Direct and continuous synthesis of VO2 nanoparticles

Synthesis of Monoclinic Vanadium Dioxide via One-Pot Hydrothermal Route

Pure monoclinic vanadium dioxide nanoparticles (VO2 NPs) with a controlled uniform size are considered essential for the preparation of thermochromic smart window coatings on desired substrates. Herein, we report a facile one-step hydrothermal synthesis of VO2(M) NPs without post-treatment of annealing, which may induce unwanted aggregation of NPs. In contrast with the annealed sample, the one-step processed VO2(M) NPs exhibit superior thermochromic performance with the solar modulation efficiency of 11.8% and luminous transmittance of 37.3%.

High Throughput Synthesis and Screening of Oxygen Reduction Catalysts in the MTiO3 (M = Ca, Sr, Ba) Perovskite Phase Diagram

A library of 66 perovskite Ba_xSr_yCa_zTiO₃ (x + y + z = 1) samples (ca. three grams per sample) was made in ca. 14 h using a high-throughput continuous hydrothermal flow synthesis system. The as-synthesized samples were collected from the outlet of the process and then cleaned and freeze-dried before being evaluated individually as oxygen reduction catalysts using a rotating disk electrode testing technique. To establish any correlations between physical and electrochemical characterization data, the as-synthesized samples were investigated using analytical methods including BET surface area, powder X-ray diffraction (PXRD) and in selected cases, transmission electron microscopy (TEM). The aforementioned approach was validated as being able to quickly identify oxygen reduction catalysts from new libraries of electrocatalysts.

Continuous Synthesis of Nanocrystals via Flow Chemistry Technology

Modern nanotechnologies bring humanity to a new age, and advanced methods for preparing functional nanocrystals are cornerstones. A considerable variety of nanomaterials has been created over the past decades, but few were prepared on the macro scale, even fewer making it to the stage of industrial production. The gap between academic research and engineering production is expected to be filled by flow chemistry technology, which relies on microreactors. Microreaction devices and technologies for synthesizing different kinds of nanocrystals are discussed from an engineering point of view. The advantages of microreactors, the important features of flow chemistry systems, and methods to apply them in the syntheses of salt, oxide, metal, alloy, and quantum dot nanomaterials are summarized. To further exhibit the scaling-up of nanocrystal synthesis, recent reports on using microreactors with gram per hour and larger production rates are highlighted. Finally, an industrial example for preparing 10 tons of CaCO₃ nanoparticles per day is introduced, which shows the great potential for flow chemistry processes to transfer lab research to industry.

Bifunctionally active nanosized spinel cobalt nickel sulfides for sustainable secondary zinc–air batteries: examining the effects of compositional tuning on OER and ORR activity

Nanosized cobalt nickel sulfides were prepared via a continuous hydrothermal method and evaluated as electrocatalysts, with the catalytic activity being linked to the cationic composition.

Inorganic nanoparticle synthesis in flow reactors – applications and future directions

The use of flow technologies for obtaining nanoparticles can play an important role in the development of ecological and sustainable processes for obtaining inorganic nanomaterials, and the continuous methods are part of the Flow Chemistry trend.

Hydrothermal epitaxy growth of self-organized vanadium dioxide 3D structures with metal–insulator transition and THz transmission switch properties

The hydrothermal method is an effective approach for the synthesis of VO₂ films with unique crystallites morphology and sharp electrical and optical switch properties.

Chemistry in supercritical fluids for the synthesis of metal nanomaterials

The supercritical flow synthesis of metal nanomaterials is sustainable and scalable for the efficient production of materials.

Supercritical temperature synthesis of fluorine-doped VO2(M) nanoparticle with improved thermochromic property

Fluorine-doped VO₂(M) nanoparticles have been successfully synthesized using the hydrothermal method at a supercritical temperature of 490 °C. The pristine VO₂(M) has the critical phase transformation temperature of 64 °C. The morphology and homogeneity of the monoclinic structure VO₂(M) were adopted by the fluorine-doped system. The obtained particle size of the samples is smaller at the higher concentration of anion doping. The best reduction of critical temperature was achieved by fluorine doping of 0.13% up to 48 °C. The thin films of the fluorine-doped VO₂(M) showed pronounced thermochromic property and therefore are suitable for smart window applications.

Hexagonal VO2 particles: synthesis, mechanism and thermochromic properties

Monoclinic vanadium dioxide VO₂ (M) with hexagonal structure is synthesized by hydrothermal method, and the phase evolution is evidenced. Interestingly, the hexagonal morphology comes into being as a result of the low-energy coherent interfaces, (211̄)₁//(21̄1̄)₂ and (21̄1̄)₁//(020)₂. The size of hexagonal particles is well controlled by changing the concentration of precursor solutions. Hexagonal particles exhibit excellent thermochromic properties with a narrow hysteresis of 5.9 °C and high stability. In addition, the phase transition temperature can be substantially reduced down to 28 °C by simply W doping.

Monoclinic vanadium dioxide VO₂ (M) with hexagonal structure is synthesized by hydrothermal method, and the phase evolution is evidenced.

Hydrothermal Synthesis of VO2 Polymorphs: Advantages, Challenges and Prospects for the Application of Energy Efficient Smart Windows

Vanadium dioxide (VO₂ ) is a widely studied inorganic phase change material, which has a reversible phase transition from semiconducting monoclinic to metallic rutile phase at a critical temperature of τ_c ≈ 68 °C. The abrupt decrease of infrared transmittance in the metallic phase makes VO₂ a potential candidate for thermochromic energy efficient windows to cut down building energy consumption. However, there are three long-standing issues that hindered its application in energy efficient windows: high τ_c , low luminous transmittance (T_lum ), and undesirable solar modulation ability (ΔT_sol ). Many approaches, including nano-thermochromism, porous films, biomimetic surface reconstruction, gridded structures, antireflective overcoatings, etc, have been proposed to tackle these issues. The first approach-nano-thermochromism-which is to integrate VO₂ nanoparticles in a transparent matrix, outperforms the rest; while the thermochromic performance is determined by particle size, stoichiometry, and crystallinity. A hydrothermal method is the most common method to fabricate high-quality VO₂ nanoparticles, and has its own advantages of large-scale synthesis and precise phase control of VO₂ . This Review focuses on hydrothermal synthesis, physical properties of VO₂ polymorphs, and their transformation to thermochromic VO₂ (M), and discusses the advantages, challenges, and prospects of VO₂ (M) in energy-efficient smart windows application.

Continuous Hydrothermal Synthesis of Inorganic Nanoparticles: Applications and Future Directions

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 products, as well as materials or structures, are discussed (surface-functionalized hybrids, nanocomposites, nanograined coatings and monoliths, and metal-organic frameworks). Later, this Review focuses on some of the key apparatus innovations in the field, such as in situ flow/rapid heating systems (to investigate kinetics and mechanisms), approaches to high throughput flow syntheses (for nanomaterials discovery), as well as recent developments in scale-up of hydrothermal flow processes. Finally, this Review covers environmental considerations, future directions and capabilities, along with the conclusions and outlook.

Particle size, morphology and phase transitions in hydrothermally produced VO2(D)

An easy and reproducible method to synthesise thermochromic VO₂[M] via VO₂[D] at a low calcination temperature.

One-Step Hydrothermal Synthesis of W-Doped VO2 (M) Nanorods with a Tunable Phase-Transition Temperature for Infrared Smart Windows

Vanadium dioxide (VO₂), with reversible metal-semiconductor transition near room temperature, is a compelling candidate for thermochromic windows. Nanocomposite coatings derived from VO₂ nanoparticles are particularly superior to VO₂ films due to their advantages in large-scale preparation, flexible shaping, and regulation of optical properties. In this work, we developed a novel method for one-step hydrothermal synthesis of W-doped VO₂ (M) nanorods and studied their application in large-scale infrared smart windows. On introducing tartaric acid as a new reductant, VO₂ underwent a two-stage phase evolution from the pure phase comprising VO₂ (A) nanobelts to VO₂ (M) nanorods, instead of the conventional three-stage B-A-M phase evolution during hydrothermal synthesis. This transition is very favorable for the large-scale hydrothermal synthesis of VO₂ (M). The phase-transition temperature of VO₂ (M) nanoparticles can be regulated systematically by W doping, with a reduction efficiency of about 24.52 °C/atom % W. Moreover, VO₂ (M) composite films were fabricated using a convenient roller coating method, which exhibited significant midinfrared transmission switching up to 31%, with a phase-transition temperature of about 37.3 °C. This work demonstrates the significant progress in the one-step hydrothermal synthesis of VO₂ (M) nanorods and provides significant insights into their applications in infrared smart windows.

Controllable synthesis of VO2(D) and their conversion to VO2(M) nanostructures with thermochromic phase transition properties

VO₂(M) nanostructures with lower thermochromic phase transition temperature and narrower thermal hysteresis width were synthesized by a hydrothermal-calcination method, making them suitable candidates for smart windows.