(1) We note that the TEM images for the carboxylated nanocellulose fiber (C-NCF) sample given in published article (Figure S1d and S1e, Supporting Information) are ambiguous due to its short length morphology resulted from an experimental error that occurred in the batchwise preparation. We regret for this error and we have provided the reimaged TEM data (Figure 1) for the C-NCF sample. Although the length is not on the micrometer scale, the calculation of percentage crystallinity from the XRD pattern in the published article (Figure S5, Supporting Information) supports the fibrous nature nanocellulose. Figure 1. TEM image of C-NCF stained with 1% PTA. (2) We understand that the sheet-like appearance that is observed in the low-magnification TEM analysis of the C-NCF/Ag⁺ system appeared to be unclear (Figure 4a in the original article). However, consistently similar observations were made each time for a different batch of samples. We presume that the sheet-like morphology is probably originated from the associated nature of the C-NCF when combined with Ag⁺ ions. The finer the fiber, the more flexible it is, and numerous C-NCFs not only easily entangle but also are capable of closer packing and internanofibril association. In addition, the negative surface charges of the C-NCF may get neutralized to some extent by the anchoring of Ag⁺ ions present in the medium, which lessens the Van der Waal’s repulsion between individual fibers and assembles them into sheet-like C-NCF/Ag⁺ bundled morphologies. This assumption is further supported by the HR-TEM images obtained from PTA-stained C-NCF/Ag⁺ samples, as shown in Figure 2. However, the particles that formed on cellulose fibers pose problems for further magnifying images under high-resolution TEM. Figure 2. TEM images of aligned C-NCF fiber bundles in the C-NCF/Ag⁺ system imaged after staining with PTA. (3) In a few cases, the TEM images presented in Figure 1a and Figure 5 of the original article showed coiled nanostructures at the periphery of the C-NCF samples. A recent report by Toth et al.(1) has demonstrated the possibility that the electron-beam-induced damage and the subsequent carbonization resulted in the formation of coiled nanostructures under high vacuum conditions.(1) With TEMPO-oxidized C-NCFs being a carbonaceous fragile material, the coiled structural features could therefore possibly originate under high electron beam irradiation. To check whether there is any possibility of the presence of carbon fiber or graphene in our original samples (that were used for TEM analysis), we performed a Raman spectroscopy analysis of C-NCF/Ag⁺ and C-NCF/Ag⁺/TiO₂ samples and compared that with the C-NCF/rGO sample under similar probing conditions. The results are presented in Figure 3a. Black, red, and blue spectra were obtained for C-NCF/rGO, C-NCF/Ag⁺, and C-NCF/Ag⁺/TiO₂, respectively. The Raman spectrum of the C-NCF/rGO sample features D and G Raman bands positioned at 1335 and 1593 cm^–1, respectively, characteristics of graphene-related structures, whereas, the absence of band peaks in the other two systems indicates that graphitic carbon nanostructures were initially absent in the C-NCF/Ag⁺ and C-NCF/Ag⁺/TiO₂ samples that were used for the TEM analysis. Figure 3. (a) Raman spectra of: (1) C-NCF/rGO, (2) C-NCF/Ag⁺, and (3) C-NCF/TiO₂/Ag⁺ systems under laser power of 1 mW. (b) Raman patterns for C-NCF/Ag⁺ acquired with increasing order of laser power: (1) 1 mW, (2, 3, 4) >4 mW. (5) Raman spectrum of C-NCF/rGO acquired under laser power of 1 mW (given for comparison). Laser wavelength, 633 nm. Nevertheless, considering the report by Lee et al.,(2) who highlighted the possibility of graphitization under laser beam irradiation, we studied the effects of different lasing conditions of Raman analysis and present them in Figure 3b. Here we have noticed a gradual emergence of D and D** bands upon high power laser irradiation (>4 mW), indicating the transformation of C-NCF/Ag⁺ to graphitic structures (Figure 3b, spectra 2, 3, and 4). The increased intensity of the D and D** bands at higher laser power (Figure 3b, spectrum 4) suggests the emergence of graphitic structures but with highly disordered features. The appearance of peaks at 1505 cm^–1 corresponds to D** being attributed to the formation of more defective graphitic nanostructures or amorphous carbon.(3) The Raman spectrum of C-NCF/rGO acquired under laser power of 1 mW is also shown for the purpose of comparison. These results suggest that the C-NCFs used in our study are vulnerable to electron beam damage, and hence one cannot rule out the possibility of graphitization during HR-TEM imaging. Interestingly, similar observations were reported for the possible graphitization phenomenon that happened during the HR-TEM imaging of cellulose under a high energy electron beam.(2,4,5) It is reported that high energy beams could introduce an upsurge in the local surface temperature in the range of 1000–2000 K that may cause local damage to samples.(6) Considering these possibilities, electron beam damage would occur to form graphite nanostructures during the HR-TEM imaging of the cellulose samples (having a low thermal decomposition temperature), resulting in the formation of coiled nanostructures. This is not surprising because the maximum energy transfer to a carbon atom even under 60 keV electron beam irradiation is ∼10.8 eV, which is higher than the bonding energy of hydrogen bonds (0.5 eV) and the activation energy for cellulose depolymerization (2.68 eV).(4,5) As a result, the high energy of the electron beam is more likely to break the intermolecular hydrogen bonds that hold β (1→4) glucan chains together. Furthermore, the C-NCF possesses several hydroxyl and carboxyl groups that evaporate to keep the temperature from rising during heating. This assumption is further supported by Raman studies (Figure 3b) and TGA results (Figure 4). The results indicate that a higher laser power could induce the emergence of D and G bands, suggesting the transformation of the C-NCF to graphitic carbon-like nanostructures. Our observation on the C-NCF/Ag⁺/TiO₂ sample is in agreement with the previous reports, suggesting that the as-prepared C-NCF is composed of randomly curved graphene layers.(7,8) Thus the HR-TEM imaging performed under a high-intensity electron beam would probably result in coiled structures due to thermal heating at the edges of the C-NCF bundles, as observed in our report. Figure 4. TGA and DTG curves of C-NCF acquired under an argon atmosphere with a heating rate of 10 °C. (4) Furthermore, we performed a TEM analysis of negative stained samples after the introduction of additives. The results are consolidated in Figure 5. It can be seen that the attempts to image the C-NCF sample after staining prove the existence of the C-NCF. It is however not possible to make a more precise determination of the structures based on the available data since the ambiguous effects of both stain and additives, making the interpretation more challenging. (5) Summary: This research investigation attempted to resolve the lattice structure of a C-NCF in the presence of Ag⁺/rGO without using negative staining by HR-TEM imaging. The loss of crystallinity of the C-NCF structure caused by beam irradiation was also observed during this study. Unfortunately, carbonization and graphitization are frequently confused even today, leading to questionable interpretation issues. Our results revealed that some of the carbon in the C-NCF could be graphitized with high-intensity electron beam irradiation during HR-TEM imaging (and Raman experiments with different lasing conditions), where microstructural changes have taken place. We assume that the fringes that are evident in the HR-TEM images are edge-on views of the graphite-like layers of carbon. The enhanced contrast is achieved by the electron dense nature of and the stabilizing effect of these additives. Further research is necessary for the fundamental understanding of structural transformations during cellulose conversion to graphitic carbon with a high-intensity electron beam using EELS combined with Raman spectroscopy or X-ray diffraction studies. Our methodology could be further extended as a suitable approach for producing conductive graphitic carbon and could find potential applications like flexible electronic devices and sensors. Figure 5. TEM images of three systems stained using 1% PTA taken under TEM: (a) C-NCF/rGO, (b,c) C-NCF/Ag⁺, and (d and e) C-NCF/Ag⁺/TiO₂. K.N. is thankful for financial support from UGC grant and R.T.T. from KSCSTE Postdoctoral fellowship (KSCSTE/309/2018- PDF). This study was supported by CSIR grants. This article references 8 other publications.

中文翻译：

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更正“羧化纳米纤维素纤维中晶畴的直接可视化”

(1) 我们注意到，已发表文章（图 S1d 和 S1e，支持信息）中给出的羧化纳米纤维素纤维 (C-NCF) 样品的 TEM 图像不明确，因为其长度较短的形态是由实验错误导致的分批制备。我们为这个错误感到遗憾，我们提供了 C-NCF 样品的重新成像 TEM 数据（图 1）。尽管长度不是微米级，但根据已发表文章（图 S5，支持信息）中的 XRD 图案计算结晶度百分比支持纤维性质的纳米纤维素。图 1. 用 1% PTA 染色的 C-NCF 的 TEM 图像。(2) 我们了解到，在 C-NCF/Ag ⁺的低倍 TEM 分析中观察到的片状外观系统似乎不清楚（原始文章中的图 4a）。然而，每次对不同批次的样品都进行了一致的类似观察。我们推测片状形态可能源于 C-NCF 与 Ag ⁺离子结合时的相关性质。纤维越细，就越柔韧，众多的 C-NCFs 不仅容易缠结，而且能够更紧密地堆积和纳米原纤维结合。此外，C-NCF 的表面负电荷可能会被介质中存在的 Ag ⁺离子的锚定在一定程度上中和，这减少了单个纤维之间的范德华排斥，并将它们组装成片状 C-NCF /银⁺捆绑形态。从 PTA 染色的 C-NCF/Ag ⁺样品中获得的 HR-TEM 图像进一步支持了这一假设，如图 2 所示。然而，在纤维素纤维上形成的颗粒对在高分辨率 TEM 下进一步放大图像造成了问题. 图 2. C-NCF/Ag ⁺中排列的 C-NCF 纤维束的 TEM 图像用 PTA 染色后的系统成像。(3) 在少数情况下，原始文章的图 1a 和图 5 中显示的 TEM 图像显示了 C-NCF 样品外围的卷曲纳米结构。Toth 等人最近的一份报告 (1) 证明了电子束诱导的损伤和随后的碳化可能导致在高真空条件下形成卷曲纳米结构。 (1) TEMPO 氧化的 C-NCFs碳质易碎材料，因此卷曲结构特征可能源于高电子束照射。为了检查我们的原始样品（用于 TEM 分析）中是否存在碳纤维或石墨烯的任何可能性，我们对 C - NCF/Ag ⁺进行了拉曼光谱分析和 C-NCF/Ag ⁺ /TiO ₂样品，并在类似的探测条件下与 C-NCF/rGO 样品进行比较。结果如图 3a 所示。分别获得了 C-NCF/rGO、C-NCF/Ag ⁺和 C-NCF/Ag ⁺ /TiO _{2 的}黑色、红色和蓝色光谱。C-NCF/rGO 样品的拉曼光谱特征分别位于 1335 和 1593 cm ^{–1 的}D 和 G 拉曼带，这是石墨烯相关结构的特征，而其他两个系统中没有带峰表明石墨C-NCF/Ag ⁺和 C-NCF/Ag ⁺ /TiO ₂中最初不存在碳纳米结构用于 TEM 分析的样品。图 3. (a) 拉曼光谱：(1) C-NCF/rGO、(2) C-NCF/Ag ⁺和 (3) C-NCF/TiO ₂ /Ag ⁺系统在 1 mW 激光功率下。(b) C-NCF/Ag ^{+ 的}拉曼图谱随着激光功率的递增顺序获得：(1) 1 mW，(2, 3, 4) > 4 mW。(5) 在 1 mW 激光功率下获得的 C-NCF/rGO 的拉曼光谱（用于比较）。激光波长，633 nm。尽管如此，考虑到 Lee 等人（2）的报告，他强调了在激光束照射下石墨化的可能性，我们研究了拉曼分析的不同激光条件的影响，并将它们呈现在图 3b 中。在这里我们注意到在高功率激光照射（> 4 mW）下逐渐出现 D 和 D** 带，表明 C-NCF/Ag ⁺到石墨结构（图 3b，光谱 2、3 和 4）。在较高激光功率下 D 和 D** 带的强度增加（图 3b，光谱 4）表明出现了石墨结构，但具有高度无序的特征。在 1505 cm ^–1处出现峰对应于 D** 归因于形成更多缺陷的石墨纳米结构或无定形碳。(3) 还显示了在 1 mW 激光功率下获得的 C-NCF/rGO 的拉曼光谱，以供比较。这些结果表明，我们研究中使用的 C-NCF 容易受到电子束损伤，因此不能排除 HR-TEM 成像过程中石墨化的可能性。有趣的是，对于在高能电子束下对纤维素进行 HR-TEM 成像期间可能发生的石墨化现象，也有类似的观察结果。 (2,4,5) 据报道，高能束可能会在局部表面引起热潮1000-2000 K 范围内的温度可能会对样品造成局部损坏。 (6) 考虑到这些可能性，在纤维素样品（具有低热分解温度）的 HR-TEM 成像过程中，会发生电子束损伤以形成石墨纳米结构，从而形成卷曲纳米结构。这并不奇怪，因为即使在 60 keV 电子束照射下，转移到碳原子的最大能量也是 ~10.8 eV，高于氢键的键能 (0.5 eV) 和纤维素解聚的活化能 (2.68 eV) .(4,5) 结果，电子束的高能量更有可能破坏将β (1→4) 葡聚糖链结合在一起的分子间氢键。此外，C-NCF 具有几个羟基和羧基，它们会蒸发以防止加热过程中温度升高。这一假设得到了拉曼研究（图 3b）和 TGA 结果（图 4）的进一步支持。结果表明，更高的激光功率可以诱导 D 和 G 带的出现，表明 C-NCF 转变为石墨类碳纳米结构。我们对 C-NCF/Ag 的观察⁺ /TiO ₂样品与之前的报道一致，表明所制备的 C-NCF 由随机弯曲的石墨烯层组成。 (7,8) 因此，在高强度电子束下进行的 HR-TEM 成像可能会导致卷曲如我们的报告中所观察到的，由于 C-NCF 束边缘处的热加热而导致的结构。图 4. 在氩气气氛下以 10 °C 的加热速率获得的 C-NCF 的 TGA 和 DTG 曲线。(4) 此外，我们在加入添加剂后对负染色样品进行了 TEM 分析。结果合并在图 5 中。可以看出，染色后对 C-NCF 样品进行成像的尝试证明了 C-NCF 的存在。然而，由于染色和添加剂的模糊影响，无法根据可用数据对结构进行更精确的确定，这使得解释更具挑战性。(5) 总结：本研究试图解析在 Ag 存在下 C-NCF 的晶格结构⁺/rGO 不使用 HR-TEM 成像的负染色。在该研究期间还观察到由光束照射引起的 C-NCF 结构的结晶度损失。不幸的是，即使在今天，碳化和石墨化也经常被混淆，导致有问题的解释问题。我们的结果表明，C-NCF 中的一些碳可以在 HR-TEM 成像（以及具有不同激光条件的拉曼实验）期间用高强度电子束照射石墨化，其中发生了微观结构变化。我们假设 HR-TEM 图像中明显的条纹是类石墨碳层的侧视图。增强的对比度是通过这些添加剂的电子密集性质和稳定作用实现的。进一步的研究对于使用 EELS 结合拉曼光谱或 X 射线衍射研究通过高强度电子束将纤维素转化为石墨碳过程中的结构转变的基本理解是必要的。我们的方法可以进一步扩展为生产导电石墨碳的合适方法，并可以找到潜在的应用，如柔性电子设备和传感器。图 5. 在 TEM 下使用 1% PTA 染色的三个系统的 TEM 图像：(a) C-NCF/rGO，(b,c) C-NCF/Ag 我们的方法可以进一步扩展为生产导电石墨碳的合适方法，并可以找到潜在的应用，如柔性电子设备和传感器。图 5. 在 TEM 下使用 1% PTA 染色的三个系统的 TEM 图像：(a) C-NCF/rGO，(b,c) C-NCF/Ag 我们的方法可以进一步扩展为生产导电石墨碳的合适方法，并可以找到潜在的应用，如柔性电子设备和传感器。图 5. 在 TEM 下使用 1% PTA 染色的三个系统的 TEM 图像：(a) C-NCF/rGO，(b,c) C-NCF/Ag⁺，和（d和e）C-NCF/Ag ⁺ /TiO ₂。KN 感谢来自 KSCSTE 博士后奖学金 (KSCSTE/309/2018-PDF) 的 UGC 赠款和 RTT 的财政支持。这项研究得到了 CSIR 赠款的支持。本文引用了 8 篇其他出版物。