Green synthesis of Ag/lignin nanoparticle-loaded cellulose aerogel for catalytic degradation and antimicrobial applications

Reacting with reductive phenolic hydroxyls (–OH) and methoxy groups (–OCH₃) on lignin, silver ions (Ag⁺) were reduced to metallic silver nanoparticles (NPs) with sizes smaller than 40 nm. The resulting Ag/lignin NPs were then physically crosslinked in the cellulose hydrogel, followed by freeze-drying to obtain the final Ag/lignin NP-loaded cellulose aerogel. Loaded with Ag/lignin NPs, the aerogel exhibited strengthened mechanical property (387 ± 11 kPa) against the external deformation at a compressive strain of 65% due to the nano-reinforcement by the loaded Ag/lignin NPs when compared with pure cellulose aerogel (246 ± 32 kPa). The Ag/lignin NP-loaded aerogel also showed robust killing efficiency against different pathogenic bacteria in aqueous solution (Escherichia coli: > 99.99%, Pseudomonas aeruginosa: > 99.9%, Vibrio cholera: > 99.99%, Staphylococcus aureus: > 99.99%, Bacillus subtilis: > 97.4%). Moreover, the loaded Ag/lignin NPs provided the aerogel with excellent catalytic degradation ability toward various organic compounds, including dyes, pollutants, and antibiotics, evidenced by the degradation of methylene blue (99.8% in 30 min) and methyl orange (99.9% in 180 min) in the presence of NaBH₄ and natural sunlight radiation, and degradation of rhodamine B (99.9% in 35 min), 4-nitrophenol (99.5% in 180 min) and doxycycline hyclate (99.8% in 30 min) in the presence of NaBH₄ without natural sunlight. In addition, the Ag/lignin NP-loaded aerogel could be reused after facile regeneration washing with water while retaining excellent performance on efficiently degrading (~ 100%) the organic dyes for at least three cycles. The roles of loaded Ag/lignin NPs as photoelectron generators and relay centers for transferring electrons from the reductant to the targeted organic compounds during the degradation process were comprehensively investigated and explained.