Anchoring silver nanoparticles on graphene quantum dots: A highly efficient, green, and rapid nano-catalyst for the reduction of nitro compounds and tandem reductive Ugi reactions

Abstract

In this work, silver nanoparticles (AgNPs) were successfully anchored on the surface of graphene quantum dots (GQDs). The resulting GQDs/AgNPs were then applied as a nano-catalyst for the reduction of nitro compounds, after confirming their stability at various pH. For this purpose, the reduction of nitrobenzene (NB) was selected as a model reaction in the presence of sodium borohydride (NaBH₄) under green conditions and controlled by UV–vis spectroscopy. The kinetic of the reaction was investigated and found that the reaction followed a pseudo-first-order kinetic model. Interestingly, further studies showed that a minimum amount of the catalyst (1 μg) exhibited excellent efficiency and achieved a high reduction rate. (observed rate constant, k_obs = 2.5 × 10⁻³ s⁻¹ and normalized rate constant, k_nor = 2500 s⁻¹mg⁻¹). Additionally, the catalytic activity of the resulting GQDs/AgNPs was examined to promote the reduction reaction of NB derivatives and the tandem Ugi reactions. The products of both reactions were prepared in good to high yields (80–94 %). The outstanding advantages of the present catalyst include its green protocol, eco-friendly, inexpensive, rapid reaction, mild reaction conditions, and operational simplicity.