Pachuta Kevin, Pentzer Emily, Sehirlioglu Alp
Department of Materials Science and Engineering, Case Western Reserve University USA
Department of Materials Science and Engineering, Texas A&M University USA.
Nanoscale Adv. 2020 Oct 16;2(11):5362-5374. doi: 10.1039/d0na00755b. eCollection 2020 Nov 11.
Two-dimensional materials have been at the forefront of chemistry and materials science research for the past decade owing to promising applications across many fields. Improvements in exfoliation processes continually give access to new two-dimensional material compositions, demanding a deeper understanding of the defect structure and exfoliation mechanisms. Chemical exfoliation processes allow for both the fabrication of new, and the production of industrial-scale quantities of two-dimensional materials. For this reason, we report a rapid, efficient, and simple method for evaluating the exfoliation behavior of protonated lithium cobalt oxide. Using a two-step chemical exfoliation method, first by proton-cation exchange, then by treatment with an organo-ammonium hydroxide, the exfoliation yield of lithium cobalt oxide was quantified with a quick and powerful technique, ultraviolet-vis spectroscopy characterization. This method provided an in-depth analysis of the exfoliation of lithium cobalt oxide confirming and discovering many key aspects of its soft-chemical exfoliation relating to layered transition metal oxides. It was determined that the exfoliation yield has a strong dependence on multiple factors, such as the concentration of protons in the powder, the presence of water and hydroxide groups in solution, and the ionic radius and concentration of the intercalating cation. Both morphological changes occurring as a function of reaction conditions and the two-dimensional nature of the final sheets were revealed through scanning electron microscopy and atomic force microscopy. Relative proton concentration of acid-treated lithium cobalt oxide was determined as a function of acid concentration using time of flight secondary ion mass spectrometry after deuterated acid treatment. These experiments led to an improved understanding of the soft-chemical exfoliation of lithium cobalt oxide and can be applied to many layered transition metal oxides.
在过去十年中，二维材料因其在众多领域的应用前景而一直处于化学和材料科学研究的前沿。剥离工艺的改进不断带来新的二维材料组成，这就需要更深入地了解缺陷结构和剥离机制。化学剥离工艺既可以制造新的二维材料，也能够实现工业规模的生产。因此，我们报告了一种快速、高效且简单的方法来评估质子化锂钴氧化物的剥离行为。采用两步化学剥离法，首先通过质子 - 阳离子交换，然后用有机氢氧化铵处理，利用快速且强大的紫外 - 可见光谱表征技术对锂钴氧化物的剥离产率进行了量化。该方法对锂钴氧化物的剥离进行了深入分析，证实并发现了其与层状过渡金属氧化物相关的软化学剥离的许多关键方面。研究发现，剥离产率强烈依赖于多个因素，例如粉末中质子的浓度、溶液中水和羟基的存在、嵌入阳离子的离子半径和浓度。通过扫描电子显微镜和原子力显微镜揭示了随反应条件变化而发生的形态变化以及最终薄片的二维性质。在氘代酸处理后，使用飞行时间二次离子质谱法测定了酸处理锂钴氧化物的相对质子浓度与酸浓度的函数关系。这些实验有助于更好地理解锂钴氧化物的软化学剥离，并且可以应用于许多层状过渡金属氧化物。
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