Preparation of silver nanoparticles through reduction of straw-extracted lignin and its antibacterial hydrogel

Silver nanoparticles (Ag NPs) have attracted much attention in the field of biomaterials due to their excellent antibacterial property. However, the reducing and stabilizing agents used for chemical reduction of Ag NPs are usually toxic and may lead to water pollution. In this work, Ag NPs (31.2 nm in diameter) was prepared by using the extract of an agricultural waste, straw, as the reducing and stabilizing agent. Experimental analysis revealed that the straw extract contains lignin, the structure of which possess phenolic hydroxyl and methoxy groups, facilitating the reduction of silver salts into Ag NPs. The surfaces of Ag NPs were negatively charged due to the encapsulation of a thin layer of lignin molecules that prevented their aggregation. Interestingly, after adding the prepared Ag NPs into the precursor solution of acrylamide, free radical polymerization was triggered without the need of extra heating or light irradiation, resulting in the rapidly formation of an Ag NPs-polyacrylamide composite hydrogel. The inhibition zone test proved that the composite hydrogel possesses excellent antibacterial ability due to the presence of Ag NPs. The prepared hydrogel may find potential applications in fabrication of biomedical materials, such as antibacterial dressings.