Abstract

Cellulose nanofiber (CNF)-derived functional papers hold promise for application in various fields due to their unique properties such as gas barriers, high strength, transparency, etc. Mechanochemistry offers environmentally benign and sustainable synthesis of the functionalized CNFs (e.g., in combination with photocatalytic TiO₂). The CNFs could also favorably work to produce oxygen vacancies in TiO₂ that enables visible responsive photocatalysis. What microstructural and physicochemical changes then occur on the CNF sol during the milling treatment? In this study, changes in the microstructure of the CNF aqueous sol before/after planetary ball milling were investigated based on its rheological behavior, crystallinity, and diameter distribution. The surface activity of the CNFs was additionally characterized by water vapor adsorption. A decreased thixotropy hysteresis loop observed in the low milling speed (100 rpm)-treated CNFs indicated a weaker interaction among the fibers, but still having a three-dimensional structure. A further increase in the milling speed (300 rpm) could collapse them. A decreased X-ray diffraction peak intensity of the (200) plane observed in the 500-rpm-treated CNFs could indicate a split in the fiber’s bundle as well as shredding. The increased amount of water vapor adsorption in the 500-rpm treated CNFs also supports exposure of the new surface with hydroxyl groups derived from the glucose unit. Such newly formed hydroxyl groups can be effective reaction sites with, for example, the TiO₂ precursor and perhaps favorably works to improve the photocatalytic performance.

Graphic abstract

中文翻译：

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机械分散的纤维素纳米纤维水溶胶的微观结构和表面活性

摘要

纤维素纳米纤维（CNF）衍生的功能纸由于其独特的特性（如阻气性，高强度，透明性等）而有望在各个领域中应用。机械化学为功能化CNF提供了环境友好和可持续的合成方法（例如，结合使用光催化TiO ₂）。CNF还可以有利地在TiO _2中产生氧空位使可见光响应光催化。在研磨过程中，CNF溶胶会发生什么微观结构和物理化学变化？在这项研究中，基于其流变行为，结晶度和直径分布，研究了球磨前后CNF溶胶的微观结构变化。CNF的表面活性另外通过水蒸气吸附来表征。在低研磨速度（100 rpm）处理的CNF中观察到的触变性磁滞回线减小，表明纤维之间的相互作用较弱，但仍具有三维结构。铣削速度（300 rpm）的进一步提高可能会使它们崩溃。在以500 rpm处理的CNF中观察到的（200）平面的X射线衍射峰强度降低，可能表明纤维束分裂和碎裂。在以500 rpm处理的CNF中，水蒸气吸附量的增加也支持新表面暴露于源自葡萄糖单元的羟基。这种新形成的羟基可以是与例如TiO的有效反应位点₂前体并可能有利地改善光催化性能。

图形摘要