Alternative source of chitosan for the direct laser synthesis of Ag@chitosan composites with antibacterial and photocatalytic properties

In this study, we used chitosan obtained from the pupal exuviae of the insect Hermetia illucens to produced silver nanoparticles (Ag@CSE) by nanosecond laser ablation in liquid technique. The physic-chemical and functional properties of the obtained nanocomposite were compared to Ag@CS prepared by using a solution of chitosan from crustaceans as liquid, in the same experimental conditions. The composites were studied by transmission electron microscopy (TEM), Uv-vis and FTIR and X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD). The composites exhibit optical absorption at around 400 nm due to the presence of silver nanoparticles with a diameter of 11 and 14 nm for Ag@CS and Ag@CSE, respectively. We evaluated the antimicrobial capacity of these nanocomposites against two bacterial strains, Escherichia coli and Micrococcus flavus, by agar diffusion test and microdilution assay. Both composites showed a zone of inhibition of approximately 9 mm against both bacterial strains. Ag@CSE showed marked antimicrobial activity against E. coli up to 0.006 g/L, at which value Ag NPs alone lost their activity. The ability to photocatalyse the methylene blue degradation reaction of Ag@CS and Ag@CSE was tested under simulated solar irradiation conditions. The obtained results suggest that chitosan from HE is a valuable alternative source to chitosan from crustaceans and that the obtained composites can be considered for biomedical and photodegradation applications.