Upon addition of zinc nitrate solution to the CMC hydrogel paste zinc nitrate reacted with water and forms zinc hydroxide (Zn (OH)2), large particles may be formed via precipitation followed by a step-like aggregation process.
Since polysaccharides i.e. CMC could form complexes with divalent metal ions due to their high number of coordinating functional groups (hydroxyl and glucoside groups) (Al-Hartomy & Shahl, 2011).
It is likely that the majority of the zinc ions were closely associated with the CMC molecules.
As the concentrations of Zn2+ and OH− ions exceed the critical values, the precipitations of nuclei starts.
The Zn(OH)2 can be transformed into the ZnO crystals via the simple chemical reaction as suggested mentioned below (Pushpamalar, Langford, Ahmad, & Lim, 2006).