Chitosan/Ag-Bentonite Nanocomposites: Preparation, Characterization, Swelling and Biological Properties

Abstract

In the present work, Chitosan/bentonite, Chitosan/Ag-bentonite and Chitosan/AgNPs-bentonite composite materials were prepared and shaped in form of beads, and characterized using several methods. After that, their thermal stability, swelling properties and antibacterial and antifungal activity were evaluated. In the case of Chitosan/AgNPs-bentonite, the XRD analysis confirms the partial intercalation of chitosan in the interlayer of bentonite and the formation of silver nanoparticles, AgNPs, with an average diameter between 10 and 25 nm. The latter is confirmed by UV–Visible diffuse reflectance spectroscopy by the apparition of the large absorption band at 442 nm. For all prepared materials, the FTIR analysis shows the presence of strong interaction between chitosan reactive groups and bentonite interlayer materials. This result is confirmed by thermal analysis where it is observed that these composite materials exhibit a higher thermal stability than the biopolymer alone. The composite materials present also a very good swelling capacity. Indeed, the swelling rate carried out in water media at pH 7 and a temperature of 30 °C is 160% higher than that of the corresponding dried material. Otherwise, Chitosan/AgNPs-bentonite sample displays a very high antibacteriaPseudomonas aeruginosal activity against pathogen bacteria strains such as Staphylococcus aureus ATCC 25923 and ATCC 27853. This activity is less important for S. aureus ATCC 43300 and no activity is observed for Escherichia coli ATCC 25922 and Candida albicans ATCC 10231. Since the starting chitosan and bentonite materials showed no antibacterial or antifungal activity, the antibacterial activity of Chitosan/AgNPs-bentonite sample is attributed to loaded AgNPs species.