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 lignin-reactors 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 × 10 3 h −1 , k 4.8 × 10 −2 s −1 ) as compared to that of Ag@PL (TOF 2.5 × 10 3 h −1 , k 2.3 × 10 −2 s −1 ) under a low NaBH 4 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. • Facile synthesis of lignin-reactors based on pH responsiveness of lignin. • Fully exposed Ag NPs with high accessibility anchored over the lignin support. • Ag/PL exhibited super catalytic reactivity toward 4-NP reduction than that of Ag@PL. • Ag/PL catalyst showed a TOF value up to 5.2 × 10 3 h −1 .