Tuning the Morphological Properties of Cellulose Aerogels: An Investigation of Salt-Mediated Preparation

Abstract

In this study, alkali and alkaline earth metal chlorides with different cationic radii (LiCl, NaCl, and KCl, MgCl2, and CaCl2) were used to gain insight into the behavior of cellulose solutions in the presence of salts. The specific focus of the study was evaluation of the effect of salts’ addition on the sol-gel transition of the cellulose solutions and on their ability to form monoliths, as well as evaluation of the morphology (e.g., specific surface area, pore characteristics, and microstructure) of aerocelluloses prepared from these solutions. The effect of the salt addition on the sol-gel transition of cellulose solutions was studied using rheology, and morphology of resultant aerogels was evaluated by Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis, while the salt influence on the aerocelluloses’ crystalline structure and thermal stability was evaluated using powder X-Ray Diffraction (pXRD) and Thermogravimetric Analysis (TGA), respectively. The study revealed that the effect of salts’ addition was dependent on the component ions and their concentration. The addition of salts in the amount below certain concentration limit significantly improved the ability of the cellulose solutions to form monoliths and reduced the sol-gel transition time. Salts of lower cationic radii had a greater effect on gelation. However, excessive amount of salts resulted in the formation of fragile monoliths or no formation of gels at all. Analysis of surface morphology demonstrated that the addition of salts resulted in a significant increase in porosity and specific surface area, with salts of lower cationic radii leading to aerogels with much larger (~1.5 and 1.6-fold for LiCl and MgCl2, respectively) specific surface area compared to aerocelluloses prepared with no added salt. Thus, by adding the appropriate salt into the cellulose solution prior to gelation, the properties of aerocelluloses that control material’s performance (specific surface area, density, and porosity) could be tailored for a specific application.

Recent Developments in Water Treatment by Cellulose Aerogels from Agricultural Waste

“…For the similar cellulose content, if replacing water with methanol, coagulating aerogels by methanol resulted in lower density than water-coagulated materials [49]. The enhancement in the physicochemical properties of aerogels and the decrease gelation time is directly related to adding a monovalent salt (LiCl, NaCl, and KCl) and divalent salts (CaCl 2 and MgCl 2 ) [50]. Sandeep A et al studied that the mechanical technicalities via high-speed homogenization or highintensity ultrasonication treatment influenced the stability of cellulose fibers dispersion in dilute suspensions, as well as cylindrical and dimensional shapes of rice straw cellulose aerogels after freezedrying.…”