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Predictable incorporation of nitrogen into carbon dots: insights from pinacol rearrangement and iminium ion cyclization.

ABSTRACT: Nitrogen-doped carbon dots (CDs) have attracted considerable attention across various research areas and applications due to their enhanced optical properties and photostability. However, the mechanism of nitrogen incorporation in CDs remains elusive, hampering the precise control over nitrogen-incorporated structures and the investigation of the effects of nitrogen on the electronic structure and optical properties of CDs. In this study, we employed a rational design approach, utilizing glucosamine and ethylene glycol as the carbon source and co-reagent, respectively, to synthesize N-doped CDs. Our synthesis strategy involved pinacol rearrangement and iminium ion cyclization reactions, enabling the reliable formation of N-doped CDs. Notably, the resulting CDs exhibited distinctive emissive states attributed to heteroatomic defect structures, including oxygenic and nitrogenic polycyclic aromatic hydrocarbons. To gain further insights into their energy levels and electronic transitions, we conducted comprehensive investigations, employing extended Hückel calculations and pump-probe spectroscopy. The synthesized CDs displayed great promise as bioimaging and photodynamic therapy agents, highlighting their potential for biomedical applications. Moreover, our study significantly contributes valuable insights into the rational design of N-doped CDs with controllable chemical and electronic structures, thereby paving the way for advancements in their diverse range of applications.

SUBMITTER: Cho S

PROVIDER: S-EPMC10563847 | biostudies-literature | 2023 Oct

REPOSITORIES: biostudies-literature

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Predictable incorporation of nitrogen into carbon dots: insights from pinacol rearrangement and iminium ion cyclization.

Cho Soohyun S Jung Chan-Woo CW Lee Dajin D Byun Yerim Y Kim Hyemin H Han Hyunho H Kim Ji-Hee JH Kwon Woosung W

Nanoscale advances 20230921 20

Nitrogen-doped carbon dots (CDs) have attracted considerable attention across various research areas and applications due to their enhanced optical properties and photostability. However, the mechanism of nitrogen incorporation in CDs remains elusive, hampering the precise control over nitrogen-incorporated structures and the investigation of the effects of nitrogen on the electronic structure and optical properties of CDs. In this study, we employed a rational design approach, utilizing glucosa ...[more]

PMID: 37822896

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Project description:The current research mainly focuses on transforming low-quality waste into value-added nanomaterials and investigating various ways of utilising them. The hydrothermal preparation of highly fluorescent N-doped carbon dots (N-CDs) was obtained from the carboxymethylcellulose (CMC) of oil palm empty fruit bunches and linear-structured polyethyleneimines (LPEI). Transmission electron microscopy (TEM) analysis showed that the obtained N-CDs had an average size of 3.4 nm. The N-CDs were monodispersed in aqueous solution and were strongly fluorescent under the irradiation of ultra-violet light. A detailed description of the morphology and shape was established using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was shown that LPEI were successfully tuned the fluorescence (PL) properties of CDs in both the intrinsic and surface electronic structures, and enhanced the quantum yield (QY) up to 44%. The obtained N-CDs exhibited remarkable PL stability, long lifetime and pH-dependence behaviour, with the excitation/emission maxima of 350/465.5 nm. Impressively, PL enhancement and blue-shifted emission could be seen with the dilution of the original N-CDs solution. The obtained N-CDs were further applied as fluorescent probe for the identification of Cu2+ in aqueous media. The mechanism could be attributed to the particularly high thermodynamic affinity of Cu2+ for the N-chelate groups over the surface of N-CDs and the fast metal-to-ligand binding kinetics. The linear relationship between the relative quenching rate and the concentration of Cu2+ were applied between 1-30 µM, with a detection limit of 0.93 µM. The fluorescent probe was successfully applied for the detection of Cu2+ in real water. Moreover, a solid-state film of N-CDs was prepared in the presence of poly (vinyl alcohol) (PVA) polymer and found to be stable even after 72-h of continuous irradiation to UV-lamp. In contrast to the aqueous N-CDs, the composite film showed only an excitation independent property, with enhanced PL QY of around 47%. Due to the strong and stable emission nature of N-CDs in both aqueous and solid conditions, the obtained N-CDs are ideal for reducing the overall preparation costs and applying them for various biological and environmental applications in the future.

Project description:In this work, we studied the combination of nitrogen-doped carbon quantum dots (N-CQD), a hydroxide-ion conducting ionomer based on polysulfone (PSU) and polyaniline (PANI), to explore the complementary properties of these materials in high-performance nanostructured electrodes for the oxygen reduction reaction (ORR) in alkaline solution. N-CQD were made by hydrothermal synthesis from glucosamine hydrochloride (GAH) or glucosamine hydrochloride and N-Octylamine (GAH-Oct), and PSU were quaternized with trimethylamine (PSU-TMA). The nanocomposite electrodes were prepared on carbon paper by drop-casting. Furthermore, we succeeded in preparing PSU-TMA + PANI + GAH-Oct fibers by electrospinning. The capacitance of the electrodes was investigated by cyclic voltammetry and impedance spectroscopy, which gave similar trends. The ORR was investigated by linear sweep voltammetry at rotating disk electrode speeds between 250 and 2000 rpm in an oxygen-saturated 1 M KOH solution. Koutecky-Levich plots showed that four electrons were exchanged for nanocomposite electrodes containing CQD. The highest reduction currents were measured for the electrodes containing GAH-Oct. The Tafel plots gave the lowest slope and the most positive half-wave potential for PSU-TMA + PANI + GAH-Oct fibers. The best electrocatalytic activity of this electrode could be related to the high amount of graphitic nitrogen in GAH-Oct. Long-term cycling tests showed no significant modification of the onset potential, but a change of the current in the mass transport limited region, indicated the evolution of the microstructure of the nanocomposite ORR electrode modifying the mass transport conditions during the first 400 cycles before reaching stationary conditions. FTIR spectra were used to study possible electrode degradation after the ORR in 1 M KOH: the only change was due to the reaction of PANI emeraldine salt to emeraldine base, whereas the other constituents of the multiphase electrode did not show any degradation.

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Predictable incorporation of nitrogen into carbon dots: insights from pinacol rearrangement and iminium ion cyclization.

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Predictable incorporation of nitrogen into carbon dots: insights from pinacol rearrangement and iminium ion cyclization.

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