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. Owing 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.