Fig. 7. UV-vis absorption spectra for the gradual reduction of 2-nitroaniline (a) in the absence of catalyst (b) in the presence of catalyst. Reaction conditions; 0.5 mM aqueous solution of 2-nitroaniline = 50 ml, NaBH₄ = 0.1 g, graphene oxide–gold catalyst = 5 mg, 30 °C, 100 rpm.