Academic literature on the topic 'Carbon nanodot'

The study was set out to explore the synthesis of Carbon Nanodots (CDs) and their potential in practical applications in lighting, sensing and biological areas. Toxicity evaluation was also involved in the investigation, because of its profound importance in the real-world applications of CDs. The study sought to answer the following questions: 1) how does the photoluminescence change when we vary the surface functional moieties and change the chemical compositions by doping? 2) For light applications, are the CDs stable enough under the operational conditions? If not, how to improve their stability? 3) How to impart sensing capabilities to CDs through surface design? 4) Are CDs really non-toxic? How does their toxicity change when surface functional groups vary? Through a series of studies, namely 1) salt-encapsulation for enhancing UV- and thermostability; 2) Transparent, yellow-emitting CD films for white light LEDs; 3) Amine-rich CDs for sensing amphetamine precursors; 4) Biocompatible CDs exhibiting antiproliferative activities, I have demonstrated that the emission of the CDs are controllable by modifying the particles surface moieties, and the excitation dependency of the emission can be refined by either fractionation or purification. Despite of what is often reported about the toxicity of CDs, the toxicity of the CDs depends on the surface functional groups of CDs and the biological entities. However, the toxicity of the CDs may be utilized as a therapeutic purpose. Further demonstration on the lighting and sensing may project the bright future of carbon based nanoparticles as an excellent candidate for these applications.<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy (PhD)<br>Griffith School of Engineering<br>Science, Environment, Engineering and Technology<br>Full Text

Carbon Nanodots (CDs) are a new protagonist of carbon-based nanoscience by which the paradigm of carbon as a black material unable to emit light has been completely revolutionised. They have been emerging as a new frontier in Nanoscience at the beginning of 2000s, and their potential is evident from the explosion of the number of studies, now ranging in the thousands per year. CDs are nanoparticles composed by carbon, oxygen and hydrogen with a size smaller than 10 nm. Their most important hallmark is their strong luminescence, which is combined with many additional benefits as the low cost and ease of synthesis, the high water solubility, the biocompatibility and non-toxicity, the great sensitivity to the external environment, and a marked electron donating and accepting capabilities. The combination of all of these characteristics guarantees the possibility to use CDs in a very broad range of applications which encompasses many different fields as optoelectronics or sensing. Actually, the term CDs includes nanomaterials which display a wide range of possible structures and variable optical properties. Indeed, in the literature, it is common to find different sub-types of CDs: they can be graphitic, amorphous, disks of graphene or with a C3N4 core; they can be hydrophilic or hydrophobic; they can emit blue, green, or red light; their emission can be independent of the excitation wavelength, or more commonly tunable (peak of the emission depends on the excitation wavelength); their fluorescence intensity can be sensitive to one particular ion in solution or they respond to a variety of interactions with other systems, such as carbon nanotubes. Besides, CDs can be synthesized by many different procedures which yield subtypes of CDs capable of emitting fluorescence at different wavelengths. In all the synthesis approaches, their surface is passivated by external agents to get bright emission. All of this leads to the existence in the literature of diverse sub-types of CDs with different core and surface structure, and different specific optical characteristics. Despite of this, there are common characteristics which are recurrent almost in every type of CDs as the small size and the core+corona structure which are found to be crucial to obtain CDs with a visible photoluminescence with a high emission efficiency. Carbon dots research is still in a developing phase despite thousands of studies have already been published on the subject, and several scientific open questions exist about their optical behaviour, the fundamental nature of the electronic states, the key factors determining their bright fluorescence, and the relation between structure and emission. As a consequence, a large effort is in progress to find the most effective ways to tailor them for specific applications. In this Thesis, we carried out an investigation of the fundamental physics of different families of CDs with the aim to achieve an exhaustive understanding of their entire photocycle from femtosecond to the steady state. To do this, it was necessary to relate the optical properties to the structural ones, and to study the influence of various possible interactions with external agents. Thus, electronic transitions of CDs having different structures or exposed to different environments have been studied by the combined use of several experimental techniques. In particular, as an important novelty in the field, a variety of new methods which involve ultrafast spectroscopic techniques have been used. Ultrafast spectroscopy is a powerful tool to investigate in real time electronic and vibrational processes with picosecond and femtosecond time resolution. With the use of these methods it was possible to map the photocycle of CDs revealing several dynamics which occur on short time scale as solvation, charge transfer, and fluorescence quenching.

Cette thèse vise à développer de nouveaux matériaux hybrides pour les applications en électrochimiluminescence. Les propriétés électrochimiluminescentes de nouveaux complexes de Pt(II) et d’Ir(III) ont été explorés comme alternative aux marqueurs existants. En plus, la combinaison de complexes et de carbon nanodots portant des groupes primaires ou tertiaires à la surface comme espèces coréactives a abouti à une stratégie intéressante pour éliminer la TPrA. Les carbon nanodots dans un systéme lié par liaison covantent avec complexes métalliques sont non seulement un support innocent pour les espèces actives d’ECL, mais agissent également comme coréactif, se révélant être une plateforme auto-améliorante en ECL. Enfin, un véritable immunoessai pour la détection des marqueurs cardiaques a été mis au point avec une sensibilité et une stabilité accrues pour les applications de détection biologique et biomédicale. La même technologie peut alors être appliquée à une variété d’autres analytes, ouvrant ainsi le site à d’autres dosages<br>This doctoral dissertation aim to develop new hybrid materials for ECL applications. In the field of metal complexes, the electrochemiluminescent properties of new Pt(II) and Ir(III) complexes were investigated as alternative of existing complexes. Passing to nanomaterials, the combination of labels and NCNDs bearing primary or tertiary groups on the surface as alternative co-reactant species resulted an interesting strategy to eliminate the toxic TPrA. In particular, NCNDs in covalently linked system with metal complexes is not only an innocent carrier for ECL active species, but act also as co-reactant in the ECL process, revealing itself an ECL self-enhancing platform. Finally, a real immunoassay for cardiac marker detection has been built with enhanced sensitivity and stability, which is of fundamental importance for biological and bio-medical detection applications. The same technology can be applied to a variety of other analytes opening the venue to other assays

Fluorescent carbon dots (C-dots) are well known for their low cell-cytotoxicity, biocompatibility, low preparation cost, excitation dependent photoluminescence, and excellent photostability. Typically, raw C-dots have low quantum efficiency and thus researchers have been utilizing biocompatible polymers such as polyethylene glycol (PEG) as a passivation agent in order to increase fluorescence signal. In this work, we report fluorescent self-passivated carbon nanodots (CNDs) synthesized from PEG by using it as a carbon source as well as a passivating agent. Importantly, the addition of graphene quantum dots (GQDs) during the synthesis of self-passivated CNDs can tune photoluminescence property. The results of bioimaging and cytotoxicity test of self-passivated CNDs hold promises for biomedicine applications.

Biological tissues are compositionally and structurally exquisite – a complex network of proteins and cells organised with molecular-precision. Unfortunately, in the absence of an organ transplant or tissue graft, there are no technologies that can completely repair or restore this complex system when it fails. With the hopes of regenerating failing tissue, tissue engineers have developed scaffold structures able to support cell life. As yet, these structures are unable to recreate the complexities of the biological environment, limiting the success of this approach. Nanotechnologies have realised methods to make materials with defined nanoscale properties. Continued research may lead to sophisticated nanobiomaterials, with properties that rival the complexities of biological environments and improve tissue regeneration. To this end, we explored the use of carbon nanotubes (CNTs) within the field of tissue engineering. We investigated the use of 3D CNT scaffolds in bone tissue engineering using strong and porous ceramic scaffold structures coated with CNTs. We abate limitations in previous fabrication methods limiting coating of CNTs throughout porous structures. We demonstrate these surfaces are high quality aligned CNTs, are non toxic and able to support attachment, spreading and proliferation of adipose derived stem cells (ASCs) and human osteoblasts. Following the development of a 3D CNT material, we investigated the potential for using CNTs to create well-defined nanoenvironments capable of regulating cell differentiation. This research is the first report of non-biased quantitative measurement of cell shape during long term differentiation. In contrast to previous techniques, it allows direct measurement of shape rather than that of the underlying substrate. This approach offers novel insights into the relationship between the nanoenvironment, cell shape and cell differentiation. The novel nanomaterials presented in this thesis, demonstrate the potential of nanotechnologies for artificially engineered tissues and organs. Continued research of nanomaterials promises to better recreate the complexities of the biological environment, instructing healthy regenerative processes and promoting tissue function.

>Magister Scientiae - MSc<br>Currently, non-renewable sources are mostly used to meet the ever-growing demand for energy. However, these sources are not sustainable. In addition to these energy sources being not sustainable, they are bad for the environment although the energy supply sectors highly depend on them. To address such issues the use of renewable energy sources has been proven to be beneficial for the supply of energy for the global population and its energy needs. Advantageous over non-renewable sources, renewable energy plays a crucial role in minimizing the use of fossil fuel and reduces greenhouse gases. Minimizing use of fossil fuels and greenhouse gases is important, because it helps in the fight against climate change. The use of renewable energy sources can also lead to less air pollution and improved air quality. Although solar energy is the most abundant source of renewable energy that can be converted into electrical energy using various techniques, there are some limitations. Among these techniques are photovoltaic cells which are challenged by low efficiencies and high costs of material fabrication. Hence, current research and innovations are sought towards the reduction of costs and increasing the efficiency of the renewable energy conversion devices.

Carbon-based nanomaterials have attracted significant attention due to their unique optical, electrical, thermal and mechanical properties. In recent years, a large number of carbon-based nanomaterials have been investigated including carbon nanotubes, graphitic carbon nitride (g-C3N4), graphene, carbon nanofibers, carbon nanodots (CNDs), heteroatom-doped carbon, and carbon-based materials obtained from biomass etc. The unique and superior properties of such carbon-based materials make them useful for a wide range of applications in the fields such as environmental remediation and energy conversions. Although significant progress has been made over the past decade or so, few drawbacks of carbon-based materials still remain unresolved. For example, as a photocatalyst, the weak van der Waals interactions between adjacent conjugated planes of g-C3N4 and poor electronic properties affect negatively on the photocatalytic activity. Despite a variety of synthetic methods have been investigated, to fabricate undoped and doped carbon-based materials, the efficiency and level of control on the resultant products are far from satisfactory. Majority of these approaches either involve tedious and complex experimental procedures or require using harsh reaction conditions, or possessing low yield production. Furthermore, to achieve heteroatom-doped carbon-based materials, the reported approaches almost exclusively require the use of synthetic chemicals as carbon and heteroatom sources, respectively. The large-scale application of fuel cells and dye-sensitized solar cells (DSSCs) using Pt-based catalysts is hindered by the inherent disadvantages of Pt such as high cost, scarcity and low resistance to crossover effect of methanol molecule. It is therefore highly desirable to realize heteroatom doping by simple, low-cost, high yield and environmentally benign synthesis methods for fabrication of commercially viable carbon-based materials for applications in solar cells and fuel cells.<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy (PhD)<br>Griffith School of Environment<br>Science, Environment, Engineering and Technology<br>Full Text