Revalorization of Coconut Husk Lignin Through ZnO Nanoparticles Synthesis: Antibacterial Assay and Photocatalytic Activities

Lignin, due to its structural diversity and biodegradability, has emerged a promising alternative of hazardous synthetic materials. The aim of this paper is to prepared value-added lignin-zinc oxide hybrid nanoparticles (L-ZnO NPs) from discarded lignin. First, lignin was extracted from coconut husk via sonochemical route in alkaline medium. Afterward, L-ZnO NPs were synthesized using zinc acetate dihydrate precursor and lignin (act as bioreducing and capping agents). Using the same method, non-coated ZnO NPs was produced in absence of lignin. The synthesized lignin, L-ZnO NPs and non-coated ZnO NPs were characterized by UV–Vis spectroscopy, FTIR spectroscopy, XRD and FESEM analysis. L-ZnO NPs have a lower band gap energy than uncoated ZnO NPs, which has impact on photocatalytic activity. The FTIR spectra of L-ZnO NPs revealed the band at 478 cm⁻¹ linked with the typical stretching of the Zn–O bond. The XRD and SEM images disclosed hexagonal wurtzite shape of L-ZnO NPs having mean diameter ≈ 77.76 nm. The antibacterial efficacies of the L-ZnO NPs and non-coated ZnO NPs were assessed against both gram-negative Escherichia coli and gram-positive Staphylococcus aureus bacteria, employing standard controls and the well diffusion method. The L-ZnO NPs exhibited marvelous bactericidal action against the test microorganisms displaying significant zone of inhibition (ZOI). The photocatalytic performance of the L-ZnO NPs and non-coated ZnO NPs were observed by methylene blue (MB) dye degradation test under UV light irradiation. In regards of dye degradation percentage and antibacterial activity, the L-ZnO NPs is much more superior to non-coated ZnO NPs.