- 7주 전
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학습트랜스크립트
00:00Hi, my name is Eun Cho, and I am studying 2D nanomaterial, called Maxine, under the supervision of Professor Yongsuk Chan.
00:10Today, I will talk about my research in-situ growth of GQD within Maxine interlayers via two-step hydrothermal method for enhanced lithium-ion supercapacitor performance.
00:25Here is the contents for this lecture.
00:29I would like to start by introducing a study that strongly influenced the conceptual direction of my research, the 2024 ACS Nanopaper by Liang and colleagues, where they developed an interlayer engineering strategy for Maxine based on in-situ carbon nanostructure growth.
00:54What stood out to me in this work was not simply the results, but the fundamental mechanism they proposed for manipulating the Maxine interlayer environment.
01:06Maxine naturally consists of tightly bonded tuted layers, separated by weak Van der Waals gaps.
01:15These interlayer spaces are extremely important because they determine how ions move, how electrons travel across layers, and how stable the overall structure becomes during electrochemical reactions.
01:30However, a critical limitation of Maxine is that electron transport in the vertical direction is much less efficient than transport along the basal plane.
01:45In addition, the layers tend to collapse and restack, closing the galleries and limiting ion accessibility.
01:54Liang approached this challenge through a simple but powerful idea.
02:01Instead of inserting pre-made carbon nanostructures, what if carbon nanostructures could be grown directly inside the Maxine interlayer?
02:11To accomplish this, they intercalated molecular precursors, metallos and ions, into the Maxine galleries through electrochemical intercalation.
02:24Because the electric potential precisely controls how deeply and uniformly charged species insert into Maxine,
02:33the Earths were able to confine these precursors between layers.
02:40When the material was later heated, these confined precursors decomposed and produced carbon nanotubes in situ, right inside the Van der Waals gaps.
02:54This mechanism was fascinating to me for two reasons.
02:59First, it showed that the Maxine interlayer is not just a passive space, but a chemically active and structurally confined environment where controlled reactions can take place.
03:14Second, the carbon nanotubes that formed between layers acted as anchored spacers and conductive bridges.
03:25In other words, the Earths demonstrated that interlayer spaces do not have to be passive intercalons.
03:32They can be deliberately formed inside the galleries to tune Maxine's electronic and structural behavior.
03:42This concept immediately connected to my own interests.
03:47I had been exploring ways to prevent Maxine restacking and to enhance its charged transport pathways.
03:55However, inserting large nanostructures like graphene quantum dots directly into the interlayer is physically impossible due to size constraints.
04:07Leon's work showed me a pathway around that limitation.
04:13If the final nanostructure is too large to insert, you can instead insert small molecular precursors and grow the desired structure in situ inside the Maxine interlayer.
04:26That principle became the starting point of my research.
04:33I asked myself, what if I intercalate small water-soluble precursors like citric acid and urea into Maxine and then use hydrothermal treatment to grow graphene quantum dots in situ between the layers.
04:48Inspired by Liang's mechanism, I realized that graphene quantum dots could play a similar role to carbon nanotube, not in morphology but in function.
05:03If graphene quantum dots form inside the interlayer, they could act as conductive sites to improve charge transport, provide additional surface area for electrochemical reactions, and physically prevent restacking of Maxine layers by serving as interlayer anchors.
05:25This conceptual link precursor intercalation to confined space reactions to in-situ growth to interlayer engineering is directly borrowed from Liang's strategy.
05:41Their work validated the idea that controlled chemical synthesis can happen inside the Maxine interlayer, and this gave me the confidence to pursue an in-situ graphene quantum dot growth approach instead of relying on traditional mixing or coating strategies.
06:02In summary, this paper provided a new way of thinking about the Maxine interlayer, not as a fixed structure gap, but as a tunable chemical reaction vessel.
06:15It demonstrated that by placing the right precursors inside this confined space, we can create entirely new carbon-based architectures that fundamentally reshape Maxine interlayer.
06:30This mechanism directly inspired the core strategy of my own research, where I aim to intercalate graphene quantum dot precursors and grow graphene quantum dots within Maxine layers to create stable, conductive, and expanded Maxine interlayer structures suitable for high-performance energy storage.
06:59Next, I would like to introduce the overall objective and scientific motivation of my research.
07:11My study focuses on engineering the interlayer environment of Maxine by inserting molecular precursors and inducing the in-situ growth of graphene quantum dots.
07:24The core idea behind this strategy is that graphene quantum dots possesses intrinsically high electrical conductivity and a large accessible surface area.
07:37Therefore, once they are formed between Maxine layers, they can significantly enhance charge transport pathways, provide additional electrochemically active sites, and simultaneously prevent undesired restacking, one of the most critical issues that limits the performance of Maxine-based energy storage devices.
08:02However, a major challenge arises from the fact that the latter dimensions of conventionally synthesized graphene quantum dots typically exceed 10 nanometers.
08:17This makes physically insertion of preformed graphene quantum dots into the Maxine interlayer realistically impossible.
08:24To overcome this limitation, my approach is to first intercalate small molecular precursors, citric acid and urea, into Maxine galleries, and then utilize a bottom-up hydrothermal reaction to grow graphene quantum dots in-situ.
08:45Through this method, the newly formed graphene quantum dots are expected to occupy fixed anchored positions between the Maxine sheets, effectively functioning as spacer units that modulate the interlayer spacing and improve structural stability.
09:06Since my research fundamentally depends on controlling and understanding Maxine's interlayer spacing, it is essential to clearly define what this term means.
09:24Interestingly, the paper shown here uses a definition that differs from what is commonly described in the broader Maxine literature.
09:34According to this paper, the commonly referenced to 10 Ohmstrang distance is actually the de-spacing, not the true interlayer de-spacing.
09:47They claim that the interlayer spacing should be calculated by subtracting the physical thickness of the Maxine sheets from the de-spacing value.
10:00If we strictly follow this definition, then inserting molecules larger than approximately 5 Ohmstrang, including citric acid and urea, should be structurally impossible.
10:18This, of course, contradicts the physical reality observed in many intercalation-based Maxine studies and would undermine the very mechanism of my research.
10:33Therefore, it became necessary to re-examine the definitions used in high-quality Maxine literature and establish a more widely accepted standard.
10:52Because the paper in the previous slide had relatively low impact factor and insufficient citations, I investigated additional authoritative references.
11:05A significant number of highly cited Maxine papers, particularly those focusing on interlayer engineering, commonly report Maxine interlayer spacing values exceeding 1 nm.
11:20The example shown here, a paper with over 800 citations and a high impact factor, demonstrates the intercalation of CTAB, a cationic surfactant.
11:38Although the authors do not provide a formal definition of interlayer spacing, figure H clearly indicates that the interlayer distance is approximately 1.3 nm.
11:53This aligns well with the more conventional understanding used in the Maxine research community and supports the definition I adopted in my study.
12:06Next, I would like to show the SAM and EDS results of the Maxine plus NGQD samples.
12:17In the SAM images, many flakes exhibit morphology corresponding to few layer or even single layer Maxine, indicating that the exfoliation process was successful.
12:34Although the characteristic layered architecture of Maxine is not very distinctly visible in this particular sample set, I plan to capture additional images from other batches to further support this observation.
12:51The EDS-Elementron mapping provides another important clue.
12:58Nitrogen is distributed relatively uniformly across the Maxine sheets.
13:05While some portion of the nitrogen signal may originate from atmospheric nitrogen, the homogeneous distribution strongly suggests that nitrogen-rich species, such as rare-derived intermediates or nitrogen-doped graphene content dust, have been incorporated throughout the Maxine structure.
13:30Of course, SAM-based morphology analysis has inherent limitations in quantum dot research, and therefore this observation will be supported with structural and spectroscopic analysis in later slides.
13:49To verify graphene quantum dot formation through the hydrothermal process, I conducted UVB spectroscopy.
14:02Because Maxine tends to obscure or flatten the spectral features of graphene quantum dots, I synthesized graphene quantum dots separately for this measurement.
14:15The UVB spectrum shows two essential features.
14:20A strong absorption peak around 250 nm corresponding to aromatic C-C-Pi-Pi transition, and a second peak near 313 nm associated with nitrogen and oxygen-containing surface states.
14:41These distinct features clearly differ from the spectra of pure citric acid or urea, confirming that graphene quantum dots were successfully synthesized under the conditions used in mymaxine system.
14:59This serves as one of the primary pieces of evidence supporting in-situ graphene quantum dot formation.
15:06Moving on to structure analysis, I performed XRD measurements on the Maxine plus nitrogen-doped graphene quantum dot samples.
15:21Although the overall intensity was relatively low and the noise level was high, the critical 002 peak of Maxine is clearly present.
15:36This confirms that the Maxine structure is successfully preserved after undergoing the hydrothermal friction.
15:45More importantly, the interlayer spacing shows a distinct expansion.
15:51While Pristine Maxine exhibits a deep spacing of approximately 11.7 Ohm, the Maxine plus nitrogen-doped graphene quantum dot sample displays an expanded spacing of 13.3 Ohm.
16:13This suggests that graphene quantum dots, or at least the precursor molecules, have intercalated into the Maxine galleries and contributed to increasing the interlayer distance.
16:28However, because the hydrothermal reaction involves citric acid and urea, the increased spacing may be partially due to precursor intercalation rather than fully formed graphene quantum dots.
16:43To address this ambiguity, I plan to rely on high-resolution TAM and additional spectroscopic evidence to directly visualize the graphene quantum dots within the interlayer spaces.
17:02Here, I analyzed the Maxine plus nitrogen-doped graphene quantum dots sample using Raman spectroscopy to further confirm the formation of carbon-based nanostructures and the preservation of the Maxine framework.
17:20First, looking at the low wave number region on the left, we can observe several characteristic Maxine peaks.
17:32Maxine typically shows strong vibrational modes below 800 wave number corresponding to TI2C and TI2O related lattice vibrations.
17:47In this spectrum, these Maxine peaks are still present, indicating that the Maxine structure remains intact even after hydrothermal reaction used for an in-situ graphene quantum dot formation.
18:03Next, in the higher wave number region shown on the right, we see two broad features that correspond to the D-band and G-band, which are signatures of graphitic carbon.
18:18The G-band, located around 1580 wave number, represent the in-plane vibrational modes of sp2-bonded carbon.
18:33The D-band, typically near 1350 wave number, arises from disorder, edge sites, or defect within the carbon structure.
18:45The presence of both bands strongly suggests the formation of graphitic domains, consistent with nitrogen-doped graphene quantum dots synthesized from citric acid and urea.
18:59Importantly, the appearance of these D-band and G-bands, along with the preserved Maxine peaks, supports our assumption that the graphene quantum dots were successfully generated during the hydrothermal treatment and coexist with the Maxine layers.
19:18Although the spectrum shows relatively broad and noisy peaks, which is expected for quantum dot structures due to their small domain size and defect-rich nature,
19:29the Raman signatures provide solid evidence for carbonization and successful graphene quantum dot formation inside the Maxine system.
19:38Moving forward, I will compare this spectrum with Pristine Maxine and separately synthesized graphene quantum dots to further deconvolute peak contributions and strengthen the structure analysis.
19:54Finally, these are the electrochemical performance results.
20:01I am currently optimizing the reaction conditions and electrode composition, and among the tested ratios, the best-performing sample exhibited more than twice the capacitance of Pristine Maxine.
20:16This strongly indicates that interlayer engineering via in-situ graphene quantum dot growth can substantially enhance charge storage behavior.
20:30However, the cycling stability results show that the performance begins to degrade rapidly after approximately 200 cycles.
20:42Because long-term stability is critical for supercapacitor applications, I am actively adjusting synthesis parameters, electro-preparation methods,
20:54and mass loadings to identify the underlying cuts and achieve more robust stability.
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