Synthesis of lignin-functionalized phenolic nanosphere supported Ag nanoparticles with excellent dispersion stability and catalytic performance

As the most abundant aromatic biopolymer, lignin has great potential to replace petroleum-based phenol to prepare phenolic resins (e.g. phenolic adhesive and foam). In this work, a novel lignin-functionalized phenolic resin (LPR) nanosphere was synthesized using a simple hydrothermal curing process and was further used as both a green reducing agent and a support for the formation of Ag nanoparticles (NPs). Interestingly, it was found that the incorporation of lignin into the phenolic resin (PR) decreased its size from microscale to nanoscale due to the surface activity of lignin. Besides, a part of lignin (the uncombined lignin) acted as a sacrificial template to increase the surface roughness of nanospheres. A decrease in the support size and an increase in the surface roughness enhanced the specific surface area of LPR nanospheres and the aqueous dispersion stability of LPR@Ag nanocomposites. Owing to the excellent reducing activity of lignin and the enhancement of the specific surface area, the loading amount Ag NPs on LPR nanospheres was considerably higher than on the lignin-free PR microspheres. Accordingly, the LPR@Ag nanocomposites showed excellent capabilities in the catalytic reduction of two typical organic pollutants (anionic methyl orange and cationic methylene blue). Particularly, due to the adsorption of cationic methylene blue by lignin, a synergistic effect of adsorption and catalysis was observed, which considerably improved the catalytic performance of LPR@Ag nanocomposites. LPR@Ag nanocomposites also exhibited good recyclability owing to the stable loading of Ag NPs on the nanosphere support. Finally, this work demonstrates the multifunctionality of lignin as a surfactant, sacrificial template, and green reducing agent in the synthesis of LPR@Ag nanocomposites and therefore, provides a new frontier in the development of lignin-based polymer materials focusing on the synergistic effect of multiple functionalities of lignin.