Sub-10 nm Ag Nanoparticles/Graphene Oxide: Controllable Synthesis, Size-Dependent and Extremely Ultrahigh Catalytic Activity.

While tremendous advancements in Ag nanoparticle (AgNP)-based materials have been made, the development of a facile protocol for preparing sub-10 nm AgNPs with controllable size and ultrahigh performance remains a formidable challenge. It is shown that AgNPs/graphene oxide (AgNPs/GO) bearing 2.5, 4.3, and 6.2 nm AgNPs (2.5-AgNPs/GO, 4.3-AgNPs/GO, and 6.2-AgNPs/GO, respectively) could be fabricated via light-induced synthesis. Their catalytic activity toward 4-nitrophenol (4-NP) reduction, which is a "gold standard" for evaluating the performance of noble metal-based catalysts, is studied. When normalized by mole and area, the activity exhibits an order of 4.3-AgNPs/GO > 6.2-AgNPs/GO > 2.5-AgNPs/GO and 6.2-AgNPs/GO > 4.3-AgNPs/GO > 2.5-AgNPs/GO, respectively. This trend is a result of GO-induced electron concentration reduction with decreasing AgNP size. Significantly, under similar conditions, the activity of 4.3-AgNPs/GO is substantially superior to that of numerous state-of-the-art noble metal-based catalysts. The ultrafine size of the AgNPs and their surface accommodation on the unobstructed 2D GO scaffolds without capping reagents/covers, which make the abundantly exposed catalytically active sites highly accessible to substrate molecules, play an important role in their extremely ultrahigh performance. This work paves a new avenue for high-performance AgNP-based materials, and by taking 4-NP reduction as a proof-of-concept, provides new scientific insights into the rational design of surface-based advanced materials.