Date of Award
5-2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
Committee Chair/Advisor
Dr. Ya-Ping Sun
Committee Member
Dr. Shiou-Jyh Hwu
Committee Member
Dr. Rhett Smith
Committee Member
Dr. Jason McNiell
Abstract
Carbon dots (CDots) are small carbon nanoparticles (CNPs) with effective surface passivation. The effective passivation has been achieved by the surface functionalization of pre-existing CNPs with organic molecules, mostly molecules containing primary or secondary amine moieties. In the studies highlighted in this dissertation, CNPs were functionalized by selected organic molecules, including especially the use of radical addition reactions, to generate CDots with strong absorption and bright fluorescence emissions. A good demonstration of the approach was the N-ethylcarbazole (NEC) radical addition to CNPs under microwave irradiation. Spectroscopy and microscopy methods were employed to characterize the resulting NEC-CDots, and the results showed that optical properties of NEC-CDots are largely the same as those of other CDots with other surface functionalization schemes, suggesting that the surface functional species do not substantially alter the intrinsic electronic transitions in CNPs. Also, the photoexcited state properties of NEC-CDots in solution and in poly(N-vinylcarbazole) polymer matrix were compared for an evaluation on the potential of the CDots in optoelectronic applications. More significantly, the structure of NEC-CDots was revealed successfully by NMR and microscopy characterization.
The classically defined CDots such as NEC-CDots are prepared from pre-existing CNPs, and their optical absorptions are largely unchanged from those of the CNPs, which are characterized by progressively decreasing absorptivity toward longer wavelengths in the visible spectrum, and correspondingly the observed progressively lower fluorescence emission quantum yields. Therefore, CDots are generally weak optical absorbers and also emitters in the red/near-IR spectral region. However, it was claimed in the literature that “red/near-IR carbon dots” could be synthesized by one-pot thermal carbonization under mild processing conditions of the selected handful of colorless organic precursors, specifically mixtures of citric acid with formamide or urea. Dot samples of similar spectroscopic features have even been marketed commercially. However, as found in the investigations highlighted in this dissertation, the experimental evidence shows unambiguously that the claimed “red/near-IR carbon dots” are simply organic mixtures containing only a small amount of non-molecular nano-carbons but some red/near-IR absorbing and emitting organic dyes from thermally induced chemical reactions of the specific organic precursors.
Also discussed in this dissertation are the current rapid advances and expansion of the carbon dots research field, including the excellent opportunities for further development both fundamentally and technologically and also the worrisome issues or myths.
Recommended Citation
Liang, Weixiong, "Carbon "Quantum" Dots: Structures, Properties, and Issues" (2024). All Dissertations. 3644.
https://open.clemson.edu/all_dissertations/3644