, also, to reduce evaporation cooling of the droplet, which tend to decrease the evaporation time. Overall, the first two effects are dominant, meaning that the droplet evaporation time increases in the presence of solutes. Local variation of the water diffusivity inside the droplet near its surface, which is a consequence of the solute-concentration dependence of the diffusion coefficient, does not significantly change the evaporation time. Crust formation on the droplet surface increases the final equilibrium size of the droplet by producing a hollow spherical particle, the outer radius of which is determined as well.

Vapor-phase production of nanomaterials

The synthesis of nanomaterials, with characteristic dimensions of 1 to 100 nm, is a key component of nanotechnology. Vapor-phase synthesis of nanomaterials has numerous advantages such as high product purity, high-throughput continuous operation, and scalability that have made it the dominant approach for the commercial synthesis of nanomaterials. At the same time, this class of methods has great potential for expanded use in research and development. Here, we present a broad review of progress in vapor-phase nanomaterial synthesis. We describe physically-based vapor-phase synthesis methods including inert gas condensation, spark discharge generation, and pulsed laser ablation; plasma processing methods including thermal- and non-thermal plasma processing; and chemically-based vapor-phase synthesis methods including chemical vapor condensation, flame-based aerosol synthesis, spray pyrolysis, and laser pyrolysis. In addition, we summarize the nanomaterials produced by each method, along with representative applications, and describe the synthesis of the most important materials produced by each method in greater detail.

Magnetic Iron Oxide Nanoparticle (IONP) Synthesis to Applications: Present and Future

Iron oxides are chemical compounds which have different polymorphic forms, including γ-Fe2O3 (maghemite), Fe3O4 (magnetite), and FeO (wustite). Among them, the most studied are γ-Fe2O3 and Fe3O4, as they possess extraordinary properties at the nanoscale (such as super paramagnetism, high specific surface area, biocompatible etc.), because at this size scale, the quantum effects affect matter behavior and optical, electrical and magnetic properties. Therefore, in the nanoscale, these materials become ideal for surface functionalization and modification in various applications such as separation techniques, magnetic sorting (cells and other biomolecules etc.), drug delivery, cancer hyperthermia, sensing etc., and also for increased surface area-to-volume ratio, which allows for excellent dispersibility in the solution form. The current methods used are partially and passively mixed reactants, and, thus, every reaction has a different proportion of all factors which causes further difficulties in reproducibility. Direct active and complete mixing and automated approaches could be solutions to this size- and shape-controlled synthesis, playing a key role in its exploitation for scientific or technological purposes. An ideal synthesis method should be able to allow reliable adjustment of parameters and control over the following: fluctuation in temperature; pH, stirring rate; particle distribution; size control; concentration; and control over nanoparticle shape and composition i.e., crystallinity, purity, and rapid screening. Iron oxide nanoparticle (IONP)-based available clinical applications are RNA/DNA extraction and detection of infectious bacteria and viruses. Such technologies are important at POC (point of care) diagnosis. IONPs can play a key role in these perspectives. Although there are various methods for synthesis of IONPs, one of the most crucial goals is to control size and properties with high reproducibility to accomplish successful applications. Using multiple characterization techniques to identify and confirm the oxide phase of iron can provide better characterization capability. It is very important to understand the in-depth IONP formation mechanism, enabling better control over parameters and overall reaction and, by extension, properties of IONPs. This work provides an in-depth overview of different properties, synthesis methods, and mechanisms of iron oxide nanoparticles (IONPs) formation, and the diverse range of their applications. Different characterization factors and strategies to confirm phase purity in the IONP synthesis field are reviewed. First, properties of IONPs and various synthesis routes with their merits and demerits are described. We also describe different synthesis strategies and formation mechanisms for IONPs such as for: wustite (FeO), hematite (α-Fe2O3), maghemite (ɤ-Fe2O3) and magnetite (Fe3O4). We also describe characterization of these nanoparticles and various applications in detail. In conclusion, we present a detailed overview on the properties, size-controlled synthesis, formation mechanisms and applications of IONPs.

Microstructural and Nanostructural Evolution of Light Harvester Perovskite Thin Film under the Influence of Ultrasonic Vibrations

A key step of inexpensive and scalable perovskite thin-film formation is defect-free fabrication through low-cost and facile post-treatment processes. Methods using high annealing temperatures are not favorable for the scale-up of solution-processed thin-film solar cells, particularly on plastic/flexible substrates. This contribution analyzes the effect of ultrasonic vibrations, a recently developed low-cost post-treatment process, on thin-film quality. Ultrasonic vibrations were applied to as-spun CH₃NH₃PbI₃ perovskite thin films prepared with various solvents and antisolvents deposited on substrates with compact and mesoporous textures. Then, mechanisms of solvent evaporation, nucleation, and crystallization of perovskite grains were characterized during ultrasonic vibration. These studies demonstrate that ultrasonic vibration at low temperature facilitates heterogeneous crystallization of perovskite grains with a higher conversion of nuclei into crystal, compared with the conventional annealing process. Topographic scanning electron microscopy images confirm the dense and fully covered thin films after the evaporation of solvent. Furthermore, it is shown that crystal orientation does not change with the choice of solvent, eliminating the effect of solvent on the deposition of thin-film perovskites with this method. Therefore, this ultrasonic vibration post-treatment method is applicable to any solution-processed material and deposition technique, and it can be used to fabricate a range of thin-film devices and printed electronics.

Harmonic analysis of surface instability patterns on colloidal particles

Wrinkling of colloidal particles alter a wide variety of interfacial properties but quantitative topographical descriptions have been explored experimentally to a very limited extent. In this study, we present a harmonic analysis of surface wrinkles and folds on submicron colloidal particles, obtained using an aerosol flow route, with small radius (<300 nm) and high crust thickness-to-radius ratio (>0.1). The particle surface coordinates were mapped in their entirety using cryo-electron tomography and subsequently reconstructed using spherical harmonics, allowing a spectral topographical description of the instability patterns and the identification of their surface modes by lateral wavelength. Wrinkled and crumpled particles showed a similar surface roughness spectrum, wherein differences were found most noticeable in the large wavelength region. The analysis of preferred directions of harmonic frequencies indicated a possible axial or planar alignment attributed to the directionality of the surface corrugations. The employed characterization methodology can further the study of topographical influences on colloidal interactions.

Fabrication of Semiconducting Methylammonium Lead Halide Perovskite Particles by Spray Technology

In this "nano idea" paper, three concepts for the preparation of methylammonium lead halide perovskite particles are proposed, discussed, and tested. The first idea is based on the wet chemistry preparation of the perovskite particles, through the addition of the perovskite precursor solution to an anti-solvent to facilitate the precipitation of the perovskite particles in the solution. The second idea is based on the milling of a blend of the perovskite precursors in the dry form, in order to allow for the conversion of the precursors to the perovskite particles. The third idea is based on the atomization of the perovskite solution by a spray nozzle, introducing the spray droplets into a hot wall reactor, so as to prepare perovskite particles, using the droplet-to-particle spray approach (spray pyrolysis). Preliminary results show that the spray technology is the most successful method for the preparation of impurity-free perovskite particles and perovskite paste to deposit perovskite thin films. As a proof of concept, a perovskite solar cell with the paste prepared by the sprayed perovskite powder was successfully fabricated.

One-step synthesis of luminescent YVO4:Eu3+/γ-Al2O3 nanocomposites by spray pyrolysis

Spray pyrolysis (SP) easily affords nano or sub-micro phosphor particles even on an industrial scale. However, control of the coordination environment around the emitting ion is inefficient, and the final solid matrix will dictate the symmetry of the emitter. Moreover, the fast heat treatment typical of SP usually results in heterogeneous symmetry sites. This paper aimed to obtain inorganic matrices incorporated with phosphors by SP while keeping the symmetry of the emitting ion unchanged along the pyrolysis process. Nanoparticles consisting of Eu³⁺-doped YVO₄ phosphors with average diameter of 15 nm were prepared by the co-precipitation method and were subsequently incorporated into the alumina matrix by SP, to yield YVO₄:Eu³⁺/γ-Al₂O₃ composite particles with mean size of 600 nm. X-ray powder diffraction confirmed that the vanadate particles were incorporated into the alumina matrix, and that the γ-Al₂O₃ phase emerged. The band due to the [Formula: see text] → Eu³⁺ transition intensified as a consequence of the incorporation of YVO₄:Eu³⁺ into alumina-the suppression effects caused by the surface properties of the YVO₄:Eu³⁺ phosphor nanoparticles diminished, while the structure of Eu³⁺ remained unchanged in the matrix.

Intricate Hollow Structures: Controlled Synthesis and Applications in Energy Storage and Conversion

Intricate hollow structures garner tremendous interest due to their aesthetic beauty, unique structural features, fascinating physicochemical properties, and widespread applications. Here, the recent advances in the controlled synthesis are discussed, as well as applications of intricate hollow structures with regard to energy storage and conversion. The synthetic strategies toward complex multishelled hollow structures are classified into six categories, including well-established hard- and soft-templating methods, as well as newly emerging approaches based on selective etching of "soft@hard" particles, Ostwald ripening, ion exchange, and thermally induced mass relocation. Strategies for constructing structures beyond multishelled hollow structures, such as bubble-within-bubble, tube-in-tube, and wire-in-tube structures, are also covered. Niche applications of intricate hollow structures in lithium-ion batteries, Li-S batteries, supercapacitors, Li-O₂ batteries, dye-sensitized solar cells, photocatalysis, and fuel cells are discussed in detail. Some perspectives on the future research and development of intricate hollow structures are also provided.

Estimation of critical supersaturation solubility ratio for predicting diameters of dry particles prepared by air-jet atomization of solutions

Air-jet atomization of solution into droplets followed by controlled drying is increasingly being used for producing nanoparticles for drug delivery applications. Nanoparticle size is an important parameter that influences the stability, bioavailability and efficacy of the drug. In air-jet atomization technique, dry particle diameters are generally predicted by using solute diffusion models involving the key concept of critical supersaturation solubility ratio (Sc) that dictates the point of crust formation within the droplet. As no reliable method exists to determine this quantity, the present study proposes an aerosol based method to determine Sc for a given solute-solvent system and process conditions. The feasibility has been demonstrated by conducting experiments for stearic acid in ethanol and chloroform as well as for anti-tubercular drug isoniazid in ethanol. Sc values were estimated by combining the experimentally observed particle and droplet diameters with simulations from a solute diffusion model. Important findings of the study were: (i) the measured droplet diameters systematically decreased with increasing precursor concentration (ii) estimated Sc values were 9.3±0.7, 13.3±2.4 and 18±0.8 for stearic acid in chloroform, stearic acid and isoniazid in ethanol respectively (iii) experimental results pointed at the correct interfacial tension pre-factor to be used in theoretical estimates of Sc and (iv) results showed a consistent evidence for the existence of induction time delay between the attainment of theoretical Sc and crust formation. The proposed approach has been validated by testing its predictive power for a challenge concentration against experimental data. The study not only advances spray-drying technique by establishing an aerosol based approach to determine Sc, but also throws considerable light on the interfacial processes responsible for solid-phase formation in a rapidly supersaturating system. Until satisfactory theoretical formulae for predicting CSS are developed, the present approach appears to offer the best option for engineering nanoparticle size through solute diffusion models.

A deep look into the spray coating process in real-time-the crucial role of x-rays

Tailoring functional thin films and coating by rapid solvent-based processes is the basis for the fabrication of large scale high-end applications in nanotechnology. Due to solvent loss of the solution or dispersion inherent in the installation of functional thin films and multilayers the spraying and drying processes are strongly governed by non-equilibrium kinetics, often passing through transient states, until the final structure is installed. Therefore, the challenge is to observe the structural build-up during these coating processes in a spatially and time-resolved manner on multiple time and length scales, from the nanostructure to macroscopic length scales. During installation, the interaction of solid-fluid interfaces and between the different layers, the flow and evaporation themselves determine the structure of the coating. Advanced x-ray scattering methods open a powerful pathway for observing the involved processes in situ, from the spray to the coating, and allow for gaining deep insight in the nanostructuring processes. This review first provides an overview over these rapidly evolving methods, with main focus on functional coatings, organic photovoltaics and organic electronics. Secondly the role and decisive advantage of x-rays is outlined. Thirdly, focusing on spray deposition as a rapidly emerging method, recent advances in investigations of spray deposition of functional materials and devices via advanced x-ray scattering methods are presented.

A single-step aerosol process for in-situ surface modification of nanoparticles: Preparation of stable aqueous nanoparticle suspensions

HYPOTHESIS

Surface modification of nanoparticles during aerosol or gas-phase synthesis, followed by direct transfer into liquid media can be used to produce stable water-dispersed nanoparticle suspensions.

EXPERIMENT

This work investigates a single-step, aerosol process for in-situ surface-modification of nanoparticles. Previous studies have used a two-step sublimation-condensation mechanism following droplet drying, for surface modification, while the present process uses a liquid precursor containing two solutes, a matrix lipid and a surface modifying agent. A precursor solution in chloroform, of stearic acid lipid, with 4 %w/w of surface-active, physiological molecules [1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol)-sodium salt (DPPG) or 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy (polyethylene glycol) 2000]-ammonium salt (DPPE-PEG)] was processed in an aerosol reactor at a low gas temperatures. The surface modified nanoparticles were characterized for morphology, surface composition and suspension properties.

FINDINGS

Spherical, surface-modified lipid nanoparticles with median mobility diameters in the range of 105-150nm and unimodal size distributions were obtained. Fourier transform infra-red spectroscopy (FTIR) measurements confirmed the presence of surface-active molecules on external surfaces of modified lipid nanoparticles. Surface modified nanoparticles exhibited improved suspension stability, compared to that of pure lipid nanoparticles for a period of 30days. Lowest aggregation was observed in DPPE-PEG modified nanoparticles from combined electrostatic and steric effects. The study provides a single-step aerosol method for in-situ surface modification of nanoparticles, using minimal amounts of surface active agents, to make stable, aqueous nanoparticle suspensions.

Synthesis of LiFePO4 by Ultrasonic and Nozzle Spray Pyrolysis

Lithium iron phosphate LiFePO4 (LFP) is one of the promising new cathode materials for next generation lithium secondary batteries. Various synthesis strategies have been proposed to create LiFePO4 particles with maximum efficiency. The spray pyrolysis is a suitable synthesis technique which allows to direct the particle formation in multiple ways. LiFePO4 has successfully been synthesized by ultrasonic and nozzle spray pyrolysis. The obtained products were characterized by means of XRD and SEM analysis. Furthermore, the mechanism of the particle formation was investigated.

Nano-designing of Mg doped phosphate tungsten bronzes and SiO2 composite obtained by ultrasonic spray pyrolysis method

In this study, the structure and substructure of SiO(2)-Mg phosphate tungsten bronzes, MgPTB, (MgHPW(12)O(40).29H(2)O) obtained by ultrasonic spray pyrolysis method from a silica sol, and a MgPTB solution, obtained by the ion exchange method, as precursors were investigated. The mechanism of the formation of aerosol droplets is discussed. Phase composition, structure and substructure of SiO(2)-MgPTB particles were investigated by X-ray powder diffraction (XRPD) analysis, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Good agreement between the theoretically predicted values for the mean diameters of particles and subparticles (1.27 microm and 75.4 nm, respectively) and the experimentally obtained ones (1.17 microm and 65-90 nm) was found. This agreement confirms the applicability of the model to get a satisfactory prediction of the most important data related to the nano-structural design of SiO(2)-MgPTB powders.

Modelling and experimental investigations of thin films of Mg phosphorus-doped tungsten bronzes obtained by ultrasonic spray pyrolysis

In this study, the synthesis of thin films of Mg phosphorus doped tungsten bronzes (MgPTB; MgHPW(12)O(40).29H(2)O) by the self-assembly of nano-structured particles of MgPTB obtained using the ultrasonic spray pyrolysis method was investigated. As the precursor, MgPTB, prepared by the ionic exchange method, was used. Nano-structured particles of MgPTB were obtained using the ultrasonic spray pyrolysis method. The nano-structure of the particles used as the building blocks in the MgPTB thin film were investigated experimentally and theoretically, applying the model given in this article. The obtained data for the mean particle size and their size distribution show a high degree of agreement. These previously tailored particles used for the preparation of thin films during the next synthesis step, by their self-assembly over slow deposition on a silica glass substrate, show how it is possible to create thin MgPTB films under advance projected conditions of the applied physical fields with a fully determined nanostructure of their building block particles, with a relatively small roughness and unique physical properties.

Synthesis and characterization of core-shell structural MWNT-zirconia nanocomposites

Core-shell structural MWNT/ZrO2 nanocomposites were successfully prepared by one-step hydrolyzing of MWNT-dispersed ZrOCl2.8H2O aqueous solution. A highly conformal and uniform monoclinic zirconia coating was deposited on MWNTs by this new and simple method, and the thickness of the coating increased with the reaction time.