Synthesis, properties, and applications of magnetic iron oxide nanoparticles

Nanomaterials are at the leading edge of the emerging field of nanotechnology. Their unique and tunable size-dependent properties (in the range 1–100 nm) make these materials indispensable in many modern technological applications. In this Review, we summarize the state-of-art in the manufacture and applications of inorganic nanoparticles made using continuous hydrothermal flow synthesis (CHFS) processes. First, we introduce ideal requirements of any flow process for nanoceramics production, outline different approaches to CHFS, and introduce the pertinent properties of supercritical water and issues around mixing in flow, to generate nanoparticles. This Review then gives comprehensive coverage of the current application space for CHFS-made nanomaterials including optical, healthcare, electronics (including sensors, information, and communication technologies), catalysis, devices (including energy harvesting/conversion/fuels), and energy storage applications. Thereafter, topics of precursor chemistry and ...

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Continuous Hydrothermal Synthesis of Inorganic Nanoparticles: Applications and Future Directions

Synthesis of metal oxide nanostructures by direct sol-gel chemistry in supercritical fluids.

Synthesis of metal nanoparticles with specific properties is a newly established research area attracting a great deal of attention. Several methods have been put forward for synthesis of these materials, namely chemical vapor condensation, arc discharge, hydrogen plasma—metal reaction, and laser pyrolysis in the vapor phase, microemulsion, hydrothermal, sol-gel, sonochemical, and microbial processes taking place in the liquid phase, and ball milling carried out in the solid phase. The properties of metal nanoparticles depend largely on their synthesis procedures. In this paper the fundamentals, advantages, and disadvantages of each synthesis method are discussed.

A Review of Methods for Synthesis of Nanostructured Metals with Emphasis on Iron Compounds

I12 is the Joint Engineering, Environmental and Processing (JEEP) beamline, constructed during Phase II of the Diamond Light Source. I12 is located on a short (5 m) straight section of the Diamond storage ring and uses a 4.2 T superconducting wiggler to provide polychromatic and monochromatic X-rays in the energy range 50–150 keV. The beam energy enables good penetration through large or dense samples, combined with a large beam size (1 mrad horizontally × 0.3 mrad vertically). The beam characteristics permit the study of materials and processes inside environmental chambers without unacceptable attenuation of the beam and without the need to use sample sizes which are atypically small for the process under study. X-ray techniques available to users are radiography, tomography, energy-dispersive diffraction, monochromatic and white-beam two-dimensional diffraction/scattering and small-angle X-ray scattering. Since commencing operations in November 2009, I12 has established a broad user community in materials science and processing, chemical processing, biomedical engineering, civil engineering, environmental science, palaeontology and physics.

https://journals.iucr.org/s/issues/2015/03/00/ie5138/ie5138.pdf

I12: the Joint Engineering, Environment and Processing (JEEP) beamline at Diamond Light Source.

Supercritical water hydrothermal synthesis (scWHS) is a relatively simple and environmentally friendly process for the production of potentially valuable metal oxide nanoparticles. However, it has never found industrial application to date due to poor process reliability, reproducibility and control. This paper presents the conclusions of collaborative work between chemical engineers and chemists that attempts to optimise the reaction engineering of this process, with the goal of reducing or even eliminating these fundamental process flaws. Initial investigations on the mixing in a T-piece highlighted that the environment within the scWHS reactor is highly unusual in terms of conventional reaction engineering because the fluid properties were significantly different in terms of temperature, viscosity and density. This led to the development of an optimised reactor, termed the Nozzle Reactor, which was designed on the basis of Light Adsorption Imaging (LAI) and Computational Fluid Dynamics (CFD) modeling, both of which show excellent mixing mechanics. Light Adsorption Imaging is an image analysis visualization method using fluids of different densities at ambient conditions. Experimental results using the Nozzle Reactor are presented showing how different metal oxide particles can be produced including titania, ceria, zirconia, copper, zinc and silver. The reactor shows a dramatic improvement in process reproducibility (±5 m2/g for BET surface area) and in reliability such that, given further investigation, will lead to process optimisation. Preliminary evidence suggests that the reactor could eventually lead to the ability to control particle properties, such as size, composition and shape, through the manipulation of process variables.

Reaction engineering: The supercritical water hydrothermal synthesis of nano-particles

Time resolved void fraction data and flow pattern information have been obtained for two-phase air/water flows in a small diameter (5 mm) vertical pipe using conductance probes. The time averaged void fractions are seen to agree with values measured using a completely different approach. Analysis of high speed videos reveals that the probability density function (PDF) technique is inadequate for accurately delineating the transition between slug and churn flows but performs better for the churn to annular flow transition. Instead a novel approach has been developed for transitions between flow patterns using the velocity of structures. This gives good agreement with the present experiments. Additionally, a modification to the bubble-to-slug flow transition of Taitel et al . (1980) gives improved predictions in narrow passages. A flow pattern specific method for void fraction prediction has been applied and its predictions are in good agreement with the measured mean void fraction. The slug flow model gives better predictions of void fraction in churn flow that the annular flow model. The velocities of disturbance waves on the wall film in annular flow are well predicted using the model of Pearce (1979). However, pipe diameter dependence of one of the constants is required.

B.J. Azzopardi

Papers

Reaction engineering: The supercritical water hydrothermal synthesis of nano-particles

A Study of Flow Patterns for Gas/Liquid Flow in Small Diameter Tubes

The split of stratified gas–liquid flow at a small diameter T-junction

The characteristics of gas/liquid flow in large risers at high pressures

The split of vertical two-phase flow at a small diameter T-junction