Sustainable Approach for Cellulose Aerogel Preparation from the DBU–CO₂ Switchable Solvent

Abstract

We report a sustainable and easy approach for the preparation of cellulose-based aerogels from the DBU–CO2 switchable solvent system via a solubilization and coagulation approach followed by freeze-drying. The easy, fast, and mild solubilization step (15 min at 30 °C) allows for a rapid preparation procedure. The effect of various processing parameters, such as cellulose concentration, coagulating solvent, and the superbase, on important aerogel characteristics including density, porosity, pore size, and morphology, were investigated. Density values obtained ranged between 0.05 and 0.12 g/cm3, with porosity values between 92% and 97%. The morphology of the obtained cellulose aerogels was studied using scanning electron microscopy (SEM) showing a random and open large macroporous cellulose network with pore sizes ranging between 1.1 and 4.5 μm, depending on the processing conditions. In addition, specific surface areas determined by N2 adsorption applying the BET equation ranged between 19 and 26 m2/g. The effect of the coagulating solvent and superbase on the crystallinity was investigated using X-ray diffraction (XRD) showing an amorphous crystal structure with a broad 2θ diffraction peak at 20.6°. In addition, no chemical modification was observed in the prepared aerogels from infrared spectroscopy. Finally, the recovery and reuse of the solvent system was demonstrated, thus making the process more sustainable.

Synthesis of nanocellulose aerogels and Cu-BTC/nanocellulose aerogel composites for adsorption of organic dyes and heavy metal ions

“…The aerogel, first synthesized in the late 1930s by Kistler 41 , can be inorganic 42 , organic 43 , and hybrid 44 aerogels according to their composition 45 . Silica aerogel is the most common inorganic aerogels, whereas resorcinol–formaldehyde aerogels are the most common organic aerogels prepared via the sol–gel process 46 . However, due to the fragility and brittleness of inorganic aerogels, organic aerogels (from natural or synthetic polymers) that are more flexible and less brittle are used if mechanical strength is required 47 .…”

Recent Developments in Water Treatment by Cellulose Aerogels from Agricultural Waste

“…Chemical gel processes are replaced from a liquid into another liquid phase, typically water (polar) and a non-polar organic solvent. 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].…”

Direct electrospinning of cellulose in the DBU-CO2 switchable solvent system

“…Such mild solubilization conditions allowed us to explore this switchable solvent system to show a more sustainable succinylation of cellulose, (Söyler et al 2018) transesterification of cellulose using plant oils directly, (Onwukamike et al 2018c) and in multicomponent reaction, in which the CO 2 was employed as a C1-carbon source (Onwukamike et al 2018b). In addition, we employed this solvent system to produce cellulose aerogels with porosity higher than 95 % (Onwukamike et al 2019). These examples showed the high versatility of the CO 2 switchable solvent system and equally open up their potential for other cellulose-based applications.…”