Assembly of RGO composite aerogels embedded with ultrasmall Au nanoparticles as an active and recyclable catalyst for reduction of 4-nitrophenol

Abstract

Metallic Au nanoparticles (NPs) are active catalysts in many chemical reactions. However, small-size Au NPs are difficult to obtain since they tend to agglomerate due to their high surface energies. Herein, we reported a facile and green hydrothermal process, using graphene oxide (GO) as the RGO precursor, HAuCl4 as Au precursor and L-cysteine (L-cys) as both cross-linker and reducing agent, to fabricate an Au/RGO composite aerogel. During the hydrothermal process, the reduction of GO/HAuCl4, the oxidation of L-cys to produce disulfide linkage, and the self-assembly of RGO aerogel occurs simultaneously, leading to the resultant RGO aerogels uniformly and intimately embedded with disulfide protected ultrasmall Au NPs with an average size of 1.3 nm. The as-obtained Au/RGO composite aerogel exhibited superior catalytic performance for reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), with a total transformation of 4-NP achieved in 4 min. The much higher activity over Au/RGO aerogel as compared with unsupported thiol-capped Au NPs can be attributed to the synergistic effect of metallic Au and RGO. Moreover, Au/RGO composite aerogel also showed high stability and can be easily separated from the reaction systems for recycling. No obvious decrease of catalytic reduction activity was observed over the Au/RGO aerogel after five cycles. Considering the high price of metallic Au, the embedding of Au NPs in three-dimensional RGO aerogels to facilitate its recycling is extremely appealing for its practical applications.