Supercritical Hydrothermal Synthesis of Nanoparticles

Supercritical hydrothermal synthesis harnesses the unique solvent properties of water beyond its critical point (374 °C, 22.1 MPa) to produce nanoparticles with tightly controlled size, morphology and crystallinity. In this regime, reduced viscosity and enhanced diffusivity promote rapid mixing and heat transfer, while the variable density of supercritical water allows precise tuning of supersaturation and nucleation rates. Both batch and continuous flow reactors are employed, the latter offering enhanced reproducibility and scalability. Advances in reactor geometries and process modelling have revealed distinct mixing and growth regimes, enabling the production of narrow size distributions and tailored surface chemistries. Worldwide interest spans catalysts for clean energy, advanced ceramics, electronic materials and environmental remediation, reflecting the method’s green credentials and industrial potential.

Research from Nature Portfolio

Recent studies have introduced an infinity-shaped spiral continuous flow reactor that exploits the large density contrast between precursor solution and supercritical water to achieve ultrafast mixing. Coupling computational fluid dynamics with population balance modelling, researchers identified three flow regimes—declining, recovering and stable—determined by the flow ratio. The initial spiral turns act as a mixed flow zone, ensuring uniform supersaturation, while downstream coils behave as a plug flow section stabilising crystal growth. This design yields nanoparticles with smaller mean diameters and tighter size distributions than conventional stirred or T-mixers, offering a route to scalable, continuous production under moderate temperatures and pressures.

Supercritical Hydrothermal Synthesis of Nanoparticles publication trend

The graph below shows the total number of articles in supercritical hydrothermal synthesis of nanoparticles across all publications each year (not limited to Nature Index journals).

Technical terms

Supercritical fluid: A state of matter above the critical temperature and pressure where liquid and gas phases merge, exhibiting unique solvent properties such as tunable density and high diffusivity.

Supersaturation: The condition in which the concentration of dissolved precursor exceeds its equilibrium solubility, driving nucleation and particle formation.

Nucleation: The initial step in particle formation where solute molecules aggregate to form stable nuclei that grow into nanoparticles.

Continuous flow synthesis: A process configuration in which reactants are pumped steadily through a reactor, enabling reproducible conditions, rapid heat and mass transfer, and facile scale-up.

Population balance modelling: A mathematical framework that describes the evolution of particle size distributions by accounting for nucleation, growth and aggregation mechanisms.

References

1. Hydrothermal Synthesis of Metal Oxide Nanoparticles in Supercritical Water. Materials (2010).
2. A novel spiral infinity reactor for continuous hydrothermal synthesis of nanoparticles. Scientific Reports (2022).
3. Continuous Hydrothermal Flow Synthesis and Characterization of ZrO2 Nanoparticles Doped with CeO2 in Supercritical Water. Nanomaterials (2022).
4. Continuous Supercritical Water Impregnation Method for the Preparation of Metal Oxide on Activated Carbon Composite Materials. Energies (2024).