Employing photoluminescence to rapidly follow aggregation and dispersion of cellulose nanofibrils.
Employing photoluminescence to rapidly follow aggregation and dispersion of cellulose nanofibrils.
复制标题
DOI：
10.1039/d0an00868k
复制
发表时间：
2020-06
期刊：
影响因子：
--
通讯作者：
M. Johns;A. Lewandowska;E. Green;S. Eichhorn
中科院分区：
文献类型：
--
作者：
M. Johns;A. Lewandowska;E. Green;S. Eichhorn
纤维素和其他多糖的光致发光一直被认为是由于其他自发荧光化合物（如木质素或蛋白质）对材料的污染。这归因于多糖分子结构中缺乏已知的荧光化学基团，并且与典型的荧光团相比发射强度较弱。然而，最近的研究表明，所观察到的发光可能实际上是由于涉及包含存在于氧基中的孤电子对的n轨道的跃迁，通过多糖链之间的分子力稳定。在这里，我们进一步研究这一理论，通过改变氧化纤维素纳米纤维悬浮液的物理化学环境（浓度和pH值），并观察所得的荧光光谱，使用多通道共聚焦激光扫描光谱。我们证实，这两个因素影响材料的光致发光，特别是改变两个局部发射最大值之间的强度比，支持目前的理论。此外，我们证明，这种变化使得能够确定的临界聚集浓度和表观pKa值的羟基进行去质子化在检查的pH值范围内，使使用该技术来跟踪快速变化的原纤维的物理化学环境。
Photoluminescence of cellulose, and other polysaccharides, has long been presumed to be due to contamination of the material by other autofluorescent compounds - such as lignin, or proteins. This is attributed to the lack of known fluorescent chemical groups present in the molecular structure of polysaccharides and the weak emission intensity when compared to typical fluorophores. However, recent research suggests that the observed luminescence may actually be due to transitions involving the n orbitals containing lone electron pairs present in oxyl groups, stabilised by the molecular forces between the polysaccharide chains. Here we investigate this theory further by varying the physicochemical environment (concentration and pH) of oxidised cellulose nanofibril suspensions and observing the resultant fluorescent spectra using multi-channel confocal laser scanning spectroscopy. We confirm that both factors affect the material photoluminescence, specifically changing the intensity ratio between two localised emission maxima, supporting current theories. Furthermore, we demonstrate that this variation enables the determination of critical aggregation concentrations and the apparent pKa values of hydroxyl groups that undergo deprotonation within the examined pH range, enabling use of the technique to track rapid changes in the fibril physicochemical environment.