An aqueous solution of 4-nitrophenol has a maximum absorption at 317 nm, as shown by a trace in Fig.  4 a.

But it has been observed that, after immediate addition of freshly prepared aqueous solution of NaBH ₄ , the peak due to 4-nitrophenol was red shifted from 317 to 400 nm (see Fig.  4 b).

The UV–vis absorption spectrum after the addition of pure Fe ₂ O ₃ nanoparticles in the mixture of 4-nitrophenol and NaBH ₄ also remains unaltered with time, as shown in Fig.  4 c, which means that the pure Fe ₂ O ₃ nanoparticles do not work as catalyst for this reaction. .