石墨烯合成與透明可撓式導電膜,有機汙染物吸收及場發射性能應用之研究

Graphene is defined as a flat monolayer of sp2-hybridized carbon atoms tightly packed into a two-dimensional (2D) honeycomb structure. This stringently 2D material exhibits a broad range of extraordinary properties, such as excellent electrical and thermal conductivities, and extremely high strength, which hold great promises in a variety of applications in micro/nanoelectronics, composites, and clean energy. Of special interests are the physicochemical properties of graphene materials strongly dependent on synthetic methods, resulting in diverse practical uses employed. This dissertation mainly aims to develop new approaches for production of graphene materials using wet chemistry as well as chemical vapor deposition (CVD) methods. Subsequently, the as-synthesized graphene materials are employed for applications as flexible and transparent conductors, a key component for removal of organic contaminants (including oils or organic solvents) from water, a supporting barrier for growth of carbon nanotubes (CNTs), and effective fillers for enhancing electron field emission performance of a vacuum filtered CNT film. Generally, exfoliation of graphite into graphene sheets by wet chemistry approaches require intercalating chemicals into interspaces of graphite layers followed by harsh oxidation and reduction or selecting a solvent with surface tension close to that of graphite. In our approach, we prepared ethanol soluble fewlayer graphene nanosheets (FLGs) without adopting the common receipts, thus avoided using toxic oxidizing/reducing agents or poisonous solvents. Atomic force microscopy and high-resolution transmission electron microscopy studies reveal that FLGs have average thicknesses in the range of 2.6–2.8 nm, corresponding to 8–9 layers. A graphene/nafion composite film has a sheet resistance of 9.70 kΩsq-1 at the transmittance of 74.5% (at 550 nm) while the nafion film on polyethylene II terephthalate has a sheet resistance of 128 kΩsq-1 at transmittance of 90.0%. For the cycling/bending test, almost no change in resistance was exhibited when the film was bent at an angle up to 1400, and no obvious deviation in resistance could be found after 100 bending cycles. In addition, a FLGs/poly(3,4- ethylenedioxythiophene): poly(styrenesulfonate) composite layer was demonstrated as the effective hole transporting layer to improve the hole transporting ability in an organic photovoltaic device, with which the power conversion efficiency was enhanced from 3.10% to 3.70%. We further investigated the hydrophobic properties of the ethanol soluble FLG material and its combination with a type of commercial sponge. The FLG films possess strong hydrophobic properties besides their opto/mechano-electrical properties aforementioned. By coating an appropriate amount of FLGs on the sponge skeletons with polydimethylsiloxane (PDMS) binder, superhydrophobic (water contact angle of ~1620) and superoleophilic (oil contact angle of ~00) graphene-based sponges were obtained. The as-fabricated graphene-based sponges perform as an efficient absorbent for a broad range of oils and organic solvents with high selectivity, good recyclability, and excellent absorption capacities up to 165 times their own weight. In addition to wet chemistry method, we also developed a CVD method to grow graphene and integrate thin CNT networks on the surface of the graphene film using the same CVD system. The thickness of graphene and the CNT density on graphene surface can be controlled properly. Graphene films are demonstrated as an effective supporting barrier for preventing poisoning of iron nanoparticles which catalyze the growth of CNTs on copper substrates. Based on this method, the opto-electronic and field emission properties of the graphene integrated with CNTs can be remarkably tailored. A graphene film exhibits a sheet resistance of III 2.15 kΩsq-1 with a transmittance of 85.6% (at 550 nm) while a CNT–graphene hybrid film shows an improved sheet resistance of 420 Ωsq-1 with an optical transmittance of 72.9%. Moreover, CNT–graphene films reveal as effective electron field emitters with low turn-on and threshold electric fields of 2.9 and 3.3 Vμm-1, respectively. In order to combine the merits of the two-dimensional graphene and onedimensional CNT nanocarbon materials, many efforts have recently been made to obtain graphene-CNT hybrid materials or composites. Most studies on these hybrid materials focused on optoelectronic and electrical properties. Several attempts to create ohmic contact between CVD grown graphene and CNTs to enhance the field emission properties have been investigated. However, no studies utilizing reduced graphene oxide (RGO) nanosheets as the conductive fillers as well as the secondary emitters for enhancing field emission performance of CNT film have been reported to date. Herein, the composite films composing of CNTs and chemically reduced graphene nanosheets were fabricated using the vacuum filtration method. Compared to other processing methods such as chemical vapor deposition, electrophoresis, or screen-printing, this method is more beneficial for fabrication of low-cost field emitters with density controllable and additive avoidable. The composite films with different weight ratios between CNTs and graphene oxide (GO) are prepared by varying the volumes of CNTs and GO dispersions. The results show that the composite film with GO:CNT weight ratio of 1:3 after hydrazine treatment reveals the best field emission performance with low turn on and threshold fields of 2.82 and 2.98 V/μm, respectively.

並列關鍵字

graphene ； flexible and transparent conductors ； electron field emitters ； contaminant absorbents

參考文獻

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石墨烯合成與透明可撓式導電膜,有機汙染物吸收及場發射性能應用之研究

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