Sandwich-like N-C/Cu/N-C porous beads derived from alginate with enhanced catalytic activity and excellent recyclability for 4-nitrophenol reduction

Abstract

The development of metal nanoparticles supported on carbon-based materials with high catalytic activity and good stability is a significant issue in the areas of catalytic synthesis and degradation. Herein, we successfully synthesized sandwich-like N-doped carbon layer-coated on Cu nanoparticles supported on N-doped porous carbon (N-C/Cu/N-C) by depositing a polydopamine (PDA) layer on alginate-based hydrogel beads, followed by a high-temperature pyrolysis in N2. The as-prepared N-C/Cu/N-C porous beads were characterized by SEM, XPS, BET, XRD, and EDS techniques. The results showed that Cu nanoparticles with a narrow size distribution in the range of 10−30 nm were uniformly immobilized on the frameworks of porous carbon beads due to the protection of the outer N-C layer. Also, the layer derived from PDA on the porous beads effectively enhanced the mechanical strength, thus avoiding the loss of Cu nanoparticles during the catalytic reaction. As a sequence, the N-C/Cu/N-C catalyst exhibited the enhanced catalytic activity towards the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with the reaction rate constant of 4.16 × 10−3 s-1. Importantly, the N-C/Cu/N-C-700 beads displayed good cycling stability with the conversion of up to 97.3 % even after 10 cycles. The presented work provides a new strategy to improve the catalytic activity for metal nanoparticles supported on carbon-based materials.