Diatom enabled advanced functional materials

Diatoms are incredibly diverse, photosynthetic microalgae, which are widely distributed in aquatic environments. The wide array and intricate morphology of the micro- and nanostructured silica exoskeletons (also known as frustules) encasing the single-celled diatoms offer a tremendous opportunity for myriad applications. In this thesis work, diatom frustules, as bio-silica templates, are further leveraged to develop into advanced materials, with the aim that their advanced functionalities could benefit a broad range of applications. The lack of effective methods for arranging diatoms into large area, uniformly oriented monolayers has greatly hindered their applications in scale. Therefore, this work first explores the method to develop large-scale compact monolayers of diatom frustules. Specifically, frustule assembly at the water-air interface is discussed with experimental and numerical efforts to demonstrate the mechanisms to form nearly uniformly oriented frustule monolayers. In the second part of the work, the material properties of diatom frustules are enhanced by synthesizing nanowire structures on diatom frustule templates. A detailed analysis reveals that the nanowire growth is governed by the silicon dioxide precipitation at their root region and tip region, and enhancements in the light scattering and surface area have been achieved with the composite materials. The hierarchical pore structures of diatom frustules can be used as templates for the “stencil” fabrication of hierarchical nanoparticle patterns. Inspired by the hierarchical arrangement of such nanoparticle patterns, similar designs are applied to electromagnetic metamaterial absorbers. It has been revealed that the hierarchy introduced an addition resonance state to the device, broadening the absorption spectrum. It is further demonstrated that the resonance peaks shift linearly with the inter-unit-cell spacing, which is attributed to the effective dipole resonances due to the collective resonances in the grouped nanoparticles. By developing batch manipulation method to assemble diatom frustules, enhancing the intrinsic frustule material properties, and using diatom frustule pore designs as a source of inspiration in metamaterial design and nano fabrications, this thesis work aims to use diatom frustules as basic templates for the development of engineering tool sets, with the aim of transforming and translating these mesoporous bio-silica particles into advanced functional materials.2020-12-24T00:00:00