Electrospun Silicon Oxycarbide (SiOC) Fibre Mats and its Composites: Fabrication and Properties

Abstract

Silicon oxycarbide (SiOC) is a class of glass or glass-ceramic materials which integrate the characteristic inertness of traditional ceramics and many functional properties offered by its unique silicate network architecture and presence of both carbidic and free carbon phase. Stimulated by its functional prospects, the fabrication of SiOC materials into small-dimensional structures has been intensively explored through different processing techniques. In particular, the fabrication of SiOC fibres via Electrospinning, which has newly emerged since the past decade, offers additional flexibility and free-standing features to the SiOC materials, and has thus significantly facilitated its practical application. Although considerable efforts have been devoted to the preparation of electrospun SiOC fibres from different preceramic precursors, the electrospinning systems to yield SiOC fibres still need further improvement in terms of eliminating the spinning-aid, achieving better composition and morphology control, and obtaining special surface functionalisation of the SiOC fibre mats. Through the combination with the sol-gel method, ultrafine SiOC fibre mats have been prepared through a spinning-aid-free electrospinning process. Based on the kinetics and mechanism analysis of the sol-gel reaction, elimination of the spinning-aid was achieved by regulating the precursor sols' spinnability from the concentration and molecular configuration aspects, respectively. The influence of the precursor sols' spinnability on the morphology of resulted SiOC fibres has been thoroughly studied. Uniform ultrafine SiOC fibre in the sub-micro size (d̄ = ~256.7 nm) has been synthesised for the first time. Based on the comprehension of sols' spinnability, additional polymer components have been incorporated in the precursor systems to further enrich the carbon content in electrospun SiOC fibre mats. The influence of polyacrylonitrile(PAN) addition on the enrichment of carbon in SiOC and its subsequent electrochemical performance have been investigated. Enrichment of carbon in both carbidic and free carbon phases have been realised in resulted SiOC fibres by tailoring the addition of PAN in the precursor system. When serving as the supercapacitor electrodes, the ii carbon-enriched SiOC fibre mats demonstrated wider potential window and higher capacitance as compared to the pure SiOC or carbon fibres, and its performance was proportional to the total carbon content. SiOC fibre mats derived from the most PAN addition ratio delivered the highest specific capacitance of 11.8 F/g. The preparation of electrospun porous SiOC fibre mats with different porosities has been achieved for the first time through either polymer blending along the electrospinning process or Potassium hydroxide(KOH) etching after the fibre formation. Significantly enlarged surface areas have been created on the polymer blending derived hollow SiOC fibres (54.4 m²/g) and KOH etched surface porous SiOC fibres (133.3 m²/g). The influence of SiOC fibres' porosity on its adsorption performance have been investigated through batch experiments and model fitting. Convenient regenerations and reusability have been verified on the porous SiOC fibre mats. Surface functionalisation of the SiOC fibres mats has been achieved by constructing different hierarchical Titanium dioxide(TiO₂) nanostructures on electrospun SiOC fibre mats through hydro/thermal reactions. The growth manner of different TiO₂ nanostructures has been explored based on investigations regarding the morphology, loading density, and crystallinity of the TiO₂ nanostructures. The hierarchical SiOC/TiO₂ composite fibre mats demonstrated distinct water remediation performance in terms of photodegradation of organic dyes and separation of oil-in-water emulsion owing to the different crystal phase and morphology of the TiO₂ nanostructures.