Revalorization of coconut husk lignin through ZnO nanoparticles synthesis: antibacterial assay and photocatalytic activities

Abstract Lignin, due to its structural diversity and biodegradability has emerged as a promising alternative to hazardous synthetic materials in multidisciplinary research area. The aim of this paper is to evaluate the lignin potential in value-added applications to be exact zinc oxide nanoparticle synthesis. First, lignin was extracted from coconut husk via sonochemical route in alkaline medium. Afterward, lignin-zinc oxide hybrid nanoparticles (L-ZnO NPs) were synthesized by the reaction of zinc acetate dihydrate salt and lignin, where lignin acts as bioreducing and capping agent. The synthesized lignin and L-ZnO NPs were characterized by UV-Vis spectroscopy, FTIR Spectroscopy, XRD and FESEM analysis. All the identification tests supported the existence of lignin and L-ZnO NPs. The XRD and SEM images disclosed the formation of hexagonal wurtzite shape L-ZnO NPs having mean diameter ≈ 77.76 nm. The antibacterial efficacies of the L-ZnO NPs were assessed against both gram-negative E. coli and gram-positive S. aureus bacteria, employing standard controls and the well diffusion method. The L-ZnO NPs exhibited marvelous bactericidal action against the test microorganisms displaying sufficient zone of inhibition. The photocatalytic performance of the L-ZnO NPs was observed by methylene blue (MB) dye degradation test under UV light irradiation. The UV-Vis absorbance and conductivity tests suggested that the L-ZnO NPs has noticeable photocatalytic efficiency on MB dye degradation. Therefore, the synthesized L-ZnO NPs possess excellent versatile properties and it can be used in medicinal applications and environmental management.