J. Appl. Cryst.の発刊に際して

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

Fuel Process. Technol.

Heterogeneous catalysis is a term normally used to describe a group of catalytic processes, yet it could equally be employed to describe the catalytic solid itself. A better understanding of the chemical and structural variation within such materials is thus a pre-requisite for the rationalising of structure–function relationships and ultimately to the design of new, more sustainable catalytic processes. The past 20 years has witnessed marked improvements in technologies required for analytical measurements at synchrotron sources, including higher photon brightness, nano-focusing, rapid, high resolution data acquisition and in the handling of large volumes of data. It is now possible to image materials using the entire synchrotron radiative profile, thus heralding a new era of in situ/operando measurements of catalytic solids. In this tutorial review we discuss the recent work in this exciting new research area and finally conclude with a future outlook on what will be possible/challenging to measure in the not-too-distant future.

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Chemical imaging of catalytic solids with synchrotron radiation

A confined jet reactor (mixer) is presented as a novel solution for the scalable continuous hydrothermal flow synthesis (CHFS) of nanoceramics. In CHFS, nanoceramics are formed upon mixing of two streams consisting of an aqueous metal salt solution at room temperature with a flow of less dense supercritical water (at 240 bar and 450 °C). Upon mixing, hydrolysis and dehydration occurs, resulting in the particles being formed in a continuous manner. The confined jet mixer used herein overcomes previous designs of mixers that can accumulate material internally and block. A method for scaling up the jet mixer (reactor) is described, to determine the size of jet mixer (internal mixer diameter 13.5 mm) prior to its use in a newly commissioned pilot plant designed to process flow rates 40 times greater than the equivalent laboratory-scale process (internal mixer diameter 4.6 mm). It was confirmed that the pilot plant scale mixer allowed safe and continuous operation with no blockages at much higher concentration...

Scaling-up a Confined Jet Reactor for the Continuous Hydrothermal Manufacture of Nanomaterials

Continuous hydrothermal flow synthesis (CHFS) offers a controllable route to the production of nanocrystalline materials. We describe the application of tomographic X-ray methods to image, for the first time, crystallization at the interior of an in operando CHFS reactor. In the experiment, the steady-state formation of nanoparticulate CeO2 was followed: the synthesis proceeds by rapid hydrolysis of cerium ammonium nitrate and hydrothermal coprecipitation in a near/super-critical water environment (T = 340−450 °C, P = 24 MPa). The results identify the location of particle growth with accompanying indications of crystallite size, and also reveal the build-up of material on the reactor wall during long syntheses. The imaging represents a significant achievement in that information of this kind can be gleaned from such an inhospitable environment as that of a CHFS reactor. The novel combination of tomographic angle- and energy-dispersive diffraction employed was particularly appropriate for this in situ stud...

Imaging the inside of a Continuous Nanoceramic Synthesizer under Supercritical Water Conditions Using High-Energy Synchrotron X-Radiation

An X-ray diffraction computed tomography data-collection strategy that allows, post experiment, a choice between temporal and spatial resolution is reported. This strategy enables time-resolved studies on comparatively short timescales, or alternatively allows for improved spatial resolution if the system under study, or components within it, appear to be unchanging. The application of the method for studying an Mn–Na–W/SiO2 fixed-bed reactor in situ is demonstrated. Additionally, the opportunities to improve the data-collection strategy further, enabling post-collection tuning between statistical, temporal and spatial resolutions, are discussed. In principle, the interlaced scanning approach can also be applied to other pencil-beam tomographic techniques, like X-ray fluorescence computed tomography, X-ray absorption fine structure computed tomography, pair distribution function computed tomography and tomographic scanning transmission X-ray microscopy.

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Simon D. M. Jacques

Papers

Imaging the inside of a Continuous Nanoceramic Synthesizer under Supercritical Water Conditions Using High-Energy Synchrotron X-Radiation

Interlaced X-ray diffraction computed tomography