Tough, Stretchable, Compressive Double Network Hydrogel Using Natural Glycyrrhizic Acid-Tailored Low-Molecular-Weight Gelator Strategy: In Situ Spontaneous Formation of Au Nanoparticles to Generate Continuous Flow Reactor.

Traditional solid supports of metal nanoparticles (MNPs) often suffer from the poor mechanical performance, the low recycling efficiency and the mass loss in regeneration process. To overcome this limit, in this work we reported a natural triterpenoid-tailored low-molecular-weight gelator (LMWG) strategy to fabricate double network (DN) hydrogels with excellent mechanical properties for supporting MNPs. In this strategy, the supramolecular fibrillar structure of glycyrrhizic acid (GL) and the cross-linked polyacrylamide (PAAm) were used as the first physical network and the second chemical network, respectively. The resulting GL/PAAm DN gels possessed tough, stretchable and compressive properties, as well as high fatigue resistance. In addition, ice-templating technique has been used to recast the DN gel through the anisotropical growth of ice crystals for increasing the porosity and surface area. On account of the reductibility of the diglucuronic moiety of GL, gold nanoparticles (AuNPs) were in situ spontaneously reduced from Au(Ⅲ) ions without external reducing reagents and anchored on the pore surface of Recast-GL/PAAm DN gel. This AuNPs-anchored Recast-GL/PAAm DN gel can be used as a continuous flow reactor to catalyze the reduction of 4-nitrophenol to 4-aminophenol with high catalytic activity, good recyclability and long-term stability. Our work provided an effective strategy to generate promising supports of MNPs with highly mechanical properties and excellent catalytic efficiency.