The effect of zinc oxide (ZnO) addition on the physical and morphological properties of cellulose aerogel beads

Abstract

In the present work, microsized open porous cellulose aerogel beads were made using an aqueous solution of 7 wt% NaOH and 12 wt% urea and additionally various concentrations of ZnO added to study its effect on physical and morphological properties of the beads formed. It has been observed that such cellulose aerogel beads prepared with lower concentrations of ZnO show considerable shrinkage while drying whereas beads prepared with higher concentrations of ZnO do not exhibit much shrinkage. The dried cellulose aerogel beads were spherical with diameters between 2-2.5 mm. The skeletal density of all dried cellulose aerogel beads was measured as 1.5 g/cm3. FT-IR spectra reveal that the structure of cellulose I transformed to cellulose II during dissolution and regeneration in a coagulation medium, which also confirmed from XRD measurements. The beads prepared with NaOH/urea/ZnO aqueous solution exhibit better thermal stability. We found that the addition of 0.5 wt% ZnO to NaOH/urea mixture greatly increased the specific surface area of cellulose aerogel beads up to 407 m2/g compared to control cellulose aerogel beads (341 m2/g) and also increased the pore volume to 1.56 cm3/g (0.5 wt% ZnO added sample) compared to control cellulose aerogel beads (1.48 cm3/g). SEM images indicate that a dense nano-fibrillar network structure was formed in the interior of the cellulose aerogel beads prepared with 0.5 wt% ZnO. These results indicate that the bulk density, surface area, pore volume and pore size of the cellulose aerogel beads can be tuned by changing the concentration of ZnO.