Fully exposed silver nanoparticles stabilized on pH-responsive lignin-reactors for enhanced 4-nitrophenol reduction

Lignin as an advanced catalyst support has attracted much attention owing to its sufficient functional groups and natural cross-linked network structure, as well as good biodegradability. Herein, we fabricate a pair of ligninreactors with silver nanoparticles (Ag NPs) supported outside or embedded in pre-hydrolyzed lignin (designated as Ag/PL or Ag@PL, respectively) via the self-assembly approach, which could be used for efficient catalytic reduction of 4-nitrophenol (4-NP). Through this strategy, the phase transitions and morphology changes of reactors could be achieved based on the pH responsiveness of lignin. The resultant Ag/PL exhibits a much higher catalytic activity (TOF 5.2 x 10(3) h(-1), k 4.8 x 10(-2) s(-1)) as compared to that of Ag@PL (TOF 2.5 x 10(3) h(-1), k 2.3 x 10(-2) s(-1)) under a low NaBH4 concentration (n([NaBH4])/n([4-NP]), 100) at room temperature, which notably surpasses those of previously reported carbon-supported catalysts. The enhanced catalytic performance of Ag/PL is attributed to the fact that the fully exposed Ag NPs on the interface possess close proximity to the reactant. This work not only provides a promising route to design advanced catalysts in wastewater treatment system, but also paves the way for lignin valorization into functional-materials.

Automated summary

Lignin is used as a catalyst support for efficient reduction of 4-nitrophenol using silver nanoparticles embedded in or supported outside pre-hydrolyzed lignin. The phase transitions and morphology changes of the reactors are achieved based on lignin's pH responsiveness. The lignin-supported catalyst with fully exposed silver nanoparticles exhibits higher catalytic activity due to closer proximity to the reactants.