Lignin-Directed Control of Silver Nanoparticles with Tunable Size in Porous Lignocellulose Hydrogels and Their Application in Catalytic Reduction

Inspired by its unique porous structure, high value-added functional hydrogels combined with metal nanoparticles can lead to applications in different areas, including environmental catalysis. For this purpose, controlling the metal nanoparticle size is paramount. Herein, the porous lignocellulose hydrogel (LCG) with different lignin contents served as the matrix for in situ-synthesizing silver–lignin nanoparticles (Ag-L NPs), with lignin in the LCG as the reducing and capping agent of Ag-L NPs and the lignin content to control the size of Ag-L NPs. The well-dispersed lignin in the LCG network ensures immobilization and dispersion of Ag-L NPs. The particle size of Ag-L NPs is tailored by adjusting the lignin content (0.5, 6.5, 11.6, and 18.4%) of the LCG: the higher the lignin content, the smaller the Ag-L NPs. The smallest Ag-L NPs obtained were of 9.5 nm. The as-prepared Ag-L NPs/LCG composite samples showed outstanding catalytic reduction capability, with superior stability/reusability when applied for the catalytic reduction of 4-nitrophenol. Moreover, the Ag-L NPs/LCG composites exhibited high antibacterial activity, thus contributing to long-term storage stability.