This thesis describes approaches to develop new types of graphene-based nanomaterials and their practical applications in various fields. Various functionalities can be achieved through the chemical modification of graphene oxide (GO), making it easy to host and grow functional nanomaterials on the surface of graphene.
Introduction of Carbon-Based Nanomaterials
Carbon-Based Nanomaterials
Graphene and Graphene Oxide (GO)
Chemical Modification of Carbon-Based Nanomaterials
Hybrid Carbon-Based Nanomaterials
Overview of Thesis
Defective Graphene: Synthesis and Characterizations
Introduction
Experimental
- Exfoliation
- Synthesis of nGO
Results and Discussion
Conclusion
Chemical Modification of Graphene Oxide for Non-Aqueous Suspensions
Introduction
Hydrophilic functional groups of GO provide good dispersion stability in water; however, aggregation is still observed at high concentrations and becomes stronger in organic solvents. To overcome these challenges, here we have developed various chemical functionalized GO derivatives to improve dispersion stability in non-aqueous suspensions.
Tailoring Graphene Derivatives for Superior Dispersion Stability and Quantitative
- Abstract
- Introduction
- Experimental
- Preparation of GO Suspension and Covalent Surface Modification
- Stability Test
- Characterizations
- Results and Discussion
- Preparation of GO-Derivatives through Covalent Functionalization
- Characterization of GO-Derivatives
- Quantitative Assessment for the Dispersion Stability
- Dispersion Stability in Other Non-Aqueous Solvents
- Rheological Behaviors of GO-Based Dispersions
- Instability Index
- Conclusion
- References
- Introduction
- Experimental
- Synthesis of GO-OA and TRGO-OA
- Synthesis of GO-OA_CDI and TRGO-OA_CDI
- Characterization
- Results and Discussion
- Conclusion
- References
Bifunctional Graphene-Based Carbocatalyst for Biomass Reforming
Introduction
The demand for energy has increased rapidly, but fossil fuels are not sufficient to meet this ever-increasing global energy demand. Furthermore, the combustion of fossil fuels has led to large increases in greenhouse gases and the breakdown of the carbon cycle.1-3 The cumulative impact of fossil fuels has fueled the search for alternative energy sources. Energy production from biomass has the advantage of creating smaller amounts of greenhouse gases than from fossil fuels.
Among biomass feedstocks, the two most abundant carbohydrates, glucose and fructose, are ideal candidates to replace fossil fuels and have significant potential as future energy resources.7 Until now, many approaches have been developed to provide efficient ways to convert biomass into valuable fuels and chemicals.8 Among the many bio-based products, furan-based compounds are rich sources of a variety of derivatives for fuel and chemical production. To convert glucose to HMF, strong acid catalysts are typically required for each step, and therefore considerable research efforts have focused on the use of metal-based catalysts.7, 13-14 Despite their good. Although prior research exists on the use of carbon-based catalysts to convert fructose to HMF, 31-33 there are few cases using glucose or cellulose as the starting substrate due to the challenges of the process.
Recently, Chen's group used sulfonated graphene quantum dots as a nonmetallic catalyst to convert glucose into HMF; however, it had low catalytic activity for glucose conversion and its quasi-heterogeneous structure limited its easy recycling [34] . Tailored GO-based catalysts with unique bifunctional groups showed significant catalytic performance for HMF production, compared to homogeneous catalysts. Finally, we propose a putative mechanism for the conversion of glucose to HMF based on NMR results, which suggest a unique bifunctional catalytic effect involving the boronic acid and phenylsulfonic acid groups in BS-GO.
Experimental
- Synthesis of the Carbocatalysts
- Structural Characterization
- Investigating the Catalytic Performance
Results and Discussion
- Synthesis of GO-Derivatives
A slight decrease in the C/O ratio from B-GO to BS-GO indicates that the sulfonic acid group was successfully grafted onto the graphene sheets. Similarly, the ID/IG ratios of B-GO and BS-GO were higher than that of pristine GO due to boron doping. The decrease in yield of HMF compared to B-GO and BS-GO could originate from their structures.
The two disjoint parts, boric acid and phenylsulfonic acid, show a unique bifunctional effect in a single nanosheet BS-GO catalyst, resulting in excellent catalytic performance. The BS-GO catalyzed reaction proceeded through a different reaction mechanism compared to the Cr-based catalyst. Based on these results, we propose a putative mechanism for the conversion of glucose to HMF over the BS-GO catalyst (Figure 4.11).
To verify the suitability of BS-GO as a heterogeneous catalyst, a recycling test was performed up to the fifth cycle. Two separate groups; boric acid and phenylsulfonic acid exhibit a unique bifunctional effect in a single nanosheet of BS-GO catalyst, resulting in excellent catalytic performance for the production of HMF. In the BS-GO catalyst, the boronic acid site plays a crucial role in converting glucose to HMF.
Introduction
- Carbon-Based Electrocatalysts
- Electro-Reforming of Biomass
- Nanoarchitectonics
- References
Since it has a lower overpotential, hydrogen evolution is therefore much more favorable compared to water electrolysis. For example, 2,5-furandicarboxylic acid (FDCA), one of the products of HMF oxidation, is considered an important monomer for the synthesis of a renewable polymer, poly(ethylene furanoate), instead of petroleum-derived poly(ethylene terephthalate). 17. To meet the global demand for efficient use of materials and resources with appropriate applications, continuous scientific efforts are needed regarding the synthesis of molecules from materials, the fabrication of devices or biological treatments.
One of the important keys to these efforts is precise control of structures and organization at the nanoscale level to enable efficient flow, and conversion of materials and energy. In addition to the development of new materials, a new concept to fabricate architectures of functional materials and systems has been proposed as a nano-architectural concept, which was initiated by Masakazu Aono.18. F.; Ocakoglu, K.; van de Krol, R., Water-splitting catalysis and solar fuel devices: artificial leaves on the move.
Dai, L., Nitrogen-doped graphene as efficient metal-free electrocatalyst for oxygen reduction in fuel cells. Oberhauser, W.; Caporali, S.; Innocenti, M.; Vizza, F., Carbon-supported Rh nanoparticles for the production of hydrogen and chemicals through the electroreforming of biomass-derived alcohols. A.; Bevilacqua, M.; Filippi, J.; Innocenti, M.; Marchionni, A.; Oberhauser, W.; Wang, L.; Vizza, F., Nanotechnology makes biomass electrolysis more energy efficient than water electrolysis.
Covalent Functionalization Based Heteroatom Doped Graphene Nanosheet for Oxygen
- Abstract
- Introduction
- Experimental
- Preparation of Graphene Oxide (GO) Suspension and Covalent Surface
- Preparation of Nitrogen-Doped Graphene Oxide (NRGO) and Thermally
- Preparation of Catalyst Ink for the Rotating Disk Electrode
- Rotating Disk Electrode (RDE) Experiment
- Rotating Ring-Disk Electrode (RRDE) Experiment
- Characterizations
- Results and Discussion
- Conclusion
- References
Preparation of nitrogen-doped graphene oxide (NRGO) and thermally reduced graphene oxide (TRGO) graphene oxide (TRGO). The surface morphology of the GO and NGO was investigated using an atomic force microscope (AFM, Dimension D3100, Veeco), and we used a silicon wafer as a substrate to obtain AFM image of NGO3 graphene nanosheets before thermal annealing. As a first step, the GO suspension was prepared by the modified Hummers method from a graphite powder.33 After the sonication step to exfoliate graphite oxide to graphene oxide, the oxygen-containing functional groups are introduced onto the surface of the graphene nanosheet, such as e.g. as carboxylic acids and alcohol groups.
One of the representative examples, the NGO3, showed that the graphene nanoplates possessed a higher average thickness of nm with no noticeable changes in the lateral dimension of graphene nanoplates of µm.36-37 This observation reflects the presence of long chain triethylenetetramine on both sides of the GO nanosheets after functionality. Furthermore, it highlights the mild nature of this synthetic condition that does not alter the intrinsic properties regarding the dimensions of the graphene nanosheet. The electron transfer number (n), based on the Koutecky-Levich equation, is located at the top of the bar graph. d) The graph of peroxide yields (%) and electron transfer number (n) of electrocatalysts.
Due to the charge polarization of the carbon network caused by the doped heteroatoms, oxygen molecules can easily interact with heteroatom-doped graphene nanosheets. Taking advantage of the facile synthesis process, we expect that this covalent functionality would provide other routes for the controlled introduction of heteroatoms onto the graphene nanosheets for different applications. M; Armand, M., Issues and challenges in rechargeable lithium batteries. R; Ishikawa, Y., Searching for the active site in nitrogen-doped carbon nanotube electrodes for the oxygen reduction reaction.
Architecture-Performance Relationship in Graphene-Based Multilayer Electrodes for
- Abstract
- Introduction
- Experimental
- Preparation of Nano Sized GO (nGO)
- Preparation of Au and Pd NPs
- LbL Assembly of Hybrid Electrode Films
- Electrochemical Analysis
- Characterizations
- Results and Discussion
- Conclusion
- References
Using transmission electron microscopy, the average diameters of the Au and Pd NPs were determined to be 5.8 nm and 3.4 nm, respectively (TEM, Figure 5.12). The multilayer electrodes with different architectures were clearly observed using the contrast difference in elemental mapping between the Au and Pd NPs (Figure 5.14). The Au NPs provided an additional reactant, that is, HFCA, to the surface of the Pd NPs and increased the concentration, resulting in improved mass transfer for the 3D multilayer electrodes.
Therefore, when Au NPs were on the outer layer, as in the case of the Pd7/Au7 electrode, the current density was high due to the enhanced mass transfer to Pd NPs in the inner layer for the effective oxidation to FDCA. To verify this interpretation, we investigated the electrocatalytic oxidation of the intermediate HFCA compound using Pd7/Au7 and Au7/Pd7 electrodes (Figure 5.23). As described in the section related to the HMF oxidation reaction, the HER activity strongly depends on the architecture of the multilayer electrodes.
In the case of the same number of contact layers between Au and Pd layers, e.g. Au7/Pd7 and Pd7/Au7, Pd NPs located at the inner layer (Pd7/Au7) may be more advantageous, not only to form a high concentration profile of Hads in the Nernst diffusion layer at the lower end of the catalytic electrodes below, but also to facilitate the HER kinetics, with a low Rct value of 190 Ω (compared to 1397 Ω for the Au7Pd7 electrode). Thus, the observed product distribution was very sensitive to the nature of the outer layer. In the case of HER, an architecture with adjacent Pd and Au (fully alternating (AuPd)7 electrode) was highly desirable for the rapid spillover of hydrogen from the Pd NPs to the Au NPs.
Summary and Outlook
오랜 시간 동안 많은 분들의 격려와 도움 덕분에 잘 마무리할 수 있었습니다. 교수님 덕분에 학부 시절 논문을 작성하고 연구자의 길을 걸을 수 있었습니다. 또한, 싱가포르에서 연구할 수 있는 기회를 주신 싱가포르국립대학교 Kian Ping Loh 교수님께도 감사의 말씀을 전하고 싶습니다.
그리고 오랫동안 KBS그룹에 함께 해 주신 멤버들에게도 감사드립니다. 선배님들의 잘 관리된 연구실 덕분에 편안하게 연구를 진행할 수 있었습니다. 우리 드디어 졸업했어요!
다들 사회에 나가서도 좋은 사람들을 만날 수 있었으면 좋겠습니다. 더욱 성장한 모습 보여드리겠습니다. 다시 한 번 모든 분들께 감사의 말씀을 전하고 싶습니다.
