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专业: 高分子合成化学

[求助] 审稿意见请教，仿生合成碳酸钙方面，谢谢！已有1人参与

审稿专家如下意见，请多多赐教，谢谢！

问题1) Interactions between NHCS and calcium carbonate (or calcium ion and CO2) are rather speculatively discussed in this manuscript without showing concrete evidences of interaction. IR is usually powerful tool for analyzing interaction between molecules and materials. However, interpretation and discussion on IR data in this manuscript are rather insufficient. Please assign chemical bonds and vibration modes to these peaks. Without this information, proper discussion cannot be done. In addition, please take IR spectra of NHCS and NHCS with calcium carbonate. Please assign NHCS peak and discuss about peak shifts to clarify interaction with calcium carbonate.

疑问：本文采用NHCS作为有机基质仿生合成碳酸钙，少量NHCS可溶于反应体系中，碳酸钙沉淀后离心分离后产物只有碳酸钙，而没有NHCS，如何谈及please take IR spectra of NHCS with calcium carbonate但是NHCS的红外可以添加。此外，chemical bonds and vibration modes是否类似下面描述：Figure 2b clearly shows the evidence of the VS homopolymerization by the absence of the absorption band at 962 cm-1 corresponding to C=C bond of the VS monomer. Additionally, new absorption bands assigned to the PVS can be also observed at2930 cm-1 and 1448 cm-1 due to -CH- and -CH2- stretching vibrations, respectively.

我的原文是：
Figure 1 shows FTIR spectra of peaks at 712 cm-1, 746 cm-1, and 876 cm-1. It is interesting to note that the new band at 746 cm-1 corresponding to vaterite also appears (Figure 1b-e) [27-30], which is different from that of calcium carbonate obtained in the pure water system without any additive of NHCS(Figure 1a). In addition, the different intensity of these peaks (712 cm-1, 746 cm-1, and 876 cm-1) may result from the different contents of the vaterite formed at different aging times. In addition to vaterite and calcite, the higher of the initial concentration of NHCS, the more vaterite present, the higher intensity ratio of bands at 746 and 712 cm−1 (I746/ I712) respond in FTIR spectrum of the sample prepared with using NHCS as an organic matrix to biomimetic synthesize calcium carbonate. This observation is supplemented by XRD analysis (shown in Figure 2).

问题2) The first sentence of Introduction is too common and meaningless. Please add more details to this sentence. Generally speaking, reference selection of this manuscript is not well updated. Addition of sufficient numbers of recent papers can be recommended. For example, the initial sentence may be replaced by the following extended sentence.

Biomineralization and related bio-related processes are multifactorial, fantastic and complex processes that often become a nice guide for fabrication of functional materials and keys for understanding of biophenomena [references].
Reference examples: ACS Nano 10, 3453-3460 (2016), Bull. Chem. Soc. Jpn. 88, 1459-1465 (2015), J. Mater. Res. 31, 547-555 (2016)

疑问：是不是就增加专家提供三篇文献，修改首句就好了嘛？

问题3) Discussions in this manuscript is interesting. However, bad organization of the manuscript may make it difficult to read with good understanding. This manuscript includes both very short paragraphs and very long ones. Especially, reader may have difficulty in following main opinions by the authors in the latter long paragraph. Please divide and combine paragraphs with bad length to make them into paragraphs with comfortable lengths.
疑问：这部分比较难整，我多多请教我的原文是：
The possible growth mechanism has been proposed by investigating the transition of crystal phase and formation of the vaterite during the growth process in the study.
Based on the above study and experimental process, the following “molecular recognition” - “electrostatic interaction” - “formation nucleus” - “aggregation” - “ripening” - “dissolution-reprecipitation-limited growth” mechanism (Showed in Figure 6) is proposed to explain the transition of crystal phase and formation of the vaterite during the growth process.
The pI of NHCS is 6.54, which can be seen in previously report [24]. In addition, the pKa of chitosan is 6.30  and the pKa of active-centre histidine imidazole group is 6.00 [32,33]. When the pH value of NHCS system is 7.0 (pH > pI(NHCS)), deprotonation of hydroxyl group, imidazole group and amino groups leads to the whole NHCS with negative charges. The Zeta potential of NHCS is negative (-10.8 mV) [26], which demonstrates that the NHCS polymer under the present crystallization conditions carries negative surface charge. This presents that a speciﬁc interaction does exist between NHCS and calcium ions. As a result, NHCS can first capture and collect Ca2+ ion from CaCl2 solution (Figure 6a) by molecular recognition (Figure 6b), which leads to the enrichment of Ca2+ near the surface of NHCS. These calcium ions can further attract more CO32− ions by electrostatic interaction, thus remarkably increasing the number of nucleus (Figure 6c).
The increase of the degree of supersaturation favors the nucleation of precipitation according to the Gibbs-Thomson formula of classical nucleation theory [34]:
J = A exp -B (lnS)-2                         (3)
Where J and S are the nucleation rate and degree of supersaturation, respectively, and both A and B are constants. According to the equation (3), nucleation rate increases along with the increase of supersaturation degree [29]. Thus, as NHCS is added into CaCl2 solution, numerous nucleuses will form in the supersaturation zone on the surface of NHCS. High supersaturation on NHCS leads to increase of the nucleation rate as well as the nucleation number. These nucleuses then grow into nanoﬂakes and nanolayers rapidly. Large amount of crystal nucleus will facilitate the formation of nanoﬂakes and nanolayers and the reﬁnement of precipitation. Due to their high surface energy, the nanoﬂakes and nanolayers have the tendency to aggregate. Concequently, the “ﬂaky-ﬂoret” or multilayered particles by nanoﬂakes and nanolayers are presented as shown in Figure 5a in the initial stage (at aging time 0 h, Figure 5a, Figure 6d).
As time progresses (aging time 0.5 h), on the one hand, these metastable vaterite phase bounded by NHCS aggregate continuously as “spherical-like” vaterite particles. On the other hand, those unbounded crystal nucleuses are not limited by NHCS or its surface grows as rhombohedral calcite phase (Figure 5b, Figure 6e).
After aging for 1.0 h, the dissolved particles reprecipitated again and its surface is adsorbed by NHCS molecular, so the initial crude “ﬂaky-ﬂoret” or multilayered vaterite disappeared completely during ripening. It is worth noting that lots of crude elliptical or spherical vaterite structures form by the reprecipitated particles and get more smooth and regular, and the crystallite size of the metastable vaterite structures is making up the large crude spherulites increased from ~100 nm to ~2 μm. Unusual “ﬂaky-ﬂoret” or multilayered vaterite are metastable and dissolve later in the Ostwald ripening progress, which can explain the above phenomena. As the same as above stage, those unbounded crystal nucleuses lead to the simultaneous growth of few rhombohedral calcite phase (Figure 5c, Figure 6f).
As is well known to all, metastable vaterite can transform into calcite through a solvent-mediate process [35]. Considering the solubility products of the different polymorphs (vaterite, 1.22×10−8 M2; aragonite, 4.61×10−9 M2; calcite, 3.31×10−9 M2 at 25 °C, respectively) [36], the phase transformation of vaterite to calcite is a thermodynamically feasible process. The “dissolution-reprecipitation-limited growth” will take place as aging time progresses. On the one hand, morphology and polymorph of the coexistence of vaterite-calcite is controlled by NHCS and leads to limited growth near the surface of NHCS. On the other hand, coexistence of vaterite-calcite growth is controlled by Ostwald ripening to keep the thermodynamics and dissolve dynamic balance in NHCS system (Figure 5d-f, Figure 6g-i). It suggests that the NHCS molecule plays an important role in the formation and stabilization of vaterite.

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