Silica modified cellulosic aerogels

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.