Synthesis And Applications Of Cabon Nanotube Sponge Macrostructures

Carbon nanotubes (CNTs) are novel nanostructures with excellent properties and promising applications in various fields. Preparation of macroscopic structures based on assembled CNTs represents an important step towards practical applications. Nano-porous materials have large specific surface area, high porosity and possess distinct optical, electrical and mechanical properties. They play an important role in materials research and development. The engineered porous structures based on CNTs will offer a combined feature of high porosity and high performance. Hence, synthesis of macro-sized CNTs with porous structure is of great significance. In this dissertation, an original macroscopic structure based on three dimensional, highly porous CNT network (CNT sponge) was synthesized in a direct and controllable way. The properties of the CNT sponges were studied for paving the way to develop high performance materials and explore new applications.CNT sponges are directly synthesized by chemical vapor deposition (CVD), using dichlorobenzene and ferrocene as carbon source and catalyst precursor, respectively. The CNT sponges consist of randomly overlapped multi-walled CNTs (MWNTs), which self-assembled into a porous, highly interconnected, three-dimensional framework. On the microscale, each CNT can be considered as a high aspect-ratio skeleton to construct the porous structure. Freestanding CNT sponges have uniform structure, high flexibility and stability, with apparent densities of 5-25 mg/cm~3, porosity of larger than 99 %. The areas of as-grown CNT sponges are larger than 150 cm~2, and the thicknesses could reach about 9 mm in 4 hours reaction period. The density, porosity, pore size distribution and mechanical strength of the CNT sponges, and the average diameter and wall thickness of CNTs in the sponge can be controlled by modulating CVD process parameters, such as growth temperature, carrier gas flowing rate and carbon source feeding rate. The CNTs in the CNT sponges are open-end, formed in the gas phase, and are connected into a network through mechanical force and van der Waals force. The growth mechanism of the CNT sponges was discussed based on the proposed growth model.The sorption properties of CNT sponges for organic solvents and spilled oil have been studied. CNT sponges are lipophilic and super-hydrophobic, and show strong affinity and active absorption to a wide range of solvents and oils with large sorption capacity, fast sorption rate, high selectivity and excellent recyclability. The sorption capacity is up to 80~180 times the sponge weight for oils and solvents with densities of 0.6~1.5 g/cm~3. The sorption capacity increased with the decrease of solvent density or CNT sponge apparent density. Reversible absorption and removal of solvents by combustion or mechanical compression for many times also provide simple approaches for recycled use. The CNT sponges maintain sorption capacities of 20 to 40 times of own weight after 10 cycles of absorption tests for oils with viscosities in the range of 3 to 204 cP.CNT sponges have excellent elasticity, high robustness and shape memory function. They can be deformed into any shapes elastically or compressed to large-strains repeatedly (over 1000 times) in air or liquids without breaking apart, and after that still recover to nearly original shape. The density of CNT sponges, strain rate and operation medium has significant influence on their energy absorption performance. CNT sponges can absorb 8-20 kJ/m3 mechanical energy in air under compressive stresses of 0.027~0.062 MPa.CNT sponge can be considered as a three-dimensional (3D) highly porous scaffold. Uniformly dispersed CNT sponges/epoxy composites have been obtained by pouring epoxy into the three-dimensional CNT framework, and completely filling the sponge pores. The embedded CNTs can simultaneously improve mechanical and electrical properties of the composites by forming a continuous and conductive network. The CNT sponges and CNT sponges/epoxy composites have excellent electromechanical characters, in which the resistivity decreased with increasing compressive stress and showed a reversible change over many compressive cycles.