Preparation and Characterization of Cellulose Crystallites via Fe(III)-, Co(II)- and Ni(II)-Assisted Dilute Sulfuric Acid Catalyzed Hydrolysis Process

Hydrolyzing the cellulose amorphous regions with high selectivity while protecting the crystallite phases unaltered during acid hydrolysis is still a great challenge in nanocellulose industry. Due to this reason, transition metal based catalysts such as Fe (NO3)3-, Co (NO3)2- and Ni (NO3)2metal salts were chosen as promoter to co-catalyze with H2SO4 in order to develop a facile hydrolysis technique for the preparation of cellulose crystallites inform nanodimension from native cellulose source. This study investigated the hydrolysis efficiency of three different transition metals (Fe3+, Co2+ and Ni2+) on cellulose crystallinity index, structure and morphology of the products.Results showed that the transition metal salts (Ni2+, Co2+ and Fe3+) were capable to selectively degraded cellulose amorphous structure with increase of crystallite sizes (8.12-27.8 nm) and improved of crystallinity index (65.5-70.3 %), as compared to native cellulose. Furthermore, surface morphology study indicated the cellulose fibers were successfully disintegrated into smaller fragments (diameter ranges of 18.5-31.5 nm) with spider-web-like nanostructured surfaces. Higher oxidation state of Fe (III)-cation with trivalent state rendered more effective hydrolysis effect in preparing the cellulose crystallites as compared to divalent state of Co (II)- and Ni (II)-cations.