Preparation and formation mechanism study of the long-term stable foamed sodium carboxymethyl cellulose loaded material

A foamed sodium carboxymethyl cellulose (CMC) material was prepared under
nitric acid conditions. Unlike traditional CMC materials, this foaming
method is straightforward and does not require additional foaming agents.
Due to its high stability and load capacity, the foam can realize
long-term quantitative storage and load a variety of metal ions,
therefore, it has broad application prospects in the field of loaded
materials for metal ions. In this work, infrared spectroscopy and nuclear
magnetic resonance (NMR) spectroscopy were used to explore the interaction
between CMC and nitric acid in the foam under these conditions. The
mechanism of foam formation was reasonably explained. Infrared spectra
reveal the hydrolysis of the cellulose framework by nitric acid. Based on
experimental observations during preparation and NMR analysis, it is
explained that nitric acid activates glucose units’ C1 (No.1 carbon in
glucose unit) in CMC, leading to the formation of reducible terminal
groups. Additionally, as the concentration of nitric acid increases during
solution evaporation, a fraction of these reducible terminal groups
undergo oxidation by nitric acid, resulting in gas production and
subsequent expansion of the system, ultimately forming a foamed structure
upon complete drying.

本研究在硝酸条件下制备了羧甲基纤维素钠（sodium carboxymethyl cellulose，CMC）发泡材料。与传统CMC材料不同，该发泡工艺简便易行，无需额外添加发泡剂。该泡沫材料凭借优异的稳定性与负载能力，可实现长期定量存储，并能负载多种金属离子，因此在金属离子负载材料领域具备广阔的应用前景。本研究采用红外光谱（infrared spectroscopy）与核磁共振（nuclear magnetic resonance，NMR）光谱技术，探究了该制备条件下泡沫中CMC与硝酸的相互作用，合理阐释了泡沫的形成机理。红外光谱结果显示，硝酸可使纤维素骨架发生水解。结合制备过程中的实验现象与NMR分析结果，本研究阐明：硝酸可活化CMC中葡萄糖单元的C1位（葡萄糖单元的1号碳原子），进而生成可还原末端基团。此外，在溶液蒸发过程中，硝酸浓度逐渐升高，部分可还原末端基团会被硝酸氧化，产生气体并引发体系膨胀，最终在完全干燥后形成发泡结构。