Formation of nanocrystalline ZnO particles into bacterial cellulose pellicle by ultrasonic-assisted in situ synthesis

Nanocrystalline zinc oxide particles were synthesized and simultaneously incorporated into a three-dimensional nanofibrous matrix of bacterial cellulose (BC) pellicles by a newly created method called “ultrasonic-assisted in situ synthesis”. The BC pellicles were first immersed in a zinc acetate solution. Then the Zn²⁺-absorbed BC pellicle was further immersed in ammonium hydroxide solution with simultaneous ultrasonic treatment. The effect of immersion time of the BC pellicles in zinc acetate solution and ultrasonic treatment time on crystalline size and percent incorporation of ZnO into the BC pellicles were determined. The crystalline size of ZnO incorporated in BC pellicles was in the range of ~54–63 nm that were similar to the diameter of BC nanofibrils. The amount of ZnO into the BC pellicles was found to increase with increasing immersion time. A longer ultrasonic treatment time resulted in smaller crystalline size of the incorporated ZnO. The particle size, morphology and dispersion of the synthesized ZnO in the BC matrix were examined by transmission electron microscope and scanning electron microscope with inbuilt energy dispersive X-ray analysis. The mechanism of the formation of the nanocrystalline ZnO particles onto the BC nanofibrils was discussed. Moreover, the antibacterial activity of the nanocrystalline ZnO particle-incorporated BC sheet against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) was also evaluated.