A Dual-Stage Hydrothermal Flow Reactor for Green and Sustainable Synthesis of Advanced Hybrid Nanomaterials

Research output: Book/anthology/dissertation/reportPh.D. thesisResearch

  • Henrik Christian Lund Hellstern
Nanocomposites are a group of materials of growing scientific interest. The combination of two different materials into a single hybrid particle on the nanoscale can result in multifunctional materials or be used to enhance existing properties through synergistic interactions. Such novel materials can be synthesized hydrothermally in a dual-stage flow reactor that is both environmentally benign and capable of producing high quantities which is a prerequisite for use in applications.
A dual-stage hydrothermal flow reactor was developed for this purpose and used to produce hybrid nanomaterials of differing morphologies: from smaller particles grafted on a larger particle for support, to spherical core-shell nanoparticles of 10-30 nm in diameter of a narrow size distribution. This is accomplished by synthesizing the core and shell in separate reactor zones to avoid a mixed product of ungrafted particles. Using TiO2@SnO2 as an example the parameters responsible for composite formation are explored.
The used characterization techniques include X-ray diffraction, electron microscopy and spectroscopy. Structural analysis is applied to demonstrate the changes in crystal growth mechanism when a material is precipitated either as a nanoshell or as a free, ungrafted particle. The presence of core-particles has profound implications for the crystal size, structure and composition of the nucleating shell material as demonstrated by depositing 2 nm shells of CuO/Cu2O, NiOxLy and Zn6(OH)6(CO3)2 on a 20 nm magnetic core.
SiO2 nanoshells on γ-Fe2O3, TiO2 and α-Fe2O3 cores demonstrate that morphology depends strongly on the synthesis pH. This factor governs if the shell is thin and uniform or thick and irregular. An electrostatic model is developed for identifying synthesis parameters which allows control of the nanohybrid morphology. The choice of reactants and temperature profile is shown also to influence whether a composite or mixture is formed.
Multiferroic γ-Fe2O3@SrTiO3 is synthesized to demonstrate the feasibility of producing highly advanced nanomaterials in flow. The hybrid is obtained through a complex synthesis route in which the formation of a γ-Fe2O3@TiO2 intermediate is central.
Finally, it is shown how metal sulphides can be produced hydrothermally using MoS2 as an example. Hydrothermal conditions generally favor oxides, but choice of precursor can be used to promote formation of polycrystalline MoS2 nanosheets. The feasibility of producing supported nanomaterials is demonstrated using TiO2 nanocatalysts on MoS2 sheets
This dissertation describes the dual-stage hydrothermal flow reactor and how advanced nanocomposites in high yields may be readily synthesized for potential use in applications.
Original languageEnglish
Number of pages177
Publication statusPublished - 1 Feb 2016

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