Salt-Induced Colloidal Destabilization, Separation, Drying, and Redispersion in Aqueous Phase of Cationic and Anionic Nanochitins

This study is aimed at facilitating the use of ocean biomass for the isolation and use of derived nanostructures. Specifically, cationic and anionic nanochitins were produced from never-dried crab shells that underwent partial deacetylation (PD-NCh) or TEMPO-oxidization (TO-NCh). The effects of different electrolyte types (NaCl, CH3COONa, Na2CO3, CaCl2, AlCl3, and NH4Cl) were investigated with regards to fractionation (via colloidal destabilization and precipitation), drying, and ultimate redispersion of the nanochitins. Sodium carbonate was most effective in the case of PD-NCh processing, whereas no significant effect of salt type was noted for TO-NCh. The results are rationalized in terms of the dispersion stability that resulted from specific counterion adsorption and nanoparticle association as well as electrostatic-charge development at a given solution pH. These effects were used to limit hydrogen bonding and nonspecific interactions upon drying of the nanochitins. The weak interactions between nanochitin and monovalent Na+ and NH4+ explain the experimental observations. Aqueous dispersions reconstituted from dried PD-NCh and TO-NCh were colloidally stable and yielded highly viscous, gel-like nanochitin dispersions at mass concentrations as low as 1.5 and 3.0%, respectively. Our findings are expected to greatly facilitate green processing of nanochitin, an emerging type of biobased nanomaterial.