Floating Catalyst Chemical Vapour Deposition (FCCVD) represents a promising method for assembling one-dimensional (1D) nanostructures into macroscopic materials for high-performance applications. This approach employs an aerosol of nanoparticles to catalyse the growth of high-aspect-ratio nanowires or nanotubes, which grow inside the reaction chamber floating in a gas stream. These nanostructures can aggregate into aerogels and then be shaped into freestanding macroscopic materials similar to nanotextiles.

Despite its promise, only a limited range of materials have been synthesised via this method. This thesis aimed to extend FCCVD synthesis to new materials, using silicon carbide (SiC) and tin oxide (SnO) nanowires, as model systems to deepen understanding of the nanowire growth mechanism and variables affecting FCCVD synthesis. Additionally, this work explores the challenges in reactor experimental setup, focusing on process monitoring, in-situ sampling, catalyst generation, and precursor injection stability.

The first phase (Chapter 3) was focused on SiC nanowires growth via FCCVD, achieving ultrafast growth rate up to 3 orders of magnitude above conventional substrate-based processes. The high aspect ratio (1800) of the nanowires favoured their entanglement into freestanding SiC nanowire networks. In situ collection of reaction products as they evolved through the reactor identified a 3-cm growth zone around 1130 C. The use of hydrogen aided the inhibition of competitive products from precursor decomposition (Si, C and SiC nanoparticles), and promoted the catalysed formation of SiC nanowires, the only thermodynamically stable product in the Fe-Si-C system.

In the second phase (Chapter 4), the insights gained from SiC nanowire research were applied to the design and construction of a new FCCVD reactor to improve reproducibility and accelerate the synthesis parameter exploration. A thermal evaporator replaced the existing system, improving control over catalyst particle size and concentration. A nebulizer-based system was developed to quantify precursor delivery and prevent premature decomposition. Additionally, an in-line monitoring system using a scanning mobility particle sizer (SMPS) was implemented to track catalyst and precursor injection and product formation in real-time.

The final phase (Chapter 5) was dedicated to the synthesis of SnO nanowires in the newly developed FCCVD reactor. The setup enabled the isolation of distinct growth stages: precursor decomposition, Au-Sn alloying and nanowire growth. Low precursor concentration and the use of H2 inhibited the formation of SnO2 soot nanoparticles. SnO growth and improved selectivity were achieved only through careful synchronisation of species injection along the catalyst path. Studies with air injection showed that the tin content in the alloy catalyst particles during oxygen exposure strongly influences nanowire nucleation over catalyst deactivation by surface oxidation. Growth termination was attributed to oxygen gradients that cause rapid oxidation of the catalyst surface or inhibit the formation of an oxide layer in the nanowire. Finally, despite their short aspect ratio, self-standing sheets were prepared by a simple wet-processing method.

This thesis provides a comprehensive overview of nanowire growth using FCCVD, comparing SiC and SnO nanowires with existing literature. It demonstrates that FCCVD enables faster growth than substrate-based CVD due to higher impingement rates of precursor species on the catalyst, shifting the growth limitation from diffusion to incorporation and solidification. The study shows that selectivity towards 1D nanostructures increases under dilute conditions, particularly in a reductive atmosphere, by minimising competing homogeneous nucleation. Its results highlight the importance of increasing nanowire length to facilitate aerogel formation at feasible catalyst concentrations to enable the production of continuous nanowire fibres.