Shiling Dong

Abstract:

Electrospinning technique is well-known for the generation of different fibers. While it is a "simple" technique, it lies in the fact that the fibers are typically produced in the form of densely packed two-dimensional (2D) mats with limited thickness, shape, and porosity. The highly demanded three-dimensional (3D) fiber assemblies have been explored by time-consuming postprocessing and/or complex setup modifications. Here, we use a classic electrospinning setup to directly produce 3D fiber macrostructures only by modulating the spinning solution. Increasing solution conductivity modifies electrodynamic jet behavior and fiber assembling process; both are observed <i>in situ</i> using a high-speed camera. More viscous solutions render thicker fibers that own enhanced mechanical stiffness as examined by finite element analysis. We reveal the correlation between the universal solution parameters and the dimensionality of fiber assemblies, thereof, enlightening the design of more "3D spinnable" solutions that are compatible with any commercial electrospinning equipment. After a calcination step, ultralightweight ceramic fiber assemblies are generated. These inexpensive materials can clean up exceptionally large fractions of oil spillages and provide high-performance thermal insulation. This work would drive the development and scale-up production of next-generation 3D fiber materials for engineering, biomedical, and environmental applications.

Abstract:

Ceramic fibres are characterised by elongated thin-strand structures, which possess intriguing physical and chemical properties unachievable by bulk ceramics. These materials have sparked substantial interest for application in catalysis, sensing, energy conversion and storage, biomedical, environmental remediation, etc. This D. Phil project adopts a combination of electrospinning technique and sol-gel synthesis to produce high-performance ceramic fibres. The primary objectives are unravelling the mechanisms governing fibre formation and achieving better control over the micro- and macroscale fibre structures. The outcomes of this work are new functional fibre materials practically feasible for thermal insulation and photocatalysis applications.

A novel ‘3D sol-gel electrospinning technique’ is proposed for the in situ creation of centimetre-scale fibre macro-assemblies. This technique leads to fibre assemblies with highly tuneable macroscopic shape, volume, density, and porosity, effectively removing the limitation of conventional electrospinning that only yields 2D-like thin fibrous nonwovens with restricted implementation. Calcining the as-spun fibres produces ultralight ceramic fibrous assemblies (CFAs). Two materials are reported, TiO2/SiO2 CFA as a super-absorbent material for soaking up spillages and oil/water separation. Al2O3/ZrO2 CFA (AZFA) is a promising high-temperature thermal insulator showing ultralow thermal conductivity (less conductive than air) and ultrahigh thermal stability (1300-1500 °C). Surface modification endows AZFA hydrophobicity, allowing them to provide reliable thermal insulation in humid environments and underwater conditions.

3D electrospinning essentially tunes the macropores between fibres, while various pore-engineering strategies are used to manipulate the microstructures of individual fibres. Mesoporous and macroporous TiO2 fibres are synthesised by phase separation and sacrificial template methods. A dual-polymer templating method has been developed to create an ingenuous hierarchical porous fibre structure, the formation mechanisms and significantly enhanced optical responses are investigated experimentally and analytically. These porous TiO2 fibres are coupled with Au nanoparticle to form plasmonic photocatalysts with high-photocatalytic performance and excellent recyclability, proposed as superior materials for photocatalytic degradation of organic species in wastewater treatment.