Silica modified cellulosic aerogels

Abstract

Shaped cellulosic aerogels-as the 'young' generation succeeding the well-established silica and synthetic polymer-based aerogels-are intriguing materials that feature properties similar to those of their antecessors combined with the additional advantages and characteristics of the re-growing biopolymer cellulose. Reinforced shaped cellulosic aerogels consisting of two interpenetrating networks of cellulose and silica were prepared from shaped cellulose solutions by (1) regenerating (reprecipitating) cellulose with ethanol, (2) subjecting the obtained shaped alcogels to sol-gel condensation with tetraethoxysilane as the principal network-forming compound, and (3) drying the reinforced cellulose bodies with supercritical carbon dioxide. The influence of different types of cellulose and sol-gel forming parameters on porosity, cellulose integrity, and silica content were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), gel permeation chromatography (GPC), and nitrogen adsorption at 77 K. The results of SEM and EDX confirmed the presence of silicon inside the obtained cellulosic aerogel. GPC of the cellulosic matrix prior and after silica coating showed no alteration of the molecular weight distribution for most of the samples, confirming a far-reaching preservation of cellulose's chemical integrity throughout the modification procedure. Nitrogen adsorption experiments at 77 K revealed that the micro-and meso-pore characteristics were largely retained throughout silica modification.

Chapter 14. Cellulose and Protein Aerogels for Oil Spill Cleaning, Life Science and Food Engineering Applications

“…73,74 The BET surface areas of the silica-cellulose composite aerogels in Table 14.6 were between approximately 198 and 296 m 2 g À1 , comparable to the surface areas found in similar studies conducted by Demilecamps et al (90-170 m 2 g À1 ) 75 and Litschauer et al (220-290 m 2 g À1 ). 76 As can be observed in Figure 14.9, the X-ray diffraction patterns of the silica-cellulose composite aerogels seem to be the superposition of those of the pure cellulose aerogels and the pure silica aerogels, which is similar to the findings of Cai et al 77 This XRD finding implies that the extent of the chemical reaction between the cellulose fibres and the silica components was quite limited, as no new compound was detected. The XRD results suggest that it was reasonable for the meso-porous structure of the silicacellulose aerogels to be controlled only by the silica components as the cellulose matrix did not possess a detectable BET surface area, and no new compound was formed.…”

Multiscale Assembly of Superinsulating Silica Aerogels Within Silylated Nanocellulosic Scaffolds: Improved Mechanical Properties Promoted by Nanoscale Chemical Compatibilization

“…Among these systems, the ones based on synthetic polyimide (Nylon) or fiberglass (Pyrogel) are commercially available and display superinsulating properties with thermal conductivity as low as 14 mW (m K) −1 . Very recently, 3D scaffolds based on regenerated cellulose or bacterial cellulose have been proposed as scaffolds for the reinforcement of silica aerogels. This biocompatible and biodegradable polymer allowed enhancing the mechanical properties of the pristine materials under compressive or tensile loading, but thermal conductivity values ( λ ) above 25 mW (m K) −1 were observed as a result of the significantly enhanced skeletal conductivity.…”

Cellulose–Silica Nanocomposite Aerogels by In Situ Formation of Silica in Cellulose Gel

“…To further utilize the regenerated cellulose gel, we herein attempted in situ synthesis of silica in cellulose gels. While a similar attempt has been reported, in which the cellulose gel was obtained from solution in N ‐methylmorpholine‐ N ‐oxide monohydrate,9 the development of the nanostructure (nitrogen BET surface area of 220–290 m 2 g −1 ) and the level of silica loading (less than 13 % w / w ) were rather limited. By using the aqueous alkali‐based solvent, we obtained the cellulose aerogel with a surface area of 356 m 2 g −1 , and a silica loading of more than 60 % w / w resulted in surface areas that exceeded 600 m 2 g −1 .…”