Valorization of lignin from pine (Pinus spp.) residual sawdust: antioxidant activity and application in the green synthesis of silver nanoparticles for antibacterial purpose

Lignin is the second most abundant biopolymer available whose functional groups make it a natural antioxidant. Pine residual sawdust is a lignocellulosic waste largely produced in sawmills by wood processing. Thus, this study aimed to evaluate the lignin from pine residual sawdust (PRSL) as an environmental-friendly antioxidant, and in the green synthesis of silver nanoparticles (LAgNPs), which were then tested against Gram-positive and Gram-negative bacteria. Three PRSL, previously obtained by sequential acid-alkaline treatment at 130, 150, and 170 °C, were assessed. The total phenolic content (TPC) and antioxidant activity of PRSL were also evaluated. PRSL showed strong potential as a natural antioxidant. LAgNPs were characterized by Fourier-transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and transmission electron microscopy (TEM). LAgNPs presented a polydispersed mixture with an average diameter of 54.18 nm and efficient antibacterial properties. Therefore, this study demonstrated the great capability of PRSL as a natural antioxidant agent and for green synthesis of silver nanoparticles.